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Micromachines, Volume 15, Issue 11 (November 2024) – 124 articles

Cover Story (view full-size image): This wireless bi-directional brain–computer interface integrates Bluetooth and Wi-Fi modes, enabling flexible neural recording and stimulation. The Bluetooth mode is optimized for low-frequency signals, while the Wi-Fi supports high-frequency recordings with exceptional fidelity. With customizable biphasic current pulses for stimulation and a compact, lightweight design, this system offers unparalleled versatility for neuroscience research and neural modulation applications. View this paper
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17 pages, 3759 KiB  
Article
Robust Control Strategy of Acoustic Micro Robots Based on Fuzzy System
by Junjie Dong and Xingguang Duan
Micromachines 2024, 15(11), 1403; https://doi.org/10.3390/mi15111403 - 20 Nov 2024
Viewed by 501
Abstract
This study presents a robust control strategy for acoustic micro robots utilizing a novel interval type-three fuzzy system. Micro robots driven by acoustic forces face significant challenges in fluid environments due to complex nonlinearities, uncertainties, and disturbances. To address these issues, we propose [...] Read more.
This study presents a robust control strategy for acoustic micro robots utilizing a novel interval type-three fuzzy system. Micro robots driven by acoustic forces face significant challenges in fluid environments due to complex nonlinearities, uncertainties, and disturbances. To address these issues, we propose a control framework that combines fuzzy logic and sliding mode control to enhance the stability and trajectory tracking performance of micro robots under varying fluid conditions. The interval type-3 fuzzy logic system provides increased robustness by better handling external disturbances and uncertainties compared to the robustness of the traditional methods. The experimental results from one-dimensional, two-dimensional, and three-dimensional fluid cavities demonstrate that the proposed control method significantly improves tracking accuracy, reducing the errors in complex environments. This control framework offers promising potential for the precise manipulation of micro robots in biomedical applications and other microfluidic systems. The minimum trajectory tracking control mean square error is 12.82 μm. Full article
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11 pages, 3345 KiB  
Article
Performance Improvement of TiO2 Ultraviolet Photodetectors by Using Atomic Layer Deposited Al2O3 Passivation Layer
by Yao-Tsung Yang, Shih-Chin Lin, Ching-Chiun Wang, Ying-Rong Ho, Jian-Zhi Chen and Jung-Jie Huang
Micromachines 2024, 15(11), 1402; https://doi.org/10.3390/mi15111402 - 20 Nov 2024
Viewed by 555
Abstract
This study employed atomic layer deposition (ALD) to fabricate an Al2O3 passivation layer to optimize the performance of ultraviolet (UV) photodetectors with a TiO2-nanorod-(NR)-containing active layer and a solid–liquid heterojunction (SLHJ). To reduce the processing time and enhance [...] Read more.
This study employed atomic layer deposition (ALD) to fabricate an Al2O3 passivation layer to optimize the performance of ultraviolet (UV) photodetectors with a TiO2-nanorod-(NR)-containing active layer and a solid–liquid heterojunction (SLHJ). To reduce the processing time and enhance light absorption, a hydrothermal method was used to grow a relatively thick TiO2-NR-containng working electrode. Subsequently, a 5-nm-thick Al2O3 passivation layer was deposited on the TiO2 NRs through ALD, which has excellent step coverage, to reduce the surface defects in the TiO2 NRs and improve the carrier transport efficiency. X-ray photoelectron spectroscopy revealed that the aforementioned layer reduced the defects in the TiO2 NRs. Moreover, high-resolution transmission electron microscopy indicated that following the annealing treatment, Al, Ti, and O atoms diffused across the interface between the Al2O3 passivation layer and TiO2 NRs, resulting in the binding of these atoms to form Al–Ti–O bonds. This process effectively filled the oxygen vacancies in TiO2. Examination of the photodetector device revealed that the photocurrent-to-dark current ratio exhibited a difference of four orders of magnitude (10−4 to 10−8 A), with the switch-on and switch-off times being 0.46 and 3.84 s, respectively. These results indicate that the Al2O3 passivation layer deposited through ALD can enhance the photodetection performance of SLHJ UV photodetectors with a TiO2 active layer. Full article
(This article belongs to the Special Issue Latest Advancements in Semiconductor Materials, Devices, and Systems)
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12 pages, 2488 KiB  
Article
A Polycarbonate-Assisted Transfer Method for van der Waals Contacts to Magnetic Two-Dimensional Materials
by Kunlin Yang, Guorui Zhao, Yibin Zhao, Jie Xiao, Le Wang, Jiaqi Liu, Wenqing Song, Qing Lan, Tuoyu Zhao, Hai Huang, Jia-Wei Mei and Wu Shi
Micromachines 2024, 15(11), 1401; https://doi.org/10.3390/mi15111401 - 20 Nov 2024
Viewed by 595
Abstract
Magnetic two-dimensional (2D) materials have garnered significant attention for their potential to revolutionize 2D spintronics due to their unique magnetic properties. However, their air-sensitivity and highly insulating nature of the magnetic semiconductors present substantial challenges for device fabrication with effective contacts. In this [...] Read more.
Magnetic two-dimensional (2D) materials have garnered significant attention for their potential to revolutionize 2D spintronics due to their unique magnetic properties. However, their air-sensitivity and highly insulating nature of the magnetic semiconductors present substantial challenges for device fabrication with effective contacts. In this study, we introduce a polycarbonate (PC)-assisted transfer method that effectively forms van der Waals (vdW) contacts with 2D materials, streamlining the fabrication process without the need for additional lithography. This method is particularly advantageous for air-sensitive magnetic materials, as demonstrated in Fe3GeTe2. It also ensures excellent interface contact quality and preserves the intrinsic magnetic properties in magnetic semiconductors like CrSBr. Remarkably, this method achieves a contact resistance four orders of magnitude lower than that achieved with traditional thermally evaporated electrodes in thin-layer CrSBr devices and enables the observation of sharp magnetic transitions similar to those observed with graphene vdW contacts. Compatible with standard dry-transfer processes and scalable to large wafer sizes, our approach provides a straightforward and effective solution for developing complex magnetic heterojunction devices and expanding the applications of magnetic 2D materials. Full article
(This article belongs to the Special Issue 2D-Materials Based Fabrication and Devices)
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11 pages, 8301 KiB  
Article
A 2-D Fully Polarized Van Atta Array Based on Wide-Beam Tri-Polarized Antennas
by Jicheng Pan, Lei Chen, Shuangdi Zhao and Tianling Zhang
Micromachines 2024, 15(11), 1400; https://doi.org/10.3390/mi15111400 - 20 Nov 2024
Viewed by 492
Abstract
This paper proposes a 2-D fully polarized Van Atta array, which consists of four tri-polarized antenna elements. The tri-polarized antenna element comprises a monopole antenna and a low-profile microstrip antenna that widens the beam by folding four electric walls. This configuration enables the [...] Read more.
