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Micromachines, Volume 9, Issue 5 (May 2018)

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Editorial

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Open AccessEditorial Editorial for the Special Issue on Piezoelectric MEMS
Micromachines 2018, 9(5), 237; https://doi.org/10.3390/mi9050237
Received: 10 May 2018 / Revised: 10 May 2018 / Accepted: 10 May 2018 / Published: 15 May 2018
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Abstract
Electromechanical transducers that utilize the piezoelectric effect have been increasingly used in micro-electromechanical systems (MEMS) either as substrates or as thin films[...] Full article
(This article belongs to the Special Issue Piezoelectric MEMS)

Research

Jump to: Editorial, Review, Other

Open AccessArticle Analysis and Design of a Polygonal Oblique Beam for the Butterfly Vibratory Gyroscope with Improved Robustness to Fabrication Imperfections
Micromachines 2018, 9(5), 198; https://doi.org/10.3390/mi9050198
Received: 3 March 2018 / Revised: 26 March 2018 / Accepted: 4 April 2018 / Published: 24 April 2018
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Abstract
This paper focuses on structural optimization of a Butterfly vibratory gyroscope (BFVG). An oblique suspension beam adopting polygonal cross-section is proposed in order to enhance the sensitivity and robustness. The operation principles of the BFVG are introduced. The suspension beam, which was found
[...] Read more.
This paper focuses on structural optimization of a Butterfly vibratory gyroscope (BFVG). An oblique suspension beam adopting polygonal cross-section is proposed in order to enhance the sensitivity and robustness. The operation principles of the BFVG are introduced. The suspension beam, which was found to be the key component, is selectively stressed. Varying cross sections of the suspension beam, including parallelogram, pentagon, hexagon, platform of pentagon, L-shaped and convex shapes are compared with each other. In particular, in order to show the advantages of the proposed polygonal cross-section, the convex cross-section is used as a reference. The influence of fabrication imperfections, which includes alignment error, silicon thickness error, etching depth error, upper width error, bottom width error and deep reactive-ion etching (DRIE) verticality error, on the oblique beam’s spindle azimuth angle of the two cross-sections is analyzed. Further, the quadrature error of two cross-sections with a fabrication defect is analyzed. The theoretical arithmetic results suggest that a polygonal cross-section beam is much more stable than a convex cross-section beam in most cases. The robustness of the fabrication imperfection is improved nine-fold and the quadrature error due to fabrication defect is reduced by 70 percent with a polygonal cross-section. It could be a better candidate for BFVG’s oblique beam, which would provide a gyroscope with good robustness and repeatability. Full article
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Open AccessArticle Mixing Performance of a 3D Micro T-Mixer with Swirl-Inducing Inlets and Rectangular Constriction
Micromachines 2018, 9(5), 199; https://doi.org/10.3390/mi9050199
Received: 16 March 2018 / Revised: 18 April 2018 / Accepted: 19 April 2018 / Published: 24 April 2018
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Abstract
In this paper, three novel 3D micro T-mixers, namely, a micro T-mixer with swirl-inducing inlets (TMSI), a micro T-mixer with a rectangular constriction (TMRC), and a micro T-mixer with swirl-inducing inlets and a rectangular constriction (TMSC), were proposed on the basis of the
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In this paper, three novel 3D micro T-mixers, namely, a micro T-mixer with swirl-inducing inlets (TMSI), a micro T-mixer with a rectangular constriction (TMRC), and a micro T-mixer with swirl-inducing inlets and a rectangular constriction (TMSC), were proposed on the basis of the original 3D micro T-mixer (OTM). The flow and mixing performance of these micromixers was numerically analyzed using COMSOL Multiphysics package at a range of Reynolds numbers from 10 to 70. Results show that the three proposed 3D micro T-mixers have achieved better mixing performance than OTM. Due to the coupling effect of two swirl-inducing inlets and a rectangular constriction, the maximum mixing index and pressure drop appeared in TMSC among the four micromixers especially; the mixing index of TMSC reaches 91.8% at Re = 70, indicating that TMSC can achieve effective mixing in a short channel length, but has a slightly higher pressure drop than TMSI and TMRC. Full article
(This article belongs to the Section Micro/Nanofluidics and Lab on a Chip)
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Open AccessArticle Flexible Tactile Sensor Array Based on Aligned MWNTs-PU Composited Sub-Microfibers
Micromachines 2018, 9(5), 201; https://doi.org/10.3390/mi9050201
Received: 27 February 2018 / Revised: 18 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
This present paper describes a novel method to fabricate tactile sensor arrays by producing aligned multi-walled carbon nanotubes (MWNTs)-polyurethane (PU) composite sub-microfiber (SMF) arrays with the electrospinning technique. The proposed sensor was designed to be used as the artificial skin for a tactile
[...] Read more.
