Micromachines

19 pages, 2387 KB

Open AccessEditor’s ChoiceReview

Electro-Elastic Instability and Turbulence in Electro-osmotic Flows of Viscoelastic Fluids: Current Status and Future Directions

by Chandi Sasmal

Micromachines 2025, 16(2), 187; https://doi.org/10.3390/mi16020187 - 4 Feb 2025

Cited by 2 | Viewed by 1100

Abstract

The addition of even minute amounts of solid polymers, measured in parts per million (ppm), into a simple Newtonian fluid like water significantly alters the flow behavior of the resulting polymer solutions due to the introduction of fluid viscoelasticity. This viscoelastic behavior, which [...] Read more.

The addition of even minute amounts of solid polymers, measured in parts per million (ppm), into a simple Newtonian fluid like water significantly alters the flow behavior of the resulting polymer solutions due to the introduction of fluid viscoelasticity. This viscoelastic behavior, which arises due to the stretching and relaxation phenomena of polymer molecules, leads to complex flow dynamics that are starkly different from those seen in simple Newtonian fluids under the same conditions. In addition to polymer solutions, many other fluids, routinely used in various industries and our daily lives, exhibit viscoelastic properties, including emulsions; foams; suspensions; biological fluids such as blood, saliva, and cerebrospinal fluid; and suspensions of biomolecules like DNA and proteins. In various microfluidic platforms, these viscoelastic fluids are often transported using electro-osmotic flows (EOFs), where an electric field is applied to control fluid movement. This method provides more precise and accurate flow control compared to pressure-driven techniques. However, several experimental and numerical studies have shown that when either the applied electric field strength or the fluid elasticity exceeds a critical threshold, the flow in these viscoelastic fluids becomes unstable and asymmetric due to the development of electro-elastic instability (EEI). These instabilities are driven by the normal elastic stresses in viscoelastic fluids and are not observed in Newtonian fluids under the same conditions, where the flow remains steady and symmetric. As the electric field strength or fluid elasticity is further increased, these instabilities can transition into a more chaotic and turbulent-like flow state, referred to as electro-elastic turbulence (EET). This article comprehensively reviews the existing literature on these EEI and EET phenomena, summarizing key findings from both experimental and numerical studies. Additionally, this article presents a detailed discussion of future research directions, emphasizing the need for further investigations to fully understand and harness the potential of EEI and EET in various practical applications, particularly in microscale flow systems where better flow control and increased transport rates are essential. Full article

(This article belongs to the Collection Micro/Nanoscale Electrokinetics)

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25 pages, 3015 KB

Open AccessFeature PaperEditor’s ChoiceReview

Magnetic Polymeric Conduits in Biomedical Applications

by Sayan Ganguly and Shlomo Margel

Micromachines 2025, 16(2), 174; https://doi.org/10.3390/mi16020174 - 31 Jan 2025

Cited by 9 | Viewed by 1770

Abstract

Magnetic polymeric conduits are developing as revolutionary materials in regenerative medicine, providing exceptional benefits in directing tissue healing, improving targeted medication administration, and facilitating remote control via external magnetic fields. The present article offers a thorough examination of current progress in the design, [...] Read more.

Magnetic polymeric conduits are developing as revolutionary materials in regenerative medicine, providing exceptional benefits in directing tissue healing, improving targeted medication administration, and facilitating remote control via external magnetic fields. The present article offers a thorough examination of current progress in the design, construction, and functionalization of these hybrid systems. The integration of magnetic nanoparticles into polymeric matrices confers distinctive features, including regulated alignment, improved cellular motility, and targeted medicinal delivery, while preserving structural integrity. Moreover, the incorporation of multifunctional attributes, such as electrical conductivity for cerebral stimulation and optical characteristics for real-time imaging, expands their range of applications. Essential studies indicate that the dimensions, morphology, surface chemistry, and composition of magnetic nanoparticles significantly affect their biocompatibility, degrading characteristics, and overall efficacy. Notwithstanding considerable advancements, issues concerning long-term biocompatibility, biodegradability, and scalability persist, in addition to the must for uniform regulatory frameworks to facilitate clinical translation. Progress in additive manufacturing and nanotechnology is overcoming these obstacles, facilitating the creation of dynamic and adaptive conduit structures designed for particular biomedical requirements. Magnetic polymeric conduits, by integrating usefulness and safety, are set to transform regenerative therapies, presenting a new avenue for customized medicine and advanced healthcare solutions. Full article

(This article belongs to the Special Issue Technological Advances in Polymer Microfabrication: Design and Processing Innovations, 2nd Edition)

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23 pages, 5559 KB

Open AccessFeature PaperEditor’s ChoiceReview

Propulsion Mechanisms in Magnetic Microrobotics: From Single Microrobots to Swarms

by Lanlan Jia, Guangfei Su, Mengyu Zhang, Qi Wen, Lihong Wang and Junyang Li

Micromachines 2025, 16(2), 181; https://doi.org/10.3390/mi16020181 - 31 Jan 2025

Cited by 3 | Viewed by 2923

Abstract

Microrobots with different structures can exhibit multiple propulsion mechanisms under external magnetic fields. Swarms dynamically assembled by microrobots inherit the advantages of single microrobots, such as degradability and small dimensions, while also offering benefits like scalability and high flexibility. With control of magnetic [...] Read more.

Microrobots with different structures can exhibit multiple propulsion mechanisms under external magnetic fields. Swarms dynamically assembled by microrobots inherit the advantages of single microrobots, such as degradability and small dimensions, while also offering benefits like scalability and high flexibility. With control of magnetic fields, these swarms demonstrate diverse propulsion mechanisms and can perform precise actions in complex environments. Therefore, the relationship between single microrobots and their swarms is a significant area of study. This paper reviews the relationship between single microrobots and swarms by examining the structural design, control methods, propulsion mechanisms, and practical applications. At first, we introduce the structural design of microrobots, including materials and manufacturing methods. Then, we describe magnetic field generation systems, including gradient, rotating, and oscillating magnetic fields, and their characteristics. Next, we analyze the propulsion mechanisms of individual microrobots and the way microrobots dynamically assemble into a swarm under an external magnetic field, which illustrates the relationship between single microrobots and swarms. Finally, we discuss the application of different swarm propulsion mechanisms in water purification and targeted delivery, summarize current challenges and future work, and explore future directions. Full article

(This article belongs to the Special Issue Magnetic Microrobots for Biomedical Applications, Second Edition)

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16 pages, 8989 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Microneedle-Assisted Delivery of Curcumin: Evaluating the Effects of Needle Length and Formulation

by Em-on Chaiprateep, Soma Sengupta and Cornelia M. Keck

Micromachines 2025, 16(2), 155; https://doi.org/10.3390/mi16020155 - 29 Jan 2025

Cited by 1 | Viewed by 1860

Abstract

Dermal drug delivery presents a significant challenge for poorly soluble active compounds like curcumin, which often struggle to penetrate the skin barrier effectively. In this study, the dermal penetration efficacy of curcumin nanocrystals and bulk suspensions when applied to skin using microneedles of [...] Read more.

Dermal drug delivery presents a significant challenge for poorly soluble active compounds like curcumin, which often struggle to penetrate the skin barrier effectively. In this study, the dermal penetration efficacy of curcumin nanocrystals and bulk suspensions when applied to skin using microneedles of varying lengths—0.25 mm, 0.5 mm, and 1.0 mm—was investigated in an ex vivo porcine ear model. The findings revealed that all formulations, in conjunction with microneedle application, facilitated transepidermal penetration; however, the combination of microneedles and curcumin nanocrystals demonstrated the highest efficacy. Notably, the 1.0 mm microneedle length provided optimal penetration, significantly enhancing curcumin delivery compared with bulk suspensions alone. Additionally, even the use of 0.25 mm microneedles resulted in a high level of efficiency, indicating that shorter microneedles can still effectively facilitate drug delivery. Overall, this study underscores the potential of microneedle technology in improving the transepidermal absorption of poorly soluble actives like curcumin, suggesting that the integration of nanocrystals with microneedles could enhance the therapeutic effects of topical curcumin applications. Full article

(This article belongs to the Special Issue Current Trends in Microneedles: Design, Fabrication and Applications)

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12 pages, 3482 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Driving Rotational Circulation in a Microfluidic Chamber Using Dual Focused Surface-Acoustic-Wave Beams

by Jin-Chen Hsu and Kai-Li Liao

Micromachines 2025, 16(2), 140; https://doi.org/10.3390/mi16020140 - 25 Jan 2025

Viewed by 1311

Abstract

In this paper, enhanced rotational circulation in a circular microfluidic chamber driven by dual focused surface-acoustic-wave (SAW) beams is presented. To characterize the resonant frequency and focusing effect, we simulate the focused SAW field excited by an arc-shaped interdigital transducer patterned on a [...] Read more.

In this paper, enhanced rotational circulation in a circular microfluidic chamber driven by dual focused surface-acoustic-wave (SAW) beams is presented. To characterize the resonant frequency and focusing effect, we simulate the focused SAW field excited by an arc-shaped interdigital transducer patterned on a 128°Y-cut lithium-niobate (LiNbO₃) substrate using a finite element method. A full three-dimensional perturbation model of the combined system of the microfluidic chamber and the SAW device is conducted to obtain the acoustic pressure and acoustic streaming fields, which show rotational acoustic pressure and encircling streaming resulted in the chamber. Accordingly, the SAW acoustofluidic system is realized using microfabrication techniques and applied to perform acoustophoresis experiments on submicron particles suspending in the microfluidic chamber. The result verifies the rotational circulation motion of the streaming flow, which is attributed to enhanced angular momentum flux injection and Eckart streaming effect through the dual focused SAW beams. Our results should be of importance in driving particle circulation and enhancing mass transfer in chamber embedded microfluidic channels, which may have promising applications in accelerating bioparticle or cell reactions and fusion, enhancing biochemical and electrochemical sensing, and efficient microfluidic mixing. Full article

(This article belongs to the Special Issue Surface and Bulk Acoustic Wave Devices)

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23 pages, 6410 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Automatic Extraction and Compensation of P-Bit Device Variations in Large Array Utilizing Boltzmann Machine Training

by Bolin Zhang, Yu Liu, Tianqi Gao, Jialiang Yin, Zhenyu Guan, Deming Zhang and Lang Zeng

Micromachines 2025, 16(2), 133; https://doi.org/10.3390/mi16020133 - 24 Jan 2025

Viewed by 1828

Abstract

A Probabilistic Bit (P-Bit) device serves as the core hardware for implementing Ising computation. However, the severe intrinsic variations of stochastic P-Bit devices hinder the large-scale expansion of the P-Bit array, significantly limiting the practical usage of Ising computation. In this work, a [...] Read more.

A Probabilistic Bit (P-Bit) device serves as the core hardware for implementing Ising computation. However, the severe intrinsic variations of stochastic P-Bit devices hinder the large-scale expansion of the P-Bit array, significantly limiting the practical usage of Ising computation. In this work, a behavioral model which attributes P-Bit variations to two parameters,

α

and

Δ V

, is proposed. Then the weight compensation method is introduced, which can mitigate

α

and

Δ V

of P-Bit device variations by rederiving the weight matrix, enabling them to compute as ideal identical P-Bits without the need for weights retraining. Accurately extracting the

α

and

Δ V

simultaneously from a large P-Bit array which is prerequisite for the weight compensation method is a crucial and challenging task. To solve this obstacle, we present the novel automatic variation extraction algorithm which can extract device variations of each P-Bit in a large array based on Boltzmann machine learning. In order for the accurate extraction of variations from an extendable P-Bit array, an Ising Hamiltonian based on a 3D ferromagnetic model is constructed, achieving precise and scalable array variation extraction. The proposed Automatic Extraction and Compensation algorithm is utilized to solve both 16-city traveling salesman problem (TSP) and 21-bit integer factorization on a large P-Bit array with variation, demonstrating its accuracy, transferability, and scalability. Full article

(This article belongs to the Special Issue Magnetic and Spin Devices, 3rd Edition)

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48 pages, 12131 KB

Open AccessFeature PaperEditor’s ChoiceReview

Review of Layered Transition Metal Oxide Materials for Cathodes in Sodium-Ion Batteries

by Mehdi Ahangari, Meng Zhou and Hongmei Luo

Micromachines 2025, 16(2), 137; https://doi.org/10.3390/mi16020137 - 24 Jan 2025

Cited by 7 | Viewed by 4987

Abstract

The growing interest in sodium-ion batteries (SIBs) is driven by scarcity and the rising costs of lithium, coupled with the urgent need for scalable and sustainable energy storage solutions. Among various cathode materials, layered transition metal oxides have emerged as promising candidates due [...] Read more.