This paper proposes a 2-D fully polarized Van Atta array, which consists of four tri-polarized antenna elements. The tri-polarized antenna element comprises a monopole antenna and a low-profile microstrip antenna that widens the beam by folding four electric walls. This configuration enables the Van Atta arrays to receive and transmit arbitrarily polarized incident waves over a wider range. The measurement results indicate that the proposed Van Atta array exhibits a −5 dB radar cross-section (RCS) greater than 95° when TE-polarized waves are incident and greater than 134° when TM-polarized waves are incident, significantly surpassing the 2-D dual-polarized array. Full article
(This article belongs to the Special Issue Microwave Passive Components, 2nd Edition)
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10 pages, 8354 KiB  
Article
Replication of Leaf Surface Structures on Flat Phosphor-Converted LEDs for Enhanced Angular Color Uniformity
by Bing-Mau Chen, Chiu-Hsiang Chen, Shang-Ping Ying and Yu-Kang Chang
Micromachines 2024, 15(11), 1399; https://doi.org/10.3390/mi15111399 - 20 Nov 2024
Viewed by 529
Abstract
We explored the use of biomimetic structures, including those that mimic leaf structures, to enhance the angular color uniformity of flat phosphor-converted light-emitting diodes (pcLEDs). The distinct microstructures found on natural leaf surfaces, such as micro-scale bumps, ridges, and hierarchical patterns, have inspired [...] Read more.
We explored the use of biomimetic structures, including those that mimic leaf structures, to enhance the angular color uniformity of flat phosphor-converted light-emitting diodes (pcLEDs). The distinct microstructures found on natural leaf surfaces, such as micro-scale bumps, ridges, and hierarchical patterns, have inspired the design of artificial microstructures that can improve light extraction, scattering, and overall optical performance in LED applications. The effects of these leaf surface microstructures on the phosphor layer of flat pcLEDs were evaluated. An imprinting technique was employed to directly replicate the surface morphology structures from fresh plant leaves. The results indicated that this method provided excellent scattering capability and reduced the disparity in light output between blue and yellow light emissions from flat pcLEDs at various angles. Subsequently, uniform correlated color temperature in the flat pcLEDs was achieved, reducing the yellow ring effect. Furthermore, the availability of diverse wrinkle and surface patterns from a wide range of natural prototypes could reduce design costs compared with traditional mold fabrication, making the method suitable for application in mass production. Full article
(This article belongs to the Special Issue Innovative Progression of Light-Emitting Diodes (LED))
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12 pages, 2219 KiB  
Article
Buckling Behavior Analysis of Kirigami Structure Under Tension
by Pengzhong Dai, Ziqi Li, Xiaoyang Zhang and Qingmin Yu
Micromachines 2024, 15(11), 1398; https://doi.org/10.3390/mi15111398 - 20 Nov 2024
Viewed by 496
Abstract
Flexible electronic technology has attracted great interest, where rigid and brittle semiconductor materials can withstand large deformation. In order to improve the stretchability of devices, many novel structures have been designed, such as the classical “wavy” structure, the island-bridge structure, and origami structures [...] Read more.
Flexible electronic technology has attracted great interest, where rigid and brittle semiconductor materials can withstand large deformation. In order to improve the stretchability of devices, many novel structures have been designed, such as the classical “wavy” structure, the island-bridge structure, and origami structures that achieve stretchability through creases. However, the stretchability of these structures is still not large enough. Inspired by traditional kirigami, the stretchability of devices is achieved by making various periodic cuts in the substrate while the devices are placed in the area around the cuts. The previous research mainly focused on the change in the electrical properties of the structure during the deformation process, and there were few studies on the mechanical mechanisms. Therefore, this paper studies the buckling behavior of the kirigami structure when the substrate is stretched, and its mechanism can provide guidance for practical applications. Full article
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11 pages, 1777 KiB  
Article
Study of Vertical Phototransistors Based on Integration of Inorganic Transistors and Organic Photodiodes
by Jui-Fen Chang, Ying-You Lin and Yu-Ming Li
Micromachines 2024, 15(11), 1397; https://doi.org/10.3390/mi15111397 - 20 Nov 2024
Viewed by 695
Abstract
We investigate the inorganic/organic hybrid vertical phototransistor (VPT) by integrating an atomic layer deposition-processed ZnO (ALD-ZnO) transistor with a prototype poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) blend organic photodiode (OPD) based on an encapsulated source electrode geometry, and discuss the [...] Read more.
We investigate the inorganic/organic hybrid vertical phototransistor (VPT) by integrating an atomic layer deposition-processed ZnO (ALD-ZnO) transistor with a prototype poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) blend organic photodiode (OPD) based on an encapsulated source electrode geometry, and discuss the device mechanism. Our preliminary studies on reference P3HT:PC61BM OPDs show non-ohmic electron injection between the ALD-ZnO and P3HT:PC61BM layers. However, the ALD-ZnO layer enables the accumulation of photogenerated holes under negative bias, which facilitates electron injection upon illumination and thereby enhances the external quantum efficiency (EQE). This mechanism underpins the photoresponse in the VPT. Furthermore, we demonstrate that the gate field in the VPT effectively modulates electron injection from the ALD-ZnO layer to the top OPD, resulting in the VPT operating as a non-ohmic OPD in the OFF state and as an ohmic OPD in the ON state. Benefiting from the unique transistor geometry and gate modulation capability, this hybrid VPT can achieve an EQE of 45,917%, a responsivity of 197 A/W, and a specific detectivity of 3.4 × 1012 Jones under 532 nm illumination and low drain-source voltage (Vds = 3 V) conditions. This transistor geometry also facilitates integration with various OPDs and the miniaturization of the ZnO channel area, offering an ideal basis for the development of highly efficient VPTs and high-resolution image sensors. Full article
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13 pages, 5261 KiB  
Article
A High-Performance Micro Differential Pressure Sensor
by Xutao Fan, Lei Wang and Songsong Zhang
Micromachines 2024, 15(11), 1396; https://doi.org/10.3390/mi15111396 - 20 Nov 2024
Viewed by 478
Abstract
With the development of the micro electromechanical system (MEMS), which widely adopts micro differential pressure sensors (MDPSs), the demand for high-performance MDPSs had continuously increased. Pressure sensors realized using MEMS technology integrated with biomedical catheters are of significant importance in the detection and [...] Read more.
