Micromachines

13 pages, 3407 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Membrane Surface Modification via In Situ Grafting of GO/Pt Nanoparticles for Nitrate Removal with Anti-Biofouling Properties

by Mohammad Khajouei, Mahsa Najafi, Seyed Ahmad Jafari and Mohammad Latifi

Micromachines 2023, 14(1), 128; https://doi.org/10.3390/mi14010128 - 3 Jan 2023

Cited by 13 | Viewed by 2510

Abstract

Nanofiltration processes for the removal of emerging contaminants such as nitrate are a focus of attention of research works as an efficient technique for providing drinking water for people. Polysulfone (PSF) nanofiltration membranes containing graphene oxide (GO)/Pt (0, 0.25, 0.5, 0.75, 1 wt%) [...] Read more.

Nanofiltration processes for the removal of emerging contaminants such as nitrate are a focus of attention of research works as an efficient technique for providing drinking water for people. Polysulfone (PSF) nanofiltration membranes containing graphene oxide (GO)/Pt (0, 0.25, 0.5, 0.75, 1 wt%) nanoparticles were generated with the phase inversion pathway. The as-synthesized samples were characterized by FTIR, SEM, AFM, and contact angle tests to study the effect of GO/Pt on hydrophilicity and antibacterial characteristics. The results conveyed that insertion of GO/Pt dramatically improved the biofouling resistance of the membranes. Permeation experiments indicated that PSF membrane embracing 0.75 wt% GO/Pt nanoparticles had the highest nitrate flux and rejection ability. The membrane’s configuration was simulated using OPEN-MX simulating software indicating membranes maintaining 0.75 wt% of GO/Pt nanoparticles revealed the highest stability, which is well in accordance with experimental outcomes. Full article

(This article belongs to the Special Issue Nanomaterial-Based Membranes and Applications)

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17 pages, 6084 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Smart Nematic Liquid Crystal Polymers for Micromachining Advances

by Sébastien Dominici, Keynaz Kamranikia, Karine Mougin and Arnaud Spangenberg

Micromachines 2023, 14(1), 124; https://doi.org/10.3390/mi14010124 - 1 Jan 2023

Cited by 2 | Viewed by 2914

Abstract

The miniaturization of tools is an important step in human evolution to create faster devices as well as precise micromachines. Studies around this topic have allowed the creation of small-scale objects capable of a wide range of deformation to achieve complex tasks. Molecular [...] Read more.

The miniaturization of tools is an important step in human evolution to create faster devices as well as precise micromachines. Studies around this topic have allowed the creation of small-scale objects capable of a wide range of deformation to achieve complex tasks. Molecular arrangements have been investigated through liquid crystal polymer (LCP) to program such a movement. Smart polymers and hereby liquid crystal matrices are materials of interest for their easy structuration properties and their response to external stimuli. However, up until very recently, their employment at the microscale was mainly limited to 2D structuration. Among the numerous issues, one concerns the ability to 3D structure the material while controlling the molecular orientation during the polymerization process. This review aims to report recent efforts focused on the microstructuration of LCP, in particular those dealing with 3D microfabrication via two-photon polymerization (TPP). Indeed, the latter has revolutionized the production of 3D complex micro-objects and is nowadays recognized as the gold standard for 3D micro-printing. After a short introduction highlighting the interest in micromachines, some basic principles of liquid crystals are recalled from the molecular aspect to their implementation. Finally, the possibilities offered by TPP as well as the way to monitor the motion into the fabricated microrobots are highlighted. Full article

(This article belongs to the Special Issue Recent Advances in Microrobotics)

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24 pages, 3136 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Exploring the Structural Variability of Dynamic Biological Complexes by Single-Particle Cryo-Electron Microscopy

by Megan C. DiIorio and Arkadiusz W. Kulczyk

Micromachines 2023, 14(1), 118; https://doi.org/10.3390/mi14010118 - 31 Dec 2022

Cited by 7 | Viewed by 3606

Abstract

Biological macromolecules and assemblies precisely rearrange their atomic 3D structures to execute cellular functions. Understanding the mechanisms by which these molecular machines operate requires insight into the ensemble of structural states they occupy during the functional cycle. Single-particle cryo-electron microscopy (cryo-EM) has become [...] Read more.

Biological macromolecules and assemblies precisely rearrange their atomic 3D structures to execute cellular functions. Understanding the mechanisms by which these molecular machines operate requires insight into the ensemble of structural states they occupy during the functional cycle. Single-particle cryo-electron microscopy (cryo-EM) has become the preferred method to provide near-atomic resolution, structural information about dynamic biological macromolecules elusive to other structure determination methods. Recent advances in cryo-EM methodology have allowed structural biologists not only to probe the structural intermediates of biochemical reactions, but also to resolve different compositional and conformational states present within the same dataset. This article reviews newly developed sample preparation and single-particle analysis (SPA) techniques for high-resolution structure determination of intrinsically dynamic and heterogeneous samples, shedding light upon the intricate mechanisms employed by molecular machines and helping to guide drug discovery efforts. Full article

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

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10 pages, 14092 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thin Film Piezoelectric Nanogenerator Based on (100)-Oriented Nanocrystalline AlN Grown by Pulsed Laser Deposition at Room Temperature

by Wei Li, Yunqi Cao and Nelson Sepúlveda

Micromachines 2023, 14(1), 99; https://doi.org/10.3390/mi14010099 - 30 Dec 2022

Cited by 9 | Viewed by 2666

Abstract

In wearable or implantable biomedical devices that typically rely on battery power for diagnostics or operation, the development of flexible piezoelectric nanogenerators (NGs) that enable mechanical-to-electrical energy harvesting is finding promising applications. Here, we present the construction of a flexible piezoelectric nanogenerator using [...] Read more.

In wearable or implantable biomedical devices that typically rely on battery power for diagnostics or operation, the development of flexible piezoelectric nanogenerators (NGs) that enable mechanical-to-electrical energy harvesting is finding promising applications. Here, we present the construction of a flexible piezoelectric nanogenerator using a thin film of room temperature deposited nanocrystalline aluminium nitride (AlN). On a thin layer of aluminium (Al), the AlN thin film was grown using pulsed laser deposition (PLD). The room temperature grown AlN film was composed of crystalline columnar grains oriented in the (100)-direction, as revealed in images from transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fundamental characterization of the AlN thin film by piezoresponse force microscopy (PFM) indicated that its electro-mechanical energy conversion metrics were comparable to those of c-axis oriented AlN and zinc oxide (ZnO) thin films. Additionally, the AlN-based flexible piezoelectric NG was encapsulated in polyimide to further strengthen its mechanical robustness and protect it from some corrosive chemicals. Full article

(This article belongs to the Special Issue Piezoelectric MEMS/NEMS—Materials, Devices, and Applications)

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10 pages, 1913 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Monitoring Xenon Capture in a Metal Organic Framework Using Laser-Induced Breakdown Spectroscopy

by Hunter B. Andrews, Praveen K. Thallapally and Alexander J. Robinson

Micromachines 2023, 14(1), 82; https://doi.org/10.3390/mi14010082 - 29 Dec 2022

Cited by 8 | Viewed by 2398

Abstract

Molten salt reactor operation will necessitate circulation of a cover gas to remove certain evolved fission products and maintain an inert atmosphere. The cover gas leaving the reactor core is expected to contain both noble and non-noble gases, aerosols, volatile species, tritium, and [...] Read more.

Molten salt reactor operation will necessitate circulation of a cover gas to remove certain evolved fission products and maintain an inert atmosphere. The cover gas leaving the reactor core is expected to contain both noble and non-noble gases, aerosols, volatile species, tritium, and radionuclides and their daughters. To remove these radioactive gases, it is necessary to develop a robust off-gas system, along with novel sensors to monitor the gas stream and the treatment system performance. In this study, a metal organic framework (MOF) was engineered for the capture of Xe, a major contributor to the off-gas source term. The engineered MOF column was tested with a laser-induced breakdown spectroscopy (LIBS) sensor for noble gas monitoring. The LIBS sensor was used to monitor breakthrough tests with various Xe, Kr, and Ar mixtures to determine the Xe selectivity of the MOF column. This study offers an initial demonstration of the feasibility of monitoring off-gas treatment systems using a LIBS sensor to aid in the development of new capture systems for molten salt reactors. Full article

(This article belongs to the Special Issue Recent Advances in Chemical Gas Sensors)

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10 pages, 4414 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Crack-Based Sensor by Using the UV Curable Polyurethane-Acrylate Coated Film with V-Groove Arrays

by Jongsung Park, Dong-Su Kim, Youngsam Yoon, Arunkumar Shanmugasundaram and Dong-Weon Lee

Micromachines 2023, 14(1), 62; https://doi.org/10.3390/mi14010062 - 26 Dec 2022

Cited by 7 | Viewed by 2696

Abstract

Over the years, several bare metal and crack-based strain sensors have been proposed for various fields of science and technology. However, due to their low gauge factor, metal-based strain sensors have limited practical applications. The crack-based strain sensor, on the other hand, demonstrated [...] Read more.