The growing interest in sodium-ion batteries (SIBs) is driven by scarcity and the rising costs of lithium, coupled with the urgent need for scalable and sustainable energy storage solutions. Among various cathode materials, layered transition metal oxides have emerged as promising candidates due to their structural similarity to lithium-ion battery (LIB) counterparts and their potential to deliver high energy density at reduced costs. However, significant challenges remain, including limited capacity at high charge/discharge rates and structural instability during extended cycling. Addressing these issues is critical for advancing SIB technology toward industrial applications, particularly for large-scale energy storage systems. This review provides a comprehensive analysis of layered sodium transition metal oxides, focusing on their structural properties, electrochemical performance, and degradation mechanisms. Special attention is given to the intrinsic and extrinsic factors contributing to their instability, such as structural phase transitions, and cationic/anionic redox behavior. Additionally, recent advancements in material design strategies, including doping, surface modifications, and composite formation, are discussed to highlight the progress toward enhancing the stability and performance of these materials. This work aims to bridge the knowledge gaps and inspire further innovations in the development of high-performance cathodes for sodium-ion batteries. Full article

(This article belongs to the Special Issue Energy Conversion Materials/Devices and Their Applications)

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17 pages, 4060 KB

Open AccessEditor’s ChoiceArticle

An Assessment of Local Geometric Uncertainties in Polysilicon MEMS: A Genetic Algorithm and POD-Kriging Surrogate Modeling Approach

by Ananya Roy, Francesco Rizzini, Gabriele Gattere, Carlo Valzasina, Aldo Ghisi and Stefano Mariani

Micromachines 2025, 16(2), 127; https://doi.org/10.3390/mi16020127 - 23 Jan 2025

Viewed by 801

Abstract

On the way toward MEMS miniaturization, the quantification of geometric uncertainties stands as a primary challenge. In this paper, an approach that combines genetic algorithms and proper orthogonal decomposition with kriging surrogate modeling was proposed to accurately predict over-etch measures through an on-chip [...] Read more.

On the way toward MEMS miniaturization, the quantification of geometric uncertainties stands as a primary challenge. In this paper, an approach that combines genetic algorithms and proper orthogonal decomposition with kriging surrogate modeling was proposed to accurately predict over-etch measures through an on-chip test device. Despite being fabricated on a single wafer under nominally identical manufacturing conditions, MEMS can display different responses under the same actuation, due to a different characteristic geometry. It is shown that the uncertainties, given in terms of over-etch values, were not only different from die to die but also within the same die, depending on the local geometric features of the device. Therefore, the proposed method provided an alternative solution to estimate the uncertainties in MEMS devices, relying only on the capacitance–voltage response. A statistical analysis was carried out based on a batch of devices tested in the laboratory. These tests and the estimation procedure allowed us to quantify the mean values of the over-etch relative to the target as +12.2 % at comb fingers, +10.0 % at the supporting springs, and −4.8 % at stoppers, showing noteworthy variability induced by the environment. Full article

(This article belongs to the Special Issue The 15th Anniversary of Micromachines)

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10 pages, 8031 KB

Open AccessFeature PaperEditor’s ChoiceArticle

An All-in-One Testing Chip for the Simultaneous Measurement of Multiple Thermoelectric Parameters in Doped Polysilicon

by Lei Shi, Na Zhou, Jintao Wu, Meng Shi, Yizhi Shi, Cheng Lei and Haiyang Mao

Micromachines 2025, 16(2), 116; https://doi.org/10.3390/mi16020116 - 21 Jan 2025

Viewed by 1021

Abstract

Polysilicon is widely used as a thermoelectric material due to its CMOS compatibility and tunability through doping. The accurate measurement of the thermoelectric parameters—such as the Seebeck coefficient, thermal conductivity, and electrical resistivity—of polysilicon with various doping conditions is essential for designing and [...] Read more.

Polysilicon is widely used as a thermoelectric material due to its CMOS compatibility and tunability through doping. The accurate measurement of the thermoelectric parameters—such as the Seebeck coefficient, thermal conductivity, and electrical resistivity—of polysilicon with various doping conditions is essential for designing and fabricating high-performance thermopile sensors. This work presents an all-in-one testing chip that incorporates double-layer thermoelectric structures on a suspended membrane-based supporting layer, with polysilicon constituting at least one of these thermoelectric layers. By employing a differential calculation approach in conjunction with thermal imaging methods, we could simultaneously measure various thermoelectric parameters—including resistivity, the Seebeck coefficient, and thermal conductivity—of polysilicon under different doping conditions. Furthermore, the method proposed in this study provides a means for accurately obtaining thermoelectric parameters for other materials, thereby facilitating the design and optimization of thermoelectric devices. Full article

(This article belongs to the Special Issue MEMS Sensors and Actuators: Design, Fabrication and Applications)

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16 pages, 5458 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Enhanced Performance of Novel Amorphous Silicon Carbide Microelectrode Arrays in Rat Motor Cortex

by Pegah Haghighi, Eleanor N. Jeakle, Brandon S. Sturgill, Justin R. Abbott, Elysandra Solis, Veda S. Devata, Gayathri Vijayakumar, Ana G. Hernandez-Reynoso, Stuart F. Cogan and Joseph J. Pancrazio

Micromachines 2025, 16(2), 113; https://doi.org/10.3390/mi16020113 - 21 Jan 2025

Cited by 1 | Viewed by 1935

Abstract

Implantable microelectrode arrays (MEAs) enable the recording of electrical activity from cortical neurons for applications that include brain–machine interfaces. However, MEAs show reduced recording capabilities under chronic implantation conditions. This has largely been attributed to the brain’s foreign body response, which is marked [...] Read more.

Implantable microelectrode arrays (MEAs) enable the recording of electrical activity from cortical neurons for applications that include brain–machine interfaces. However, MEAs show reduced recording capabilities under chronic implantation conditions. This has largely been attributed to the brain’s foreign body response, which is marked by neuroinflammation and gliosis in the immediate vicinity of the MEA implantation site. This has prompted the development of novel MEAs with either coatings or architectures that aim to reduce the tissue response. The present study examines the comparative performance of multi-shank planar, silicon-based devices and low-flexural-rigidity amorphous silicon carbide (a-SiC) MEAs that have a similar architecture but differ with respect to the shank cross-sectional area. Data from a-SiC arrays were previously reported in a prior study from our group. In a manner consistent with the prior work, larger cross-sectional area silicon-based arrays were implanted in the motor cortex of female Sprague-Dawley rats and weekly recordings were made for 16 weeks after implantation. Single unit metrics from the recordings were compared over the implantation period between the device types. Overall, the expression of single units measured from a-SiC devices was significantly higher than for silicon-based MEAs throughout the implantation period. Immunohistochemical analysis demonstrated reduced neuroinflammation and gliosis around the a-SiC MEAs compared to silicon-based devices. Our findings demonstrate that the a-SiC MEAs with a smaller shank cross-sectional area can record single unit activity with more stability and exhibit a reduced inflammatory response compared to the silicon-based device employed in this study. Full article

(This article belongs to the Special Issue Flexible and Wearable Sensors, 3rd Edition)

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13 pages, 2458 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Temperature-Responsive Hybrid Composite with Zero Temperature Coefficient of Resistance for Wearable Thermotherapy Pads

by Ji-Yoon Ahn, Dong-Kwan Lee, Min-Gi Kim, Won-Jin Kim and Sung-Hoon Park

Micromachines 2025, 16(1), 108; https://doi.org/10.3390/mi16010108 - 19 Jan 2025

Cited by 1 | Viewed by 1293

Abstract

Carbon-based polymer composites are widely used in wearable devices due to their exceptional electrical conductivity and flexibility. However, their temperature-dependent resistance variations pose significant challenges to device safety and performance. A negative temperature coefficient (NTC) can lead to overcurrent risks, while a positive [...] Read more.

Carbon-based polymer composites are widely used in wearable devices due to their exceptional electrical conductivity and flexibility. However, their temperature-dependent resistance variations pose significant challenges to device safety and performance. A negative temperature coefficient (NTC) can lead to overcurrent risks, while a positive temperature coefficient (PTC) compromises accuracy. In this study, we present a novel hybrid composite combining carbon nanotubes (CNTs) with NTC properties and carbon black (CB) with PTC properties to achieve a near-zero temperature coefficient of resistance (TCR) at an optimal ratio. This innovation enhances the safety and reliability of carbon-based polymer composites for wearable heating applications. Furthermore, a thermochromic pigment layer is integrated into the hybrid composite, enabling visual temperature indication across three distinct zones. This bilayer structure not only addresses the TCR challenge but also provides real-time, user-friendly temperature monitoring. The resulting composite demonstrates consistent performance and high precision under diverse heating conditions, making it ideal for wearable thermotherapy pads. This study highlights a significant advancement in developing multifunctional, temperature-responsive materials, offering a promising solution for safer and more controllable wearable devices. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in 'Materials and Processing' 2024)

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17 pages, 12970 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Design of Dielectric Elastomer Actuator and Its Application in Flexible Gripper

by Xiaoyu Meng, Jiaqing Xie, Haoran Pang, Wenchao Wei, Jiping Niu, Mingqiang Zhu, Fang Gu, Xiaohuan Fan and Haiyan Fan

Micromachines 2025, 16(1), 107; https://doi.org/10.3390/mi16010107 - 19 Jan 2025

Cited by 1 | Viewed by 2239

Abstract

Dielectric elastomer actuators (DEAs) are difficult to apply to flexible grippers due to their small deformation range and low output force. Hence, a DEA with a large bending deformation range and output force was designed, and a corresponding flexible gripper was developed to [...] Read more.

Dielectric elastomer actuators (DEAs) are difficult to apply to flexible grippers due to their small deformation range and low output force. Hence, a DEA with a large bending deformation range and output force was designed, and a corresponding flexible gripper was developed to realize the function of grasping objects of different shapes. The relationship between the pre-stretch ratio and DEA deformation degree was tested by experiments. Based on the performance test results of the dielectric elastomer (DE), the bending deformation process of DEAs with different shapes was simulated by Finite Element Method (FEM) simulation. DEAs with different shapes were prepared through laser cutting and the relationship between the voltage and the bending angle, and the output force of the DEAs was measured. The result shows that under uniaxial stretching, the deformation of the DEA in the stretching direction gradually increases and decreases in the unstretched direction with the increase in the pre-stretch ratio. Under biaxial stretching, DEA deformation increases with the increase in the pre-stretch ratio. The shape of the DEA has a certain influence on the bending deformation range under the same conditions, and the elliptical DEA has a larger bending deformation range and higher output force compared with the rectangular DEA and the trapezium DEA. The elliptical DEA can produce a bending deformation of 40° and an output force of 37.2 mN at a voltage of 24 kV. The three-finger flexible gripper composed of an elliptical DEA can realize the grasping of a paper cup. Full article

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11 pages, 3416 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Efficient Particle Manipulation Using Contraction–Expansion Microchannels Embedded with Hook-Shaped Arrays

by Di Huang, Yan Zhao, Chao Cao and Jiyun Zhao

Micromachines 2025, 16(1), 83; https://doi.org/10.3390/mi16010083 - 13 Jan 2025

Cited by 1 | Viewed by 1063

Abstract

Inertial microfluidics, as an efficient method for the manipulation of micro-/nanoparticles, has garnered significant attention due to its advantages of high throughput, structural simplicity, no need for external fields, and sheathless operation. Common structures include straight channels, contraction–expansion array (CEA) channels, spiral channels, [...] Read more.