With the development of the micro electromechanical system (MEMS), which widely adopts micro differential pressure sensors (MDPSs), the demand for high-performance MDPSs had continuously increased. Pressure sensors realized using MEMS technology integrated with biomedical catheters are of significant importance in the detection and treatment of various biological diseases. Biomedical catheters used in low-Fr applications (1Fr = 0.33 mm outer diameter) require miniaturized sensors that do not compromise their performance. For instance, catheters (5Fr) used for central venous pressure (CVP) monitoring require the integration of high-performance sensors with total dimensions smaller than 1.65 mm along at least two directions (length, width, or height). In this paper, a silicon-on-insulator (SOI)-based MDPS was designed and fabricated for micro-pressure detection in the range of 0–1 kPa. The dimension of the sensor is only 1 mm × 1 mm × 0.4 mm, with a sensitivity of 3.401 mV/V/kPa at room temperature, nonlinearity of 0.376% FS (full scale), and an overall accuracy of 0.59% FS. The sensor operates normally when the temperature is even increased to 160 °C, and its temperature coefficient of zero output (TCO) and temperature coefficient of sensitivity (TCS) are 0.093% FS/°C and −0.144% FS/°C. The dimension and performance results of this MDPS demonstrate its potential to play a significant role in biomedical catheters. In addition, it is fabricated using an 8-inch MEMS process, which significantly reduces the cost. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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13 pages, 2311 KiB  
Article
Multifunctional Downhole Drilling Motor Speed Sensor Based on Triboelectric Nanogenerator
by Yanbo Zhang, Shida Su, Lei Zhang, Yulin Gao and Chuan Wu
Micromachines 2024, 15(11), 1395; https://doi.org/10.3390/mi15111395 - 18 Nov 2024
Viewed by 626
Abstract
The measurement of downhole drilling motor rotational speed is crucial for optimizing drilling operations, improving work efficiency, and preventing equipment failures. However, traditional downhole rotational speed sensors suffer from power supply limitations, which can increase drilling costs. To address this issue, this study [...] Read more.
The measurement of downhole drilling motor rotational speed is crucial for optimizing drilling operations, improving work efficiency, and preventing equipment failures. However, traditional downhole rotational speed sensors suffer from power supply limitations, which can increase drilling costs. To address this issue, this study presents a novel multifunctional rotational speed sensor based on triboelectric nanogenerator (TENG) technology, enabling the self-powered measurement of rotational speed, direction, and angle. Our experimental results demonstrate that the sensor operates stably within a temperature range of 0 to 150 °C and a humidity range of 0 to 90%. It achieves rotational speed measurement with an accuracy of less than 2.5% error within a range of 0 to 1000 rpm, angular measurement with a resolution of 60 degrees and an error of less than 2% within a range of 0 to 360 degrees, and rotational direction measurement. Furthermore, the sensor exhibits self-powered functionality, achieving a maximum power output of 29.1 μW when the external load is 10 MΩ. Compared to conventional rotational speed sensors, this sensor possesses the unique advantage of integrating the measurement of rotational speed, angle, and direction, while simultaneously harnessing downhole working conditions for self-power generation. These characteristics make it highly suitable for practical downhole environments. Full article
(This article belongs to the Special Issue Emerging Applications of Triboelectric Effects/Materials)
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15 pages, 5497 KiB  
Article
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 637
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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21 pages, 5645 KiB  
Article
Design, Testing, and Validation of a Soft Robotic Sensor Array Integrated with Flexible Electronics for Mapping Cardiac Arrhythmias
by Abdellatif Ait Lahcen, Michael Labib, Alexandre Caprio, Mohsen Annabestani, Lina Sanchez-Botero, Weihow Hsue, Christopher F. Liu, Simon Dunham and Bobak Mosadegh
Micromachines 2024, 15(11), 1393; https://doi.org/10.3390/mi15111393 - 18 Nov 2024
Viewed by 765
Abstract
Cardiac mapping is a crucial procedure for diagnosing and treating cardiac arrhythmias. Still, current clinical techniques face limitations including insufficient electrode coverage, poor conformability to complex heart chamber geometries, and high costs. This study explores the design, testing, and validation of a 64-electrode [...] Read more.
Cardiac mapping is a crucial procedure for diagnosing and treating cardiac arrhythmias. Still, current clinical techniques face limitations including insufficient electrode coverage, poor conformability to complex heart chamber geometries, and high costs. This study explores the design, testing, and validation of a 64-electrode soft robotic catheter that addresses these challenges in cardiac mapping. A dual-layer flexible printed circuit board (PCB) was designed and integrated with sensors into a soft robotic sensor array (SRSA) assembly. Design considerations included flex PCB layout, routing, integration, conformity to heart chambers, sensor placement, and catheter durability. Rigorous SRSA in vitro testing evaluated the burst/leakage pressure, block force for electrode contact, mechanical integrity, and environmental resilience. For in vivo validation, a porcine model was used to demonstrate the successful deployment, conformability, and acquisition of electrograms in both the ventricles and atria. This catheter-deployable SRSA represents a meaningful step towards translating the integration of soft robotic actuators and stretchable electronics for clinical use, showcasing the unique mechanical and electrical performance that these designs enable. The high-density electrode array enabled rapid 2 s data acquisition with detailed spatial and temporal resolution, as illustrated by the clear and consistent cardiac signals recorded across all electrodes. The future of this work will lie in enabling high-density, anatomically conformable devices for detailed cardiac mapping to guide ablation therapy and other interventions. Full article
(This article belongs to the Section B:Biology and Biomedicine)
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20 pages, 5507 KiB  
Article
Analysis of Entropy Generation for Mass and Thermal Mixing Behaviors in Non-Newtonian Nano-Fluids of a Crossing Micromixer
by Ayache Lakhdar, Jribi Skander, Naas Toufik Tayeb, Telha Mostefa, Shakhawat Hossain and Sun Min Kim
Micromachines 2024, 15(11), 1392; https://doi.org/10.3390/mi15111392 - 17 Nov 2024
Viewed by 739
Abstract
This work’s objective is to investigate the laminar steady flow characteristics of non-Newtonian nano-fluids in a developed chaotic microdevice known as a two-layer crossing channels micromixer (TLCCM). The continuity equation, the 3D momentum equations, and the species transport equations have been solved numerically [...] Read more.
