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Micromachines, Volume 11, Issue 1 (January 2020) – 111 articles

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Open AccessEditorial
Acknowledgement to Reviewers of Micromachines in 2019
Micromachines 2020, 11(1), 111; https://doi.org/10.3390/mi11010111 (registering DOI) - 20 Jan 2020
Viewed by 75
Abstract
The editorial team greatly appreciates the reviewers who have dedicated their considerable time and expertise to the journal’s rigorous editorial process over the past 12 months, regardless of whether the papers are finally published or not. [...] Full article
Open AccessArticle
Dynamical Control of Broadband Coherent Absorption in ENZ Films
Micromachines 2020, 11(1), 110; https://doi.org/10.3390/mi11010110 (registering DOI) - 20 Jan 2020
Viewed by 98
Abstract
Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of [...] Read more.
Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of the scattering matrix and often requires engineered optical properties. For instance, thin film CPA benefits from complex nanostructures with suitable resonance, albeit at a loss of operational bandwidth. In this work, we theoretically and experimentally demonstrate a broadband CPA based on light-with-light modulation in epsilon-near-zero (ENZ) subwavelength films. We show that unpatterned ENZ films with different thicknesses exhibit broadband CPA with a near-unity maximum value located at the ENZ wavelength. By using Kerr optical nonlinearities, we dynamically tune the visibility and peak wavelength of the total energy modulation. Our results based on homogeneous thick ENZ media open a route towards on-chip devices that require efficient light absorption and dynamical tunability. Full article
(This article belongs to the Special Issue Nonlinear Photonics Devices)
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Open AccessArticle
Tunable-Focus Liquid Lens through Charge Injection
Micromachines 2020, 11(1), 109; https://doi.org/10.3390/mi11010109 (registering DOI) - 20 Jan 2020
Viewed by 94
Abstract
Liquid lenses are the simplest and cheapest optical lenses, and various studies have been conducted to develop tunable-focus liquid lenses. In this study, a simple and easily implemented method for achieving tunable-focus liquid lenses was proposed and experimentally validated. In this method, charges [...] Read more.
Liquid lenses are the simplest and cheapest optical lenses, and various studies have been conducted to develop tunable-focus liquid lenses. In this study, a simple and easily implemented method for achieving tunable-focus liquid lenses was proposed and experimentally validated. In this method, charges induced by a corona discharge in the air were injected into dielectric liquid, resulting in “electropressure” at the interface between the air and the liquid. Through a 3D-printed U-tube structure, a tunable-focus liquid lens was fabricated and tested. Depending on the voltage, the focus of the liquid lens can be adjusted in large ranges (−∞ to −9 mm and 13.11 mm to ∞). The results will inspire various new liquid-lens applications. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume III)
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Open AccessArticle
Durability and Recoverability of Soft Lithographically Patterned Hydrogel Molds for the Formation of Phase Separation Membranes
Micromachines 2020, 11(1), 108; https://doi.org/10.3390/mi11010108 - 19 Jan 2020
Viewed by 98
Abstract
Hydrogel-facilitated phase separation (HFPS) has recently been applied to make microstructured porous membranes by modified phase separation processes. In HFPS, a soft lithographically patterned hydrogel mold is used as a water content source that initiates the phase separation process in membrane fabrication. However, [...] Read more.
Hydrogel-facilitated phase separation (HFPS) has recently been applied to make microstructured porous membranes by modified phase separation processes. In HFPS, a soft lithographically patterned hydrogel mold is used as a water content source that initiates the phase separation process in membrane fabrication. However, after each membrane casting, the hydrogel content changes due to the diffusion of organic solvent into the hydrogel from the original membrane solution. The absorption of solvent into the hydrogel mold limits the continuous use of the mold in repeated membrane casts. In this study, we investigated a simple treatment process for hydrogel mold recovery, consisting of warm and cold treatment steps to provide solvent extraction without changing the hydrogel mold integrity. The best recovery result was 96%, which was obtained by placing the hydrogel in a warm water bath (50 °C) for 10 min followed by immersing in a cold bath (23 °C) for 4 min and finally 4 min drying in air. This recovery was attributed to nearly complete solvent extraction without any deformation of the hydrogel structure. The reusability of hydrogel can assist in the development of a continuous membrane fabrication process using HFPS. Full article
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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Open AccessArticle
Real-Time Monitoring and Detection of Single-Cell Level Cytokine Secretion Using LSPR Technology
Micromachines 2020, 11(1), 107; https://doi.org/10.3390/mi11010107 - 19 Jan 2020
Viewed by 97
Abstract
Cytokine secretion researches have been a main focus of studies among the scientists in the recent decades for its outstanding contribution to clinical diagnostics. Localized surface plasmon resonance (LSPR) technology is one of the conventional methods utilized to analyze these issues, as it [...] Read more.
Cytokine secretion researches have been a main focus of studies among the scientists in the recent decades for its outstanding contribution to clinical diagnostics. Localized surface plasmon resonance (LSPR) technology is one of the conventional methods utilized to analyze these issues, as it could provide fast, label-free and real-time monitoring of biomolecule binding events. However, numerous LSPR-based biosensors in the past are usually utilized to monitor the average performance of cell groups rather than single cells. Meanwhile, the complicated sensor structures will lead to the fabrication and economic budget problems. Thus, in this paper, we report a simple synergistic integration of the cell trapping of microwell chip and gold-capped nanopillar-structured cyclo-olefin-polymer (COP) film for single cell level Interleukin 6 (IL-6) detection. Here, in-situ cytokine secreted from the trapped cell can be directly observed and analyzed through the peak red-shift in the transmittance spectrum. The fabricated device also shows the potential to conduct the real-time monitoring which would greatly help us identify the viability and biological variation of the tested single cell. Full article
(This article belongs to the Special Issue Micro/Nanofluidic Devices for Single Cell Analysis, Volume II)
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Open AccessArticle
Development of Real-Time Measurement Platform for Stretchable and Rollable Functions of Flexible Electronics under Multiple Dynamic Loads
Micromachines 2020, 11(1), 106; https://doi.org/10.3390/mi11010106 - 19 Jan 2020
Viewed by 95
Abstract
Mainstream next generation electronic devices with miniaturized structures and high levels of performance are needed to meet the characteristic requirements of electronics with flexible and stretchable capabilities. Accordingly, several applied fields of innovative electronic component techniques, such as wearable devices, foldable curtain-like displays, [...] Read more.