Inertial microfluidics, as an efficient method for the manipulation of micro-/nanoparticles, has garnered significant attention due to its advantages of high throughput, structural simplicity, no need for external fields, and sheathless operation. Common structures include straight channels, contraction–expansion array (CEA) channels, spiral channels, and serpentine channels. In this study, we developed a CEA channel embedded with hook-shaped microstructures to modify the characteristics of vortices. Through experimental studies, we investigated the particles’ migration mechanisms within the proposed structure. The findings indicated that, in comparison to conventional rectangular microstructures, the particles within the hook-shaped microstructured CEA channels experienced a more pronounced influence from inertial lift forces. Moreover, the magnitude of the second flow within the novel configuration was directly proportional to the channel width, the length of the expansion segment, and the embedding depth of the microstructure. The innovative structure was subsequently employed for particle trapping, focusing, and separation. The experimental outcomes revealed focusing efficiency of up to 99.1% and sorting efficiency of up to 97%. This research holds the potential to enhance the foundational theory of Dean flows and broaden the application spectrum of inertial contraction–expansion microfluidic chips. Full article

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10 pages, 3639 KB

Open AccessFeature PaperEditor’s ChoiceArticle

On-Chip DNA Assembly via Dielectrophoresis

by Xichuan Rui, Lin-Sheng Wu and Xin Zhao

Micromachines 2025, 16(1), 76; https://doi.org/10.3390/mi16010076 - 11 Jan 2025

Viewed by 1132

Abstract

On-chip gene synthesis has the potential to improve the synthesis throughput and reduce the cost exponentially. While there exist several microarray-based oligo synthesis technologies, on-chip gene assembly has yet to be demonstrated. This work introduces a novel on-chip DNA assembly method via dielectrophoresis [...] Read more.

On-chip gene synthesis has the potential to improve the synthesis throughput and reduce the cost exponentially. While there exist several microarray-based oligo synthesis technologies, on-chip gene assembly has yet to be demonstrated. This work introduces a novel on-chip DNA assembly method via dielectrophoresis (DEP) that can potentially be integrated with microarray-based oligo synthesis on the same chip. Our DEP chip can selectively manipulate oligos and guide their movement without perturbing the surrounding fluid medium, thus aiding in DNA assembly. Helical forked electrode design has been optimized for compatibility with DEP, ensuring efficient control over target oligos. By applying an alternating current signal set at 2 MHz, we successfully achieve the desired directed movement of oligonucleotides. Additionally, chemical treatments combined with photoirradiation enabled the connection of complementary gene sequences and the subsequent release of single-stranded DNA products. Sequencing results validate the effective assembly of DNA fragments, approximately 500 base pairs in length, using our DEP device. Full article

(This article belongs to the Collection Micro/Nanoscale Electrokinetics)

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22 pages, 9323 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Magnetic Field-Assisted Orientation and Positioning of Magnetite for Flexible and Electrically Conductive Sensors

by David Seixas Esteves, Amanda Melo, Sónia Alves, Nelson Durães, Maria C. Paiva and Elsa W. Sequeiros

Micromachines 2025, 16(1), 68; https://doi.org/10.3390/mi16010068 - 8 Jan 2025

Cited by 1 | Viewed by 1655

Abstract

Magnetic field-assisted control of magnetite location is a promising strategy for developing flexible, electrically conductive sensors with enhanced performance and adjustable properties. This study investigates the effect of static magnetic fields applied on thermoplastic elastomer (TPE) composites with magnetite and multi-walled carbon nanotubes [...] Read more.

Magnetic field-assisted control of magnetite location is a promising strategy for developing flexible, electrically conductive sensors with enhanced performance and adjustable properties. This study investigates the effect of static magnetic fields applied on thermoplastic elastomer (TPE) composites with magnetite and multi-walled carbon nanotubes (MWCNT). The composites were prepared by compression moulding and the magnetic field was applied on the mould cavity during processing. Composites were prepared with a range of concentrations of magnetite (1, 3, and 6 wt.%) and MWCNT (1 and 3 wt.%). The effect of particle concentration on composite viscosity was investigated. Rheological analysis showed that MWCNTs significantly increased the composite viscosity while magnetite had minimal impact, ensuring stable processing and facilitating particle orientation under a static magnetic field. Particle orientation and electrical conductivity were evaluated for the composites prepared with different particle concentrations under different processing temperatures. Magnetic field application at 190 °C enhanced magnetite/MWCNT interactions, substantially reducing electrical resistivity while preserving thermal stability. The composites showed no degradation at 220 °C and above, demonstrating suitability for high-temperature applications requiring thermal resilience. Furthermore, magnetite’s magnetic response facilitated precise sensor positioning and strong adhesion to polyimide substrates at 220 °C. These findings demonstrate a scalable and adaptable approach for enhancing sensor performance and positioning, with broad potential in flexible electronics. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in 'Materials and Processing' 2024)

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15 pages, 15321 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Picosecond Laser Etching of Glass Spiral Microfluidic Channel for Microparticles Dispersion and Sorting

by Rong Chen, Shanshan He, Xiansong He, Jin Xie and Xicong Zhu

Micromachines 2025, 16(1), 66; https://doi.org/10.3390/mi16010066 - 7 Jan 2025

Cited by 1 | Viewed by 1324

Abstract

In microfluidic chips, glass free-form microchannels have obvious advantages in thermochemical stability and biocompatibility compared to polymer-based channels, but they face challenges in processing morphology and quality. Hence, picosecond laser etching with galvanometer scanning is proposed to machine spiral microfluidic channels on a [...] Read more.

In microfluidic chips, glass free-form microchannels have obvious advantages in thermochemical stability and biocompatibility compared to polymer-based channels, but they face challenges in processing morphology and quality. Hence, picosecond laser etching with galvanometer scanning is proposed to machine spiral microfluidic channels on a glass substrate. The objective is to disperse and sort microparticles from a glass microchip that is difficult to cut. First, the micropillar array and the spiral microchannel were designed to disperse and sort the particles in microchips, respectively; then, a scanning path with a scanning interval of 5 μm was designed according to the spot diameter in picosecond laser etching; next, the effects of laser power, scanning speed and accumulation times were experimentally investigated regarding the morphology of spiral microchannels; finally, the microfluidic flowing test with 5 μm and 10 μm microparticles was performed to analyze the dispersing and sorting performance. It was shown that reducing the laser power and accumulation times alongside increasing the scanning speed effectively reduced the channel depth and surface roughness. The channel surface roughness reached about 500 nm or less when the laser power was 9 W, the scanning speed was 1000 mm/s, and the cumulative number was 4. The etched micropillar array, with a width of 89 μm and an interval of 97 μm, was able to disperse the different microparticles into the spiral microchannel. Moreover, the spiral-structured channel, with an aspect ratio of 0.51, significantly influenced the velocity gradient distribution, particle focusing, and stratification. At flow rates of 300–600 μL/min, the microparticles produced stable focusing bands. Through the etched microchip, mixed 5 μm and 10 μm microparticles were sorted by stable laminar flow at flow rates of 400–500 μL/min. These findings contribute to the design and processing of high-performance glass microfluidic chips for dispersion and sorting. Full article

(This article belongs to the Special Issue Integrated Photonics and Optoelectronics, 2nd Edition)

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32 pages, 1239 KB

Open AccessFeature PaperEditor’s ChoiceReview

A Concise Review of Recent Advancements in Carbon Nanotubes for Aerospace Applications

by Silvia Zecchi, Giovanni Cristoforo, Erik Piatti, Daniele Torsello, Gianluca Ghigo, Alberto Tagliaferro, Carlo Rosso and Mattia Bartoli

Micromachines 2025, 16(1), 53; https://doi.org/10.3390/mi16010053 - 31 Dec 2024

Cited by 5 | Viewed by 4975

Abstract

Carbon nanotubes (CNTs) have attracted significant attention in the scientific community and in the industrial environment due to their unique structure and remarkable properties, including mechanical strength, thermal stability, electrical conductivity, and chemical inertness. Despite their potential, large-scale applications have been limited by [...] Read more.

Carbon nanotubes (CNTs) have attracted significant attention in the scientific community and in the industrial environment due to their unique structure and remarkable properties, including mechanical strength, thermal stability, electrical conductivity, and chemical inertness. Despite their potential, large-scale applications have been limited by challenges such as high production costs and catalyst contamination. In aerospace applications, CNTs have demonstrated considerable promise either in the form of thin layers or as reinforcements in polymer and metal matrices, where they enhance mechanical, thermal, and electromagnetic performance in lightweight composites. In this short review, we provide an overview of CNTs’ properties and structures, explore CNT growth methods, with a focus on chemical vapor deposition (CVD), and examine their integration into aerospace materials both as films and as multifunctional reinforcements. Full article

(This article belongs to the Special Issue MEMS Nano/Micro Fabrication, 2nd Edition)

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24 pages, 9570 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Fringe Texture Driven Droplet Measurement End-to-End Network Based on Physics Aberrations Restoration of Coherence Scanning Interferometry

by Zhou Zhang, Jiankui Chen, Hua Yang and Zhouping Yin

Micromachines 2025, 16(1), 42; https://doi.org/10.3390/mi16010042 - 30 Dec 2024

Viewed by 1026

Abstract

Accurate and efficient measurement of deposited droplets’ volume is vital to achieve zero-defect manufacturing in inkjet printed organic light-emitting diode (OLED), but it remains a challenge due to droplets’ featurelessness. In our work, coherence scanning interferometry (CSI) is utilized to measure the volume. [...] Read more.

Accurate and efficient measurement of deposited droplets’ volume is vital to achieve zero-defect manufacturing in inkjet printed organic light-emitting diode (OLED), but it remains a challenge due to droplets’ featurelessness. In our work, coherence scanning interferometry (CSI) is utilized to measure the volume. However, the CSI redundant sampling and image degradation led by the sample’s transparency decrease the efficiency and accuracy. Based on the prior degradation and strong representation for context, a novel method, volume measurement via fringe distribution module (VMFD), is proposed to directly measure the volume by single interferogram without redundant sampling. Firstly, the 3D point spread function (PSF) for CSI imaging is modeling to relate the degradation and image. Secondly, the Zernike to PSF (ZTP) module is proposed to efficiently compute the aberrations to PSF. Then, a physics aberration restoration network (PARN) is designed to remove the degradation via the channel Transformer and U-net architecture. The long term context is learned by PARN and beneficial to restoration. The restored fringes are used to measure the droplet’s volume by constrained regression network (CRN) module. Finally, the performances on public datasets and the volume measurement experiments show the promising deblurring, measurement precision and efficiency. Full article

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16 pages, 7509 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Highly Sensitive Non-Dispersive Infrared Gas Sensor with Innovative Application for Monitoring Carbon Dioxide Emissions from Lithium-Ion Battery Thermal Runaway

by Liang Luo, Jianwei Chen, Aisn Gioronara Hui, Rongzhen Liu, Yao Zhou, Haitong Liang, Ziyuan Wang, Haosu Luo and Fei Fang

Micromachines 2025, 16(1), 36; https://doi.org/10.3390/mi16010036 - 29 Dec 2024

Cited by 4 | Viewed by 5270

Abstract

The safety of power batteries in the automotive industry is of paramount importance and cannot be emphasized enough. As lithium-ion battery technology continues to evolve, the energy density of these batteries increases, thereby amplifying the potential risks linked to battery failures. This study [...] Read more.