Over the years, several bare metal and crack-based strain sensors have been proposed for various fields of science and technology. However, due to their low gauge factor, metal-based strain sensors have limited practical applications. The crack-based strain sensor, on the other hand, demonstrated excellent sensitivity and a high gauge factor. However, the crack-based strain sensor exhibited non-linear behavior at low strains, severely limiting its real-time applications. Generally, the crack-based strain sensors are fabricated by generating cracks by bending a polymer film on which a metal layer has been deposited with a constant curvature. However, the random formation of cracks produces nonlinear behavior in the crack sensors. To overcome the limitations of the current state of the art, we propose a V-groove-based metal strain sensor for human motion monitoring and Morse code generation. The V-groove crack-based strain sensor is fabricated on polyurethane acrylate (PUA) using the modified photolithography technique. During the procedure, a V-groove pattern formed on the surface of the sensor, and a uniform crack formed over the entire surface by concentrating stress along the groove. To improve the sensitivity and selectivity of the sensor, we generated the cracks in a controlled direction. The proposed strain sensor exhibited high sensitivity and excellent fidelity compared to the other reported metal strain sensors. The gauge factor of the proposed V-groove-induced crack sensor is 10-fold higher than the gauge factor of the reported metal strain sensors. In addition, the fabricated V-groove-based strain sensor exhibited rapid response and recovery times. The practical feasibility of the proposed V-groove-induced crack-based strain sensor is demonstrated through human motion monitoring and the generation of Morse code. The proposed V-groove crack sensor can detect multiple motions in a variety of human activities and is anticipated to be utilized in several applications due to its high durability and reproducibility. Full article

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

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16 pages, 5674 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Magnetically Driven Manipulation of Nonmagnetic Liquid Marbles: Billiards with Liquid Marbles

by Parnian Azizian, Mahbod Mohammadrashidi, Ali Abbas Azimi, Mohamad Ali Bijarchi, Mohammad Behshad Shafii and Rohollah Nasiri

Micromachines 2023, 14(1), 49; https://doi.org/10.3390/mi14010049 - 25 Dec 2022

Cited by 14 | Viewed by 4104

Abstract

Liquid marbles are droplets encapsulated by a layer of hydrophobic nanoparticles and have been extensively employed in digital microfluidics and lab-on-a-chip systems in recent years. In this study, magnetic liquid marbles were used to manipulate nonmagnetic liquid marbles. To achieve this purpose, a [...] Read more.

Liquid marbles are droplets encapsulated by a layer of hydrophobic nanoparticles and have been extensively employed in digital microfluidics and lab-on-a-chip systems in recent years. In this study, magnetic liquid marbles were used to manipulate nonmagnetic liquid marbles. To achieve this purpose, a ferrofluid liquid marble (FLM) was employed and attracted toward an electromagnet, resulting in an impulse to a water liquid marble (WLM) on its way to the electromagnet. It was observed that the manipulation of the WLM by the FLM was similar to the collision of billiard balls except that the liquid marbles exhibited an inelastic collision. Taking the FLM as the projectile ball and the WLM as the other target balls, one can adjust the displacement and direction of the WLM precisely, similar to an expert billiard player. Firstly, the WLM displacement can be adjusted by altering the liquid marble volumes, the initial distances from the electromagnet, and the coil current. Secondly, the WLM direction can be adjusted by changing the position of the WLM relative to the connecting line between the FLM center and the electromagnet. Results show that when the FLM or WLM volume increases by five times, the WLM shooting distance approximately increases by 200% and decreases by 75%, respectively. Full article

(This article belongs to the Special Issue Micro- and Nano-Systems for Manipulation, Actuation and Sensing)

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15 pages, 7678 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Low-Cost Light-Based GelMA 3D Bioprinting via Retrofitting: Manufacturability Test and Cell Culture Assessment

by Juan Enrique Pérez-Cortez, Víctor Hugo Sánchez-Rodríguez, Salvador Gallegos-Martínez, Cristina Chuck-Hernández, Ciro A. Rodriguez, Mario Moises Álvarez, Grissel Trujillo-de Santiago, Elisa Vázquez-Lepe and J. Israel Martínez-López

Micromachines 2023, 14(1), 55; https://doi.org/10.3390/mi14010055 - 25 Dec 2022

Cited by 15 | Viewed by 4690

Abstract

Light-based bioprinter manufacturing technology is still prohibitively expensive for organizations that rely on accessing three-dimensional biological constructs for research and tissue engineering endeavors. Currently, most of the bioprinting systems are based on commercial-grade-based systems or modified DIY (do it yourself) extrusion apparatuses. However, [...] Read more.

Light-based bioprinter manufacturing technology is still prohibitively expensive for organizations that rely on accessing three-dimensional biological constructs for research and tissue engineering endeavors. Currently, most of the bioprinting systems are based on commercial-grade-based systems or modified DIY (do it yourself) extrusion apparatuses. However, to date, few examples of the adoption of low-cost equipment have been found for light-based bioprinters. The requirement of large volumes of bioinks, their associated cost, and the lack of information regarding the parameter selection have undermined the adoption of this technology. This paper showcases the retrofitting and assessing of a low-cost Light-Based 3D printing system for tissue engineering. To evaluate the potential of a proposed design, a manufacturability test for different features, machine parameters, and Gelatin Methacryloyl (GelMA) concentrations for 7.5% and 10% was performed. Furthermore, a case study of a previously seeded hydrogel with C2C12 cells was successfully implemented as a proof of concept. On the manufacturability test, deviational errors were found between 0.7% to 13.3% for layer exposure times of 15 and 20 s. Live/Dead and Actin-Dapi fluorescence assays after 5 days of culture showed promising results in the cell viability, elongation, and alignment of 3D bioprinted structures. The retrofitting of low-cost equipment has the potential to enable researchers to create high-resolution structures and three-dimensional in vitro models. Full article

(This article belongs to the Special Issue 3D Bioprinting and Biofabrication for the Future of Tissue Engineering)

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33 pages, 7187 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Fundamentals and Applications of ZnO-Nanowire-Based Piezotronics and Piezo-Phototronics

by Yitong Wang, Wanli Xie, Wenbo Peng, Fangpei Li and Yongning He

Micromachines 2023, 14(1), 47; https://doi.org/10.3390/mi14010047 - 25 Dec 2022

Cited by 13 | Viewed by 4784

Abstract

The piezotronic effect is a coupling effect of semiconductor and piezoelectric properties. The piezoelectric potential is used to adjust the p-n junction barrier width and Schottky barrier height to control carrier transportation. At present, it has been applied in the fields of sensors, [...] Read more.

The piezotronic effect is a coupling effect of semiconductor and piezoelectric properties. The piezoelectric potential is used to adjust the p-n junction barrier width and Schottky barrier height to control carrier transportation. At present, it has been applied in the fields of sensors, human–machine interaction, and active flexible electronic devices. The piezo-phototronic effect is a three-field coupling effect of semiconductor, photoexcitation, and piezoelectric properties. The piezoelectric potential generated by the applied strain in the piezoelectric semiconductor controls the generation, transport, separation, and recombination of carriers at the metal–semiconductor contact or p-n junction interface, thereby improving optoelectronic devices performance, such as photodetectors, solar cells, and light-emitting diodes (LED). Since then, the piezotronics and piezo-phototronic effects have attracted vast research interest due to their ability to remarkably enhance the performance of electronic and optoelectronic devices. Meanwhile, ZnO has become an ideal material for studying the piezotronic and piezo-phototronic effects due to its simple preparation process and better biocompatibility. In this review, first, the preparation methods and structural characteristics of ZnO nanowires (NWs) with different doping types were summarized. Then, the theoretical basis of the piezotronic effect and its application in the fields of sensors, biochemistry, energy harvesting, and logic operations (based on piezoelectric transistors) were reviewed. Next, the piezo-phototronic effect in the performance of photodetectors, solar cells, and LEDs was also summarized and analyzed. In addition, modulation of the piezotronic and piezo-phototronic effects was compared and summarized for different materials, structural designs, performance characteristics, and working mechanisms’ analysis. This comprehensive review provides fundamental theoretical and applied guidance for future research directions in piezotronics and piezo-phototronics for optoelectronic devices and energy harvesting. Full article

(This article belongs to the Special Issue Advanced Technologies in Piezo-Phototronics)

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7 pages, 4766 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

An Acoustic Flat Lens for Broadband Focusing via Cross-Shape Structure

by Shenlian Gao, Qinglei Zeng, Mengyang Gong, Jun Lan and Xiaozhou Liu

Micromachines 2023, 14(1), 12; https://doi.org/10.3390/mi14010012 - 21 Dec 2022

Cited by 3 | Viewed by 2195

Abstract

The manipulation of refracted wavefronts is eye-catching for owning attractive applications. In this article, an airborne acoustic flat lens for broadband focusing via cross-shape structure was proposed and demonstrated, introducing the broadband manipulation of wavefronts. The designed metasurface employs gradient refractive index cells [...] Read more.

The manipulation of refracted wavefronts is eye-catching for owning attractive applications. In this article, an airborne acoustic flat lens for broadband focusing via cross-shape structure was proposed and demonstrated, introducing the broadband manipulation of wavefronts. The designed metasurface employs gradient refractive index cells to redirect the sound wave. Based on our theory, the effective refractive indexes of our unit cells can be easily calculated. The shackle of narrowband metasurfaces is conquered, and applications in medical ultrasound imaging are just around the corner. Full article

(This article belongs to the Section A：Physics)

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10 pages, 3561 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Sapphire Selective Laser Etching Dependence on Radiation Wavelength and Etchant

by Agnė Butkutė, Romualdas Sirutkaitis, Darius Gailevičius, Domas Paipulas and Valdas Sirutkaitis

Micromachines 2023, 14(1), 7; https://doi.org/10.3390/mi14010007 - 20 Dec 2022

Cited by 12 | Viewed by 4664

Abstract

Transparent and high-hardness materials have become the object of wide interest due to their optical and mechanical properties; most notably, concerning technical glasses and crystals. A notable example is sapphire—one of the most rigid materials having impressive mechanical stability, high melting point and [...] Read more.

Transparent and high-hardness materials have become the object of wide interest due to their optical and mechanical properties; most notably, concerning technical glasses and crystals. A notable example is sapphire—one of the most rigid materials having impressive mechanical stability, high melting point and a wide transparency window reaching into the UV range, together with impressive laser-induced damage thresholds. Nonetheless, using this material for 3D micro-fabrication is not straightforward due to its brittle nature. On the microscale, selective laser etching (SLE) technology is an appropriate approach for such media. Therefore, we present our research on C-cut crystalline sapphire microprocessing by using femtosecond radiation-induced SLE. Here, we demonstrate a comparison between different wavelength radiation (1030 nm, 515 nm, 343 nm) usage for material modification and various etchants (hydrofluoric acid, sodium hydroxide, potassium hydroxide and sulphuric and phosphoric acid mixture) comparison. Due to the inability to etch crystalline sapphire, regular SLE etchants, such as hydrofluoric acid or potassium hydroxide, have limited adoption in sapphire selective laser etching. Meanwhile, a 78% sulphuric and 22% phosphoric acid mixture at 270 °C temperature is a good alternative for this process. We present the changes in the material after the separate processing steps. After comparing different processing protocols, the perspective is demonstrated for sapphire structure formation. Full article

(This article belongs to the Special Issue Ultrafast Laser Processing of Difficult-to-Machine Materials and Micro/Nano Structures)

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11 pages, 3886 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Nitrocellulose Paper-Based Multi-Well Plate for Point-of-Care ELISA

by Zhen Qin, Zongjie Huang, Peng Pan, Yueyue Pan, Runze Zuo, Yu Sun and Xinyu Liu

Micromachines 2022, 13(12), 2232; https://doi.org/10.3390/mi13122232 - 16 Dec 2022

Cited by 13 | Viewed by 4960

Abstract

Low-cost diagnostic tools for point-of-care immunoassays, such as the paper-based enzyme-linked immunoassay (ELISA), have become increasingly important, especially so in the recent COVID-19 pandemic. ELISA is the gold-standard antibody/antigen sensing method. This paper reports an easy-to-fabricate nitrocellulose (NC) paper plate, coupled with a [...] Read more.