This present paper describes a novel method to fabricate tactile sensor arrays by producing aligned multi-walled carbon nanotubes (MWNTs)-polyurethane (PU) composite sub-microfiber (SMF) arrays with the electrospinning technique. The proposed sensor was designed to be used as the artificial skin for a tactile sensation system. Although thin fibers in micro- and nanoscale have many good mechanical characteristics and could enhance the alignment of MWNTs inside, the high impedance as a consequence of a small section handicaps its application. In this paper, unidirectional composite SMFs were fabricated orthogonally to the parallel electrodes through a low-cost method to serve as sensitive elements (SEs), and the impedances of SEs were measured to investigate the changes with deformation caused by applied force. The particular piezoresistive mechanism of MWNTs disturbed in SMF was analyzed. The static and dynamic test results of the fabricated tactile sensor were also presented to validate the performance of the proposed design. Full article
(This article belongs to the Special Issue Polymer Based MEMS and Microfabrication)
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Open AccessArticle Fabrication of a Metal Micro Mold by Using Pulse Micro Electroforming
Micromachines 2018, 9(5), 203; https://doi.org/10.3390/mi9050203
Received: 13 February 2018 / Revised: 22 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
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Abstract
Microfluidic devices have been widely used for biomedical and biochemical applications. Due to its unique characteristics, polymethyl methacrylate (PMMA) show great potential in fabricating microfluidic devices. Hot embossing technology has established itself as a popular method of preparing polymer microfluidic devices in both
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Microfluidic devices have been widely used for biomedical and biochemical applications. Due to its unique characteristics, polymethyl methacrylate (PMMA) show great potential in fabricating microfluidic devices. Hot embossing technology has established itself as a popular method of preparing polymer microfluidic devices in both academia and industry. However, the fabrication of the mold used in hot embossing is time-consuming in general and often impractical for economically efficient prototyping. This paper proposes a modified technology for preparing metal micro molds by using pulse micro electroforming directly on metallic substrate, which could save time and reduce costs. In this method, an additive was used to avoid surface defect on deposited nickel. A chemical etching process was performed on the metallic substrate before the electroforming process in order to improve the bonding strength between the deposited structure and substrate. Finally, with the aim of obtaining a metal micro mold with high surface quality (low surface roughness), an orthogonal experiment was designed and conducted to optimize the electroforming parameters. Additionally, metal micro molds with different structures were well prepared by using the optimized parameters. Full article
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Open AccessArticle Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers
Micromachines 2018, 9(5), 204; https://doi.org/10.3390/mi9050204
Received: 30 March 2018 / Revised: 18 April 2018 / Accepted: 25 April 2018 / Published: 27 April 2018
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Abstract
Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the
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Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1–80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle Preparation and Characteristics of MAPbBr3 Perovskite Quantum Dots on NiOx Film and Application for High Transparent Solar Cells
Micromachines 2018, 9(5), 205; https://doi.org/10.3390/mi9050205
Received: 12 April 2018 / Revised: 24 April 2018 / Accepted: 26 April 2018 / Published: 27 April 2018
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Abstract
In this work, a MAPbBr3 quantum dot (QD-MAPbBr3) layer was prepared by a simple and rapid method. Octylammonium bromide (OABr) gives the MAPbBr3 better exciton binding energy, good surface morphology, and stability. To form a nanocrystalline thin film on
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In this work, a MAPbBr3 quantum dot (QD-MAPbBr3) layer was prepared by a simple and rapid method. Octylammonium bromide (OABr) gives the MAPbBr3 better exciton binding energy, good surface morphology, and stability. To form a nanocrystalline thin film on indium tin oxide (ITO) glass, the QD-MAPbBr3 film was coated by a spin-coating method in a nitrogen-filled glove box and the NiOx film was used as an adhesive layer and hole transport layer. The highest transmittance of MAPbBr3 on NiOx/ITO glass was around 75% at 700 nm. This study also reported a high transparent and perovskite bulk-free ITO/NiOx/QD-MAPbBr3/C60/Ag solar cell where the NiOx, QD-MAPbBr3, and C60 were used as a hole transport layer, active layer, and electron transport layer, respectively. Full article
(This article belongs to the Special Issue Perovskite Nanomaterials: Fabrication, Devices and Applications)
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Open AccessArticle Study of the Carrier-Aided Thin Film Electrode Array Design for Cochlear Insertion
Micromachines 2018, 9(5), 206; https://doi.org/10.3390/mi9050206
Received: 28 February 2018 / Revised: 9 April 2018 / Accepted: 20 April 2018 / Published: 27 April 2018
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Abstract
The micro-fabricated thin film electrode array (TFEA) has been a promising design for cochlear implants (CIs) because of its cost-effectiveness and fabrication precision. The latest polymer-based cochlear TFEAs have faced difficulties for cochlear insertion due to the lack of structural stiffness. To stiffen
[...] Read more.