Mainstream next generation electronic devices with miniaturized structures and high levels of performance are needed to meet the characteristic requirements of electronics with flexible and stretchable capabilities. Accordingly, several applied fields of innovative electronic component techniques, such as wearable devices, foldable curtain-like displays, and flexible hybrid electronic (FHE) biosensors, are considered. This study presents a novel inspection system with multifunctions of stressing tensile and bending mechanical loads to acquire the stretchable and rollable characteristics of soft specimens. The performance of the proposed measurement platform using samples of three different geometric types is evaluated in terms of its stretchability. The results show a remarkable enhancement of mechanical reliability when the sine wave geometric structure is used. A symmetrical sine wave-shaped sample is designed to measure performance under cyclic rolling. The proposed measurement platform of flexible electronics meets the testing requirements of mechanical reliability for the development of future flexible electronic components and FHE products. Full article
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Open AccessArticle
Energy Band Gap Investigation of Biomaterials: A Comprehensive Material Approach for Biocompatibility of Medical Electronic Devices
Micromachines 2020, 11(1), 105; https://doi.org/10.3390/mi11010105 - 18 Jan 2020
Viewed by 150
Abstract
Over the past ten years, tissue engineering has witnessed significant technological and scientific advancements. Progress in both stem cell science and additive manufacturing have established new horizons in research and are poised to bring improvements in healthcare closer to reality. However, more sophisticated [...] Read more.
Over the past ten years, tissue engineering has witnessed significant technological and scientific advancements. Progress in both stem cell science and additive manufacturing have established new horizons in research and are poised to bring improvements in healthcare closer to reality. However, more sophisticated indications such as the scale-up fabrication of biological structures (e.g., human tissues and organs) still require standardization. To that end, biocompatible electronics may be helpful in the biofabrication process. Here, we report the results of our systematic exploration to seek biocompatible/degradable functional electronic materials that could be used for electronic device fabrications. We investigated the electronic properties of various biomaterials in terms of energy diagrams, and the energy band gaps of such materials were obtained using optical absorption spectroscopy. The main component of an electronic device is manufactured with semiconductor materials (i.e., Eg between 1 to 2.5 eV). Most biomaterials showed an optical absorption edge greater than 2.5 eV. For example, fibrinogen, glycerol, and gelatin showed values of 3.54, 3.02, and 3.0 eV, respectively. Meanwhile, a few materials used in the tissue engineering field were found to be semiconductors, such as the phenol red in cell culture media (1.96 eV energy band gap). The data from this research may be used to fabricate biocompatible/degradable electronic devices for medical applications. Full article
Open AccessArticle
Preparation and Characterization of Freely-Suspended Graphene Nanomechanical Membrane Devices with Quantum Dots for Point-of-Care Applications
Micromachines 2020, 11(1), 104; https://doi.org/10.3390/mi11010104 - 18 Jan 2020
Viewed by 129
Abstract
We demonstrate freely suspended graphene-based nanomechanical membranes (NMMs) as acoustic sensors in the audible frequency range. Simple and low-cost procedures are used to fabricate NMMs with various thicknesses based on graphene layers grown by graphite exfoliation and solution processed graphene oxide. In addition, [...] Read more.
We demonstrate freely suspended graphene-based nanomechanical membranes (NMMs) as acoustic sensors in the audible frequency range. Simple and low-cost procedures are used to fabricate NMMs with various thicknesses based on graphene layers grown by graphite exfoliation and solution processed graphene oxide. In addition, NMMs are grafted with quantum dots (QDs) for characterizing mass sensitive vibrational properties. Thickness, roughness, deformation, deflection and emissions of NMMs with attached QDs are experimented and analyzed by utilizing atomic force microscopy, Raman spectroscopy, laser induced deflection analyzer and spectrophotometers. Förster resonance energy transfer (FRET) is experimentally achieved between the QDs attached on NMMs and nearby glass surfaces for illustrating acousto-optic utilization in future experimental implementations combining vibrational properties of NMMs with optical emission properties of QDs. This property denoted as vibrating FRET (VFRET) is previously introduced in theoretical studies while important experimental steps are for the first time achieved in this study for future VFRET implementations. The proposed modeling and experimental methodology are promising for future novel applications such as NMM based biosensing, photonics and VFRET based point-of-care (PoC) devices. Full article
(This article belongs to the Special Issue Point-of-Care Devices)
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Open AccessArticle
Smart Tactile Sensing Systems Based on Embedded CNN Implementations
Micromachines 2020, 11(1), 103; https://doi.org/10.3390/mi11010103 - 18 Jan 2020
Viewed by 119
Abstract
Embedding machine learning methods into the data decoding units may enable the extraction of complex information making the tactile sensing systems intelligent. This paper presents and compares the implementations of a convolutional neural network model for tactile data decoding on various hardware platforms. [...] Read more.