The safety of power batteries in the automotive industry is of paramount importance and cannot be emphasized enough. As lithium-ion battery technology continues to evolve, the energy density of these batteries increases, thereby amplifying the potential risks linked to battery failures. This study explores pivotal safety challenges within the electric vehicle sector, with a particular focus on thermal runaway and gas emissions originating from lithium-ion batteries. We offer a non-dispersive infrared (NDIR) gas sensor designed to efficiently monitor battery emissions. Notably, carbon dioxide (CO₂) gas sensors are emphasized for their ability to enhance early-warning systems, facilitating the timely detection of potential issues and, in turn, improving the overall safety standards of electric vehicles. In this study, we introduce a novel CO₂ gas sensor based on the advanced pyroelectric single-crystal lead niobium magnesium titanate (PMNT), which exhibits exceptionally high pyroelectric properties compared to commercially available materials, such as lithium tantalate single crystals and lead zirconate titanate ceramics. The specific detection rate of PMNT single-crystal pyroelectric infrared detectors is more than four times higher than lithium tantalate single-crystal infrared detectors. The PMNT single-crystal NDIR gas detector is used to monitor thermal runaway in lithium-ion batteries, enabling the rapid and highly accurate detection of gases released by the battery. This research offers an in-depth exploration of real-time monitoring for power battery safety, utilizing the cutting-edge pyroelectric single-crystal gas sensor. Beyond providing valuable insights, the study also presents practical recommendations for mitigating the risks of thermal runaway in lithium-ion batteries, with a particular emphasis on the development of effective warning systems. Full article

(This article belongs to the Special Issue Gas Sensors: From Fundamental Research to Applications)

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13 pages, 5571 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Tilted-Mode All-Optical Diffractive Deep Neural Networks

by Mingzhu Song, Xuhui Zhuang, Lu Rong and Junsheng Wang

Micromachines 2025, 16(1), 8; https://doi.org/10.3390/mi16010008 - 25 Dec 2024

Viewed by 904

Abstract

Diffractive deep neural networks (D²NNs) typically adopt a densely cascaded arrangement of diffractive masks, leading to multiple reflections of diffracted light between adjacent masks, thereby affecting the network’s inference capability. It is challenging to fully simulate this multiple-reflection phenomenon. To eliminate [...] Read more.

Diffractive deep neural networks (D²NNs) typically adopt a densely cascaded arrangement of diffractive masks, leading to multiple reflections of diffracted light between adjacent masks, thereby affecting the network’s inference capability. It is challenging to fully simulate this multiple-reflection phenomenon. To eliminate this phenomenon, we designed tilted-mode all-optical diffractive deep neural networks (T-D²NNs) and proposed a theoretical model for diffraction propagation in the tilted mode. Simulation results indicate that T-D²NNs address the performance degradation caused by interlayer reflections in D²NNs constructed with high-index diffractive masks. In classification tasks, T-D²NNs achieve better classification results compared to D²NNs that consider interlayer reflections. Full article

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12 pages, 3116 KB

Open AccessEditor’s ChoiceArticle

Origin of the Temperature Dependence of Gate-Induced Drain Leakage-Assisted Erase in Three-Dimensional nand Flash Memories

by David G. Refaldi, Gerardo Malavena, Luca Chiavarone, Alessandro S. Spinelli and Christian Monzio Compagnoni

Micromachines 2024, 15(12), 1516; https://doi.org/10.3390/mi15121516 - 20 Dec 2024

Cited by 1 | Viewed by 1359

Abstract

Through detailed experimental and modeling activities, this paper investigates the origin of the temperature dependence of the Erase operation in 3D nand flash arrays. First of all, experimental data collected down to the cryogenic regime on both charge-trap and floating-gate arrays are provided [...] Read more.

Through detailed experimental and modeling activities, this paper investigates the origin of the temperature dependence of the Erase operation in 3D nand flash arrays. First of all, experimental data collected down to the cryogenic regime on both charge-trap and floating-gate arrays are provided to demonstrate that the reduction in temperature makes cells harder to Erase irrespective of the nature of their storage layer. This evidence is then attributed to the weakening, with the decrease in temperature, of the gate-induced drain leakage (GIDL) current exploited to set the electrostatic potential of the body of the nand strings during Erase. Modeling results for the GIDL-assisted Erase operation, finally, allow not only to support this conclusion but also to directly correlate the change with temperature of the electrostatic potential of the string body with the change with temperature of the erased threshold-voltage of the memory cells. Full article

(This article belongs to the Section E：Engineering and Technology)

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13 pages, 3683 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Automatic Single-Cell Harvesting for Fetal Nucleated Red Blood Cell Isolation on a Self-Assemble Cell Array (SACA) Chip

by Hsin-Yu Yang, Che-Hsien Lin, Yi-Wen Hu, Chih-Hsuan Chien, Mu-Chi Huang, Chun-Hao Lai, Jen-Kuei Wu and Fan-Gang Tseng

Micromachines 2024, 15(12), 1515; https://doi.org/10.3390/mi15121515 - 20 Dec 2024

Cited by 1 | Viewed by 1704

Abstract

(1) Background: Fetal chromosomal examination is a critical component of modern prenatal testing. Traditionally, maternal serum biomarkers such as free β-human chorionic gonadotropin (Free β-HCG) and pregnancy-associated plasma protein A (PAPPA) have been employed for screening, achieving a detection rate of approximately 90% [...] Read more.

(1) Background: Fetal chromosomal examination is a critical component of modern prenatal testing. Traditionally, maternal serum biomarkers such as free β-human chorionic gonadotropin (Free β-HCG) and pregnancy-associated plasma protein A (PAPPA) have been employed for screening, achieving a detection rate of approximately 90% for fetuses with Down syndrome, albeit with a false positive rate of 5%. While amniocentesis remains the gold standard for the prenatal diagnosis of chromosomal abnormalities, including Down syndrome and Edwards syndrome, its invasive nature carries a significant risk of complications, such as infection, preterm labor, or miscarriage, occurring at a rate of 7 per 1000 procedures. Beyond Down syndrome and Edwards syndrome, other chromosomal abnormalities, such as trisomy of chromosomes 9, 16, or Barr bodies, pose additional diagnostic challenges. Non-invasive prenatal testing (NIPT) has emerged as a powerful alternative for fetal genetic screening by leveraging maternal blood sampling. However, due to the extremely low abundance of fetal cells in maternal circulation, NIPT based on fetal cells faces substantial technical challenges. (2) Methods: Fetal nucleated red blood cells (FnRBCs) were first identified in maternal circulation in a landmark study published in The Lancet in 1959. Due to their fetal origin and presence in maternal peripheral blood, FnRBCs represent an ideal target for non-invasive prenatal testing (NIPT). In this study, we introduce a novel self-assembled cell array (SACA) chip system, a microfluidic-based platform designed to efficiently settle and align cells into a monolayer at the chip’s base within five minutes using lateral flow dynamics and gravity. This system is integrated with a fully automated, multi-channel fluorescence scanning module, enabling the real-time imaging and molecular profiling of fetal cells through fluorescence-tagged antibodies. By employing a combination of Hoechst+/CD71+/HbF+/CD45− markers, the platform achieves the precise enrichment and isolation of FnRBCs at the single-cell level from maternal peripheral blood. (3) Results: The SACA chip system effectively reduces the displacement of non-target cells by 31.2%, achieving a single-cell capture accuracy of 97.85%. This isolation and enrichment system for single cells is well suited for subsequent genetic analysis. Furthermore, the platform achieves a high purity of isolated cells, overcoming the concentration detection limit of short tandem repeat (STR) analysis, demonstrating its capability for reliable non-invasive prenatal testing. (4) Conclusions: This study demonstrates that the SACA chip, combined with an automated image positioning system, can efficiently isolate single fetal nucleated red blood cells (FnRBCs) from 50 million PBMCs in 2 mL of maternal blood, completing STR analysis within 120 min. With higher purification efficiency compared to existing NIPT methods, this platform shows great promise for prenatal diagnostics and potential applications in other clinical fields. Full article

(This article belongs to the Special Issue Application of Microfluidic Technology in Bioengineering)

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12 pages, 3196 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Hollow Fiber Microreactor Combined with Digital Twin to Optimize the Antimicrobial Evaluation Process

by Kazuhiro Noda, Toshihiro Kasama, Marie Shinohara, Masakaze Hamada, Yukiko T. Matsunaga, Madoka Takai, Yoshikazu Ishii and Ryo Miyake

Micromachines 2024, 15(12), 1517; https://doi.org/10.3390/mi15121517 - 20 Dec 2024

Viewed by 1111

Abstract

In order to reproduce pharmacokinetics (PK) profiles seen in vivo, the Hollow Fiber Infection Model (HFIM) is a useful in vitro module in the evaluation of antimicrobial resistance. In order to reduce the consumption of culture medium and drugs, we developed a hollow [...] Read more.

In order to reproduce pharmacokinetics (PK) profiles seen in vivo, the Hollow Fiber Infection Model (HFIM) is a useful in vitro module in the evaluation of antimicrobial resistance. In order to reduce the consumption of culture medium and drugs, we developed a hollow fiber microreactor applicable to the HFIM by integrating the HFIM function. Next, we constructed a novel control method by using the “digital twin” of the microreactor to achieve precise concentration control. By integrating functions of the HFIM, the extra-capillary space volume was reduced to less than 1/10 of conventional HFIM. The control method with the digital twin can keep drug concentration in the extra-capillary space within an error of 10% under simulated drug destruction. The control method with the digital twin can also stabilize the drug concentration both in the intra-capillary space and the extra-capillary space within 15 min. Full article

(This article belongs to the Section C：Chemistry)

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9 pages, 2086 KB

Open AccessFeature PaperEditor’s ChoiceArticle

White Light-Emitting Flexible Displays with Quantum-Dot Film and Greenish-Blue Organic Light-Emitting Diodes

by Young Woo Kim, Seojin Kim, Chaeyeong Lee, Joo Hyun Jeong, Yun Hyeok Jeong, Yuhwa Bak, Seo Hyeon Kim, Sung Jin Park, Ko Eun Ham, Doeun Lee, Junpyo Song, Youngjin Song, Seung-Chan Jung, Oh Kwan Kwon, Jae-Hee Han, Sang Jik Kwon, Eou-Sik Cho and Yongmin Jeon

Micromachines 2024, 15(12), 1518; https://doi.org/10.3390/mi15121518 - 20 Dec 2024

Cited by 2 | Viewed by 1470

Abstract

White organic light-emitting diodes (OLEDs) represent a significant technology in the display industry for the achievement of full color. However, sophisticated technologies are required for white light emission. In this paper, we developed a simple white light-emitting display device using a quantum-dot (QD) [...] Read more.

White organic light-emitting diodes (OLEDs) represent a significant technology in the display industry for the achievement of full color. However, sophisticated technologies are required for white light emission. In this paper, we developed a simple white light-emitting display device using a quantum-dot (QD) film and a greenish-blue OLED. The resulting QD-OLED produced a high-purity white color with a color temperature of 6000 K (CIE_x,y = 0.32, 0.34) and achieved a maximum brightness of 14,638 cd/m² at 7 V. This paper reports the fabrication of a white light-emitting QD-OLED with a straightforward structure and technology suitable for flexible displays. Full article

(This article belongs to the Special Issue Organic Electronic-Based Devices for Biomedical Applications)

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15 pages, 4141 KB

Open AccessFeature PaperEditor’s ChoiceArticle

The Role of Re-Entrant Microstructures in Modulating Droplet Evaporation Modes

by Hoang Huy Vu, Nam-Trung Nguyen and Navid Kashaninejad

Micromachines 2024, 15(12), 1507; https://doi.org/10.3390/mi15121507 - 18 Dec 2024

Cited by 1 | Viewed by 1034

Abstract

The evaporation dynamics of sessile droplets on re-entrant microstructures are critical for applications in microfluidics, thermal management, and self-cleaning surfaces. Re-entrant structures, such as mushroom-like shapes with overhanging features, trap air beneath droplets to enhance non-wettability. The present study examines the evaporation of [...] Read more.