The micro-fabricated thin film electrode array (TFEA) has been a promising design for cochlear implants (CIs) because of its cost-effectiveness and fabrication precision. The latest polymer-based cochlear TFEAs have faced difficulties for cochlear insertion due to the lack of structural stiffness. To stiffen the TFEA, dissolvable stiffening materials, TFEAs with different structures, and TFEAs with commercial CIs as carriers have been invested. In this work, the concept of enhancing a Parylene TFEA with Kapton tape as a simpler carrier for cochlear insertion has been proved to be feasible. The bending stiffness of the Kapton-aided TFEA was characterized with an analytical model, a finite element model, and a cantilever bending experiment, respectively. While the Kapton tape increased the bending stiffness of the Parylene TFEA by 103 times, the 6-μm-thick TFEA with a similar Young’s modulus, as a polyimide, in turn significantly increased the bending stiffness of the 170-μm-thick Kapton carrier by 60%. This result indicated that even the TFEA is ultra-flexible and that its bending stiffness should not be neglected in the design or selection of its carrier. Full article
(This article belongs to the Special Issue Polymer Based MEMS and Microfabrication)
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Open AccessArticle High Temperature AlGaN/GaN Membrane Based Pressure Sensors
Micromachines 2018, 9(5), 207; https://doi.org/10.3390/mi9050207
Received: 9 April 2018 / Revised: 23 April 2018 / Accepted: 25 April 2018 / Published: 28 April 2018
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Abstract
A highly sensitive Gallium Nitride (GaN) diaphragm based micro-scale pressure sensor with an AlGaN/GaN heterostructure field effect transistor (HFET) deflection transducer has been designed and fabricated for high temperature applications. The performance of the pressure sensor was studied over a pressure range of
[...] Read more.
A highly sensitive Gallium Nitride (GaN) diaphragm based micro-scale pressure sensor with an AlGaN/GaN heterostructure field effect transistor (HFET) deflection transducer has been designed and fabricated for high temperature applications. The performance of the pressure sensor was studied over a pressure range of 20 kPa, which resulted in an ultra-high sensitivity of ~0.76%/kPa, with a signal-to-noise ratio as high as 16 dB, when biased optimally in the subthreshold region. A high gauge factor of 260 was determined from strain distribution in the sensor membrane obtained from finite element simulations. A repeatable sensor performance was observed over multiple pressure cycles up to a temperature of 200 °C. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application)
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Open AccessArticle Fabrication of a Hydrophilic Line on a Hydrophobic Surface by Laser Ablation Processing
Micromachines 2018, 9(5), 208; https://doi.org/10.3390/mi9050208
Received: 23 March 2018 / Revised: 10 April 2018 / Accepted: 12 April 2018 / Published: 28 April 2018
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Abstract
A hydrophilic line on a hydrophobic surface was fabricated by using plasma etching and laser ablation processing in this paper. We fabricated the nanospikes on a polyimide surface by using the plasma etching processing. CHF3 plasma treatment for hydrophobic coating was conducted
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A hydrophilic line on a hydrophobic surface was fabricated by using plasma etching and laser ablation processing in this paper. We fabricated the nanospikes on a polyimide surface by using the plasma etching processing. CHF3 plasma treatment for hydrophobic coating was conducted on these nanospikes. We fabricated the microgrooves on the hydrophobic nanospikes surface using laser ablation processing. The microgroove had hydrophilic characteristics. In order to measure the hydrophilic characteristics of the microgroove, a solution that was dispersed with silver nanoparticles was used. The hydrophilic line on the hydrophobic surface was dipped in the silver nanoparticle solution. The silver nanoparticles were attached on the hydrophilic microgroove and not on the hydrophobic surface. We concluded that the laser heat affected zone should be reduced for reducing the hydrophilic line width. This hydrophilic pattern on the hydrophobic surface can be used for cell growth, protein manipulation, the spotting of biomolecules, micro-fluidics and water collection. This functional surface can especially be used for an electric flexible circuit, which is newly proposed in this paper. Full article
(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)
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Open AccessArticle Performance Analysis and Numerical Evaluation of Mixing in 3-D T-Shape Passive Micromixers
Micromachines 2018, 9(5), 210; https://doi.org/10.3390/mi9050210
Received: 2 April 2018 / Revised: 12 April 2018 / Accepted: 25 April 2018 / Published: 28 April 2018
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Abstract
In micromixer devices, laminar characteristics of the flow domain and small diffusion constants of the fluid samples that are mixed characterize the mixing process. The advection dominant flow and transport processes that develop in these devices not only create significant challenges for numerical