Low-cost diagnostic tools for point-of-care immunoassays, such as the paper-based enzyme-linked immunoassay (ELISA), have become increasingly important, especially so in the recent COVID-19 pandemic. ELISA is the gold-standard antibody/antigen sensing method. This paper reports an easy-to-fabricate nitrocellulose (NC) paper plate, coupled with a desktop scanner for ELISA, which provides a higher protein immobilization efficiency than the conventional cellulose paper-based ELISA platforms. The experiments were performed using spiked samples for the direct ELISA of rabbit IgG with a limit of detection (LOD) of 1.016 μg/mL, in a measurement range of 10 ng/mL to 1 mg/mL, and for the sandwich ELISA of sperm protein (SP-10) with an LOD of 88.8 ng/mL, in a measurement range of 1 ng/mL to 100 μg/mL. The described fabrication method, based on laser-cutting, is a highly flexible one-step laser micromachining process, which enables the rapid production of low-cost NC paper-based multi-well plates with different sizes for the ELISA measurements. Full article

(This article belongs to the Topic Advances in Microfluidics and Lab on a Chip Technology)

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13 pages, 2497 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Vibration-Assisted Synthesis of Nanoporous Anodic Aluminum Oxide (AAO) Membranes

by Urte Cigane, Arvydas Palevicius and Giedrius Janusas

Micromachines 2022, 13(12), 2236; https://doi.org/10.3390/mi13122236 - 16 Dec 2022

Cited by 5 | Viewed by 1994

Abstract

In recent years, many research achievements in the field of anodic aluminum oxide (AAO) membranes can be observed. Nevertheless, it is still an interesting research topic due to its high versatility and applications in various fields, such as template-assisted methods, filtration, sensors, etc. [...] Read more.

In recent years, many research achievements in the field of anodic aluminum oxide (AAO) membranes can be observed. Nevertheless, it is still an interesting research topic due to its high versatility and applications in various fields, such as template-assisted methods, filtration, sensors, etc. Nowadays, miniaturization is an integral part of different technologies; therefore, research on micro- and nanosized elements is relevant in areas such as LEDs and OLEDs, solar cells, etc. To achieve an efficient mixing process of fluid flow in straight nanopores, acoustofluidic physics has attracted great interest in recent decades. Unfortunately, the renewal of the electrolyte concentration at the bottom of a pore is limited. Thus, excitation is used to improve fluid mixing along nanosized diameters. The effect of excitation by high-frequency vibrations on pore geometry is also investigated. In this study, theoretical simulations were performed. Using theoretical calculations, the acoustic pressure, acoustic velocity, and velocity magnitude were obtained at frequencies of 2, 20, and 40 kHz. Moreover, nanoporous AAO membranes were synthesized, and the influence of high-frequency vibrations on the geometry of the pores was determined. Using a high-frequency excitation of 20 kHz, the thickness of the AAO membrane increased by 17.8%. In addition, the thickness increased by 31.1% at 40 kHz and 33.3% at the resonant frequency of 40 kHz. Using high-frequency vibrations during the anodization process, the electrolyte inside the pores is mixed, and as a result, a higher oxide growth rate and a deeper structure can be achieved. On the other hand, to obtain pores of the same depth, the reaction can be performed in a shorter time. Full article

(This article belongs to the Special Issue Advance in Energy Conversion and Storage: Material, Design and Application)

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8 pages, 1456 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Fabrication and Properties of InGaZnO Thin-Film Transistors Based on a Sol–Gel Method with Different Electrode Patterns

by Xingzhen Yan, Bo Li, Kaian Song, Yiqiang Zhang, Yanjie Wang, Fan Yang, Chao Wang, Yaodan Chi and Xiaotian Yang

Micromachines 2022, 13(12), 2207; https://doi.org/10.3390/mi13122207 - 13 Dec 2022

Cited by 9 | Viewed by 2526

Abstract

The preparation of thin-film transistors (TFTs) with InGaZnO (IGZO) channels using sol–gel technology has the advantages of simplicity in terms of process and weak substrate selectivity. We prepared a series of TFT devices with a top contact and bottom gate structure, in which [...] Read more.

The preparation of thin-film transistors (TFTs) with InGaZnO (IGZO) channels using sol–gel technology has the advantages of simplicity in terms of process and weak substrate selectivity. We prepared a series of TFT devices with a top contact and bottom gate structure, in which the top contact was divided into rectangular and circular structures of drain/source electrodes. The field-effect performance of TFT devices with circular pattern drain/source electrodes was better than that with a traditional rectangular structure on both substrates. The uniform distribution of the potential in the circular electrode structure was more conducive to the regulation of carriers under the same channel length at different applied voltages. In addition, with the development of transparent substrate devices, we also constructed a hafnium oxide (HfO₂) insulation layer and an IGZO active layer on an indium tin oxide conductive substrate, and explored the effect of circular drain/source electrodes on field-effect properties of the semitransparent TFT device. The IGZO deposited on the HfO₂ dielectric layer by spin-coating can effectively reduce the surface roughness of the HfO₂ layer and optimize the scattering of carriers at the interface in TFT devices. Full article

(This article belongs to the Special Issue Recent Advances in Thin Film Transistors)

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13 pages, 10691 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Flexible Heater Fabrication Using Amino Acid-Based Ink and Laser-Direct Writing

by Sangmo Koo

Micromachines 2022, 13(12), 2209; https://doi.org/10.3390/mi13122209 - 13 Dec 2022

Cited by 1 | Viewed by 2128

Abstract

Nature’s systems have evolved over a long period to operate efficiently, and this provides hints for metal nanoparticle synthesis, including the enhancement, efficient generation, and transport of electrons toward metal ions for nanoparticle synthesis. The organic material-based ink composed of the natural materials [...] Read more.

Nature’s systems have evolved over a long period to operate efficiently, and this provides hints for metal nanoparticle synthesis, including the enhancement, efficient generation, and transport of electrons toward metal ions for nanoparticle synthesis. The organic material-based ink composed of the natural materials used in this study requires low laser power for sintering compared to conventional nanoparticle ink sintering. This suggests applicability in various and sophisticated pattern fabrication applications without incurring substrate damage. An efficient electron transfer mechanism between amino acids (e.g., tryptophan) enables silver patterning on flexible polymer substrates (e.g., PET) by laser-direct writing. The reduction of silver ions to nanoparticles was induced and sintered by simultaneous photo/thermalchemical reactions on substrates. Furthermore, it was possible to fabricate a stable, transparent, and flexible heater that operates under mechanical deformation. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications, Volume III: Advanced Hybrid Processes in Micro-Manufacturing)

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25 pages, 3606 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Synergistic Electric and Thermal Effects of Electrochromic Devices

by Meng Yuan, Hanlin Yin, Yitong Liu, Xiaohua Wang, Long Yuan and Yu Duan

Micromachines 2022, 13(12), 2187; https://doi.org/10.3390/mi13122187 - 10 Dec 2022

Cited by 8 | Viewed by 3115

Abstract

Electrochromic devices are the preferred devices for smart windows because they work independently of uncontrollable environmental factors and rely more on the user’s personal feelings to adjust actively. However, in practical applications, the ambient temperature still has an impact on device performance, such [...] Read more.

Electrochromic devices are the preferred devices for smart windows because they work independently of uncontrollable environmental factors and rely more on the user’s personal feelings to adjust actively. However, in practical applications, the ambient temperature still has an impact on device performance, such as durability, reversibility and switching performance, etc. These technical issues have significantly slowed down the commercialization of electrochromic devices (ECDs). It is necessary to investigate the main reasons for the influence of temperature on the device and make reasonable optimization to enhance the effectiveness of the device and extend its lifetime. In recent years, with the joint efforts of various outstanding research teams, the performance of electrochromic devices has been rapidly improved, with a longer lifetime, richer colors, and better color contrast. This review highlights the important research on temperature–dependent electrochromic properties in recent years. Also, the reported structures, mechanisms, characteristics, and methods for improving electrochromic properties are discussed in detail. In addition, the challenges and corresponding strategies in this field are presented in this paper. This paper will inspire more researchers to enrich the temperature–dependent properties of ECDs and their related fields with innovative means and methods to overcome the technical obstacles faced. Full article

(This article belongs to the Special Issue Light Emitting Devices: From Fundamental Research to Applications)

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10 pages, 2962 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Curvature-Adjustable Polymeric Nanolens Fabrication Using UV-Controlled Nanoimprint Lithography

by Qiang Li, Myung Gi Ji, Ashish Chapagain, In Ho Cho and Jaeyoun Kim

Micromachines 2022, 13(12), 2183; https://doi.org/10.3390/mi13122183 - 9 Dec 2022

Cited by 5 | Viewed by 2163

Abstract

Nanolenses are gaining importance in nanotechnology, but their challenging fabrication is thwarting their wider adoption. Of particular challenge is facile control of the lens’ curvature. In this work, we demonstrate a new nanoimprinting technique capable of realizing polymeric nanolenses in which the nanolens’ [...] Read more.