Embedding machine learning methods into the data decoding units may enable the extraction of complex information making the tactile sensing systems intelligent. This paper presents and compares the implementations of a convolutional neural network model for tactile data decoding on various hardware platforms. Experimental results show comparable classification accuracy of 90.88% for Model 3, overcoming similar state-of-the-art solutions in terms of time inference. The proposed implementation achieves a time inference of 1.2 ms while consuming around 900 μ J. Such an embedded implementation of intelligent tactile data decoding algorithms enables tactile sensing systems in different application domains such as robotics and prosthetic devices. Full article
(This article belongs to the Special Issue Tactile Sensing Technology and Systems)
Open AccessArticle
Paper-Supported High-Throughput 3D Culturing, Trapping, and Monitoring of Caenorhabditis Elegans
Micromachines 2020, 11(1), 99; https://doi.org/10.3390/mi11010099 - 17 Jan 2020
Viewed by 112
Abstract
We developed an innovative paper-based platform for high-throughput culturing, trapping, and monitoring of C. elegans. A 96-well array was readily fabricated by placing a nutrient-replenished paper substrate on a micromachined 96-well plastic frame, providing high-throughput 3D culturing environments and in situ analysis [...] Read more.
We developed an innovative paper-based platform for high-throughput culturing, trapping, and monitoring of C. elegans. A 96-well array was readily fabricated by placing a nutrient-replenished paper substrate on a micromachined 96-well plastic frame, providing high-throughput 3D culturing environments and in situ analysis of the worms. The paper allows C. elegans to pass through the porous and aquatic paper matrix until the worms grow and reach the next developmental stages with the increased body size comparable to the paper pores. When the diameter of C. elegans becomes larger than the pore size of the paper substrate, the worms are trapped and immobilized for further high-throughput imaging and analysis. This work will offer a simple yet powerful technique for high-throughput sorting and monitoring of C. elegans at a different larval stage by controlling and choosing different pore sizes of paper. Furthermore, we developed another type of 3D culturing system by using paper-like transparent polycarbonate substrates for higher resolution imaging. The device used the multi-laminate structure of the polycarbonate layers as a scaffold to mimic the worm’s 3D natural habitats. Since the substrate is thin, mechanically strong, and largely porous, the layered structure allowed C. elegans to move and behave freely in 3D and promoted the efficient growth of both C. elegans and their primary food, E. coli. The transparency of the structure facilitated visualization of the worms under a microscope. Development, fertility, and dynamic behavior of C. elegans in the 3D culture platform outperformed those of the standard 2D cultivation technique. Full article
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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Open AccessArticle
A Robotic Biopsy Endoscope with Magnetic 5-DOF Locomotion and a Retractable Biopsy Punch
Micromachines 2020, 11(1), 98; https://doi.org/10.3390/mi11010098 - 17 Jan 2020
Viewed by 126
Abstract
Capsule endoscopes (CEs) have emerged as an advanced diagnostic technology for gastrointestinal diseases in recent decades. However, with regard to robotic motions, they require active movability and multi-functionalities for extensive, untethered, and precise clinical utilization. Herein, we present a novel wireless biopsy CE [...] Read more.
Capsule endoscopes (CEs) have emerged as an advanced diagnostic technology for gastrointestinal diseases in recent decades. However, with regard to robotic motions, they require active movability and multi-functionalities for extensive, untethered, and precise clinical utilization. Herein, we present a novel wireless biopsy CE employing active five degree-of-freedom locomotion and a biopsy needle punching mechanism for the histological analysis of the intestinal tract. A medical biopsy punch is attached to a screw mechanism, which can be magnetically actuated to extrude and retract the biopsy tool, for tissue extraction. The external magnetic field from an electromagnetic actuation (EMA) system is utilized to actuate the screw mechanism and harvest biopsy tissue; therefore, the proposed system consumes no onboard energy of the CE. This design enables observation of the biopsy process through the capsule’s camera. A prototype with a diameter of 12 mm and length of 30 mm was fabricated with a medical biopsy punch having a diameter of 1.5 mm. Its performance was verified through numerical analysis, as well as in-vitro and ex-vivo experiments on porcine intestine. The CE could be moved to target lesions and obtain sufficient tissue samples for histological examination. The proposed biopsy CE mechanism utilizing punch biopsy and its wireless extraction–retraction technique can advance untethered intestinal endoscopic capsule technology at clinical sites. Full article
(This article belongs to the Special Issue Microrobotics for Biological, Biomedical, and Surgical Applications)
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Open AccessArticle
Mechanical Behavior Investigation of 4H-SiC Single Crystal at the Micro–Nano Scale
Micromachines 2020, 11(1), 102; https://doi.org/10.3390/mi11010102 - 17 Jan 2020
Viewed by 129
Abstract
In this paper, theoretical models of the critical indentation depth and critical force on brittle materials using cleavage strength and contact theory are proposed. A Berkovich indenter is adopted for nanoindentation tests on a 4H-SiC single crystal sample to evaluate its mechanical behaviors. [...] Read more.
In this paper, theoretical models of the critical indentation depth and critical force on brittle materials using cleavage strength and contact theory are proposed. A Berkovich indenter is adopted for nanoindentation tests on a 4H-SiC single crystal sample to evaluate its mechanical behaviors. The stages of brittle material deformation (elastic, plastic, and brittle) can be characterized by the load versus indentation depth curves through the nanoindentation test. The curve of the elastic deformation stage follows the Hertz contact theory, and plastic deformation occurs at an indentation depth of up to 10 nm. The mechanism of 4H-SiC single crystal cracking is discussed, and the critical indentation depth and critical force for the plastic–brittle transition are obtained through the occurrence of the pop-in point. This shows that the theoretical results have good coherence with the test results. Both the values of the elastic modulus and hardness decrease as the crack length increases. In order to obtain more accurate mechanical property values in the nanoindentation test for brittle materials such as SiC, GaN, and sapphire, an appropriate load that avoids surface cracks should be adopted. Full article
Open AccessArticle
Vertical Leakage in GaN-on-Si Stacks Investigated by a Buffer Decomposition Experiment
Micromachines 2020, 11(1), 101; https://doi.org/10.3390/mi11010101 - 17 Jan 2020
Viewed by 103
Abstract
We investigated the origin of vertical leakage and breakdown in GaN-on-Si epitaxial structures. In order to understand the role of the nucleation layer, AlGaN buffer, and C-doped GaN, we designed a sequential growth experiment. Specifically, we analyzed three different structures grown on silicon [...] Read more.