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In micromixer devices, laminar characteristics of the flow domain and small diffusion constants of the fluid samples that are mixed characterize the mixing process. The advection dominant flow and transport processes that develop in these devices not only create significant challenges for numerical solution of the problem, but they are also the source of numerical errors which may lead to confusing performance evaluations that are reported in the literature. In this study, the finite volume method (FVM) and finite element method (FEM) are used to characterize these errors and critical issues in numerical performance evaluations are highlighted. In this study, we used numerical methods to evaluate the mixing characteristics of a typical T-shape passive micromixer for several flow and transport parameters using both FEM and FVM, although the numerical procedures described are also equally applicable to other geometric designs as well. The outcome of the study shows that the type of stabilization technique used in FEM is very important and should be documented and reported. Otherwise, erroneous mixing performance may be reported since the added artificial diffusion may significantly affect the mixing performance in the device. Similarly, when FVM methods are used, numerical diffusion errors may become important for certain unstructured discretization techniques that are used in the idealization of the solution domain. This point needs to be also analyzed and reported when FVM is used in performance evaluation of micromixer devices. The focus of this study is not on improving the mixing performance of micromixers. Instead, we highlight the bench scale characteristics of the solutions and the mixing evaluation procedures used when FVM and FEM are employed. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle Novel EMD-Based Extraction Approach of Electric Field Fringe Impacts on a Micro Capacitive Displacement Sensor
Micromachines 2018, 9(5), 211; https://doi.org/10.3390/mi9050211
Received: 12 February 2018 / Revised: 25 April 2018 / Accepted: 26 April 2018 / Published: 1 May 2018
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Abstract
This paper presents an EMD (empirical mode decomposition)-based extraction approach to decouple the electric field fringe component impacts on the nonlinearity errors of a micro encoder-like capacitive displacement sensor. A calculated capacitance model built under Maxwell’s equations against the impacts of electric field
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This paper presents an EMD (empirical mode decomposition)-based extraction approach to decouple the electric field fringe component impacts on the nonlinearity errors of a micro encoder-like capacitive displacement sensor. A calculated capacitance model built under Maxwell’s equations against the impacts of electric field fringe component indicates that signals of this sensor are all in periodic co-sinusoidal waveforms. Applying the proposed EMD scheme, signals are decomposed into sets of intrinsic mode functions (IMFs) and a residual, in which a fundamental component represents all the features of sensor signal and reserves the local information. Interpreting sensor information from the extracted component instead of the original signal drastically diminishes the impacts of electric field fringe effect. Results from a test bench shows that after applying the EMD-based extraction approach, waveform errors were decreased from over 4.18% to less than 0.89%. Nonlinearity of the interpreted displacement was decreased from 1.54% to 0.29% for 8 mm stroke. Full article
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Open AccessArticle Fabricating and Characterizing the Microfluidic Solid Phase Extraction Module Coupling with Integrated ESI Emitters
Micromachines 2018, 9(5), 212; https://doi.org/10.3390/mi9050212
Received: 5 March 2018 / Revised: 13 April 2018 / Accepted: 24 April 2018 / Published: 1 May 2018
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Abstract
Microfluidic chips coupling with mass spectrometry (MS) will be of great significance to the development of relevant instruments involving chemical and bio-chemical analysis, drug detection, food and environmental applications and so on. In our previous works, we proposed two types of microfluidic electrospray
[...] Read more.
Microfluidic chips coupling with mass spectrometry (MS) will be of great significance to the development of relevant instruments involving chemical and bio-chemical analysis, drug detection, food and environmental applications and so on. In our previous works, we proposed two types of microfluidic electrospray ionization (ESI) chip coupling with MS: the two-phase flow focusing (FF) ESI microfluidic chip and the corner-integrated ESI emitter, respectively. However the pretreatment module integrated with these ESI emitters is still a challenging problem. In this paper, we concentrated on integrating the solid phase micro-extraction (SPME) module with our previous proposed on-chip ESI emitters; the fabrication processes of such SPME module are fully compatible with our previous proposed ESI emitters based on the multi-layer soft lithography. We optimized the structure of the integrated chip and characterized its performance using standard samples. Furthermore, we verified its abilities of salt removal, extraction of multiple analytes and separation through on-chip elution using mimic biological urine spiked with different drugs. The results indicated that our proposed integrated module with ESI emitters is practical and effective for real biological sample pretreatment and MS detection. Full article
(This article belongs to the Special Issue Microfluidic Sensors)
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Open AccessArticle Technology for 3D System Integration for Flexible Wireless Biomedical Applications
Micromachines 2018, 9(5), 213; https://doi.org/10.3390/mi9050213
Received: 16 March 2018 / Revised: 24 April 2018 / Accepted: 27 April 2018 / Published: 2 May 2018
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Abstract
This paper presents a new 3D bottom-up packing technology for integrating a chip, an induction coil, and interconnections for flexible wireless biomedical applications. Parylene was used as a flexible substrate for the bottom-up embedding of the chip, insulation layer, interconnection, and inductors to