This work’s objective is to investigate the laminar steady flow characteristics of non-Newtonian nano-fluids in a developed chaotic microdevice known as a two-layer crossing channels micromixer (TLCCM). The continuity equation, the 3D momentum equations, and the species transport equations have been solved numerically at low Reynolds numbers with the commercial CFD software Fluent. A procedure has been verified for non-Newtonian flow in studied geometry that is continuously heated. Secondary flows and thermal mixing performance with two distinct intake temperatures of nano-shear thinning fluids is involved. For an extensive range of Reynolds numbers (0.1 to 25), the impact of fluid characteristics and various concentrations of Al2O3 nanoparticles on thermal mixing capabilities and pressure drop were investigated. The simulation for performance enhancement was run using a power-law index (n) at intervals of different nanoparticle concentrations (0.5 to 5%). At high nano-fluid concentrations, our research findings indicate that hydrodynamic and thermal performances are considerably improved for all Reynolds numbers because of the strong chaotic flow. The mass fraction visualization shows that the suggested design has a fast thermal mixing rate that approaches 0.99%. As a consequence of the thermal and hydrodynamic processes, under the effect of chaotic advection, the creation of entropy governs the second law of thermodynamics. Thus, with the least amount of friction and thermal irreversibilities compared to other studied geometries, the TLCCM arrangement confirmed a significant enhancement in the mixing performance. Full article
(This article belongs to the Collection Micromixers: Analysis, Design and Fabrication)
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13 pages, 2708 KiB  
Article
Fused Deposition Modeling of Chemically Resistant Microfluidic Chips in Polyvinylidene Fluoride
by Christof Rein, Leonhard Hambitzer, Zahra Soraya, Han Zhang, Henning J. Jessen, Frederik Kotz-Helmer and Bastian E. Rapp
Micromachines 2024, 15(11), 1391; https://doi.org/10.3390/mi15111391 - 17 Nov 2024
Viewed by 997
Abstract
Fused deposition modeling (FDM) is well suited for microfluidic prototyping due to its low investment cost and a wide range of accessible materials. Nevertheless, most commercial FDM materials exhibit low chemical and thermal stability. This reduces the scope of applications and limits their [...] Read more.
Fused deposition modeling (FDM) is well suited for microfluidic prototyping due to its low investment cost and a wide range of accessible materials. Nevertheless, most commercial FDM materials exhibit low chemical and thermal stability. This reduces the scope of applications and limits their use in research and development, especially for on-chip chemical synthesis. In this paper, we present FDM fabrication of microfluidic chips with polyvinylidene fluoride (PVDF) for applications that require high thermal or chemical resistance. Embedded microchannels with a minimum channel width and heights of ~200 µm × 200 µm were fabricated, and the resistance against common solvents was analyzed. A procedure was developed to increase the optical transmission to result in translucent components by printing on glass. Chips for fluid mixing were printed, as well as microreactors that were packed with a catalytically active phase and used for acetal deprotection with a conversion of more than 99%. By expanding the use of fluorinated polymers to FDM printing, previously challenging microfluidic applications will be conducted with ease at the lab scale. Full article
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12 pages, 21486 KiB  
Article
Laser Cutting of Non-Woven Fabric Using UV Nanosecond Pulsed Laser
by Jiajun Fu, Chao Liu, Runhan Zhao, Huixin Wang, Zhongjie Yu and Qinghua Wang
Micromachines 2024, 15(11), 1390; https://doi.org/10.3390/mi15111390 - 17 Nov 2024
Viewed by 653
Abstract
The efficient cutting of non-woven fabric shows great significance to the development of the textile industry. In recent years, laser cutting technology has been widely applied in the clothing industry due to its high efficiency and cutting quality. In this work, a UV [...] Read more.
The efficient cutting of non-woven fabric shows great significance to the development of the textile industry. In recent years, laser cutting technology has been widely applied in the clothing industry due to its high efficiency and cutting quality. In this work, a UV nanosecond pulsed laser with a wavelength of 355 nm and a max power of 6.5 W is used to cut non-woven fabric with a thickness of 0.15 mm. The variation of kerf width, surface morphology, and chemical contents are investigated under different laser processing parameters, and the optimal processing parameter is determined. The experimental results demonstrate that the degree of crystallization and chemical composition of the kerf on the non-woven fabric surface is significantly influenced by laser cutting parameters such as laser scanning speed (from 100 to 700 mm/s) and frequency (from 20 to 70 kHz). The scanning speed of 500 mm/s and frequency of 30 kHz are considered the best parameters for achieving abundant energy for the complete and efficient cutting of non-woven fabric. In addition, the level of carbonization and oxidation reaches a relatively low value, and the kerf width is 0.214 mm, which is considered a reasonable value under the optimal processing parameters, showing high cutting quality. Furthermore, the effect of different cutting treatments on surface morphology and chemical contents is also studied. The experimental results present that the non-woven fabric cut by laser possesses a flat kerf, showing a similar effect to that of scissor cutting. Moreover, due to the programmability of laser processing patterns, it is possible to create more intricate designs on non-woven fabric. This facilitates the application and promotion of laser-cut non-woven fabrics. These results can provide a certain reference for laser cutting in the textile industry and are expected to allow for the cutting of high-quality kerf with low carbonization and oxidation. Full article
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11 pages, 6036 KiB  
Article
A Compact Wideband Vivaldi Antenna for Non-Invasive Glucose Monitoring
by Shasha Yang, Yu Wang, Shiwen Gao, Yi Zhuang, Lifeng Wang, Zhenxiang Yi and Weixun Zhang
Micromachines 2024, 15(11), 1389; https://doi.org/10.3390/mi15111389 - 16 Nov 2024
Viewed by 748
Abstract
Due to the high gain, wide bandwidth, and directional radiation characteristics of Vivaldi antennas, this paper conducted relevant research on the feasibility of non-destructive blood glucose detection based on Vivaldi antennas. The research included finite element method (FEM) simulation and glucose concentration monitoring. [...] Read more.