We investigated the origin of vertical leakage and breakdown in GaN-on-Si epitaxial structures. In order to understand the role of the nucleation layer, AlGaN buffer, and C-doped GaN, we designed a sequential growth experiment. Specifically, we analyzed three different structures grown on silicon substrates: AlN/Si, AlGaN/AlN/Si, C:GaN/AlGaN/AlN/Si. The results demonstrate that: (i) the AlN layer grown on silicon has a breakdown field of 3.25 MV/cm, which further decreases with temperature. This value is much lower than that of highly-crystalline AlN, and the difference can be ascribed to the high density of vertical leakage paths like V-pits or threading dislocations. (ii) the AlN/Si structures show negative charge trapping, due to the injection of electrons from silicon to deep traps in AlN. (iii) adding AlGaN on top of AlN significantly reduces the defect density, thus resulting in a more uniform sample-to-sample leakage. (iv) a substantial increase in breakdown voltage is obtained only in the C:GaN/AlGaN/AlN/Si structure, that allows it to reach VBD > 800 V. (v) remarkably, during a vertical I–V sweep, the C:GaN/AlGaN/AlN/Si stack shows evidence for positive charge trapping. Holes from C:GaN are trapped at the GaN/AlGaN interface, thus bringing a positive charge storage in the buffer. For the first time, the results summarized in this paper clarify the contribution of each buffer layer to vertical leakage and breakdown. Full article
(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)
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Open AccessArticle
Dye-Doped ZnO Microcapsules for High Throughput and Sensitive Optofluidic Micro-Thermometry
Micromachines 2020, 11(1), 100; https://doi.org/10.3390/mi11010100 - 17 Jan 2020
Viewed by 124
Abstract
The main objective of this work is to show the proof of concept of a new optofluidic method for high throughput fluorescence-based thermometry, which enables the measure of temperature inside optofluidic microsystems at the millisecond (ms) time scale (high throughput). We used droplet [...] Read more.
The main objective of this work is to show the proof of concept of a new optofluidic method for high throughput fluorescence-based thermometry, which enables the measure of temperature inside optofluidic microsystems at the millisecond (ms) time scale (high throughput). We used droplet microfluidics to produce highly monodisperse microspheres from dispersed zinc oxide (ZnO) nanocrystals and doped them with rhodamine B (RhB) or/and rhodamine 6G (Rh6G). The fluorescence intensities of these two dyes are known to depend linearly on temperature but in two opposite manner. Their mixture enables for the construction of reference probe whose fluorescence does not depend practically on temperature. The use of zinc oxide microparticles as temperature probes in microfluidic channels has two main advantages: (i) avoid the diffusion and the adsorption of the dyes inside the walls of the microfluidic channels and (ii) enhance dissipation of the heat generated by the focused incident laser beam thanks to the high thermal conductivity of this material. Our results show that the fluorescence intensity of RhB decreases linearly with increasing temperature at a rate of about −2.2%/°C, in a very good agreement with the literature. In contrast, we observed for the first time a nonlinear change of the fluorescence intensity of Rh6G in ZnO microparticles with a minimum intensity at a temperature equal to 40 °C. This behaviour is reproducible and was observed only with ZnO microparticles doped with Rh6G. Full article
(This article belongs to the Special Issue Optofluidic Devices and Applications)
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Open AccessArticle
Physical-Based Simulation of the GaN-Based Grooved-Anode Planar Gunn Diode
Micromachines 2020, 11(1), 97; https://doi.org/10.3390/mi11010097 - 16 Jan 2020
Viewed by 114
Abstract
In this paper, a novel gallium nitride (GaN)-based heterostructure Gunn diode is proposed for the first time to enhance the output characteristics of Gunn oscillation waveforms. A well-designed grooved anode contact is adopted to separate the long-channel diode into two short-channel diodes in [...] Read more.
In this paper, a novel gallium nitride (GaN)-based heterostructure Gunn diode is proposed for the first time to enhance the output characteristics of Gunn oscillation waveforms. A well-designed grooved anode contact is adopted to separate the long-channel diode into two short-channel diodes in parallel. If the grooved anode contact is positioned in the middle of the device, the output power nearly doubles in the grooved-anode diode compared with the single-channel ones, as does the output frequency. Based on the numerical results, the best output characteristics are obtained at the 2.0-µm symmetrical grooved-anode diode, which produces nearly 5.48 mW of power at the fundamental frequency of 172.81 GHz, with 3.13% efficiency of power conversion. If the grooved anode contact is not positioned in the middle of the diode, the harmonic frequency would be enhanced. The GaN heterostructure grooved-anode Gunn diode has been demonstrated to be an excellent solid-state source of terahertz oscillator. Full article
(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)
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Open AccessArticle
Diagnosis and Improvement of Combustion Characteristics of Methanol Miniature Reciprocating Piston Internal Combustion Engine
Micromachines 2020, 11(1), 96; https://doi.org/10.3390/mi11010096 - 16 Jan 2020
Viewed by 114
Abstract
A micro-reciprocating piston internal combustion engine with liquid hydrocarbon fuel has the potential to supply ultrahigh density energy to micro electro mechanical system because of its high-density energy, simple structure, and mature energy conversion principle. However, the diagnostic test of the combustion characteristics [...] Read more.