Nanolenses are gaining importance in nanotechnology, but their challenging fabrication is thwarting their wider adoption. Of particular challenge is facile control of the lens’ curvature. In this work, we demonstrate a new nanoimprinting technique capable of realizing polymeric nanolenses in which the nanolens’ curvature is optically controlled by the ultraviolet (UV) dose at the pre-curing step. Our results reveal a regime in which the nanolens’ height changes linearly with the UV dose. Computational modeling further uncovers that the polymer undergoes highly nonlinear dynamics during the UV-controlled nanoimprinting process. Both the technique and the process model will greatly advance nanoscale science and manufacturing technology. Full article

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

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26 pages, 8160 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Film Thickness and Glycerol Concentration Mapping of Falling Films Based on Fluorescence and Near-Infrared Technique

by Isabel Medina, Stephan Scholl and Matthias Rädle

Micromachines 2022, 13(12), 2184; https://doi.org/10.3390/mi13122184 - 9 Dec 2022

Cited by 5 | Viewed by 3333

Abstract

Falling film evaporation processes involve high fluid velocities with continuous variations in local film thickness, fluid composition, and viscosity. This contribution presents a parallel and complementary film thickness and concentration mapping distribution in falling films using a non-invasive fluorescence and near-infrared imaging technique. [...] Read more.

Falling film evaporation processes involve high fluid velocities with continuous variations in local film thickness, fluid composition, and viscosity. This contribution presents a parallel and complementary film thickness and concentration mapping distribution in falling films using a non-invasive fluorescence and near-infrared imaging technique. The experiments were performed with a mixture of glycerol/water with a mass fraction from 0 to 0.65

g_{g l y c} g_{t o t a l}^{- 1}

and operating ranges similar to evaporation processes. The measurement system was designed by integrating two optical measurement methods for experimental image analysis. The film thickness was evaluated using a VIS camera and high-power LEDs at 470 nm. The local glycerol concentration

g_{g l y c} g_{t o t a l}^{- 1}

was determined using a NIR camera and high-power LEDs at 1050, 1300, 1450 and 1550 nm. A multiwavelength analysis with all NIR wavelengths was implemented with a better correlation for falling films at low flow velocity. The results show an improvement in the analysis of falling films with high flow velocities up to almost 500 mm/s by using only the 1450 nm wavelength and the fluorescence measurement. Simultaneous imaging analysis of film thickness and concentration in falling films provides further insight into understanding mass and heat transport and thus supports the optimization of falling film evaporators. Full article

(This article belongs to the Special Issue Optics and Photonics in Micromachines)

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12 pages, 2663 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Additive Nanosecond Laser-Induced Forward Transfer of High Antibacterial Metal Nanoparticle Dose onto Foodborne Bacterial Biofilms

by Alena Nastulyavichus, Liliana Khaertdinova, Eteri Tolordava, Yulia Yushina, Andrey Ionin, Anastasia Semenova and Sergey Kudryashov

Micromachines 2022, 13(12), 2170; https://doi.org/10.3390/mi13122170 - 8 Dec 2022

Cited by 7 | Viewed by 1577

Abstract

Additive laser-induced forward transfer (LIFT) of metal bactericidal nanoparticles from a polymer substrate directly onto food bacterial biofilms has demonstrated its unprecedented efficiency in combating pathogenic microorganisms. Here, a comprehensive study of laser fluence, metal (gold, silver and copper) film thickness, and the [...] Read more.

Additive laser-induced forward transfer (LIFT) of metal bactericidal nanoparticles from a polymer substrate directly onto food bacterial biofilms has demonstrated its unprecedented efficiency in combating pathogenic microorganisms. Here, a comprehensive study of laser fluence, metal (gold, silver and copper) film thickness, and the transfer distance effects on the antibacterial activity regarding biofilms of Gram-negative and Gram-positive food bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Listeria monocytogenes, Salmonella spp.) indicated the optimal operation regimes of the versatile modality. LIFT-induced nanoparticle penetration into a biofilm was studied by energy-dispersion X-ray spectroscopy, which demonstrated that nanoparticles remained predominantly on the surface of the biofilm. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Light-Matter Interactions in Laser Metal Additive Manufacturing)

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16 pages, 5926 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Continuous Particle Aggregation and Separation in Acoustofluidic Microchannels Driven by Standing Lamb Waves

by Jin-Chen Hsu and Chih-Yu Chang

Micromachines 2022, 13(12), 2175; https://doi.org/10.3390/mi13122175 - 8 Dec 2022

Cited by 2 | Viewed by 2104

Abstract

In this study, we realize acoustic aggregation and separation of microparticles in fluid channels driven by standing Lamb waves of a 300-μm-thick double-side polished lithium-niobate (LiNbO₃) plate. We demonstrate that the counter-propagating lowest-order antisymmetric and symmetric Lamb modes can be excited [...] Read more.

In this study, we realize acoustic aggregation and separation of microparticles in fluid channels driven by standing Lamb waves of a 300-μm-thick double-side polished lithium-niobate (LiNbO₃) plate. We demonstrate that the counter-propagating lowest-order antisymmetric and symmetric Lamb modes can be excited by double interdigitated transducers on the LiNbO₃ plate to produce interfacial coupling with the fluid in channels. Consequently, the solid–fluid coupling generates radiative acoustic pressure and streaming fields to actuate controlled acoustophoretic motion of particles by means of acoustic radiation and Stokes drag forces. We conducted finite-element simulations based on the acoustic perturbation theory with full-wave modeling to tailor the acoustic and streaming fields in the channels driven by the standing Lamb waves. As a result, the acoustic process and the mechanism of particle aggregation and separation were elucidated. Experiments on acoustic manipulation of particles in channels validate the capability of aggregation and separation by the designed devices. It is observed that strong streaming dominates the particle aggregation while the acoustic radiation force differentially expels particles with different sizes from pressure antinodes to achieve continuous particle separation. This study paves the way for Lamb-wave acoustofluidics and may trigger more innovative acoustofluidic systems driven by Lamb waves and other manipulating approaches incorporated on a thin-plate platform. Full article

(This article belongs to the Special Issue Acoustofluidics: Applications, Phenomena and Fabrication Technique)

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9 pages, 2559 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Viscosity-Controllable Graphene Oxide Colloids Using Electrophoretically Deposited Graphene Oxide Sheets

by Jinseok Choi, Seong-Gyu Park, Yeo-Jin Choi, Seung-Mun Baek, Han-Jung Kim, Yoonkap Kim, Ki-Sik Im and Sung-Jin An

Micromachines 2022, 13(12), 2157; https://doi.org/10.3390/mi13122157 - 7 Dec 2022

Cited by 1 | Viewed by 1938

Abstract

Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the [...] Read more.

Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the specific process requirements. Here, we report on the relatively rapid fabrication of viscosity-increased GO (VIGO) colloids mixed with electrophoretically deposited GO sheets (EPD-GO). As the GO colloid concentration, applied voltage, and deposition time increase, the viscosity of the GO colloids becomes high. The reason for the improved viscosity of GO colloids is because EPD-GO has parallel stacked GO sheets. The GO and VIGO colloids are compared and characterized using various chemical and structural analyzers. Consequently, our simple and fast method for the fabrication of GO colloids with enhanced viscosity can be used for producing inks for flexible and printed electronics. Full article

(This article belongs to the Special Issue Smart Carbon Nanostructures and Applications)

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21 pages, 8451 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress in Blue Thermally Activated Delayed Fluorescence Emitters and Their Applications in OLEDs: Beyond Pure Organic Molecules with Twist D-π-A Structures

by Yiting Gao, Siping Wu, Guogang Shan and Gang Cheng

Micromachines 2022, 13(12), 2150; https://doi.org/10.3390/mi13122150 - 5 Dec 2022

Cited by 13 | Viewed by 7138

Abstract

Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with [...] Read more.

Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with the aid of ambient thermal energy under the reverse inter-system crossing owing to the small singlet–triplet splitting energy (ΔE_ST). This results from a specific molecular design consisting of minimal overlap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, due to the spatial separation of the electron-donating and electron-releasing part. When a well-designed device structure is applied, high-performance blue-emitting TADF organic light-emitting diodes can be realized with an appropriate molecular design. Unlike the previous literature that has reviewed general blue-emitting TADF materials, in this paper, we focus on materials other than pure organic molecules with twist D-π-A structures, including multi-resonance TADF, through-space charge transfer TADF, and metal-TADF materials. Cutting-edge molecules with extremely small and even negative ΔE_ST values are also introduced as candidates for next-generation TADF materials. In addition, OLED structures used to exploit the merits of the abovementioned TADF emitters are also described in this review. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes (OLEDs))

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23 pages, 4528 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Micro-Sized pH Sensors Based on Scanning Electrochemical Probe Microscopy

by Muhanad Al-Jeda, Emmanuel Mena-Morcillo and Aicheng Chen

Micromachines 2022, 13(12), 2143; https://doi.org/10.3390/mi13122143 - 4 Dec 2022

Cited by 11 | Viewed by 3660

Abstract

Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), [...] Read more.

Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), these sensors can provide measurements with high spatial resolution. This article reviews the state-of-the-art design and fabrication of micro-/nano-sized pH sensors, as well as their applications based on SECM. Considerations for selecting sensing probes for use in biological studies, corrosion science, in energy applications, and for environmental research are examined. Different types of pH sensitive probes are summarized and compared. Finally, future trends and emerging applications of micro-/nano-sized pH sensors are discussed. Full article

(This article belongs to the Special Issue MEMS Sensors: Fabrication and Application)

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14 pages, 3144 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Battery-Free Tattooing Mechanism-Based Functional Active Capsule Endoscopy

by Manh-Cuong Hoang, Jong-Oh Park and Jayoung Kim

Micromachines 2022, 13(12), 2111; https://doi.org/10.3390/mi13122111 - 29 Nov 2022

Cited by 5 | Viewed by 1955

Abstract

This paper presents a novel tattooing capsule endoscope (TCE) for delivering a certain amount of ink to the submucosal layer of digestive tract organs. A dual-function permanent magnet is used for locomotion and injection activation. The developed capsule endoscope can move actively in [...] Read more.