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This paper presents a new 3D bottom-up packing technology for integrating a chip, an induction coil, and interconnections for flexible wireless biomedical applications. Parylene was used as a flexible substrate for the bottom-up embedding of the chip, insulation layer, interconnection, and inductors to form a flexible wireless biomedical microsystem. The system can be implanted on or inside the human body. A 50-μm gold foil deposited through laser micromachining by using a picosecond laser was used as an inductor to yield a higher quality factor than that yielded by thickness-increasing methods such as the fold-and-bond method or thick-metal electroplating method at the operation frequency of 1 MHz. For system integration, parylene was used as a flexible substrate, and the contact pads and connections between the coil and chip were generated using gold deposition. The advantage of the proposed process can integrate the chip and coil vertically to generate a single biocompatible system in order to reduce required area. The proposed system entails the use of 3D integrated circuit packaging concepts to integrate the chip and coil. The results validated the feasibility of this technology. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle FR4-Based Electromagnetic Scanning Micromirror Integrated with Angle Sensor
Micromachines 2018, 9(5), 214; https://doi.org/10.3390/mi9050214
Received: 30 March 2018 / Revised: 21 April 2018 / Accepted: 26 April 2018 / Published: 2 May 2018
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Abstract
This paper presents a flame retardant 4 (FR4)-based electromagnetic scanning micromirror, which aims to overcome the limitations of conventional microelectromechanical systems (MEMS) micromirrors for the large-aperture and low-frequency scanning applications. This micromirror is fabricated through a commercial printed circuit board (PCB) technology at
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This paper presents a flame retardant 4 (FR4)-based electromagnetic scanning micromirror, which aims to overcome the limitations of conventional microelectromechanical systems (MEMS) micromirrors for the large-aperture and low-frequency scanning applications. This micromirror is fabricated through a commercial printed circuit board (PCB) technology at a low cost and with a short process cycle, before an aluminum-coated silicon mirror plate with a large aperture is bonded on the FR4 platform to provide a high surface quality. In particular, an electromagnetic angle sensor is integrated to monitor the motion of the micromirror in real time. A prototype has been assembled and tested. The results show that the micromirror can reach the optical scan angle of 11.2 with a low driving voltage of only 425 mV at resonance (361.8 Hz). At the same time, the signal of the integrated angle sensor also shows good signal-to-noise ratio, linearity and sensitivity. Finally, the reliability of the FR4 based micro-mirror has been tested. The prototype successfully passes both shock and vibration tests. Furthermore, the results of the long-term mechanical cycling test (50 million cycles) suggest that the maximum variations of resonant frequency and scan angle are less than 0.3% and 6%, respectively. Therefore, this simple and robust micromirror has great potential in being useful in a number of optical microsystems, especially when large-aperture or low-frequency is required. Full article
(This article belongs to the Special Issue Optical MEMS)
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Open AccessArticle CO2 Laser-Based Rapid Prototyping of Micropumps
Micromachines 2018, 9(5), 215; https://doi.org/10.3390/mi9050215
Received: 6 March 2018 / Revised: 25 April 2018 / Accepted: 27 April 2018 / Published: 3 May 2018
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Abstract
The fabrication of microdevices for fluidic control often requires the use of flexible diaphragms in a way that requires cleanroom equipment and compromises performance. We use a CO 2 laser to perform the standard ablative techniques of cutting and engraving materials, but we
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The fabrication of microdevices for fluidic control often requires the use of flexible diaphragms in a way that requires cleanroom equipment and compromises performance. We use a CO 2 laser to perform the standard ablative techniques of cutting and engraving materials, but we also apply a method that we call laser placement. This allows us to fabricate precisely-positioned and precisely-sized, isolated diaphragms. This in turn enables the rapid prototyping of integrated multilayer microfluidic devices to form complex structures without the need for manual positioning or cleanroom equipment. The fabrication process is also remarkably rapid and capable of being scaled to manufacturing levels of production. We explore the use of these devices to construct a compact system of peristaltic pumps that can form water in oil droplets without the use of the non-pulsatile pumping systems typically required. Many devices can be fabricated at a time on a sheet by sheet basis with a fabrication process that, to our knowledge, is the fastest reported to date for devices of this type (requiring only 3 h). Moreover, this system is unusually compact and self-contained. Full article
(This article belongs to the Special Issue Polymer Based MEMS and Microfabrication)
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Open AccessArticle A Non-Resonant Kinetic Energy Harvester for Bioimplantable Applications
Micromachines 2018, 9(5), 217; https://doi.org/10.3390/mi9050217
Received: 27 March 2018 / Revised: 26 April 2018 / Accepted: 4 May 2018 / Published: 5 May 2018
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Abstract