The evaporation dynamics of sessile droplets on re-entrant microstructures are critical for applications in microfluidics, thermal management, and self-cleaning surfaces. Re-entrant structures, such as mushroom-like shapes with overhanging features, trap air beneath droplets to enhance non-wettability. The present study examines the evaporation of a water droplet on silicon carbide (SiC) and silicon dioxide (SiO₂) re-entrant structures, focusing on the effects of material composition and solid area fraction on volume reduction, contact angle, and evaporation modes. Using surface free energy (SFE) as an indicator of wettability, we find that the low SFE of SiC promotes quick depinning and contact line retraction, resulting in shorter CCL phases across different structures. For instance, the CCL phase accounts for 55–59% of the evaporation time on SiC surfaces, while on SiO₂ it extends to 51–68%, reflecting a 7–23% increase in duration due to stronger pinning effects. Additionally, narrower pillar gaps, which increase the solid area fraction, further stabilize droplets by extending both CCL and constant contact angle (CCA) phases, while wider gaps enable faster depinning and evaporation. These findings illustrate how hydrophobicity (via SFE) and structural geometry (via solid area fraction) influence microscale interactions, offering insights for designing surfaces with optimized liquid management properties. Full article

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9 pages, 2483 KB

Open AccessFeature PaperEditor’s ChoiceArticle

PET-PZT Dielectric Polarization: Electricity Harvested from Photon Energy

by Alex Nikolov, Sohail Murad and Jongju Lee

Micromachines 2024, 15(12), 1505; https://doi.org/10.3390/mi15121505 - 18 Dec 2024

Cited by 1 | Viewed by 1050

Abstract

The effect of residual stress or heat on ferroelectrics used to convert photons into electricity was investigated. The data analysis reveals that when the PET-PZT piezoelectric transducer is UV-irradiated with a 405 nm wavelength, it becomes a photon–heat–stress electric energy converter and capacitator. [...] Read more.

The effect of residual stress or heat on ferroelectrics used to convert photons into electricity was investigated. The data analysis reveals that when the PET-PZT piezoelectric transducer is UV-irradiated with a 405 nm wavelength, it becomes a photon–heat–stress electric energy converter and capacitator. Our objective was to evaluate the PET-PZT photon–heat–stress electric energy conversion performance and the role of the light’s wavelength and intensity. Converting waste energy from energy-intensive processes and systems is crucial to reducing the environmental impact and achieving net-zero emissions. To achieve these, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. Full article

(This article belongs to the Collection Piezoelectric Transducers: Materials, Devices and Applications)

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19 pages, 506 KB

Open AccessEditor’s ChoiceReview

MOSFET-Based Voltage Reference Circuits in the Last Decade: A Review

by Elisabetta Moisello, Edoardo Bonizzoni and Piero Malcovati

Micromachines 2024, 15(12), 1504; https://doi.org/10.3390/mi15121504 - 17 Dec 2024

Cited by 5 | Viewed by 4518

Abstract

Voltage reference circuits are a basic building block in most integrated microsystems, covering a wide spectrum of applications. Hence, they constitute a subject of great interest for the entire microelectronics community. MOSFET-based solutions, in particular, have emerged as the implementation of choice for [...] Read more.

Voltage reference circuits are a basic building block in most integrated microsystems, covering a wide spectrum of applications. Hence, they constitute a subject of great interest for the entire microelectronics community. MOSFET-based solutions, in particular, have emerged as the implementation of choice for realizing voltage reference circuits, given the supply voltage scaling and the ever-lower power consumption specifications in various applications. For these reasons, this paper aims to review MOSFET-based voltage reference circuits, illustrating their principles of operation, as well as presenting a detailed overview of the state-of-the-art, in order to paint an accurate picture of the encountered challenges and proposed solutions found in the field in the last decade, thus providing a starting point for future research in the field. Full article

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21 pages, 4915 KB

Open AccessFeature PaperEditor’s ChoiceReview

A Review of Cascaded Metasurfaces for Advanced Integrated Devices

by Lingyun Zhang, Zeyu Zhao, Leying Tao, Yixiao Wang, Chi Zhang, Jianing Yang, Yongqiang Jiang, Huiqi Duan, Xiaoguang Zhao, Shaolong Chen and Zilun Wang

Micromachines 2024, 15(12), 1482; https://doi.org/10.3390/mi15121482 - 10 Dec 2024

Cited by 2 | Viewed by 2720

Abstract

This paper reviews the field of cascaded metasurfaces, which are advanced optical devices formed by stacking or serially arranging multiple metasurface layers. These structures leverage near-field and far-field electromagnetic (EM) coupling mechanisms to enhance functionalities beyond single-layer metasurfaces. This review comprehensively discusses the [...] Read more.

This paper reviews the field of cascaded metasurfaces, which are advanced optical devices formed by stacking or serially arranging multiple metasurface layers. These structures leverage near-field and far-field electromagnetic (EM) coupling mechanisms to enhance functionalities beyond single-layer metasurfaces. This review comprehensively discusses the physical principles, design methodologies, and applications of cascaded metasurfaces, focusing on both static and dynamic configurations. Near-field-coupled structures create new resonant modes through strong EM interactions, allowing for efficient control of light properties like phase, polarization, and wave propagation. Far-field coupling, achieved through greater interlayer spacing, enables traditional optical methods for design, expanding applications to aberration correction, spectrometers, and retroreflectors. Dynamic configurations include tunable devices that adjust their optical characteristics through mechanical motion, making them valuable for applications in beam steering, varifocal lenses, and holography. This paper concludes with insights into the potential of cascaded metasurfaces to create multifunctional, compact optical systems, setting the stage for future innovations in miniaturized and integrated optical devices. Full article

(This article belongs to the Special Issue Terahertz and Infrared Metamaterial Devices, 3nd Edition)

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18 pages, 6309 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Near-Field Direct Writing Based on Piezoelectric Micromotion for the Programmable Manufacturing of Serpentine Structures

by Xun Chen, Xuanzhi Zhang, Jianfeng Sun, Rongguang Zhang, Xuanyang Liang, Jiecai Long, Jingsong Yao, Xin Chen, Han Wang, Yu Zhang, Jiewu Leng and Renquan Lu

Micromachines 2024, 15(12), 1478; https://doi.org/10.3390/mi15121478 - 7 Dec 2024

Cited by 1 | Viewed by 1436

Abstract

Serpentine microstructures offer excellent physical properties, making them highly promising in applications in stretchable electronics and tissue engineering. However, existing fabrication methods, such as electrospinning and lithography, face significant challenges in producing microscale serpentine structures that are cost-effective, efficient, and controllable. These methods [...] Read more.

Serpentine microstructures offer excellent physical properties, making them highly promising in applications in stretchable electronics and tissue engineering. However, existing fabrication methods, such as electrospinning and lithography, face significant challenges in producing microscale serpentine structures that are cost-effective, efficient, and controllable. These methods often struggle with achieving precise control over fiber morphology and scalability. In this study, we developed a near-field direct writing (NFDW) technique incorporating piezoelectric micromotion to enable the precise fabrication of serpentine micro-/nanofibers by incorporating micromotion control with macroscopic movement. Modifying the fiber structure allowed for adjustments to the mechanical properties, including tunable extensibility and distinct characteristics. Through the control of the frequency and amplitude of the piezoelectric signal, the printing errors were reduced to below 9.48% in the cycle length direction and 6.33% in the peak height direction. A predictive model for the geometrical extensibility of serpentine structures was derived from Legendre’s incomplete elliptic integral of the second kind and incorporated an error correction factor, which significantly reduced the calculation errors in predicting geometric elongation, by 95.85%. The relationship between microstructure bending and biomimetic non-linear mechanical behavior was explored through tensile testing. By controlling the input electrical signals, highly ordered serpentine microstructures were successfully fabricated, demonstrating potential for use in biomimetic mechanical scaffolds. Full article

(This article belongs to the Special Issue Advanced Manufacturing Technology and Systems, 3rd Edition)

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23 pages, 11501 KB

Open AccessFeature PaperEditor’s ChoiceReview

Advances in 2D Molybdenum Disulfide Transistors for Flexible and Wearable Electronics

by Kyoungwon Kwak, Hyewon Yoon, Seongin Hong and Byung Ha Kang

Micromachines 2024, 15(12), 1476; https://doi.org/10.3390/mi15121476 - 5 Dec 2024

Cited by 1 | Viewed by 2763

Abstract

As the trajectory of developing advanced electronics is shifting towards wearable electronics, various methods for implementing flexible and bendable devices capable of conforming to curvilinear surfaces have been widely investigated. In particular, achieving high-performance and stable flexible transistors remains a significant technical challenge, [...] Read more.

As the trajectory of developing advanced electronics is shifting towards wearable electronics, various methods for implementing flexible and bendable devices capable of conforming to curvilinear surfaces have been widely investigated. In particular, achieving high-performance and stable flexible transistors remains a significant technical challenge, as transistors are fundamental components of electronics, playing a key role in overall performance. Among the wide range of candidates for flexible transistors, two-dimensional (2D) molybdenum disulfide (MoS₂)-based transistors have emerged as potential solutions to address these challenges. Unlike other 2D materials, the 2D MoS₂ offers numerous advantages, such as high carrier mobility, a tunable bandgap, superior mechanical strength, and exceptional chemical stability. This review emphasizes the novel techniques of the fabrication process, structure, and material to achieve flexible MoS₂ transistor-based applications. Furthermore, the distinctive feature of this review is its focus on studies published in high-impact journals over the past decade, emphasizing their methods for developing MoS₂ transistors into various applications. Finally, the review addresses technical challenges and provides an outlook for flexible and wearable MoS₂ transistors. Full article

(This article belongs to the Special Issue New Advances in Wearable and Flexible Sensor Devices and Their Future Prospects)

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59 pages, 20006 KB

Open AccessFeature PaperEditor’s ChoiceReview

Magnetoelectric BAW and SAW Devices: A Review

by Bin Luo, Prasanth Velvaluri, Yisi Liu and Nian-Xiang Sun

Micromachines 2024, 15(12), 1471; https://doi.org/10.3390/mi15121471 - 3 Dec 2024

Cited by 6 | Viewed by 3586

Abstract

Magnetoelectric (ME) devices combining piezoelectric and magnetostrictive materials have emerged as powerful tools to miniaturize and enhance sensing and communication technologies. This paper examines recent developments in bulk acoustic wave (BAW) and surface acoustic wave (SAW) ME devices, which demonstrate unique capabilities in [...] Read more.

Magnetoelectric (ME) devices combining piezoelectric and magnetostrictive materials have emerged as powerful tools to miniaturize and enhance sensing and communication technologies. This paper examines recent developments in bulk acoustic wave (BAW) and surface acoustic wave (SAW) ME devices, which demonstrate unique capabilities in ultra-sensitive magnetic sensing, compact antennas, and quantum applications. Leveraging the mechanical resonance of BAW and SAW modes, ME sensors achieve the femto- to pico-Tesla sensitivity ideal for biomedical applications, while ME antennas, operating at acoustic resonance, allow significant size reduction, with high radiation gain and efficiency, which is suited for bandwidth-restricted applications. In addition, ME non-reciprocal magnetoacoustic devices using hybrid magnetoacoustic waves present novel solutions for RF isolation, which have also shown potential for the efficient control of quantum defects, such as negatively charged nitrogen-vacancy (NV⁻) centers. Continued advancements in materials and device structures are expected to further enhance ME device performance, positioning them as key components in future bio-sensing, wireless communication, and quantum information technologies. Full article

(This article belongs to the Special Issue Novel Surface and Bulk Acoustic Wave Devices)

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14 pages, 4290 KB

Open AccessFeature PaperEditor’s ChoiceArticle

A Thermal Cycler Based on Magnetic Induction Heating and Anti-Freezing Water Cooling for Rapid PCR

by Yaping Xie, Qin Jiang, Chang Chang, Xin Zhao, Haochen Yong, Xingxing Ke and Zhigang Wu

Micromachines 2024, 15(12), 1462; https://doi.org/10.3390/mi15121462 - 30 Nov 2024

Cited by 2 | Viewed by 1961

Abstract

Distinguished by its exceptional sensitivity and specificity, Polymerase Chain Reaction (PCR) is a pivotal technology for pathogen detection. However, traditional PCR instruments that employ thermoelectric cooling (TEC) are often constrained by cost, efficiency, and performance variability resulting from the fluctuations in ambient temperature. [...] Read more.