This paper presents a novel tattooing capsule endoscope (TCE) for delivering a certain amount of ink to the submucosal layer of digestive tract organs. A dual-function permanent magnet is used for locomotion and injection activation. The developed capsule endoscope can move actively in 5 DOF due to the interaction between the permanent magnet and a controllable external magnetic field produced by an electromagnet actuation system. In addition, the permanent magnet is involved in a specially designed mechanism to activate a process that creates a squeezing motion to eject the liquid from the storage room to the target. The dimension of the prototype is 12.5 mm in diameter and 34.6 mm in length. The proposed TCE is tested ex vivo using a fresh porcine small-intestine segment. We were able to direct the TCE to the target and deliver the tattoo agent into the tissue. The proposed mechanism can be used for drug delivery or lesion tattooing, as well as to accelerate the realization of the functional capsule endoscope in practice. Full article

(This article belongs to the Special Issue Integrated Robotics for Micromanipulation, Diagnosis and Microsurgery)

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11 pages, 2113 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel Memristive Neural Network Circuit and Its Application in Character Recognition

by Xinrui Zhang, Xiaoyuan Wang, Zhenyu Ge, Zhilong Li, Mingyang Wu and Shekharsuman Borah

Micromachines 2022, 13(12), 2074; https://doi.org/10.3390/mi13122074 - 25 Nov 2022

Cited by 11 | Viewed by 3909

Abstract

The memristor-based neural network configuration is a promising approach to realizing artificial neural networks (ANNs) at the hardware level. The memristors can effectively simulate the strength of synaptic connections between neurons in neural networks due to their diverse significant characteristics such as nonvolatility, [...] Read more.

The memristor-based neural network configuration is a promising approach to realizing artificial neural networks (ANNs) at the hardware level. The memristors can effectively simulate the strength of synaptic connections between neurons in neural networks due to their diverse significant characteristics such as nonvolatility, nanoscale dimensions, and variable conductance. This work presents a new synaptic circuit based on memristors and Complementary Metal Oxide Semiconductor(CMOS), which can realize the adjustment of positive, negative, and zero synaptic weights using only one control signal. The relationship between synaptic weights and the duration of control signals is also explained in detail. Accordingly, Widrow–Hoff algorithm-based memristive neural network (MNN) circuits are proposed to solve the recognition of three types of character pictures. The functionality of the proposed configurations is verified using SPICE simulation. Full article

(This article belongs to the Special Issue Novel Computing Architectures and Digital Circuit Designs Using Memristors and Memristive Systems)

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18 pages, 3237 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Ultrafast Pulse Generation from Quantum Cascade Lasers

by Feihu Wang, Xiaoqiong Qi, Zhichao Chen, Manijeh Razeghi and Sukhdeep Dhillon

Micromachines 2022, 13(12), 2063; https://doi.org/10.3390/mi13122063 - 24 Nov 2022

Cited by 6 | Viewed by 3806

Abstract

Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful [...] Read more.

Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful to study ultrafast processes in MIR and THz using the targeted wavelength-by-design properties of QCLs. Since the first demonstration in 2009, mode-locking of QCLs has undergone considerable development in the past decade, which includes revealing the underlying mechanism of pulse formation, the development of an ultrafast THz detection technique, and the invention of novel pulse compression technology, etc. Here, we review the history and recent progress of ultrafast pulse generation from QCLs in both the THz and MIR regimes. Full article

(This article belongs to the Special Issue Quantum Cascade Laser: Physics, Technology and Applications)

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21 pages, 1683 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Temperature-to-Digital Converters’ Evolution, Trends and Techniques across the Last Two Decades: A Review

by Antonio Aprile, Edoardo Bonizzoni and Piero Malcovati

Micromachines 2022, 13(11), 2025; https://doi.org/10.3390/mi13112025 - 19 Nov 2022

Cited by 7 | Viewed by 3390

Abstract

This paper presents an extensive review of the main highlights in the Temperature-to-Digital Converters (TDCs) field, which has gained importance and research interest throughout the last two decades. The key techniques and approaches that have led to the evolution of this kind of [...] Read more.

This paper presents an extensive review of the main highlights in the Temperature-to-Digital Converters (TDCs) field, which has gained importance and research interest throughout the last two decades. The key techniques and approaches that have led to the evolution of this kind of systems are presented and compared; their peculiarities are identified in order to highlight the pros and cons of the different design methods, and the main trade-offs are extracted from this analysis. Finally, the trends that have emerged from the performance evaluation of the large amount of published works in this field are identified with the purpose of providing a directional view of the past, present and future features of these devices. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in Engineering and Technology 2021)

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14 pages, 6781 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micro Light Flow Controller on a Programmable Waveguide Engine

by Tao Chen, Zhangqi Dang, Zeyu Deng, Zhenming Ding and Ziyang Zhang

Micromachines 2022, 13(11), 1990; https://doi.org/10.3390/mi13111990 - 16 Nov 2022

Cited by 8 | Viewed by 3345

Abstract

A light flow controller that can regulate the three-port optical power in both lossless and lossy modus is realized on a programmable multimode waveguide engine. The microheaters on the waveguide chip mimic the tunable “pixels” that can continuously adjust the local refractive index. [...] Read more.

A light flow controller that can regulate the three-port optical power in both lossless and lossy modus is realized on a programmable multimode waveguide engine. The microheaters on the waveguide chip mimic the tunable “pixels” that can continuously adjust the local refractive index. Compared to the conventional method where the tuning takes place only on single-mode waveguides, the proposed structure is more compact and requires less electrodes. The local index changes in a multimode waveguide can alter the mode numbers, field distribution, and propagation constants of each individual mode, all of which can alter the multimode interference pattern significantly. However, these changes are mostly complex and not governed by analytical equations as in the single-mode case. Though numerical simulations can be performed to predict the device response, the thermal and electromagnetic computing involved is mostly time-consuming. Here, a multi-level search program is developed based on experiments only. It can reach a target output in real time by adjusting the microheaters collectively and iteratively. It can also jump over local optima and further improve the cost function on a global level. With only a simple waveguide structure and four microheaters, light can be routed freely into any of the three output ports with arbitrary power ratios, with and without extra attenuation. This work may trigger new ideas in developing compact and efficient photonic integrated devices for applications in optical communication and computing. Full article

(This article belongs to the Special Issue Micro/Nano-Structure Based Optoelectronics and Photonics Devices)

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10 pages, 2085 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rapid Bacterial Motility Monitoring Using Inexpensive 3D-Printed OpenFlexure Microscopy Allows Microfluidic Antibiotic Susceptibility Testing

by Tai The Diep, Sarah Helen Needs, Samuel Bizley and Alexander D. Edwards

Micromachines 2022, 13(11), 1974; https://doi.org/10.3390/mi13111974 - 14 Nov 2022

Cited by 6 | Viewed by 3862

Abstract

Antibiotic susceptibility testing is vital to tackle the emergence and spread of antimicrobial resistance. Inexpensive digital CMOS cameras can be converted into portable digital microscopes using 3D printed x-y-z stages. Microscopic examination of bacterial motility can rapidly detect the response of microbes to [...] Read more.

Antibiotic susceptibility testing is vital to tackle the emergence and spread of antimicrobial resistance. Inexpensive digital CMOS cameras can be converted into portable digital microscopes using 3D printed x-y-z stages. Microscopic examination of bacterial motility can rapidly detect the response of microbes to antibiotics to determine susceptibility. Here, we present a new simple microdevice-miniature microscope cell measurement system for multiplexed antibiotic susceptibility testing. The microdevice is made using melt-extruded plastic film strips containing ten parallel 0.2 mm diameter microcapillaries. Two different antibiotics, ceftazidime and gentamicin, were prepared in Mueller-Hinton agar (0.4%) to produce an antibiotic-loaded microdevice for simple sample addition. This combination was selected to closely match current standard methods for both antibiotic susceptibility testing and motility testing. Use of low agar concentration permits observation of motile bacteria responding to antibiotic exposure as they enter capillaries. This device fits onto the OpenFlexure 3D-printed digital microscope using a Raspberry Pi computer and v2 camera, avoiding need for expensive laboratory microscopes. This inexpensive and portable digital microscope platform had sufficient magnification to detect motile bacteria, yet wide enough field of view to monitor bacteria behavior as they entered antibiotic-loaded microcapillaries. The image quality was sufficient to detect how bacterial motility was inhibited by different concentrations of antibiotic. We conclude that a 3D-printed Raspberry Pi-based microscope combined with disposable microfluidic test strips permit rapid, easy-to-use bacterial motility detection, with potential for aiding detection of antibiotic resistance. Full article

(This article belongs to the Special Issue Advances in Microfluidic Flow Cytometry)

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13 pages, 1861 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improving Swimming Performance of Photolithography-Based Microswimmers Using Curvature Structures

by Liyuan Tan, Zihan Wang, Zhi Chen, Xiangcheng Shi and U Kei Cheang

Micromachines 2022, 13(11), 1965; https://doi.org/10.3390/mi13111965 - 12 Nov 2022

Cited by 4 | Viewed by 2546

Abstract

The emergence of robotic microswimmers and their huge potential in biomedical applications such as drug delivery, non-invasive surgery, and bio-sensing facilitates studies to improve their effectiveness. Recently, achiral microswimmers that have neither flexible nor helical structures have garnered attention because of their simple [...] Read more.

The emergence of robotic microswimmers and their huge potential in biomedical applications such as drug delivery, non-invasive surgery, and bio-sensing facilitates studies to improve their effectiveness. Recently, achiral microswimmers that have neither flexible nor helical structures have garnered attention because of their simple structures and fabrication process while preserving adequate swimming velocity and controllability. In this paper, the crescent shape was utilized to create photolithography-fabricated crescent-shaped achiral microswimmers. The microswimmers were actuated using rotating magnetic fields at low Reynolds numbers. Compared with the previously reported achiral microswimmers, the crescent-shaped microswimmers showed significant improvement in forward swimming speed. The effects of different curvatures, arm angles, and procession angles on the velocities of microswimmers were investigated. Moreover, the optimal swimming motion was defined by adjusting the field strength of the magnetic field. Finally, the effect of the thickness of the microswimmers on their swimming velocity was investigated. Full article

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

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14 pages, 7178 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Interface Dynamics and the Influence of Gravity on Droplet Generation in a Y-microchannel

by Alexandra Bran, Nicoleta Octavia Tanase and Corneliu Balan

Micromachines 2022, 13(11), 1941; https://doi.org/10.3390/mi13111941 - 10 Nov 2022

Cited by 1 | Viewed by 2085

Abstract

The present experimental investigation is focused on the influence of gravity upon water-droplet formation in a Y-microchannel filled with oil. The flows are in the Stokes regime, with very small capillary numbers and Ohnesorge numbers less than one. The study was performed in [...] Read more.