A linear non-resonant kinetic energy harvester for implantable devices is presented. The design contains a metal platform with permanent magnets, two stators with three-dimensional helical coils for increased power generation, ball bearings, and a polydimethylsiloxane (PDMS) package for biocompatibility. Mechanical excitation of this
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A linear non-resonant kinetic energy harvester for implantable devices is presented. The design contains a metal platform with permanent magnets, two stators with three-dimensional helical coils for increased power generation, ball bearings, and a polydimethylsiloxane (PDMS) package for biocompatibility. Mechanical excitation of this device within the body due to daily activities leads to a relative motion between the platform and stators, resulting in electromagnetic induction. Initial prototypes without packaging have been fabricated and characterized on a linear shaker. Dynamic tests showed that the friction force acting on the platform is on the order of 0.6 mN. The resistance and the inductance of the coils were measured to be 2.2 Ω and 0.4 µH, respectively. A peak open circuit voltage of 1.05 mV was generated per stator at a platform speed of 5.8 cm/s. Further development of this device offers potential for recharging the batteries of implantable biomedical devices within the body. Full article
(This article belongs to the Special Issue Microsystems for Power, Energy, and Actuation)
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Open AccessArticle Gimbal-Less Two-Axis Electromagnetic Microscanner with Twist Mechanism
Micromachines 2018, 9(5), 219; https://doi.org/10.3390/mi9050219
Received: 2 April 2018 / Revised: 24 April 2018 / Accepted: 3 May 2018 / Published: 6 May 2018
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Abstract
We present an electromagnetically driven microscanner based on a gimbal-less twist mechanism. In contrast to conventional microscanners using a gimbal-less leverage mechanism, our device utilizes a gimbal-less twist mechanism to increase the scan angle in optical applications requiring a large scanning mirror. The
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We present an electromagnetically driven microscanner based on a gimbal-less twist mechanism. In contrast to conventional microscanners using a gimbal-less leverage mechanism, our device utilizes a gimbal-less twist mechanism to increase the scan angle in optical applications requiring a large scanning mirror. The proposed gimbal-less scanner with twist mechanism increases the scan angle by 1.55 and 1.97 times for the slow and fast axes, respectively, under the same force; 3.64 and 1.97 times for the slow and fast axes, respectively, under the same maximum stress, compared to the gimbal-less leverage mechanism. The scanner with a 3-mm-diameter mirror and a current path composed of a single-turn coil was fabricated, and it showed the maximum scan angle of 5° (quasi-static) and 22° (resonant) for the slow and fast axes, respectively. The experimentally estimated crosstalk was as small as 0.47% and 0.97% for the fast and slow axes affected by the other axes, respectively, which was determined using a newly employed methodology based on fast Fourier transform. Full article
(This article belongs to the Special Issue Microsystems for Power, Energy, and Actuation)
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Open AccessArticle Features in Microfluidic Paper-Based Devices Made by Laser Cutting: How Small Can They Be?
Micromachines 2018, 9(5), 220; https://doi.org/10.3390/mi9050220
Received: 9 April 2018 / Revised: 25 April 2018 / Accepted: 4 May 2018 / Published: 7 May 2018
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Abstract
In this paper, we determine the smallest feature size that enables fluid flow in microfluidic paper-based analytical devices (µPADs) fabricated by laser cutting. The smallest feature sizes fabricated from five commercially available paper types: Whatman filter paper grade 50 (FP-50), Whatman 3MM Chr
[...] Read more.
In this paper, we determine the smallest feature size that enables fluid flow in microfluidic paper-based analytical devices (µPADs) fabricated by laser cutting. The smallest feature sizes fabricated from five commercially available paper types: Whatman filter paper grade 50 (FP-50), Whatman 3MM Chr chromatography paper (3MM Chr), Whatman 1 Chr chromatography paper (1 Chr), Whatman regenerated cellulose membrane 55 (RC-55) and Amershan Protran 0.45 nitrocellulose membrane (NC), were 139 ± 8 µm, 130 ± 11 µm, 103 ± 12 µm, 45 ± 6 µm, and 24 ± 3 µm, respectively, as determined experimentally by successful fluid flow. We found that the fiber width of the paper correlates with the smallest feature size that has the capacity for fluid flow. We also investigated the flow speed of Allura red dye solution through small-scale channels fabricated from different paper types. We found that the flow speed is significantly slower through microscale features and confirmed the similar trends that were reported previously for millimeter-scale channels, namely that wider channels enable quicker flow speed. Full article
(This article belongs to the Section Micro/Nanofluidics and Lab on a Chip)
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Open AccessArticle A Handy Liquid Metal Based Non-Invasive Electrophoretic Particle Microtrap
Micromachines 2018, 9(5), 221; https://doi.org/10.3390/mi9050221
Received: 5 April 2018 / Revised: 3 May 2018 / Accepted: 5 May 2018 / Published: 7 May 2018
PDF Full-text (1977 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A handy liquid metal based non-invasive particle microtrap was proposed and demonstrated in this work. This kind of microtrap can be easily designed and fabricated at any location of a microfluidic chip to perform precise particle trapping and releasing without disturbing the microchannel
[...] Read more.