Due to the high gain, wide bandwidth, and directional radiation characteristics of Vivaldi antennas, this paper conducted relevant research on the feasibility of non-destructive blood glucose detection based on Vivaldi antennas. The research included finite element method (FEM) simulation and glucose concentration monitoring. In the simulation stage, the power transmission and reflection characteristics, radiation characteristics, and electric field distribution characteristics of the antenna were described in detail. In the test stage, the S11 response of the antenna to variation in glucose concentration in the range of 0–6.11 mg/mL was measured, including the S11 amplitude and phase. The experimental results show that there is a high linear correlation between the S11 response and glucose concentration, and the sensitivity of the S11 amplitude response to the variation in glucose concentration is close to 0.3445 (dB/(mg/mL)) at 14.2556 GHz, and the sensitivity of the S11 phase response to the variation in glucose concentration is about 0.5652 (degree/(mg/mL)) at 14.37 GHz. In addition, the predicted results of the glucose concentration based on linear regression are discussed. Full article
(This article belongs to the Special Issue RF MEMS Technology and Progress)
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16 pages, 5328 KiB  
Article
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
Viewed by 692
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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11 pages, 4423 KiB  
Article
Proposal of a Rapid Detection System Using Image Analysis for ELISA with an Autonomous Centrifugal Microfluidic System
by Shunya Okamoto, Yuto Mori, Shota Nakamura, Yusuke Kanai, Yoshiaki Ukita, Moeto Nagai and Takayuki Shibata
Micromachines 2024, 15(11), 1387; https://doi.org/10.3390/mi15111387 - 16 Nov 2024
Viewed by 613
Abstract
In this study, with the aim of adapting an enzyme-linked immunosorbent assay (ELISA) system for point-of-care testing (POCT), we propose an image analysis method for ELISAs using a centrifugal microfluidic device that automatically executes the assay. The developed image analysis method can be [...] Read more.
In this study, with the aim of adapting an enzyme-linked immunosorbent assay (ELISA) system for point-of-care testing (POCT), we propose an image analysis method for ELISAs using a centrifugal microfluidic device that automatically executes the assay. The developed image analysis method can be used to quantify the color development reaction on a TMB (3,3′,5,5′-tetramethylbenzidine) substrate. In a conventional ELISA, reaction stopping reagents are required at the end of the TMB reaction. In contrast, the developed image analysis method can analyze color in the color-developing reaction without a reaction stopping reagent. This contributes to a reduction in total assay time. The microfluidic devices used in this study could execute reagent control for ELISAs by steady rotation. In the demonstration of the assay and image analysis, a calibration curve for mouse IgG detection was successfully prepared, and it was confirmed that the image analysis method had the same performance as the conventional analysis method. Moreover, the changes in the amount of color over time confirmed that a calibration curve equal to the endpoint analysis was obtained within 2 min from the start of the TMB reaction. As the assay time before the TMB reaction was approximately 7.5 min, the developed ELISA system could detect TMB in just 10 min. In conventional methods using a plate reader, the assay required a time of 90 min for manual handling using microwell plates, and in the case of using automatic microfluidic devices, 30 min were required. The time of 10 min realized by this proposed method is equal to the time required for detection in an immunochromatographic assay with a lateral flow assay; therefore, it is expected that ELISAs can be performed sufficiently to adapt to POCT. Full article
(This article belongs to the Section B4: Point-of-Care Devices)
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15 pages, 6266 KiB  
Article
Broadband S-Parameter-Based Characterization of Multilayer Ceramic Capacitors Submitted to Mechanical Stress Through Bending Tests on a PCB
by Victoria Gutiérrez-Vicente, Jesús Alejandro Torres-Torres and Reydezel Torres-Torres
Micromachines 2024, 15(11), 1386; https://doi.org/10.3390/mi15111386 - 16 Nov 2024
Viewed by 485
Abstract
A full characterization of multilayer ceramic capacitors including variations in capacitance, series resistance, and series inductance is accomplished by measuring their RF response while being submitted to mechanical stress. This allows for the first time quantifying the degradation of the device’s RF performance [...] Read more.
A full characterization of multilayer ceramic capacitors including variations in capacitance, series resistance, and series inductance is accomplished by measuring their RF response while being submitted to mechanical stress. This allows for the first time quantifying the degradation of the device’s RF performance when cracks form within its structure. In this regard, the main challenge is designing an interface for measuring the high-frequency response of a capacitor using a vector network analyzer as a bending test on a PCB in progress, which is achieved here by using a microstrip-based test fixture. The results indicate that there is an overestimation of its response to microwave stimuli when considering only the degradation impact as a reduction in capacitance. Capacitors of representative sizes and capacitances are analyzed to show the usefulness of the proposal, whereas the validity of the results is verified by observing the correlation with measurements collected using microprobes and performing optical inspections of cross-sectioned samples. Full article
(This article belongs to the Section E:Engineering and Technology)
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15 pages, 14093 KiB  
Article
Integrating Multiple Hierarchical Parameters to Achieve the Self-Compensation of Scale Factor in a Micro-Electromechanical System Gyroscope
by Rui Zhou, Rang Cui, Daren An, Chong Shen, Yu Bai and Huiliang Cao
Micromachines 2024, 15(11), 1385; https://doi.org/10.3390/mi15111385 - 16 Nov 2024
Viewed by 594
Abstract
The scale factor of thermal sensitivity serves as a crucial performance metric for micro-electromechanical system (MEMS) gyroscopes, and is commonly employed to assess the temperature stability of inertial sensors. To improve the temperature stability of the scale factor of MEMS gyroscopes, a self-compensation [...] Read more.