Distinguished by its exceptional sensitivity and specificity, Polymerase Chain Reaction (PCR) is a pivotal technology for pathogen detection. However, traditional PCR instruments that employ thermoelectric cooling (TEC) are often constrained by cost, efficiency, and performance variability resulting from the fluctuations in ambient temperature. Here, we present a thermal cycler that utilizes electromagnetic induction heating at 50 kHz and anti-freezing water cooling with a velocity of 0.06 m/s to facilitate rapid heating and cooling of the PCR reaction chamber, significantly enhancing heat transfer efficiency. A multi-physics theoretical heat transfer model, developed using the digital twin approach, enables precise temperature control through advanced algorithms. Experimental results reveal average heating and cooling rates of 14.92 °C/s and 13.39 °C/s, respectively, significantly exceeding those of conventional methods. Compared to commercial PCR instruments, the proposed system further optimizes cost, efficiency, and practicality. Finally, PCR experiments were successfully performed using cDNA (Hepatitis B virus) at various concentrations. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2024)

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29 pages, 10952 KB

Open AccessFeature PaperEditor’s ChoiceReview

Resolution Enhancement Strategies in Photoacoustic Microscopy: A Comprehensive Review

by Jinying Zhang, Yifan Shi, Yexiaotong Zhang, Haoran Liu, Shihao Li and Linglu Liu

Micromachines 2024, 15(12), 1463; https://doi.org/10.3390/mi15121463 - 30 Nov 2024

Cited by 3 | Viewed by 5593

Abstract

Photoacoustic imaging has emerged as a promising modality for medical imaging since its introduction. Photoacoustic microscopy (PAM), which is based on the photoacoustic effect, combines the advantages of both optical and acoustic imaging modalities. PAM facilitates high-sensitivity, high-resolution, non-contact, and non-invasive imaging by [...] Read more.

Photoacoustic imaging has emerged as a promising modality for medical imaging since its introduction. Photoacoustic microscopy (PAM), which is based on the photoacoustic effect, combines the advantages of both optical and acoustic imaging modalities. PAM facilitates high-sensitivity, high-resolution, non-contact, and non-invasive imaging by employing optical absorption as its primary contrast mechanism. The ability of PAM to specifically image parameters such as blood oxygenation and melanin content makes it a valuable addition to the suite of modern biomedical imaging techniques. This review aims to provide a comprehensive overview of the diverse technical approaches and methods employed by researchers to enhance the resolution of photoacoustic microscopy. Firstly, the fundamental principles of the photoacoustic effect and photoacoustic imaging will be presented. Subsequently, resolution enhancement methods for both acoustic-resolution photoacoustic microscopy (AR-PAM) and optical-resolution photoacoustic microscopy (OR-PAM) will be discussed independently. Finally, the aforementioned resolution enhancement methods for photoacoustic microscopy will be critically evaluated, and the current challenges and future prospects of this technology will be summarized. Full article

(This article belongs to the Special Issue Photoacoustic-Based Sensing Systems: Advances, Applications, and Innovative Measurement Strategies)

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13 pages, 8436 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Series-Fed Microstrip Patch Antenna Array with Additive-Manufactured Foldable Honeycomb-Shaped Substrate

by Sima Noghanian, Yi-Hsiang Chang, Patricio Guerron and Reena Dahle

Micromachines 2024, 15(12), 1449; https://doi.org/10.3390/mi15121449 - 29 Nov 2024

Viewed by 1561

Abstract

This paper presents a novel foldable S-band microstrip patch antenna array operating in the 2.4–2.45 GHz band. The substrate is designed to allow the array to be folded and arranged in tiles, forming a versatile, reconfigurable antenna array. Additive manufacturing is used to [...] Read more.

This paper presents a novel foldable S-band microstrip patch antenna array operating in the 2.4–2.45 GHz band. The substrate is designed to allow the array to be folded and arranged in tiles, forming a versatile, reconfigurable antenna array. Additive manufacturing is used to fabricate the substrate for ease of fabrication and flexibility in its design. The major challenge in this type of design is creating a proper method of feeding the elements while maintaining the array’s optimal performance. A novel hinge design that can hold a coaxial cable for the series-fed array is introduced. The hinge provides the capability of folding the array from a flat orientation into various folded orientations. In this paper, a 2 × 1 microstrip array unit is presented as proof of concept. The antenna was fabricated and measured, and the results of the measurements are in close agreement with the simulations. The antenna can provide a gain as high as 7.72 dBi in flat conditions. Full article

(This article belongs to the Special Issue Exploring the Potential of 5G and Millimeter-Wave Array Antennas)

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11 pages, 4563 KB

Open AccessFeature PaperEditor’s ChoiceArticle

A Spectroscopy Solution for Contactless Conductivity Detection in Capillary Electrophoresis

by Tomas Drevinskas, Audrius Maruška, Hirotaka Ihara, Makoto Takafuji, Linas Jonušauskas, Domantas Armonavičius, Mantas Stankevičius, Kristina Bimbiraitė-Survilienė, Elzbieta Skrzydlewska, Ona Ragažinskienė, Yutaka Kuwahara, Shoji Nagaoka, Vilma Kaškonienė and Loreta Kubilienė

Micromachines 2024, 15(12), 1430; https://doi.org/10.3390/mi15121430 - 28 Nov 2024

Viewed by 1403

Abstract

This paper introduces a novel contactless single-chip detector that utilizes impedance-to-digital conversion technology to measure impedance in the microfluidic channel or capillary format analytical device. The detector is designed to operate similarly to capacitively coupled contactless conductivity detectors for capillary electrophoresis or chromatography [...] Read more.

This paper introduces a novel contactless single-chip detector that utilizes impedance-to-digital conversion technology to measure impedance in the microfluidic channel or capillary format analytical device. The detector is designed to operate similarly to capacitively coupled contactless conductivity detectors for capillary electrophoresis or chromatography but with the added capability of performing frequency sweeps up to 200 kHz. At each recorded data point, impedance and phase-shift data can be extracted, which can be used to generate impedance versus frequency plots, or phase-shift versus frequency plots. Real and imaginary parts can also be calculated from the data, allowing for the generation of Nyquist diagrams. This detector represents the first of its kind in the contactless conductivity class to provide spectrum-type data, as demonstrated in capillary electrophoresis experiments. Full article

(This article belongs to the Special Issue Flows in Micro- and Nano-Systems)

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11 pages, 2125 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Novel Deposition Technique for Fabricating Films with Customized Thickness Profiles

by Chi-Yung Hsieh, Yu-Chi Lin, Xuan-Shan Huang, Jing-Ting Lin and Cheng-Sheng Huang

Micromachines 2024, 15(12), 1412; https://doi.org/10.3390/mi15121412 - 23 Nov 2024

Viewed by 1157

Abstract

This study introduces a novel deposition technique capable of depositing thin films with any arbitrary thickness profile. The apparatus consists of a fixed shadow mask and a rotating sample carrier plate. The shadow mask features a specifically designed opening curve that corresponds to [...] Read more.

This study introduces a novel deposition technique capable of depositing thin films with any arbitrary thickness profile. The apparatus consists of a fixed shadow mask and a rotating sample carrier plate. The shadow mask features a specifically designed opening curve that corresponds to the particular thickness profile of the deposited film. We successfully designed two shadow masks and used them to deposit films with linear thickness gradients of 49.3 and 86.8 Å/mm and films with sinusoidal thickness profiles with a period of 40 mm. Furthermore, a linear variable filter was designed on the basis of a quarter-wavelength stack of Si₃N₄ and SiO₂, combined with a TiO₂ cavity layer with a linearly varying thickness. By coaxially rotating the sample carrier plate relative to the shadow mask, films with the desired thickness profiles could be fabricated in a single deposition step without the need for additional rotational or translational devices inside the deposition chamber. By rotating the carrier plate, the chips attached at different circumferential positions can achieve consistent thickness profiles, making this method well-suited for mass production. Full article

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15 pages, 5497 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Spatial Discrimination Limit Analysis of Macrophage Phagocytosis Between Target Antigens and Non-Target Objects Using Microcapillary Manipulation Assay

by Maiha Ando, Dan Horonushi, Haruka Yuki, Shinya Kato, Amane Yoshida and Kenji Yasuda

Micromachines 2024, 15(11), 1394; https://doi.org/10.3390/mi15111394 - 18 Nov 2024

Viewed by 1521

Abstract

During phagocytosis, the FcGR–IgG bond is thought to be necessary to promote cell-membrane extension as the zipper mechanism. However, does this zipper mechanism provide a spatial antigen discrimination capability that allows macrophages to selectively phagocytose only antigens, especially for clusters with a mixture [...] Read more.

During phagocytosis, the FcGR–IgG bond is thought to be necessary to promote cell-membrane extension as the zipper mechanism. However, does this zipper mechanism provide a spatial antigen discrimination capability that allows macrophages to selectively phagocytose only antigens, especially for clusters with a mixture of antigens and non-antigens? To elucidate the ability and limitation of the zipper mechanism, we fed a coupled 2 μm IgG-coated and 4.5 μm non-coated polystyrene bead mixtures to macrophages and observed their phagocytosis. Macrophage engulfed the mixed clusters, including the 4.5 μm non-coated polystyrene part, indicating that the non-coated particles can be engulfed even without the zipper mechanism as far as coupled to the opsonized particles. In contrast, when the non-opsonized particle part was held by the microcapillary manipulation assay, macrophages pinched off the non-coated polystyrene particle part and internalized the opsonized particle part only. The results suggest that (1) an IgG-coated surface is needed to anchor phagocytosis by cell-membrane protrusion; however, (2) once the antibody-dependent cell phagocytosis is started, phagocytosis can proceed with the uncoated objects as the followers of the internalizing opsonized particles even without the support of the zipper mechanism. They may also indicate the concern of misleading the immune system to target unexpected objects because of their aggregation with target pathogens and the possibility of new medical applications to capture the non-opsonized target objects by the aggregation with small antigens to activate an immune response. Full article

(This article belongs to the Section B：Biology and Biomedicine)

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16 pages, 5328 KB

Open AccessEditor’s ChoiceArticle

A Polarization-Insensitive and Highly Sensitive THz Metamaterial Multi-Band Perfect Absorber

by Gang Tao, Qian Zhao, Qianju Song, Zao Yi, Yougen Yi and Qingdong Zeng

Micromachines 2024, 15(11), 1388; https://doi.org/10.3390/mi15111388 - 16 Nov 2024

Cited by 2 | Viewed by 1302

Abstract

In this article, we present a terahertz (THz) metamaterial absorber that blends two types of coordinated materials: Dirac semimetals and vanadium dioxide. Compared to other absorbers on the market, which are currently non-adjustable or have a single adjustment method, our absorber is superior [...] Read more.