A handy liquid metal based non-invasive particle microtrap was proposed and demonstrated in this work. This kind of microtrap can be easily designed and fabricated at any location of a microfluidic chip to perform precise particle trapping and releasing without disturbing the microchannel itself. The microsystem demonstrated in this work utilized silicon oil as the continuous phase and fluorescent particles (PE-Cy5, SPHEROTM Fluorescent Particles, BioLegend, San Diego, CA, USA, 10.5 μm) as the target particles. To perform the particle trapping, the micro system utilized liquid-metal-filled microchannels as noncontact electrodes to generate different patterns of electric field inside the fluid channel. According to the experimental results, the target particle can be selectively trapped and released by switching the electric field patterns. For a better understanding the control mechanism, a numerical simulation of the electric field was performed to explain the trapping mechanism. In order to verify the model, additional experiments were performed and are discussed. Full article
(This article belongs to the collection Lab-on-a-Chip)
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Open AccessArticle Surface Modification of Electroosmotic Silicon Microchannel Using Thermal Dry Oxidation
Micromachines 2018, 9(5), 222; https://doi.org/10.3390/mi9050222
Received: 30 March 2018 / Revised: 2 May 2018 / Accepted: 4 May 2018 / Published: 7 May 2018
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Abstract
A simple fabrication method for the surface modification of an electroosmotic silicon microchannel using thermal dry oxidation is presented. The surface modification is done by coating the silicon surface with a silicon dioxide (SiO2) layer using a thermal oxidation process. The
[...] Read more.
A simple fabrication method for the surface modification of an electroosmotic silicon microchannel using thermal dry oxidation is presented. The surface modification is done by coating the silicon surface with a silicon dioxide (SiO2) layer using a thermal oxidation process. The process aims not only to improve the surface quality of the channel to be suitable for electroosmotic fluid transport but also to reduce the channel width using a simple technique. Initially, the parallel microchannel array with dimensions of 0.5 mm length and a width ranging from 1.8 µm to 2 µm are created using plasma etching on the 2 cm × 2 cm silicon substrate <100>. The oxidation of the silicon channel in a thermal chamber is then conducted to create the SiO2 layer. The layer properties and the quality of the surface are analyzed using scanning electron microscopy (SEM) and a surface profiler, respectively. The results show that the maximum oxidation growth rate occurs in the first 4 h of oxidation time and the rate decreases over time as the oxide layer becomes thicker. It is also found that the surface roughness is reduced with the increase of the process temperature and the oxide thickness. The scallop effect on the vertical wall due to the plasma etching process also improved with the presence of the oxide layer. After oxidation, the channel width is reduced by ~40%. The demonstrated method is suggested for the fabrication of a uniform channel cross section with high aspect ratio in sub-micro and nanometer scale that will be useful for the electroosmotic (EO) ion manipulation of the biomedical fluid sample. Full article
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Open AccessArticle Continuous-Flow Cell Dipping and Medium Exchange in a Microdevice using Dielectrophoresis
Micromachines 2018, 9(5), 223; https://doi.org/10.3390/mi9050223
Received: 22 March 2018 / Revised: 25 April 2018 / Accepted: 29 April 2018 / Published: 8 May 2018
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Abstract
Medium exchange is the process of changing the suspension medium of cells/particles, and has applications in washing, surface modifications, nutrient replenishment, or simply changing the environment of the target entities. Dipping involves diverting the path of target cells in the carrying fluid to
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Medium exchange is the process of changing the suspension medium of cells/particles, and has applications in washing, surface modifications, nutrient replenishment, or simply changing the environment of the target entities. Dipping involves diverting the path of target cells in the carrying fluid to immerse them in another fluid for a short duration, and pushing them again into the original medium. In this paper, a simple microfluidic platform is introduced that employs dielectrophoresis to achieve medium exchange and dipping of micro-objects in a continuous manner. The essential feature of the platform is a microchannel that includes two arrays of microelectrodes that partly enter the bottom surface from both sides. In the first step, numerous finite element-based parametric studies are carried out to obtain the optimized geometrical and operational parameters ensuring successful dipping and medium exchange processes. The results of those studies are utilized to fabricate the platform using standard photolithography techniques. The electrodes are patterned on a glass substrate, while the channel, made out of polydimethylsiloxane, is bonded on top of the glass. Trajectories of blood cells from numerical studies and experimentations are reported, and both results exhibited close agreement. Full article
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Open AccessArticle Study on Micro-Crack Induced Precision Severing of Quartz Glass Chips
Micromachines 2018, 9(5), 224; https://doi.org/10.3390/mi9050224
Received: 11 April 2018 / Revised: 3 May 2018 / Accepted: 5 May 2018 / Published: 8 May 2018
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Abstract
It is difficult to cut hard and brittle quartz glass chips. Hence, a method involving micro-crack-induced severing along a non-crack microgroove-apex by controlling the loading rate is proposed. The objective is to realize the rapid and precision severing of the hardest quartz glass
[...] Read more.