The scale factor of thermal sensitivity serves as a crucial performance metric for micro-electromechanical system (MEMS) gyroscopes, and is commonly employed to assess the temperature stability of inertial sensors. To improve the temperature stability of the scale factor of MEMS gyroscopes, a self-compensation method is proposed. This is achieved by integrating the primary and secondary relevant parameters of the scale factor using the partial least squares regression (PLSR) algorithm. In this paper, a scale factor prediction model is presented. The model indicates that the resonant frequency and demodulation phase angle are the primary correlation terms of the scale factor, while the drive control voltage and quadrature feedback voltage are the secondary correlation terms of the scale factor. By employing a weighted fusion of correlated terms through PLSR, the scale factor for temperature sensitivity is markedly enhanced by leveraging the predicted results to compensate for the output. The results indicate that the maximum error of the predicted scale factor is 0.124% within the temperature range of −40 °C to 60 °C, and the temperature sensitivity of the scale factor decreases from 6180 ppm/°C to 9.39 ppm/°C. Full article
(This article belongs to the Special Issue MEMS Sensors and Actuators: Design, Fabrication and Applications)
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13 pages, 5049 KiB  
Article
Quantum Channel Extreme Bandgap AlGaN HEMT
by Michael Shur, Grigory Simin, Kamal Hussain, Abdullah Mamun, M. V. S. Chandrashekhar and Asif Khan
Micromachines 2024, 15(11), 1384; https://doi.org/10.3390/mi15111384 - 15 Nov 2024
Viewed by 577
Abstract
An extreme bandgap Al0.64Ga0.36N quantum channel HEMT with Al0.87Ga0.13N top and back barriers, grown by MOCVD on a bulk AlN substrate, demonstrated a critical breakdown field of 11.37 MV/cm—higher than the 9.8 MV/cm expected for [...] Read more.
An extreme bandgap Al0.64Ga0.36N quantum channel HEMT with Al0.87Ga0.13N top and back barriers, grown by MOCVD on a bulk AlN substrate, demonstrated a critical breakdown field of 11.37 MV/cm—higher than the 9.8 MV/cm expected for the channel’s Al0.64Ga0.36N material. We show that the fraction of this increase is due to the quantization of the 2D electron gas. The polarization field maintains electron quantization in the quantum channel even at low sheet densities, in contrast to conventional HEMT designs. An additional increase in the breakdown field is due to quantum-enabled real space transfer of energetic electrons into high-Al barrier layers in high electric fields. These results show the advantages of the quantum channel design for achieving record-high breakdown voltages and allowing for superior power HEMT devices. Full article
(This article belongs to the Special Issue RF and Power Electronic Devices and Applications)
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11 pages, 3968 KiB  
Article
Comparison of Interfaces Between In Situ Laser Beam Deposition Forming and Electron Beam Welding for Thick-Walled Titanium Alloy Structures
by Pingchuan Yang, Fei Li, Zongtao Zhu and Hui Chen
Micromachines 2024, 15(11), 1383; https://doi.org/10.3390/mi15111383 - 15 Nov 2024
Viewed by 606
Abstract
An investigation was conducted on electron beam-welded and additively manufactured joints on a thick-walled titanium alloy utilizing in situ laser beam deposition and electron beam welding techniques. The surface morphology, microstructural characteristics, and mechanical properties of both joint types were comprehensively analyzed using [...] Read more.
An investigation was conducted on electron beam-welded and additively manufactured joints on a thick-walled titanium alloy utilizing in situ laser beam deposition and electron beam welding techniques. The surface morphology, microstructural characteristics, and mechanical properties of both joint types were comprehensively analyzed using stereomicroscopy, scanning electron microscopy (SEM), microhardness and tensile strength testing, and electron backscatter diffraction (EBSD) techniques. The electron-beam-welded joint exhibited distinct fusion and heat-affected zones, whereas the laser-beam-deposited joint exhibited a smoother surface that was free from excess spatter. Both joints featured a sharp microstructural boundary with a pronounced hardness gradient across the interface, lacking a gradual transition area. During tensile testing, both joint types demonstrated a mixed brittle-ductile fracture mode; however, the electron beam-welded joints surpassed the laser-beam-deposited joints in terms of tensile strength, achieving over 1183 MPa with an elongation of more than 7.3%, compared to 1123 MPa and 5.9% elongation, respectively. Full article
(This article belongs to the Special Issue Future Prospects of Additive Manufacturing)
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12 pages, 1594 KiB  
Review
Exploring the Connection Between Nanomaterials and Neurodegenerative Disorders
by Sitansu Sekhar Nanda and Dong Kee Yi
Micromachines 2024, 15(11), 1382; https://doi.org/10.3390/mi15111382 - 15 Nov 2024
Viewed by 803
Abstract
Drug delivery, tissue engineering, and cell promotion in biomedical fields heavily rely on the use of nanomaterials (NMs). When they penetrate cells, NPs undergo degradation and initiate the generation of reactive oxygen species (ROS) by causing changes in the structures of organelles linked [...] Read more.
Drug delivery, tissue engineering, and cell promotion in biomedical fields heavily rely on the use of nanomaterials (NMs). When they penetrate cells, NPs undergo degradation and initiate the generation of reactive oxygen species (ROS) by causing changes in the structures of organelles linked to mitochondria. Inside the cell, the excess production of ROS can initiate a chain reaction, along with the autophagy process that helps maintain ROS balance by discarding unnecessary materials. At present, there is no effective treatment for Alzheimer’s disease (AD), a progressive neurodegenerative disease. The use of NMs for siRNA delivery could become a promising treatment for AD and other CNS disorders. Recent research demonstrates that the use of combined NPs can induce autophagy in cells. This article emphasizes the importance of the shape of siRNA-encapsulated NMs in determining their efficiency in delivering and suppressing gene activity in the central nervous system. Because of its strict selectivity against foreign substances, the blood–brain barrier (BBB) significantly hinders the delivery of therapeutic agents to the brain. Conventional chemotherapeutic drugs are significantly less effective against brain cancers due to this limitation. As a result, NMs have become a promising approach for targeted drug delivery, as they can be modified to carry specific ligands that direct them to their intended targets. This review thoroughly examines the latest breakthroughs in using NMs to deliver bioactive compounds across the BBB, focusing on their use in cancer treatments. The review starts by examining the structure and functions of the BBB and BBTB, and then emphasizes the benefits that NMs offer. Full article
(This article belongs to the Section B3: Nanoparticles in Biomedicine)
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15 pages, 5787 KiB  
Review
A Review of Ku-Band GaN HEMT Power Amplifiers Development
by Jihoon Kim
Micromachines 2024, 15(11), 1381; https://doi.org/10.3390/mi15111381 - 15 Nov 2024
Viewed by 946
Abstract
This review article investigates the current status and advances in Ku-band gallium nitride (GaN) high-electron mobility transistor (HEMT) high-power amplifiers (HPAs), which are critical for satellite communications, unmanned aerial vehicle (UAV) systems, and military radar applications. The demand for high-frequency, high-power amplifiers is [...] Read more.