The present experimental investigation is focused on the influence of gravity upon water-droplet formation in a Y-microchannel filled with oil. The flows are in the Stokes regime, with very small capillary numbers and Ohnesorge numbers less than one. The study was performed in a square-cross-section channel, with a = 1.0 mm as the characteristic dimension and a flow rate ratio

κ

in a range between 0.55 and 1.8. The interface dynamics in the vicinity of breakup and the transitory plug flow regime after the detachment of the droplet were analysed. The dependence of droplet length L was correlated with the channel position against the gravity and

κ

parameters. The results of the work prove that, for

κ = 1

, the droplet length L is independent of channel orientation. Full article

(This article belongs to the Special Issue Microfluidics for Health Monitoring)

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12 pages, 1713 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Picoliter Droplet Generation and Dense Bead-in-Droplet Encapsulation via Microfluidic Devices Fabricated via 3D Printed Molds

by Tochukwu D. Anyaduba, Jonas A. Otoo and Travis S. Schlappi

Micromachines 2022, 13(11), 1946; https://doi.org/10.3390/mi13111946 - 10 Nov 2022

Cited by 11 | Viewed by 5394

Abstract

Picoliter-scale droplets have many applications in chemistry and biology, such as biomolecule synthesis, drug discovery, nucleic acid quantification, and single cell analysis. However, due to the complicated processes used to fabricate microfluidic channels, most picoliter (pL) droplet generation methods are limited to research [...] Read more.

Picoliter-scale droplets have many applications in chemistry and biology, such as biomolecule synthesis, drug discovery, nucleic acid quantification, and single cell analysis. However, due to the complicated processes used to fabricate microfluidic channels, most picoliter (pL) droplet generation methods are limited to research in laboratories with cleanroom facilities and complex instrumentation. The purpose of this work is to investigate a method that uses 3D printing to fabricate microfluidic devices that can generate droplets with sizes <100 pL and encapsulate single dense beads mechanistically. Our device generated monodisperse droplets as small as ~48 pL and we demonstrated the usefulness of this droplet generation technique in biomolecule analysis by detecting Lactobacillus acidophillus 16s rRNA via digital loop-mediated isothermal amplification (dLAMP). We also designed a mixer that can be integrated into a syringe to overcome dense bead sedimentation and found that the bead-in-droplet (BiD) emulsions created from our device had <2% of the droplets populated with more than 1 bead. This study will enable researchers to create devices that generate pL-scale droplets and encapsulate dense beads with inexpensive and simple instrumentation (3D printer and syringe pump). The rapid prototyping and integration ability of this module with other components or processes can accelerate the development of point-of-care microfluidic devices that use droplet-bead emulsions to analyze biological or chemical samples with high throughput and precision. Full article

(This article belongs to the Special Issue Droplet-Based Microfluidics: Design, Fabrication and Applications)

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12 pages, 4057 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication and Evaluation of Tubule-on-a-Chip with RPTEC/HUVEC Co-Culture Using Injection-Molded Polycarbonate Chips

by Ju-Bi Lee, Hyoungseob Kim, Sol Kim and Gun Yong Sung

Micromachines 2022, 13(11), 1932; https://doi.org/10.3390/mi13111932 - 9 Nov 2022

Cited by 13 | Viewed by 3420

Abstract

To simulate the ADME process such as absorption, distribution, metabolism, and excretion in the human body after drug administration and to confirm the applicability of the mass production process, a microfluidic chip injection molded with polycarbonate (injection-molded chip (I-M chip)) was fabricated. Polycarbonate [...] Read more.

To simulate the ADME process such as absorption, distribution, metabolism, and excretion in the human body after drug administration and to confirm the applicability of the mass production process, a microfluidic chip injection molded with polycarbonate (injection-molded chip (I-M chip)) was fabricated. Polycarbonate materials were selected to minimize drug absorption. As a first step to evaluate the I-M chip, RPTEC (Human Renal Proximal Tubule Epithelial Cells) and HUVEC (Human Umbilical Vein Endothelial Cells) were co-cultured, and live and dead staining, TEER (trans-epithelial electrical resistance), glucose reabsorption, and permeability were compared using different membrane pore sizes of 0.4 μm and 3 μm. Drug excretion was confirmed through a pharmacokinetic test with metformin and cimetidine, and the gene expression of drug transporters was confirmed. As a result, it was confirmed that the cell viability was higher in the 3 μm pore size than in the 0.4 μm, the cell culture performed better, and the drug secretion was enhanced when the pore size was large. The injection-molded polycarbonate microfluidic chip is anticipated to be commercially viable for drug screening devices, particularly ADME tests. Full article

(This article belongs to the Special Issue Advances and Challenges in Biofabrication and Organ-on-a-Chip Platforms)

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6 pages, 2008 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermo-Optic Phase Shifter with Interleaved Suspended Design for Power Efficiency and Speed Adjustment

by Feng Gao, Wu Xie, James You Sian Tan, Chew Ping Leong, Chao Li, Xianshu Luo and Guo-Qiang Lo

Micromachines 2022, 13(11), 1925; https://doi.org/10.3390/mi13111925 - 8 Nov 2022

Cited by 5 | Viewed by 2575

Abstract

Conventional thermo-optic devices—which can be broadly categorized to that with and without a thermal isolation trench—typically come with a tradeoff between thermal tuning efficiency and tuning speed. Here, we propose a method that allows us to directly define the tradeoff using a specially [...] Read more.

Conventional thermo-optic devices—which can be broadly categorized to that with and without a thermal isolation trench—typically come with a tradeoff between thermal tuning efficiency and tuning speed. Here, we propose a method that allows us to directly define the tradeoff using a specially designed thermo-optic phase shifter with an interleaved isolation trench. With the design, the tuning efficiency and speed can be precisely tailored simply by controlling the duty ratio (suspended length over total heater length) of the suspended design. Phase shifters are one of the main components in photonic-integrated circuits, and having phase shifters with a flexible design approach may enable the wide adoption of photonic applications such as an optical neural network and LiDAR. Full article

(This article belongs to the Special Issue Silicon Photonic Devices and Integration)

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30 pages, 4456 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Lossy Mode Resonance-Based Fiber Optic Sensors: A Review

by Vikas, Satyendra Kumar Mishra, Akhilesh Kumar Mishra, Paola Saccomandi and Rajneesh Kumar Verma

Micromachines 2022, 13(11), 1921; https://doi.org/10.3390/mi13111921 - 7 Nov 2022

Cited by 20 | Viewed by 5058

Abstract

Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which [...] Read more.

Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which mainly utilizes the thin film of metals, a wide range of materials such as conducting metal oxides and polymers support LMR. The past several years have witnessed a remarkable development in the field of LMR-based fiber optic sensors; through this review, we have tried to summarize the overall development of LMR-based fiber optic sensors. This review article not only provides the fundamental understanding and detailed explanation of LMR generation but also sheds light on the setup/configuration required to excite the lossy modes. Several geometries explored in the literature so far have also been addressed. In addition, this review includes a survey of the different materials capable of supporting lossy modes and explores new possible LMR supporting materials and their potential applications in sensing. Full article

(This article belongs to the Section A：Physics)

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14 pages, 3395 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Dynamic Behaviours of Monodisperse Double Emulsion Formation in a Tri-Axial Capillary Device

by Yuchen Dai, Haotian Cha, Nhat-Khuong Nguyen, Lingxi Ouyang, Fariba Galogahi, Ajeet Singh Yadav, Hongjie An, Jun Zhang, Chin Hong Ooi and Nam-Trung Nguyen

Micromachines 2022, 13(11), 1877; https://doi.org/10.3390/mi13111877 - 31 Oct 2022

Cited by 7 | Viewed by 2474

Abstract

We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally [...] Read more.

We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally and numerically. We propose a semi-analytical model using the match ratio between the pinch-off length of the shell droplet and the product of the core growth rate and its pinch-off time. The mismatch issue can be avoided if the match ratio is lower than unity. We considered a model with the wall effect to predict the size of the matched double emulsion. The model shows slight deviations with experimental data if the Reynolds number of the continuous phase is lower than 0.06 but asymptotically approaches good agreement if the Reynolds number increases from 0.06 to 0.14. The numerical simulation generally agrees with the experiments under various flow conditions. Full article

(This article belongs to the Special Issue Droplet-Based Microfluidics: Design, Fabrication and Applications)

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11 pages, 3146 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Quality Fiber Bragg Gratings Inscribed by Femtosecond Laser Point-by-Point Technology

by Runxiao Chen, Jun He, Xizhen Xu, Jiafeng Wu, Ying Wang and Yiping Wang

Micromachines 2022, 13(11), 1808; https://doi.org/10.3390/mi13111808 - 23 Oct 2022

Cited by 17 | Viewed by 4798

Abstract

We experimentally studied the inscription of fiber Bragg gratings by using femtosecond (fs) laser point-by-point (PbP) technology. The effects of the focusing geometry, grating order, laser energy and grating length on the spectral characteristics of the PbP FBG were investigated. After [...] Read more.