A micro-reciprocating piston internal combustion engine with liquid hydrocarbon fuel has the potential to supply ultrahigh density energy to micro electro mechanical system because of its high-density energy, simple structure, and mature energy conversion principle. However, the diagnostic test of the combustion characteristics of the micro reciprocating piston internal combustion engine shows that its combustion characteristics are poor, and the combustion rate was lower with the combustion duration of more than 50 °CA. The mean indicated pressure (Pmi) value was only 0.137 MPa, the combustion stability was very poor, and the cycle variation rate of the Pmi was up to 60%. To improve its combustion performance, the method to enhance combustion in micro-space is explored then. Mechanism studies have shown that the pyrolysis reaction of nitromethane and hydrogen peroxide can produce amounts of free radicals OH, with the possibility of improving the combustion of methanol. Therefore, a method for adjusting the composition of methanol fuel to enhance combustion is proposed, and the method is theoretically confirmed. Finally, based on this method, the test was carried out. The results showed that the combustion rate increased and the combustion duration decreased by 6% after adding nitromethane. The power performance was enhanced, and the Pmi value was increased by 30%. The combustion stability was enhanced, and the cycle variation rate of the Pmi was reduced to 16.9%. Nitromethane has a significant effect on improving the combustion characteristics of methanol, and the enhancement of the latter was mainly reflected in the ignition phase of the combustion process. This study indicates that exploring the fuel additive that can increase the concentration of OH radical in the reaction is an effective method to improve the micro-space combustion, which will facilitate the development of micro-piston internal combustion engine to supply energy to a micro electro mechanical system. Full article
(This article belongs to the Section A:Physics)
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Open AccessArticle
A Programmable Nanofabrication Method for Complex 3D Meta-Atom Array Based on Focused-Ion-Beam Stress-Induced Deformation Effect
Micromachines 2020, 11(1), 95; https://doi.org/10.3390/mi11010095 - 16 Jan 2020
Viewed by 120
Abstract
Due to their unique electromagnetic properties, meta-atom arrays have always been a hotspot to realize all kinds of particular functions, and the research on meta-atom structure has extended from two-dimensions (2D) to three-dimensions (3D) in recent years. With the continuous pursuit of complex [...] Read more.
Due to their unique electromagnetic properties, meta-atom arrays have always been a hotspot to realize all kinds of particular functions, and the research on meta-atom structure has extended from two-dimensions (2D) to three-dimensions (3D) in recent years. With the continuous pursuit of complex 3D meta-atom arrays, the increasing demand for more efficient and more precise nanofabrication methods has encountered challenges. To explore better fabrication methods, we presented a programmable nanofabrication method for a complex 3D meta-atom array based on focused-ion-beam stress-induced deformation (FIB-SID) effect and designed a distinctive nanostructure array composed of periodic 3D meta-atoms to demonstrate the presented method. After successful fabrication of the designed 3D meta-atom arrays, measurements were conducted to investigate the electric/magnetic field properties and infrared spectral characteristics using scanning cathodoluminescence (CL) microscopic imaging and Fourier transform infrared (FTIR) spectroscopy, which revealed a certain excitation mode induced by polarized incident IR light near 8 μm. Besides the programmability for complex 3D meta-atoms and wide applicability of materials, a more significant advantage of the method is that a large-scale array composed of complex 3D meta-atoms can be processed in a quasi-parallel way, which improves the processing efficiency and the consistency of unit cells dramatically. Full article
(This article belongs to the Section A:Physics)
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Open AccessArticle
Improving Single-Cell Encapsulation Efficiency and Reliability through Neutral Buoyancy of Suspension
Micromachines 2020, 11(1), 94; https://doi.org/10.3390/mi11010094 - 15 Jan 2020
Viewed by 139
Abstract
Single-cell analysis is of critical importance in revealing cell-to-cell heterogeneity by characterizing individual cells and identifying minority sub-populations of interest. Droplet-based microfluidics has been widely used in the past decade to achieve high-throughput single-cell analysis. However, to maximize the proportion of single-cell emulsification [...] Read more.
Single-cell analysis is of critical importance in revealing cell-to-cell heterogeneity by characterizing individual cells and identifying minority sub-populations of interest. Droplet-based microfluidics has been widely used in the past decade to achieve high-throughput single-cell analysis. However, to maximize the proportion of single-cell emulsification is challenging due to cell sedimentation and aggregation. The purpose of this study was to investigate the influence of single-cell encapsulation and incubation through the use of neutral buoyancy. As a proof of concept, OptiPrep™ was used to create neutrally buoyant cell suspensions of THP-1, a human monocytic leukemia cell line, for single-cell encapsulation and incubation. We found that using a neutrally buoyant suspension greatly increased the efficiency of single-cell encapsulation in microdroplets and eliminated unnecessary cell loss. Moreover, the presence of OptiPrep™ was shown to not affect cellular viability. This method significantly improved the effectiveness of single-cell study in a non-toxic environment and is expected to broadly facilitate single-cell analysis. Full article
(This article belongs to the Special Issue Microfluidic for High-Throughput Screening)
Open AccessArticle
Angle-Sensitive Photonic Crystals for Simultaneous Detection and Photocatalytic Degradation of Hazardous Diazo Compounds
Micromachines 2020, 11(1), 93; https://doi.org/10.3390/mi11010093 - 15 Jan 2020
Viewed by 143
Abstract
Congo Red (CR) and Amido Black 10B (AB-10B) are anionic diazo dyes, which are metabolized to produce a bioaccumulative and persistent carcinogen, benzidine. In this regard, an angle sensitive sensor composed of photonic crystal supported photocatalyst was fabricated for the simultaneous detection and [...] Read more.