In this article, we present a terahertz (THz) metamaterial absorber that blends two types of coordinated materials: Dirac semimetals and vanadium dioxide. Compared to other absorbers on the market, which are currently non-adjustable or have a single adjustment method, our absorber is superior because it has two coordinated modes with maximum adjustment ranges of 80.7% and 0.288 THz. The device contains four flawless absorption peaks (M1, M2, M3, and M4) spanning the frequency range of 2.0 THz to 6.0 THz, all with absorption rates greater than 99%. After calculation, the relative impedance of the device matches with that in free space, resulting in perfect absorption. In addition, our absorber has extremely excellent polarization insensitivity but is highly sensitive to changes in the environmental refractive index, with the highest environmental refractive index sensitivity of 716 GHz/RIU (gigahertz per refractive index unit). To sum up, the terahertz metamaterial absorber we showed has four perfect absorption peaks, high sensitivity, and stable polarization. This means it could be useful in areas like changing electromagnetic waves, making new sensors, and switching. Full article

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16 pages, 9416 KB

Open AccessFeature PaperEditor’s ChoiceArticle

An Image Processing Approach to Quality Control of Drop-on-Demand Electrohydrodynamic (EHD) Printing

by Yahya Tawhari, Charchit Shukla and Juan Ren

Micromachines 2024, 15(11), 1376; https://doi.org/10.3390/mi15111376 - 14 Nov 2024

Cited by 1 | Viewed by 1319

Abstract

Droplet quality in drop-on-demand (DoD) Electrohydrodynamic (EHD) inkjet printing plays a crucial role in influencing the overall performance and manufacturing quality of the operation. The current approach to droplet printing analysis involves manually outlining/labeling the printed dots on the substrate under a microscope [...] Read more.

Droplet quality in drop-on-demand (DoD) Electrohydrodynamic (EHD) inkjet printing plays a crucial role in influencing the overall performance and manufacturing quality of the operation. The current approach to droplet printing analysis involves manually outlining/labeling the printed dots on the substrate under a microscope and then using microscope software to estimate the dot sizes by assuming the dots have a standard circular shape. Therefore, it is prone to errors. Moreover, the dot spacing information is missing, which is also important for EHD DoD printing processes, such as manufacturing micro-arrays. In order to address these issues, the paper explores the application of feature extraction methods aimed at identifying characteristics of the printed droplets to enhance the detection, evaluation, and delineation of significant structures and edges in printed images. The proposed method involves three main stages: (1) image pre-processing, where edge detection techniques such as Canny filtering are applied for printed dot boundary detection; (2) contour detection, which is used to accurately quantify the dot sizes (such as dot perimeter and area); and (3) centroid detection and distance calculation, where the spacing between neighboring dots is quantified as the Euclidean distance of the dot geometric centers. These stages collectively improve the precision and efficiency of EHD DoD printing analysis in terms of dot size and spacing. Edge and contour detection strategies are implemented to minimize edge discrepancies and accurately delineate droplet perimeters for quality analysis, enhancing measurement precision. The proposed image processing approach was first tested using simulated EHD printed droplet arrays with specified dot sizes and spacing, and the achieved quantification accuracy was over 98% in analyzing dot size and spacing, highlighting the high precision of the proposed approach. This approach was further demonstrated through dot analysis of experimentally EHD-printed droplets, showing its superiority over conventional microscope-based measurements. Full article

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26 pages, 6673 KB

Open AccessFeature PaperEditor’s ChoiceReview

Neural Network Methods in the Development of MEMS Sensors

by Yan Liu, Mingda Ping, Jizhou Han, Xiang Cheng, Hongbo Qin and Weidong Wang

Micromachines 2024, 15(11), 1368; https://doi.org/10.3390/mi15111368 - 12 Nov 2024

Cited by 1 | Viewed by 4345

Abstract

As a kind of long-term favorable device, the microelectromechanical system (MEMS) sensor has become a powerful dominator in the detection applications of commercial and industrial areas. There have been a series of mature solutions to address the possible issues in device design, optimization, [...] Read more.

As a kind of long-term favorable device, the microelectromechanical system (MEMS) sensor has become a powerful dominator in the detection applications of commercial and industrial areas. There have been a series of mature solutions to address the possible issues in device design, optimization, fabrication, and output processing. The recent involvement of neural networks (NNs) has provided a new paradigm for the development of MEMS sensors and greatly accelerated the research cycle of high-performance devices. In this paper, we present an overview of the progress, applications, and prospects of NN methods in the development of MEMS sensors. The superiority of leveraging NN methods in structural design, device fabrication, and output compensation/calibration is reviewed and discussed to illustrate how NNs have reformed the development of MEMS sensors. Relevant issues in the usage of NNs, such as available models, dataset construction, and parameter optimization, are presented. Many application scenarios have demonstrated that NN methods can enhance the speed of predicting device performance, rapidly generate device-on-demand solutions, and establish more accurate calibration and compensation models. Along with the improvement in research efficiency, there are also several critical challenges that need further exploration in this area. Full article

(This article belongs to the Special Issue MEMS/NEMS Sensors and Actuators, 2nd Edition)

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9 pages, 4045 KB

Open AccessFeature PaperEditor’s ChoiceArticle

A Laterally Excited Bulk Acoustic Wave Resonator Based on LiNbO₃ with Arc-Shaped Electrodes

by Jieyu Liu, Wenjuan Liu, Zhiwei Wen, Min Zeng and Chengliang Sun

Micromachines 2024, 15(11), 1367; https://doi.org/10.3390/mi15111367 - 12 Nov 2024

Cited by 2 | Viewed by 2413

Abstract

High frequency and large bandwidth are growing trends in communication radio-frequency devices. The LiNbO₃ thin film material is expected to become the preferred piezoelectric material for high coupling resonators in the 5G frequency band due to its ultra-high piezoelectric coefficient and low [...] Read more.

High frequency and large bandwidth are growing trends in communication radio-frequency devices. The LiNbO₃ thin film material is expected to become the preferred piezoelectric material for high coupling resonators in the 5G frequency band due to its ultra-high piezoelectric coefficient and low loss characteristics. The main mode of laterally excited bulk acoustic wave resonators (XBAR) have an ultra-high sound velocity, which enables high-frequency applications. However, the interference of spurious modes is one of the main reasons hindering the widespread application of XBAR. In this paper, a Z-cut LiNbO₃ thin film-based XBAR with arc-shaped electrodes is presented. We investigate the electric field distribution of the XBAR, while the irregular boundary of the arc-shaped electrodes affects the electric field between the existing interdigital transducers (IDTs). The mode shapes and impedance response of the XBAR with arc-shaped electrodes and the XBARs with traditional IDTs are compared in this work. The fabricated XBAR on a 350 nm Z-cut LiNbO₃ thin film with arc-shaped electrodes operating at over 5 GHz achieves a high effective electromechanical coupling coefficient of 29.8% and the spurious modes are well suppressed. This work promotes an XBAR with an optimized electrode design to further achieve the desired performance. Full article

(This article belongs to the Special Issue Piezoelectric Devices and System in Micromachines)

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22 pages, 4110 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Silicon Microthermocycler for Point-of-Care Analytical Systems: Modeling, Design, and Fabrication

by Borut Pečar, Aljaž Zadravec, Danilo Vrtačnik and Matej Možek

Micromachines 2024, 15(11), 1325; https://doi.org/10.3390/mi15111325 - 30 Oct 2024

Viewed by 2720

Abstract

A four-tether silicon microthermocycler for point-of-care PCR analytical systems is proposed. Substituting the commonly employed platinum with titanium in the fabrication of thin film resistance temperature detectors and heaters enabled the realization of a smaller device without compromising temperature accuracy or increasing heater [...] Read more.

A four-tether silicon microthermocycler for point-of-care PCR analytical systems is proposed. Substituting the commonly employed platinum with titanium in the fabrication of thin film resistance temperature detectors and heaters enabled the realization of a smaller device without compromising temperature accuracy or increasing heater lead power losses. The device was extensively analyzed through analytical modeling and FEM numerical simulations using a 3-D thermo-mechanical simulation model in COMSOL. Numerical simulations revealed that the four-tether design provides a 460% improvement in mechanical strength and a 57% reduction in the thermal time constant compared with a similar three-tether design, with a trade-off of a 22% increase in heat losses. Detailed structural and thermal analyses of crucial design parameters guided the optimization of the final geometry, leading to the successful fabrication of prototypes. It was shown that the current of 60 mA was sufficient to heat the fabricated solid and hollow silicon structure to 132 °C and 134 °C in 10 s for an applied heater power of 510 mW and 525 mW, respectively. Full article

(This article belongs to the Special Issue Exploration and Application of Micro-Devices/Sensors in Analytical Chemistry)

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15 pages, 2370 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Optimization of a Fan-Out Wafer-Level Packaging- Based Integrated Passive Device Structure for FMCW Radar Applications

by Jiajie Yang, Lixin Xu and Ke Yang

Micromachines 2024, 15(11), 1311; https://doi.org/10.3390/mi15111311 - 29 Oct 2024

Cited by 2 | Viewed by 1634

Abstract

This paper presents an integrated passive device (IPD) structure based on fan-out wafer-level packaging (FOWLP) for the front end of frequency-modulated continuous wave (FMCW) radar systems, focusing on enhancing the integration efficiency and performance of large passive components like antennas. Additionally, a new [...] Read more.

This paper presents an integrated passive device (IPD) structure based on fan-out wafer-level packaging (FOWLP) for the front end of frequency-modulated continuous wave (FMCW) radar systems, focusing on enhancing the integration efficiency and performance of large passive components like antennas. Additionally, a new metric is introduced to assess this structure’s effect on the average noise figure in FMCW systems. Using this metric as a loss function, we apply the support vector machine (SVM) for electromagnetic simulation and the genetic algorithm (GA) for optimization. The sample fitting variance is 2.42 dB, reducing computation time from 12 min to under 1 millisecond, with the entire optimization completed in less than 100 s. The optimized IPD structure is 0.7 × 0.9 × 0.014

{λ_{0}}^{3}

in size and achieves over 35 dB isolation between the transmitter and receiver. Compared to the IPD model calculated by empirical formulas, the optimized device lowers the average noise figure by 15.2 dB and increases maximum gain by 4.19 dB. Full article

(This article belongs to the Special Issue Advanced Packaging for Microsystem Applications, 3rd Edition)

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16 pages, 7786 KB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances of PDMS In Vitro Biomodels for Flow Visualizations and Measurements: From Macro to Nanoscale Applications

by Andrews Souza, Glauco Nobrega, Lucas B. Neves, Filipe Barbosa, João Ribeiro, Conrado Ferrera and Rui A. Lima

Micromachines 2024, 15(11), 1317; https://doi.org/10.3390/mi15111317 - 29 Oct 2024

Cited by 7 | Viewed by 2780

Abstract

Polydimethylsiloxane (PDMS) has become a popular material in microfluidic and macroscale in vitro models due to its elastomeric properties and versatility. PDMS-based biomodels are widely used in blood flow studies, offering a platform for improving flow models and validating numerical simulations. This review [...] Read more.

Polydimethylsiloxane (PDMS) has become a popular material in microfluidic and macroscale in vitro models due to its elastomeric properties and versatility. PDMS-based biomodels are widely used in blood flow studies, offering a platform for improving flow models and validating numerical simulations. This review highlights recent advances in bioflow studies conducted using both PDMS microfluidic devices and macroscale biomodels, particularly in replicating physiological environments. PDMS microchannels are used in studies of blood cell deformation under confined conditions, demonstrating the potential to distinguish between healthy and diseased cells. PDMS also plays a critical role in fabricating arterial models from real medical images, including pathological conditions such as aneurysms. Cutting-edge applications, such as nanofluid hemodynamic studies and nanoparticle drug delivery in organ-on-a-chip platforms, represent the latest developments in PDMS research. In addition to these applications, this review critically discusses PDMS properties, fabrication methods, and its expanding role in micro- and nanoscale flow studies. Full article

(This article belongs to the Special Issue The 15th Anniversary of Micromachines)

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17 pages, 7556 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Laterally Actuated Si-to-Si DC MEMS Switch for Power Switching Applications

by Abdurrashid Hassan Shuaibu, Almur A. S. Rabih, Yves Blaquière and Frederic Nabki

Micromachines 2024, 15(11), 1295; https://doi.org/10.3390/mi15111295 - 24 Oct 2024

Cited by 2 | Viewed by 1477

Abstract

Electrothermal actuators are highly advantageous for microelectromechanical systems (MEMS) due to their capability to generate significant force and large displacements. Despite these benefits, their application in reconfigurable conduction line switches is limited, particularly when employing commercial processes. In DC MEMS switches, electrothermal actuators [...] Read more.