We experimentally studied the inscription of fiber Bragg gratings by using femtosecond (fs) laser point-by-point (PbP) technology. The effects of the focusing geometry, grating order, laser energy and grating length on the spectral characteristics of the PbP FBG were investigated. After optimizing these parameters, a high-quality first-order PbP FBG with a reflectivity > 99.9% (i.e., Bragg resonance attenuation of 37.7 dB) and insertion loss (IL) of 0.03 dB was successfully created. Moreover, taking advantage of the excellent flexibility of the fs laser PbP technology, high-quality FBGs with various Bragg wavelengths ranging from 856 to 1902.6 nm were inscribed. Furthermore, wavelength-division-multiplexed (WDM) FBG arrays consisting of 10 FBGs were rapidly constructed. Additionally, a Fabry-Perot cavity was realized by using two high-quality FBGs, and its birefringence could be reduced from 3.04 × 10⁻⁵ to 1.77 × 10⁻⁶ by using a slit beam shaping-assisted femtosecond laser PbP technology. Therefore, such high-quality FBGs are promising to improve the performance of optical fiber sensors, lasers and communication devices. Full article

(This article belongs to the Special Issue Advanced Laser Fabrication for Optical Sensors)

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7 pages, 2605 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Heterogeneous CMOS Integration of InGaAs-OI nMOSFETs and Ge pMOSFETs Based on Dual-Gate Oxide Technique

by Xiaoyu Tang, Tao Hua, Yujie Liu and Zhezhe Han

Micromachines 2022, 13(11), 1806; https://doi.org/10.3390/mi13111806 - 23 Oct 2022

Cited by 1 | Viewed by 1750

Abstract

A compatible fabrication technology for integrating InGaAs nMOSFETs and Ge pMOSFETs is developed based on the development of the two-step gate oxide fabrication strategy. The direct wafer bonding method was utilized to obtain the InGaAs-Insulator-Ge structure, providing the heterogeneous channels for CMOS integration. [...] Read more.

A compatible fabrication technology for integrating InGaAs nMOSFETs and Ge pMOSFETs is developed based on the development of the two-step gate oxide fabrication strategy. The direct wafer bonding method was utilized to obtain the InGaAs-Insulator-Ge structure, providing the heterogeneous channels for CMOS integration. Superior transistor characteristics were achieved by optimizing the InGaAs gate oxide with a self-cleaning process in atomic layer deposition, and modifying the Ge gate oxide by the ozone post oxidation (OPO) technique, in the sequential two-step gate oxide fabrication process. With the combination of the gate-first fabrication process, superior on- and off-state characteristics, i.e., on current up to 8.3 µA/μm and leakage as low as 10⁻⁶ µA/μm, have been demonstrated in the integrated MOSFETs, together with the preferable symmetric output characteristics that promises excellent CMOS performances. Full article

(This article belongs to the Section D1: Semiconductor Devices)

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12 pages, 5301 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Origami Inspired Laser Scanner

by Yu-Shin Wu and Shao-Kang Hung

Micromachines 2022, 13(10), 1796; https://doi.org/10.3390/mi13101796 - 21 Oct 2022

Viewed by 2658

Abstract

Diverse origami techniques and various selections of paper open new possibilities to create micromachines. By folding paper, this article proposes an original approach to build laser scanners, which manipulate optical beams precisely and realize valuable applications, including laser marking, cutting, engraving, and displaying. [...] Read more.

Diverse origami techniques and various selections of paper open new possibilities to create micromachines. By folding paper, this article proposes an original approach to build laser scanners, which manipulate optical beams precisely and realize valuable applications, including laser marking, cutting, engraving, and displaying. A prototype has been designed, implemented, actuated, and controlled. The experimental results demonstrate that the angular stroke, repeatability, full scale settling time, and resonant frequency are 20°, 0.849 m°, 330 ms, 68 Hz, respectively. Its durability, more than 35 million cycles, shows the potential to carry out serious tasks. Full article

(This article belongs to the Special Issue Origami Devices: Design and Application)

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17 pages, 1526 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Developments in FRET- and BRET-Based Biosensors

by Yuexin Wu and Tianyu Jiang

Micromachines 2022, 13(10), 1789; https://doi.org/10.3390/mi13101789 - 20 Oct 2022

Cited by 31 | Viewed by 10099

Abstract

Resonance energy transfer technologies have achieved great success in the field of analysis. Particularly, fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) provide strategies to design tools for sensing molecules and monitoring biological processes, which promote the development of biosensors. [...] Read more.

Resonance energy transfer technologies have achieved great success in the field of analysis. Particularly, fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) provide strategies to design tools for sensing molecules and monitoring biological processes, which promote the development of biosensors. Here, we provide an overview of recent progress on FRET- and BRET-based biosensors and their roles in biomedicine, environmental applications, and synthetic biology. This review highlights FRET- and BRET-based biosensors and gives examples of their applications with their design strategies. The limitations of their applications and the future directions of their development are also discussed. Full article

(This article belongs to the Special Issue Prospects and Challenges of Biosensors towards Diagnostics of the Diseases and Health Monitoring)

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10 pages, 21721 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Millimeter-Wave Permittivity Variations of an HR Silicon Substrate from the Photoconductive Effect

by Charlotte Tripon-Canseliet and Jean Chazelas

Micromachines 2022, 13(10), 1782; https://doi.org/10.3390/mi13101782 - 19 Oct 2022

Cited by 1 | Viewed by 1881

Abstract

The photoinduced microwave complex permittivity of a highly resistive single-crystal silicon wafer was extracted from a bistatic free-space characterization test bench operating in the 26.5–40 GHz frequency band under CW optical illumination at wavelengths of 806 and 971 nm. Significant variations in the [...] Read more.

The photoinduced microwave complex permittivity of a highly resistive single-crystal silicon wafer was extracted from a bistatic free-space characterization test bench operating in the 26.5–40 GHz frequency band under CW optical illumination at wavelengths of 806 and 971 nm. Significant variations in the real and imaginary parts of the substrate’s permittivity induced by direct photoconductivity are reported, with an optical power density dependence, in agreement with the theoretical predictions. These experimental results open the route to ultrafast system reconfiguration of microwave devices in integrated technology by an external EMI-protected and contactless control with unprecedented performance. Full article

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13 pages, 5642 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Sensitive and Portable Double-Layer Microfluidic Biochip for Harmful Algae Detection

by Ping Li, Le Qiang, Yingkuan Han, Yujin Chu, Jiaoyan Qiu, Fangteng Song, Min Wang, Qihang He, Yunhong Zhang, Mingyuan Sun, Caiwen Li, Shuqun Song, Yun Liu, Lin Han and Yu Zhang

Micromachines 2022, 13(10), 1759; https://doi.org/10.3390/mi13101759 - 18 Oct 2022

Cited by 7 | Viewed by 2992

Abstract

Harmful algal blooms (HABs) are common disastrous ecological anomalies in coastal waters. An effective algae monitoring approach is important for natural disaster warning and environmental governance. However, conducting rapid and sensitive detection of multiple algae is still challenging. Here, we designed an ultrasensitive, [...] Read more.

Harmful algal blooms (HABs) are common disastrous ecological anomalies in coastal waters. An effective algae monitoring approach is important for natural disaster warning and environmental governance. However, conducting rapid and sensitive detection of multiple algae is still challenging. Here, we designed an ultrasensitive, rapid and portable double-layer microfluidic biochip for the simultaneous quantitative detection of six species of algae. Specific DNA probes based on the 18S ribosomal DNA (18S rDNA) gene fragments of HABs were designed and labeled with the fluorescent molecule cyanine-3 (Cy3). The biochip had multiple graphene oxide (GO) nanosheets-based reaction units, in which GO nanosheets were applied to transfer target DNA to the fluorescence signal through a photoluminescence detection system. The entire detection process of multiple algae was completed within 45 min with the linear range of fluorescence recovery of 0.1 fM–100 nM, and the detection limit reached 108 aM. The proposed approach has a simple detection process and high detection performance and is feasible to conduct accurate detection with matched portable detection equipment. It will have promising applications in marine natural disaster monitoring and environmental care. Full article

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12 pages, 61097 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Metasurfaces as Energy Valves for Sustainable Energy Management

by Yoshiaki Nishijima, Syunya Kimura, Yu Takeshima and Saulius Juodkazis

Micromachines 2022, 13(10), 1769; https://doi.org/10.3390/mi13101769 - 18 Oct 2022

Cited by 6 | Viewed by 2661

Abstract

Control of light absorption and transmission by metal–insulator–metal (MIM) metasurfaces are promising for applications in optical windows. This study shows the realization of photo-thermal energy conversion for radiative cooling by MIM metasurfaces with thin metal substrate and Indium–Tin–Oxide (ITO). High transparency of ITO [...] Read more.

Control of light absorption and transmission by metal–insulator–metal (MIM) metasurfaces are promising for applications in optical windows. This study shows the realization of photo-thermal energy conversion for radiative cooling by MIM metasurfaces with thin metal substrate and Indium–Tin–Oxide (ITO). High transparency of ITO at visible wavelengths and high absorption at mid-infrared wavelengths were realized for future applications of efficient cooling or heating applicable for living and working spaces. The MIM (ITO/CaF₂/ITO) metasurface was patterned with low-resolution photo-lithography as a demonstration of further simplification and possible scalability of the patterning for practical window applications. Full article

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12 pages, 2388 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Vertical Single Transistor Neuron with Core–Shell Dual-Gate for Excitatory–Inhibitory Function and Tunable Firing Threshold Voltage

by Taegoon Lee, Seung-Bae Jeon and Daewon Kim

Micromachines 2022, 13(10), 1740; https://doi.org/10.3390/mi13101740 - 14 Oct 2022

Cited by 2 | Viewed by 3255

Abstract

A novel inhibitable and firing threshold voltage tunable vertical nanowire (NW) single transistor neuron device with core–shell dual-gate (CSDG) was realized and verified by TCAD simulation. The CSDG NW neuron is enclosed by an independently accessed shell gate and core gate to serve [...] Read more.

A novel inhibitable and firing threshold voltage tunable vertical nanowire (NW) single transistor neuron device with core–shell dual-gate (CSDG) was realized and verified by TCAD simulation. The CSDG NW neuron is enclosed by an independently accessed shell gate and core gate to serve an excitatory–inhibitory transition and a firing threshold voltage adjustment, respectively. By utilizing the shell gate, the firing of specific neuron can be inhibited for winner-takes-all learning. It was confirmed that the independently accessed core gate can be used for adjustment of the firing threshold voltage to compensate random conductance variation before the learning and to fix inference error caused by unwanted synapse conductance change after the learning. This threshold voltage tuning can also be utilized for homeostatic function during the learning process. Furthermore, a myelination function which controls the transmission rate was obtained based on the inherent asymmetry between the source and drain in vertical NW structure. Finally, using the CSDG NW neuron device, a letter recognition test was conducted by SPICE simulation for a system-level validation. This multi-functional neuron device can contribute to construct a high-density monolithic SNN hardware combining with the previously developed vertical synapse MOSFET devices. Full article

(This article belongs to the Special Issue Self-Powered Devices and Systems)

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31 pages, 4256 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Micromachined Thermal Time-of-Flight Flow Sensors and Their Applications

by Liji Huang

Micromachines 2022, 13(10), 1729; https://doi.org/10.3390/mi13101729 - 13 Oct 2022

Cited by 10 | Viewed by 4410

Abstract

Micromachined thermal flow sensors on the market are primarily manufactured with the calorimetric sensing principle. The success has been in limited industries such as automotive, medical, and gas process control. Applications in some emerging and abrupt applications are hindered due to technical challenges. [...] Read more.