Congo Red (CR) and Amido Black 10B (AB-10B) are anionic diazo dyes, which are metabolized to produce a bioaccumulative and persistent carcinogen, benzidine. In this regard, an angle sensitive sensor composed of photonic crystal supported photocatalyst was fabricated for the simultaneous detection and photocatalytic degradation of diazo dyes from aqueous solutions. Reflectance spectroscopy was used in the detection of CR and AB-10B, which was based on the emergence of the incident angle dependent reflection peaks from the TiO2 coated two-dimensional photonic crystal (2D-PhC) surfaces and their subsequent quenching due to the presence of dye molecules whose absorbance peak intensity overlapped the reflection peak intensity of TiO2 at the respective angle. Interestingly, ultraviolet (UV) mediated photocatalytic degradation of CR and AB-10B was achieved using the same TiO2 coated 2D-PhC surfaces. 2D-PhC underneath the TiO2 layer was able to confine and localize the light on the TiO2 coated 2D-PhC surface, which enhanced the light absorption by dye molecules on the TiO2 surface and the photocatalytic efficiency in the degradation of CR and AB-10B. Finally, this proof-of-concept study demonstrated the fabrication of copolymer film based photonic crystal supported photocatalytic device, which can be used for developing miniaturized sensors competent in on-field detection and degradation of pollutants. Full article
(This article belongs to the Section C:Chemistry)
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Open AccessArticle
Low-Concentration Ammonia Gas Sensors Manufactured Using the CMOS–MEMS Technique
Micromachines 2020, 11(1), 92; https://doi.org/10.3390/mi11010092 - 15 Jan 2020
Viewed by 159
Abstract
This study describes the fabrication of an ammonia gas sensor (AGS) using a complementary metal oxide semiconductor (CMOS)–microelectromechanical system (MEMS) technique. The structure of the AGS features interdigitated electrodes (IDEs) and a sensing material on a silicon substrate. The IDEs are the stacked [...] Read more.
This study describes the fabrication of an ammonia gas sensor (AGS) using a complementary metal oxide semiconductor (CMOS)–microelectromechanical system (MEMS) technique. The structure of the AGS features interdigitated electrodes (IDEs) and a sensing material on a silicon substrate. The IDEs are the stacked aluminum layers that are made using the CMOS process. The sensing material; polypyrrole/reduced graphene oxide (PPy/RGO), is synthesized using the oxidation–reduction method; and the material is characterized using an electron spectroscope for chemical analysis (ESCA), a scanning electron microscope (SEM), and high-resolution X-ray diffraction (XRD). After the CMOS process; the AGS needs post-processing to etch an oxide layer and to deposit the sensing material. The resistance of the AGS changes when it is exposed to ammonia. A non-inverting amplifier circuit converts the resistance of the AGS into a voltage signal. The AGS operates at room temperature. Experiments show that the AGS response is 4.5% at a concentration of 1 ppm NH3; and it exhibits good repeatability. The lowest concentration that the AGS can detect is 0.1 ppm NH3 Full article
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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Open AccessArticle
System-Level Model and Simulation of a Frequency-Tunable Vibration Energy Harvester
Micromachines 2020, 11(1), 91; https://doi.org/10.3390/mi11010091 - 14 Jan 2020
Viewed by 176
Abstract
In this paper, we present a macroscale multiresonant vibration-based energy harvester. The device features frequency tunability through magnetostatic actuation on the resonator. The magnetic tuning scheme uses external magnets on linear stages. The system-level model demonstrates autonomous adaptation of resonance frequency to the [...] Read more.
In this paper, we present a macroscale multiresonant vibration-based energy harvester. The device features frequency tunability through magnetostatic actuation on the resonator. The magnetic tuning scheme uses external magnets on linear stages. The system-level model demonstrates autonomous adaptation of resonance frequency to the dominant ambient frequencies. The harvester is designed such that its two fundamental modes appear in the range of (50,100) Hz which is a typical frequency range for vibrations found in industrial applications. The dual- frequency characteristics of the proposed design together with the frequency agility result in an increased operative harvesting frequency range. In order to allow a time-efficient simulation of the model, a reduced order model has been derived from a finite element model. A tuning control algorithm based on maximum-voltage tracking has been implemented in the model. The device was characterized experimentally to deliver a power output of 500 µW at an excitation level of 0.5 g at the respected frequencies of 63.3 and 76.4 Hz. In a design optimization effort, an improved geometry has been derived. It yields more close resonance frequencies and optimized performance. Full article
(This article belongs to the Special Issue Piezoelectric Transducers: Materials, Devices and Applications)
Open AccessCommunication
Auxiliary Optomechanical Tools for 3D Cell Manipulation
Micromachines 2020, 11(1), 90; https://doi.org/10.3390/mi11010090 - 13 Jan 2020
Viewed by 152
Abstract
Advances in laser and optoelectronic technologies have brought the general concept of optomechanical manipulation to the level of standard biophysical tools, paving the way towards controlled experiments and measurements of tiny mechanical forces. Recent developments in direct laser writing (DLW) have enabled the [...] Read more.
Advances in laser and optoelectronic technologies have brought the general concept of optomechanical manipulation to the level of standard biophysical tools, paving the way towards controlled experiments and measurements of tiny mechanical forces. Recent developments in direct laser writing (DLW) have enabled the realization of new types of micron-scale optomechanical tools, capable of performing designated functions. Here we further develop the concept of DLW-fabricated optomechanically-driven tools and demonstrate full-3D manipulation capabilities over biological objects. In particular, we resolved the long-standing problem of out-of-plane rotation in a pure liquid, which was demonstrated on a living cell, clamped between a pair of forks, designed for efficient manipulation with holographic optical tweezers. The demonstrated concept paves the way for the realization of flexible tools for performing on-demand functions over biological objects, such as cell tomography and surgery to name just few. Full article
(This article belongs to the Special Issue Optical Trapping and Manipulation: From Fundamentals to Applications)
Open AccessArticle
A Novel Characterization and Performance Measurement of Memristor Devices for Synaptic Emulators in Advanced Neuro-Computing
Micromachines 2020, 11(1), 89; https://doi.org/10.3390/mi11010089 - 13 Jan 2020
Viewed by 171
Abstract
The advanced neuro-computing field requires new memristor devices with great potential as synaptic emulators between pre- and postsynaptic neurons. This paper presents memristor devices with TiO2 Nanoparticles (NPs)/Ag(Silver) and Titanium Dioxide (TiO2) Nanoparticles (NPs)/Au(Gold) electrodes for synaptic emulators in an [...] Read more.