This review article investigates the current status and advances in Ku-band gallium nitride (GaN) high-electron mobility transistor (HEMT) high-power amplifiers (HPAs), which are critical for satellite communications, unmanned aerial vehicle (UAV) systems, and military radar applications. The demand for high-frequency, high-power amplifiers is growing, driven by the global expansion of high-speed data communication and enhanced national security requirements. First, we compare the main GaN HEMT process technologies employed in Ku-band HPA development, categorizing the HPAs into monolithic microwave integrated circuits (MMICs) and internally matched power amplifier modules (IM-PAMs) and examining their respective characteristics. Then, by reviewing the literature, we explore design topologies, major issues like oscillation prevention and bias circuits, and heat sink technologies for thermal management. Our findings indicate that silicon carbide (SiC) substrates with gate lengths of 0.25 μm and 0.15 μm are predominantly used, with ongoing developments enabling MMICs and IM-PAMs to achieve up to 100 W output power and 30% power-added efficiency. Notably, the performance of MMIC power amplifiers is advancing more rapidly than that of IM-PAMs, highlighting MMICs as a promising direction for achieving higher efficiency and integration in future Ku-band applications. This paper can provide insights into the overall key technologies for Ku-band GaN HPA design and future development directions. Full article
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22 pages, 5925 KiB  
Article
Research on Energy Dissipation Mechanism of Cobweb-like Disk Resonator Gyroscope
by Huang Yi, Bo Fan, Feng Bu, Fang Chen and Xiao-Qing Luo
Micromachines 2024, 15(11), 1380; https://doi.org/10.3390/mi15111380 - 15 Nov 2024
Viewed by 541
Abstract
The micro disk resonator gyroscope is a micro-mechanical device with potential for navigation-grade applications, where the performance is significantly influenced by the quality factor, which is determined by various energy dissipation mechanisms within the micro resonant structure. To enhance the quality factor, these [...] Read more.
The micro disk resonator gyroscope is a micro-mechanical device with potential for navigation-grade applications, where the performance is significantly influenced by the quality factor, which is determined by various energy dissipation mechanisms within the micro resonant structure. To enhance the quality factor, these gyroscopes are typically enclosed in high-vacuum packaging. This paper investigates a wafer-level high-vacuum-packaged (<0.1 Pa) cobweb-like disk resonator gyroscope, presenting a systematic and comprehensive theoretical analysis of the energy dissipation mechanisms, including air damping, thermoelastic damping, anchor loss, and other factors. Air damping is analyzed using both a continuous fluid model and an energy transfer model. The analysis results are validated through quality factor testing on batch samples and temperature characteristic testing on individual samples. The theoretical results obtained using the energy transfer model closely match the experimental measurements, with a maximum error in the temperature coefficient of less than 2%. The findings indicate that air damping and thermoelastic damping are the predominant energy dissipation mechanisms in the cobweb-like disk resonant gyroscope under high-vacuum conditions. Consequently, optimizing the resonator to minimize thermoelastic and air damping is crucial for designing high-performance gyroscopes. Full article
(This article belongs to the Special Issue Advances in MEMS Inertial Sensors)
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15 pages, 4488 KiB  
Article
Multi-Frame Vibration MEMS Gyroscope Temperature Compensation Based on Combined GWO-VMD-TCN-LSTM Algorithm
by Ao Li, Ke Cui, Daren An, Xiaoyi Wang and Huiliang Cao
Micromachines 2024, 15(11), 1379; https://doi.org/10.3390/mi15111379 - 15 Nov 2024
Viewed by 645
Abstract
This paper presents a temperature compensation model for the Multi-Frame Vibration MEMS Gyroscope (DMFVMG) based on Grey Wolf Optimization Variational Mode Decomposition (GWO-VMD) for denoising and a combination of the Temporal Convolutional Network (TCN) and the Long Short-Term Memory (LSTM) network for temperature [...] Read more.
This paper presents a temperature compensation model for the Multi-Frame Vibration MEMS Gyroscope (DMFVMG) based on Grey Wolf Optimization Variational Mode Decomposition (GWO-VMD) for denoising and a combination of the Temporal Convolutional Network (TCN) and the Long Short-Term Memory (LSTM) network for temperature drift prediction. Initially, the gyroscope output signal was denoised using GWO-VMD, retaining the useful signal components and eliminating noise. Subsequently, the denoised signal was utilized to predict temperature drift using the TCN-LSTM model. The experimental results demonstrate that the compensation model significantly enhanced the gyroscope’s performance across various temperatures, reducing the rate random wander from 102.929°/h/√Hz to 17.6903°/h/√Hz and the bias instability from 63.70°/h to 1.38°/h, with reductions of 82.81% and 97.83%, respectively. This study validates the effectiveness and superiority of the proposed temperature compensation model. Full article
(This article belongs to the Special Issue MEMS Sensors and Actuators: Design, Fabrication and Applications)
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14 pages, 4040 KiB  
Article
Analysis of the Radial Force of a Piezoelectric Actuator with Interdigitated Spiral Electrodes
by Yateng Wang, Tianxing Ren, Yuan Ren, Ruijie Gu and Yonggang Liu
Micromachines 2024, 15(11), 1378; https://doi.org/10.3390/mi15111378 - 15 Nov 2024
Viewed by 619
Abstract
The actuator is a critical component of the micromanipulator. By utilizing the properties of expansion and contraction, the piezoelectric actuator enables the manipulator to handle and grasp miniature objects during micromanipulation. However, in piezoelectric ceramic disc actuators with conventional surface electrode configurations, the [...] Read more.