Micromachined thermal flow sensors on the market are primarily manufactured with the calorimetric sensing principle. The success has been in limited industries such as automotive, medical, and gas process control. Applications in some emerging and abrupt applications are hindered due to technical challenges. This paper reviews the current progress with micromachined devices based on the less popular thermal time-of-flight sensing technology: its theory, design of the micromachining process, control schemes, and applications. Thermal time-of-flight sensing could effectively solve some key technical hurdles that the calorimetric sensing approach has. It also offers fluidic property-independent data acquisition, multiparameter measurement, and the possibility for self-calibration. This technology may have a significant perspective on future development. Full article

(This article belongs to the Special Issue Novel Devices and Advances in MEMS Fabrication Processes)

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18 pages, 3687 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electromechanical Properties of 3D-Printed Stretchable Carbon Fiber Composites

by Teemu Salo, Donato Di Vito, Aki Halme and Jukka Vanhala

Micromachines 2022, 13(10), 1732; https://doi.org/10.3390/mi13101732 - 13 Oct 2022

Cited by 18 | Viewed by 3827

Abstract

The addition of fillers has been implemented in fused filament fabrication (FFF), and robust carbon fillers have been found to improve the mechanical, electrical, and thermal properties of 3D-printed matrices. However, in stretchable matrices, the use of fillers imposes significant challenges related to [...] Read more.

The addition of fillers has been implemented in fused filament fabrication (FFF), and robust carbon fillers have been found to improve the mechanical, electrical, and thermal properties of 3D-printed matrices. However, in stretchable matrices, the use of fillers imposes significant challenges related to quality and durability. In this work, we show that long carbon staple fibers in the form of permeable carbon fiber cloth (CFC) can be placed into a stretchable thermoplastic polyurethane (TPU) matrix to improve the system. Four CFC sample series (nominally 53–159-µm-thick CFC layers) were prepared with a permeable and compliant thin CFC layer and a highly conductive and stiff thick CFC layer. The sample series was tested with single pull-up tests and cyclic tensile tests with 10,000 cycles and was further studied with digital image correlation (DIC) analyses. The results showed that embedded CFC layers in a TPU matrix can be used for stretchable 3D-printed electronics structures. Samples with a thin 53 µm CFC layer retained electrical properties at 50% cyclic tensile deformations, whereas the samples with a thick >150-µm CFC layer exhibited the lowest resistance (5 Ω/10 mm). Between those structures, the 106-µm-thick CFC layer exhibited balanced electromechanical properties, with resistance changes of 0.5% in the cyclic tests after the orientation of the samples. Furthermore, the suitability of the structure as a sensor was estimated. Full article

(This article belongs to the Special Issue Flexible and Wearable Sensors)

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14 pages, 8513 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Scalable, Dual-Band Metasurface Array for Electromagnetic Energy Harvesting and Wireless Power Transfer

by Yiqing Wei, Junping Duan, Huihui Jing, Huimin Yang, Hao Deng, Chengwei Song, Jiayun Wang, Zeng Qu and Binzhen Zhang

Micromachines 2022, 13(10), 1712; https://doi.org/10.3390/mi13101712 - 11 Oct 2022

Cited by 17 | Viewed by 3481

Abstract

A dual-band metasurface array is presented in this paper for electromagnetic (EM) energy harvesting in the Wi-Fi band and Ku band. The array consists of metasurface unit cells, rectifiers, and load resistors. The metasurface units within each column are interconnected to establish two [...] Read more.

A dual-band metasurface array is presented in this paper for electromagnetic (EM) energy harvesting in the Wi-Fi band and Ku band. The array consists of metasurface unit cells, rectifiers, and load resistors. The metasurface units within each column are interconnected to establish two channels of energy delivery, enabling the transmission and aggregation of incident power. At the terminals of two channels, a single series diode rectifier and a voltage doubler rectifier are integrated into them to rectify the energy in the Wi-Fi band and the Ku band, respectively. A 7 × 7 prototype of the metasurface array is fabricated and tested. The measured results in the anechoic chamber show that the RF-to-dc efficiencies of the prototype at 2.4 GHz and 12.6 GHz reach 64% and 55% accordingly, when the available incident power at the surface is 3 dBm and 14 dBm, respectively. Full article

(This article belongs to the Topic Advanced Energy Harvesting Technology)

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26 pages, 4364 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Microfluidic Gas Sensors: Detection Principle and Applications

by Sreerag Kaaliveetil, Juliana Yang, Saud Alssaidy, Zhenglong Li, Yu-Hsuan Cheng, Niranjan Haridas Menon, Charmi Chande and Sagnik Basuray

Micromachines 2022, 13(10), 1716; https://doi.org/10.3390/mi13101716 - 11 Oct 2022

Cited by 22 | Viewed by 7059

Abstract

With the rapid growth of emerging point-of-use (POU)/point-of-care (POC) detection technologies, miniaturized sensors for the real-time detection of gases and airborne pathogens have become essential to fight pollution, emerging contaminants, and pandemics. However, the low-cost development of miniaturized gas sensors without compromising selectivity, [...] Read more.

With the rapid growth of emerging point-of-use (POU)/point-of-care (POC) detection technologies, miniaturized sensors for the real-time detection of gases and airborne pathogens have become essential to fight pollution, emerging contaminants, and pandemics. However, the low-cost development of miniaturized gas sensors without compromising selectivity, sensitivity, and response time remains challenging. Microfluidics is a promising technology that has been exploited for decades to overcome such limitations, making it an excellent candidate for POU/POC. However, microfluidic-based gas sensors remain a nascent field. In this review, the evolution of microfluidic gas sensors from basic electronic techniques to more advanced optical techniques such as surface-enhanced Raman spectroscopy to detect analytes is documented in detail. This paper focuses on the various detection methodologies used in microfluidic-based devices for detecting gases and airborne pathogens. Non-continuous microfluidic devices such as bubble/droplet-based microfluidics technology that have been employed to detect gases and airborne pathogens are also discussed. The selectivity, sensitivity, advantages/disadvantages vis-a-vis response time, and fabrication costs for all the microfluidic sensors are tabulated. The microfluidic sensors are grouped based on the target moiety, such as air pollutants such as carbon monoxide and nitrogen oxides, and airborne pathogens such as E. coli and SARS-CoV-2. The possible application scenarios for the various microfluidic devices are critically examined. Full article

(This article belongs to the Special Issue Micro- and Nano-Systems for Manipulation, Actuation and Sensing)

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14 pages, 2409 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Effect of Non-Uniform Magnetic Field on the Efficiency of Mixing in Droplet-Based Microfluidics: A Numerical Investigation

by Masoud Rezaeian, Moein Nouri, Mojtaba Hassani-Gangaraj, Amir Shamloo and Rohollah Nasiri

Micromachines 2022, 13(10), 1661; https://doi.org/10.3390/mi13101661 - 2 Oct 2022

Cited by 12 | Viewed by 2831

Abstract

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power [...] Read more.

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power source is utilized to mix two fluids. One of these active methods is magnetic micromixers using ferrofluid. In this technique, magnetic nanoparticles are used to make one phase responsive to magnetic force, and then by applying a magnetic field, two fluid phases, one of which is magneto-responsive, will sufficiently mix. In this study, we investigated the effect of the magnetic field’s characteristics on the efficiency of the mixing process inside droplets. When different concentrations of ferrofluids are affected by a constant magnetic field, there is no significant change in mixing efficiency. As the magnetic field intensifies, the magnetic force makes the circulation flow inside the droplet asymmetric, leading to chaotic advection, which creates a flow that increases the mixing efficiency. The results show that the use of magnetic fields is an effective method to enhance the mixing efficiency within droplets, and the efficiency of mixing increases from 65.4 to 86.1% by increasing the magnetic field intensity from 0 to 90 mT. Besides that, the effect of ferrofluid’s concentration on the mixing efficiency is studied. It is shown that when the concentration of the ferrofluid changes from 0 to 0.6 mol/m³, the mixing efficiency increases considerably. It is also shown that by changing the intensity of the magnetic field, the mixing efficiency increases by about 11%. Full article

(This article belongs to the Special Issue Digital Microfluidics for Liquid Handling and Biochemical Analysis)

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19 pages, 7111 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

RETRACTED: Transient Response Characteristics Analysis of High-Power Piezoelectric Transducers

by Zhaopeng Dong, Liang Xu and Tianyue Yang

Micromachines 2022, 13(10), 1638; https://doi.org/10.3390/mi13101638 - 29 Sep 2022

Cited by 4 | Viewed by 2347

Abstract

To improve suitability in applications with high dynamic performance requirements, the transient response characteristics of high-power piezoelectric transducers should be studied quantitatively. This paper proposes the vector reduction method to solve the complex transient equations and obtains a transient matching scheme clarifying the [...] Read more.

To improve suitability in applications with high dynamic performance requirements, the transient response characteristics of high-power piezoelectric transducers should be studied quantitatively. This paper proposes the vector reduction method to solve the complex transient equations and obtains a transient matching scheme clarifying the mechanism of electrical matching resistance on electromechanical damping. A matching scheme with a combination of full-bridge inverter, transformer and series LC circuit is designed and validated, which can provide suitable electrical damping without causing energy losses. Consequently, the experiment verifies the transient properties of the proposed scheme. For a typical piezoelectric cutting transducer with 100.8 ms response time, our scheme is verified to have high dynamic performance within frequency response time of 5.5 ms and vibration response time of 15.0 ms. Full article

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