The advanced neuro-computing field requires new memristor devices with great potential as synaptic emulators between pre- and postsynaptic neurons. This paper presents memristor devices with TiO2 Nanoparticles (NPs)/Ag(Silver) and Titanium Dioxide (TiO2) Nanoparticles (NPs)/Au(Gold) electrodes for synaptic emulators in an advanced neurocomputing application. A comparative study between Ag(Silver)- and Au(Gold)-based memristor devices is presented where the Ag electrode provides the improved performance, as compared to the Au electrode. Device characterization is observed by the Scanning Electron Microscope (SEM) image, which displays the grown electrode, while the morphology of nanoparticles (NPs) is verified by Atomic Force Microscopy (AFM). The resistive switching (RS) phenomena observed in Ag/TiO2 and Au/TiO2 shows the sweeping mechanism for low resistance and high resistance states. The resistive switching time of Au/TiO2 NPs and Ag/TiO2 NPs is calculated, while the theoretical validation of the memory window demonstrates memristor behavior as a synaptic emulator. Measurement of the capacitor–voltage curve shows that the memristor with Ag contact is a good candidate for charge storage as compared to Au. The classification of 3 × 3 pixel black/white image is demonstrated by the 3 × 3 cross bar memristor with pre- and post-neuron system. The proposed memristor devices with the Ag electrode demonstrate the adequate performance compared to the Au electrode, and may present noteworthy advantages in the field of neuromorphic computing. Full article
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Open AccessArticle
Role of a 193 nm ArF Excimer Laser in Laser-Assisted Plasma-Enhanced Chemical Vapor Deposition of SiNx for Low Temperature Thin Film Encapsulation
Micromachines 2020, 11(1), 88; https://doi.org/10.3390/mi11010088 - 13 Jan 2020
Viewed by 157
Abstract
In this study, silicon nitride thin films are deposited on organic polyethylene-naphthalate (PEN) substrates by laser assisted plasma enhanced chemical vapor deposition (LAPECVD) at a low temperature (150 °C) for the purpose of evaluating the encapsulation performance. A plasma generator is placed above [...] Read more.
In this study, silicon nitride thin films are deposited on organic polyethylene-naphthalate (PEN) substrates by laser assisted plasma enhanced chemical vapor deposition (LAPECVD) at a low temperature (150 °C) for the purpose of evaluating the encapsulation performance. A plasma generator is placed above the sample stage as conventional plasma enhanced chemical vapor deposition (PECVD) configuration, and the excimer laser beam of 193 nm wavelength illuminated in parallel to the sample surface is coupled to the reaction zone between the sample and plasma source. Major roles of the laser illumination in LAPECVD process are to compete with or complement the plasma decomposition of reactant gases. While a laser mainly decomposes ammonia molecules in the plasma, it also contributes to the photolysis of silane in the plasma state, possibly through the resulting hydrogen radicals and the excitation of intermediate disilane products. It will also be shown that the LAPECVD with coupled laser illumination of 193 nm wavelength improves the deposition rate of silicon nitride thin film, and the encapsulation performance evaluated via the measurement of water vapor transmission rate (WVTR). Full article
(This article belongs to the Special Issue Selected Papers from the ICAE 2019)
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Open AccessArticle
Methacrylate Coatings for Titanium Surfaces to Optimize Biocompatibility
Micromachines 2020, 11(1), 87; https://doi.org/10.3390/mi11010087 - 13 Jan 2020
Viewed by 260
Abstract
Currently, there are more than 1.5 million knee and hip replacement procedures carried out in the United States. Implants have a 10–15-year lifespan with up to 30% of revision surgeries showing complications with osteomyelitis. Titanium and titanium alloys are the favored implant materials [...] Read more.
Currently, there are more than 1.5 million knee and hip replacement procedures carried out in the United States. Implants have a 10–15-year lifespan with up to 30% of revision surgeries showing complications with osteomyelitis. Titanium and titanium alloys are the favored implant materials because they are lightweight and have high mechanical strength. However, this increased strength can be associated with decreased bone density around the implant, leading to implant loosening and failure. To avoid this, current strategies include plasma-spraying titanium surfaces and foaming titanium. Both techniques give the titanium a rough and irregular finish that improves biocompatibility. Recently, researchers have also sought to surface-conjugate proteins to titanium to induce osteointegration. Cell adhesion-promoting proteins can be conjugated to methacrylate groups and crosslinked using a variety of methods. Methacrylated proteins can be conjugated to titanium surfaces through atom transfer radical polymerization (ATRP). However, surface conjugation of proteins increases biocompatibility non-specifically to bone cells, adding to the risk of biofouling which may result in osteomyelitis that causes implant failure. In this work, we analyze the factors contributing to biofouling when coating titanium to improve biocompatibility, and design an experimental scheme to evaluate optimal coating parameters. Full article
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Open AccessArticle
Experimental Study on Machinability of Zr-Based Bulk Metallic Glass during Micro Milling
Micromachines 2020, 11(1), 86; https://doi.org/10.3390/mi11010086 - 13 Jan 2020
Viewed by 168
Abstract
The micro machinability of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (BMG) was investigated by micro milling with coated cemented carbide tools. The corresponding micro milling tests on Al6061 were conducted for comparison. The results showed that [...] Read more.