The actuator is a critical component of the micromanipulator. By utilizing the properties of expansion and contraction, the piezoelectric actuator enables the manipulator to handle and grasp miniature objects during micromanipulation. However, in piezoelectric ceramic disc actuators with conventional surface electrode configurations, the actuating force generated in the radial direction is relatively limited. When used as the actuation element of the manipulator, achieving regulation over a wide range of operating strokes becomes challenging. Therefore, altering the electrode structure is necessary to generate a greater radial force, thus enhancing the positioning and grasping capabilities of the operating arm. This paper investigates a piezoelectric actuator with interdigitated spiral electrodes, featuring a constant pitch between adjacent electrodes. The radial force was tested under mechanical clamping conditions, and the influence of the electrical signal was examined. The characteristics of the electrode structure were described, and the working principles of the piezoelectric actuators were analyzed. Theoretical equations were derived for the macroscopic characterization of the radial clamping force of the actuator, based on the piezoelectric constitutive equation, geometric principles, and Bond matrix transformation relationships. A finite element model was developed, reflecting the features of the electrode structure, and finite element simulations were employed to verify the theoretical equations for radial force. To prepare the samples, encircled interdigitated spiral electrode lines were printed on the PZT-52 piezoelectric ceramic disc using a screen printing method. The clamping force experimental platform was established, and experiments on the clamping radial force were conducted with electrical signals of varying waveforms, frequencies, and voltages. The experimental results show that the piezoelectric ceramic disc actuator with an interdigitated spiral electrode line structure, when excited by a stable sine wave operating at 200 V and 0.2 Hz, generated a peak force of 0.37 N. It was 1.76 times greater than that produced by a previously utilized piezoelectric disc with conventional electrode structures. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications, 2nd Edition)
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16 pages, 14457 KiB  
Article
ScAlN PMUTs Based on Flexurally Suspended Membrane for Long-Range Detection
by Shutao Yao, Wenling Shang, Guifeng Ta, Jinyan Tao, Haojie Liu, Xiangyong Zhao, Jianhe Liu, Bin Miao and Jiadong Li
Micromachines 2024, 15(11), 1377; https://doi.org/10.3390/mi15111377 - 14 Nov 2024
Viewed by 608
Abstract
Piezoelectric micromachined ultrasonic transducers (PMUTs) have been widely applied in distance sensing applications. However, the rapid movement of miniature robots in complex environments necessitates higher ranging capabilities from sensors, making the enhancement of PMUT sensing distance critically important. In this paper, a scandium-doped [...] Read more.
Piezoelectric micromachined ultrasonic transducers (PMUTs) have been widely applied in distance sensing applications. However, the rapid movement of miniature robots in complex environments necessitates higher ranging capabilities from sensors, making the enhancement of PMUT sensing distance critically important. In this paper, a scandium-doped aluminum nitride (ScAlN) PMUT based on a flexurally suspended membrane is proposed. Unlike the traditional fully clamped design, the PMUT incorporates a partially clamped membrane, thereby extending the vibration displacement and enhancing the output sound pressure. Experimental results demonstrate that at a resonant frequency of 78 kHz, a single PMUT generates a sound pressure level (SPL) of 112.2 dB at a distance of 10 mm and achieves a high receiving sensitivity of 12.3 mV/Pa. Distance testing reveals that a single PMUT equipped with a horn can achieve a record-breaking distance sensing range of 11.2 m when used alongside a device capable of simultaneously transmitting and receiving ultrasound signals. This achievement is significant for miniaturized and integrated applications that utilize ultrasound for long-range target detection. Full article
(This article belongs to the Special Issue MEMS Ultrasonic Transducers)
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16 pages, 9416 KiB  
Article
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
Viewed by 540
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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12 pages, 2475 KiB  
Article
Effect of Hot Junction Size on the Temperature Measurement of Proton Exchange Membrane Fuel Cells Using NiCr/NiSi Thin-Film Thermocouple Sensors
by Huijin Guo, Zhihui Liu, Tengda Guo, Yi Sun, Kai Shen, Bi Wang, Yongjun Cheng, Yuming Wang, Tiancai Ma, Zixi Wang and Wanyu Ding
Micromachines 2024, 15(11), 1375; https://doi.org/10.3390/mi15111375 - 14 Nov 2024
Viewed by 466
Abstract
In the process of using thin-film thermocouples for contact measurement of the reaction temperature in proton exchange membrane fuel cells (PEMFC), the impact of thin-film thermocouple volume on the system’s reaction temperature field variation, reaction efficiency, and the lifespan of thermocouples under these [...] Read more.
In the process of using thin-film thermocouples for contact measurement of the reaction temperature in proton exchange membrane fuel cells (PEMFC), the impact of thin-film thermocouple volume on the system’s reaction temperature field variation, reaction efficiency, and the lifespan of thermocouples under these conditions is not thoroughly studied. Using magnetron sputtering technology, NiCr/NiSi thin-film thermocouples (NiCr/NiSi TFTCs) with different junction sizes were fabricated on the proton exchange membrane (PEM). These NiCr/NiSi TFTCs exhibit excellent compactness, with thickness and planar dimensions in the micrometer range. When PEMFCs are equipped with built-in NiCr/NiSi TFTCs of different hot junction sizes, the time required for the system to reach a steady state varies with the size of the hot junction, with smaller hot junction sizes reaching a steady state more quickly. In a 500-h continuous operation test, the failure rates of NiCr/NiSi TFTCs also vary based on the hot junction size. Both smaller and larger hot junction sizes have relatively higher failure rates, whereas medium-sized junctions have a lower failure rate. These extensive and repetitive comparative experiments provide significant reference value for the size design of TFTCs operating inside PEMFCs, promoting both industrial production and scientific research. Full article
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11 pages, 1223 KiB  
Article
Open-End Control of Neurite Outgrowth Lengths with Steep Bending Confinement Microchannel Patterns for Miswiring-Free Neuronal Network Formation
by Naoya Takada, Soya Hagiwara, Nanami Abe, Ryohei Yamazaki, Kazuhiro Tsuneishi and Kenji Yasuda
Micromachines 2024, 15(11), 1374; https://doi.org/10.3390/mi15111374 - 14 Nov 2024
Viewed by 543
Abstract
Wiring technology to control the length and direction of neurite outgrowth and to connect them is one of the most crucial development issues for forming single-cell-based neuronal networks. However, with current neurite wiring technology, it has been difficult to stop neurite extension at [...] Read more.
Wiring technology to control the length and direction of neurite outgrowth and to connect them is one of the most crucial development issues for forming single-cell-based neuronal networks. However, with current neurite wiring technology, it has been difficult to stop neurite extension at a specific length and connect it to other neurites without causing miswiring due to over-extension. Here, we examined a novel method of wiring neurites without miswiring by controlling the length of neurites in open-ended bending microchannel arrays connected beyond the maximum bending angle of neurite outgrowth. First, we determined the maximum bending angle of neurite elongation to pass through the bending point of a bending microfluidic channel; the maximum angle (the critical angle) was 90°. Next, we confirmed the control of neurite outgrowth length in open-ended microchannels connected at 120°, an angle beyond the maximum bending angle. The neurites stopped when elongated to the bend point, and no further elongation was observed. Finally, we observed that in bending microchannel arrays connected at an angle of 120°, two neurite outgrowths stopped and contacted each other without crossing over the bend point. The results show that the steep bending connection pattern is a robust open-end neurite wiring technique that prevents over-extension and miswiring. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2024)
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