Electrothermal actuators are highly advantageous for microelectromechanical systems (MEMS) due to their capability to generate significant force and large displacements. Despite these benefits, their application in reconfigurable conduction line switches is limited, particularly when employing commercial processes. In DC MEMS switches, electrothermal actuators require electrical insulation between the biasing voltage and the transmission line to prevent interference and maintain the integrity of the switch. This work presents a chevron-type electrothermal actuator utilizing a stack of

S i O_{2} /

Al thin films on a silicon (Si) structural layer beam to create a DC MEMS switch. The design leverages a thin film Al heater to drive the actuator while the

S i O_{2}

layer provides electrical insulation, suppressing crosstalk with the Si layer. The electrical contact resistance of a Si-to-Si interface was evaluated by applying a controlled current and measuring the resultant voltage. A low contact resistance of 150 Ω was achieved when an initial contact gap of 2.52 μm was closed using an actuator with an actuation voltage of 1.2 V and a current of 205 mA, with a switching speed of less than 5 ms. Factors such as the contact force, the temperature, and the residual device layer etching angle significantly impact the Si-to-Si contact resistance and the switch’s longevity. The switch withstands a breakdown voltage up to 350 V at its terminal contacts. Thus, it will be robust to self-actuation caused by unwanted voltage contributions, making it suitable for high-voltage and harsh environment applications. Full article

(This article belongs to the Special Issue MEMS/NEMS Devices and Applications, 2nd Edition)

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26 pages, 3502 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of a Low-Cost Sensor System for Accurate Soil Assessment and Biological Activity Profiling

by Antonio Ruiz-Gonzalez, Harriet Kempson and Jim Haseloff

Micromachines 2024, 15(11), 1293; https://doi.org/10.3390/mi15111293 - 24 Oct 2024

Cited by 2 | Viewed by 2335

Abstract

The development of low-cost tools for rapid soil assessment has become a crucial field due to the increasing demands in food production and carbon storage. However, current methods for soil evaluation are costly and cannot provide enough information about the quality of samples. [...] Read more.

The development of low-cost tools for rapid soil assessment has become a crucial field due to the increasing demands in food production and carbon storage. However, current methods for soil evaluation are costly and cannot provide enough information about the quality of samples. This work reports for the first time a low-cost 3D printed device that can be used for soil classification as well as the study of biological activity. The system incorporated multiple physical and gas sensors for the characterisation of sample types and profiling of soil volatilome. Sensing data were obtained from 31 variables, including 18 individual light wavelengths that could be used to determine seed germination rates of tomato plants. A machine learning algorithm was trained using the data obtained by characterising 75 different soil samples. The algorithm could predict seed germination rates with high accuracy (RSMLE = 0.01, and R² = 0.99), enabling an objective and non-invasive study of the impact of multiple environmental parameters in soil quality. To allow for a more complete profiling of soil biological activity, molecular imprinted-based fine particles were designed to quantify tryptophol, a quorum-sensing signalling molecule commonly used by fungal populations. This device could quantify the concentration of tryptophol down to 10 nM, offering the possibility of studying the interactions between fungi and bacterial populations. The final device could monitor the growth of microbial populations in soil, and offering an accurate assessment of quality at a low cost, impacting germination rates by incorporating hybrid data from the microsensors. Full article

(This article belongs to the Special Issue Biosensors for Biomedical and Environmental Applications, Third Edition)

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15 pages, 7197 KB

Open AccessFeature PaperEditor’s ChoiceArticle

A Wireless Bi-Directional Brain–Computer Interface Supporting Both Bluetooth and Wi-Fi Transmission

by Wei Ji, Haoyang Su, Shuang Jin, Ye Tian, Gen Li, Yingkang Yang, Jiazhi Li, Zhitao Zhou, Xiaoling Wei, Tiger H. Tao, Lunming Qin, Yifei Ye and Liuyang Sun

Micromachines 2024, 15(11), 1283; https://doi.org/10.3390/mi15111283 - 22 Oct 2024

Cited by 1 | Viewed by 5706

Abstract

Wireless neural signal transmission is essential for both neuroscience research and neural disorder therapies. However, conventional wireless systems are often constrained by low sampling rates, limited channel counts, and their support of only a single transmission mode. Here, we developed a wireless bi-directional [...] Read more.

Wireless neural signal transmission is essential for both neuroscience research and neural disorder therapies. However, conventional wireless systems are often constrained by low sampling rates, limited channel counts, and their support of only a single transmission mode. Here, we developed a wireless bi-directional brain–computer interface system featuring dual transmission modes. This system supports both low-power Bluetooth transmission and high-sampling-rate Wi-Fi transmission, providing flexibility for various application scenarios. The Bluetooth mode, with a maximum sampling rate of 14.4 kS/s, is well suited for detecting low-frequency signals, as demonstrated by both in vitro recordings of signals from 10 to 50 Hz and in vivo recordings of 16-channel local field potentials in mice. More importantly, the Wi-Fi mode, offering a maximum sampling rate of 56.8 kS/s, is optimized for recording high-frequency signals. This capability was validated through in vitro recordings of signals from 500 to 2000 Hz and in vivo recordings of single-neuron spike firings with amplitudes reaching hundreds of microvolts and high signal-to-noise ratios. Additionally, the system incorporates a wireless stimulation function capable of delivering current pulses up to 2.55 mA, with adjustable pulse width and polarity. Overall, this dual-mode system provides an efficient and flexible solution for both neural recording and stimulation applications. Full article

(This article belongs to the Special Issue Neural Interface: From Material to System)

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33 pages, 22149 KB

Open AccessFeature PaperEditor’s ChoiceReview

MEMS Micromirror Actuation Techniques: A Comprehensive Review of Trends, Innovations, and Future Prospects

by Mansoor Ahmad, Mohamed Bahri and Mohamad Sawan

Micromachines 2024, 15(10), 1233; https://doi.org/10.3390/mi15101233 - 30 Sep 2024

Cited by 11 | Viewed by 5012

Abstract

Micromirrors have recently emerged as an essential component in optical scanning technology, attracting considerable attention from researchers. Their compact size and versatile capabilities, such as light steering, modulation, and switching, are leading them as potential alternatives to traditional bulky galvanometer scanners. The actuation [...] Read more.

Micromirrors have recently emerged as an essential component in optical scanning technology, attracting considerable attention from researchers. Their compact size and versatile capabilities, such as light steering, modulation, and switching, are leading them as potential alternatives to traditional bulky galvanometer scanners. The actuation of these mirrors is critical in determining their performance, as it contributes to factors such as response time, scanning angle, and power consumption. This article aims to provide a thorough exploration of the actuation techniques used to drive micromirrors, describing the fundamental operating principles. The four primary actuation modalities—electrostatic, electrothermal, electromagnetic, and piezoelectric—are thoroughly investigated. Each type of actuator’s operational principles, key advantages, and their limitations are discussed. Additionally, the discussion extends to hybrid micromirror designs that combine two types of actuation in a single device. A total of 208 closely related papers indexed in Web of Science were reviewed. The findings indicate ongoing advancements in the field, particularly in terms of size, controllability, and field of view, making micromirrors ideal candidates for applications in medical imaging, display projections, and optical communication. With a comprehensive overview of micromirror actuation strategies, this manuscript serves as a compelling resource for researchers and engineers aiming to utilize the appropriate type of micromirror in the field of optical scanning technology. Full article

(This article belongs to the Collection Optical MEMS: Design, Fabrication, Control, Modeling and Developments)

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12 pages, 2389 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Scan-Rate-Dependent Ion Current Rectification in Bipolar Interfacial Nanopores

by Xiaoling Zhang, Yunjiao Wang, Jiahui Zheng, Chen Yang and Deqiang Wang

Micromachines 2024, 15(9), 1176; https://doi.org/10.3390/mi15091176 - 23 Sep 2024

Cited by 1 | Viewed by 1632

Abstract

This study presents a theoretical investigation into the voltammetric behavior of bipolar interfacial nanopores due to the effect of potential scan rate (1–1000 V/s). Finite element method (FEM) is utilized to explore the current–voltage (I–V) properties of bipolar interfacial nanopores at different bulk [...] Read more.

This study presents a theoretical investigation into the voltammetric behavior of bipolar interfacial nanopores due to the effect of potential scan rate (1–1000 V/s). Finite element method (FEM) is utilized to explore the current–voltage (I–V) properties of bipolar interfacial nanopores at different bulk salt concentrations. The results demonstrate a strong impact of the scan rate on the I–V response of bipolar interfacial nanopores, particularly at relatively low concentrations. Hysteresis loops are observed in bipolar interfacial nanopores under specific scan rates and potential ranges and divided by a cross-point potential that remains unaffected by the scan rate employed. This indicates that the current in bipolar interfacial nanopores is not just reliant on the bias potential that is imposed but also on the previous conditions within the nanopore, exhibiting history-dependent or memory effects. This scan-rate-dependent current–voltage response is found to be significantly influenced by the length of the nanopore (membrane thickness). Thicker membranes exhibit a more pronounced scan-rate-dependent phenomenon, as the mass transfer of ionic species is slower relative to the potential scan rate. Additionally, unlike conventional bipolar nanopores, the ion current passing through bipolar interfacial nanopores is minimally affected by the membrane thickness, making it easier to detect. Full article

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20 pages, 7194 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Deep Learning-Driven Prediction of Mechanical Properties of 316L Stainless Steel Metallographic by Laser Powder Bed Fusion

by Zhizhou Zhang, Paul Mativenga, Wenhua Zhang and Shi-qing Huang

Micromachines 2024, 15(9), 1167; https://doi.org/10.3390/mi15091167 - 21 Sep 2024

Cited by 5 | Viewed by 2999

Abstract

This study developed a new metallography–property relationship neural network (MPR-Net) to predict the relationship between the microstructure and mechanical properties of 316L stainless steel built by laser powder bed fusion (LPBF). The accuracy R² of MPR-Net was 0.96 and 0.91 for tensile [...] Read more.

This study developed a new metallography–property relationship neural network (MPR-Net) to predict the relationship between the microstructure and mechanical properties of 316L stainless steel built by laser powder bed fusion (LPBF). The accuracy R² of MPR-Net was 0.96 and 0.91 for tensile strength and Vickers hardness predictions, respectively, based on optical metallurgy images. Feature visualisation methods, such as gradient-weighted class activation mapping (Grad-CAM) and clustering, were employed to interpret the abstract features within the MPR-Net, providing insights into the molten pool morphology and grain formation mechanisms during the LPBF process. Experimental results showed that the optimal process parameters—190 W laser power and 700 mm/s scanning speed—yielded a maximum tensile strength of 762.83 MPa and a Vickers hardness of 253.07 HV_0.2 with nearly full densification (99.97%). The study marks the first application of a convolutional neural network (MPR-Net) to predict the mechanical properties of 316L stainless steel samples manufactured through laser powder bed fusion (LPBF) based on metallography. It innovatively employs techniques such as gradient-weighted class activation mapping (Grad-CAM), spatial coherence testing, and clustering to provide deeper insights into the workings of the machine learning model, enhancing the interpretability of complex neural network decisions in material science. Full article

(This article belongs to the Special Issue Optical and Laser Material Processing)

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