The micro machinability of Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (BMG) was investigated by micro milling with coated cemented carbide tools. The corresponding micro milling tests on Al6061 were conducted for comparison. The results showed that the tool was still in stable wear stage after milling 300 mm, and the surface roughness Ra could be maintained around 0.06 μm. The tool experienced only slight chipping and rubbing wear after milling the BMG, while a built-up edge and the coating peeling off occurred severely when milling Al6061. The influence of rotation speed on surface roughness was insignificant, while surface roughness decreased with the reduction of feed rate, and then increased dramatically when the feed rate was below 2 μm/tooth. The surface roughness increased gradually with the axial depth of cut (DOC). Milling force decreased slightly with the increase in rotation speed, while it increased with the increase in axial DOC, and the size effect on milling force occurred when the feed rate decreased below 1 μm/tooth. The results of X-ray diffraction (XRD) showed that all milled surfaces were still dominated by an amorphous structure. This study could pave a solid foundation for structural and functional applications. Full article
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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Open AccessArticle
Controlling Shapes in a Coaxial Flow Focusing Microfluidic Device: Experiments and Theory
Micromachines 2020, 11(1), 85; https://doi.org/10.3390/mi11010085 - 13 Jan 2020
Viewed by 175
Abstract
A coaxial flow focusing PDMS (polydimethylsiloxane) microfluidic device has been designed and manufactured by soft lithography in order to experimentally study a miscible inner flow. We studied a coaxially focused inner flow (formed by an aqueous fluorescein solution) which was fully isolated from [...] Read more.
A coaxial flow focusing PDMS (polydimethylsiloxane) microfluidic device has been designed and manufactured by soft lithography in order to experimentally study a miscible inner flow. We studied a coaxially focused inner flow (formed by an aqueous fluorescein solution) which was fully isolated from all microchannel surfaces by an additional water outer flow. Different flow rates were used to produce a variety of flow ratios and a 3D reconstruction of the cross-section was performed using confocal microscope images. The results showed an elliptical section of the coaxially focused inner flow that changes in shape depending on the flow rate ratio applied. We have also developed a mathematical model that allows us to predict and control the geometry of the coaxially focused inner flow. Full article
(This article belongs to the Section A:Physics)
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Open AccessArticle
Single-Neuron Adaptive Hysteresis Compensation of Piezoelectric Actuator Based on Hebb Learning Rules
Micromachines 2020, 11(1), 84; https://doi.org/10.3390/mi11010084 - 12 Jan 2020
Viewed by 210
Abstract
This paper presents an adaptive hysteresis compensation approach for a piezoelectric actuator (PEA) using single-neuron adaptive control. For a given desired trajectory, the control input to the PEA is dynamically adjusted by the error between the actual and desired trajectories using Hebb learning [...] Read more.
This paper presents an adaptive hysteresis compensation approach for a piezoelectric actuator (PEA) using single-neuron adaptive control. For a given desired trajectory, the control input to the PEA is dynamically adjusted by the error between the actual and desired trajectories using Hebb learning rules. A single neuron with self-learning and self-adaptive capabilities is a non-linear processing unit, which is ideal for time-variant systems. Based on the single-neuron control, the compensation of the PEA’s hysteresis can be regarded as a process of transmitting biological neuron information. Through the error information between the actual and desired trajectories, the control input is adjusted via the weight adjustment method of neuron learning. In addition, this paper also integrates the combination of Hebb learning rules and supervised learning as teacher signals, which can quickly respond to control signals. The weights of the single-neuron controller can be constantly adjusted online to improve the control performance of the system. Experimental results show that the proposed single-neuron adaptive hysteresis compensation method can track continuous and discontinuous trajectories well. The single-neuron adaptive controller has better adaptive and self-learning performance against the rate-dependence of the PEA’s hysteresis. Full article
(This article belongs to the Special Issue Piezoelectric Transducers: Materials, Devices and Applications)
Open AccessReview
Microfluidics Mediated Production of Foams for Biomedical Applications
Micromachines 2020, 11(1), 83; https://doi.org/10.3390/mi11010083 - 12 Jan 2020
Viewed by 208
Abstract
Within the last decade, there has been increasing interest in liquid and solid foams for several industrial uses. In the biomedical field, liquid foams can be used as delivery systems for dermatological treatments, for example, whereas solid foams are frequently used as scaffolds [...] Read more.
Within the last decade, there has been increasing interest in liquid and solid foams for several industrial uses. In the biomedical field, liquid foams can be used as delivery systems for dermatological treatments, for example, whereas solid foams are frequently used as scaffolds for tissue engineering and drug screening. Most of the foam functionalities are largely correlated to their mechanical properties and their structure, especially bubble/pore size, shape, and interconnectivity. However, the majority of conventional foaming fabrication techniques lack pore size control which can induce important inhomogeneities in the foams and subsequently decrease their performance. In this perspective, new advanced technologies have been introduced, such as microfluidics, which offers a highly controlled production, allowing for design customization of both liquid foams and solid foams obtained through liquid-templating. This short review explores both the fabrication and the characterization of foams, with a focus on solid polymer foams, and sheds the light on how microfluidics can overcome some existing limitations, playing a crucial role in their production for biomedical applications, especially as scaffolds in tissue engineering. Full article
(This article belongs to the Special Issue Micro/Nano-system for Drug Delivery)
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Open AccessArticle
An Empirical Model for GaN Light Emitters with Dot-in-Wire Polar Nanostructures
Micromachines 2020, 11(1), 82; https://doi.org/10.3390/mi11010082 (registering DOI) - 11 Jan 2020
Viewed by 191
Abstract
A set of empirical equations were developed to describe the optical properties of III-nitride dot-in-wire nanostructures. These equations depend only on the geometric properties of the structures, enabling the design process of a III-nitride light emitter comprised of dot-in-wire polar nanostructures, to be [...] Read more.
A set of empirical equations were developed to describe the optical properties of III-nitride dot-in-wire nanostructures. These equations depend only on the geometric properties of the structures, enabling the design process of a III-nitride light emitter comprised of dot-in-wire polar nanostructures, to be greatly simplified without first-principle calculations. Results from the empirical model were compared to experimental measurements and reasonably good agreements were observed. Strain relaxation was found to be the dominant effect in determining the optical properties of dot-in-wire nanostructures. Full article
(This article belongs to the Section A:Physics)
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