It is difficult to cut hard and brittle quartz glass chips. Hence, a method involving micro-crack-induced severing along a non-crack microgroove-apex by controlling the loading rate is proposed. The objective is to realize the rapid and precision severing of the hardest quartz glass in chip materials. Firstly, micro-grinding was employed to machine smooth microgrooves of 398–565 μ m in depth; then the severing force was modelled by the microgroove shape and size; finally, the severing performance of a 4-mm thick substrate was investigated experimentally. It is shown that the crack propagation occurred at the same time from the microgroove-apex and the loading point during 0.5 ms in micro-crack-induced severing. The severing efficiency is dominated by the severing time rather than the crack propagation time. When the loading rate is less than 20–60 mm/min, the dynamic severing is transferred to static severing. With increasing microgroove-apex radius, the severing force decreases to the critical severing force of about 160–180 N in the static severing, but it increases to the critical severing force in the dynamic severing. The static severing force and time are about two times and about nine times larger than the dynamic ones, respectively, but the static severing form error of 16.3 μ m/mm and surface roughness of 19.7 nm are less. It is confirmed that the ideal static severing forces are identical to the experimental results. As a result, the static severing is controllable for the accurate and smooth separation of quartz glass chips in 4 s and less. Full article
(This article belongs to the Special Issue Glassy Materials Based Microdevices)
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Open AccessArticle Theoretical and Experimental Research on Bubble Actuated Micro-Pumps
Micromachines 2018, 9(5), 225; https://doi.org/10.3390/mi9050225
Received: 11 April 2018 / Revised: 2 May 2018 / Accepted: 7 May 2018 / Published: 9 May 2018
PDF Full-text (4760 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Bubble actuated micro-pumps have great potential to be integrated into microfluidic systems to allow the independence of peripheral equipment. Previous studies on bubble actuated valveless micro-pumps have been mainly limited to experimental studies and numerical simulations due to the complex behavior of bubbles.
[...] Read more.
Bubble actuated micro-pumps have great potential to be integrated into microfluidic systems to allow the independence of peripheral equipment. Previous studies on bubble actuated valveless micro-pumps have been mainly limited to experimental studies and numerical simulations due to the complex behavior of bubbles. In this paper, the construction of a mathematical model for a bubble actuated valveless micro-pump considering fluid dynamics, heat and mass transfer and bubble dynamics is described. A prototype was fabricated and tested to verify this theoretical model. The morphological evolution of the driving bubbles during the heating process was observed by a high-speed charge-coupled device (CCD) camera, the flow rate produced by the micro-pump under different working conditions was recorded and the test results were explained by the heat dissipation model. The model in this study was able to precisely predict the flow of micro-pumps in different drive modes. The principle behind defining the heating frequency and the duty cycle based on the pump chamber volume was determined. The study shows the mechanism of bubble controlling and the good prospects of bubble actuated valveless micro-pumps. Full article
(This article belongs to the Section Micro/Nanofluidics and Lab on a Chip)
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Open AccessArticle Optimization of Pulley-Type Ring Resonator with Waveguide Offset
Micromachines 2018, 9(5), 226; https://doi.org/10.3390/mi9050226
Received: 15 April 2018 / Revised: 30 April 2018 / Accepted: 3 May 2018 / Published: 10 May 2018
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Abstract
In this work, we dealt with the optimization of the pulley-type ring resonator using the offset of the straight input and output waveguide at the junction with the curved waveguide. We adopted the finite-difference time-domain method to simulate the structure. It was found
[...] Read more.
In this work, we dealt with the optimization of the pulley-type ring resonator using the offset of the straight input and output waveguide at the junction with the curved waveguide. We adopted the finite-difference time-domain method to simulate the structure. It was found that the coupling loss could be significantly reduced and the critical coupling could be precisely tuned. This results in the possibility of the Q-factor being higher than that of the structure without waveguide offset. In this study, the Q-factor of the ring resonator is increased from 9180 to 11,302. The corresponding enhancement is 23.1%. Full article
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Open AccessArticle High-Precision Lens-Less Flow Cytometer on a Chip
Micromachines 2018, 9(5), 227; https://doi.org/10.3390/mi9050227
Received: 17 April 2018 / Revised: 3 May 2018 / Accepted: 9 May 2018 / Published: 10 May 2018
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Abstract
We present a flow cytometer on a microfluidic chip that integrates an inline lens-free holographic microscope. High-speed cell analysis necessitates that cells flow through the microfluidic channel at a high velocity, but the image sensor of the in-line holographic microscope needs a long
[...] Read more.
We present a flow cytometer on a microfluidic chip that integrates an inline lens-free holographic microscope. High-speed cell analysis necessitates that cells flow through the microfluidic channel at a high velocity, but the image sensor of the in-line holographic microscope needs a long exposure time. Therefore, to solve this problem, this paper proposes an S-type micro-channel and a pulse injection method. To increase the speed and accuracy of the hologram reconstruction, we improve the iterative initial constraint method and propose a background removal method. The focus images and cell concentrations can be accurately calculated by the developed method. Using whole blood cells to test the cell counting precision, we find that the cell counting error of the proposed method is less than 2%. This result shows that the on-chip flow cytometer has high precision. Due to its low price and small size, this flow cytometer is suitable for environments far away from laboratories, such as underdeveloped areas and outdoors, and it is especially suitable for point-of-care testing (POCT). Full article
(This article belongs to the Special Issue Micro/Nano Devices for Blood Analysis)
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Open AccessArticle A Microfluidic Platform for Investigating Transmembrane Pressure-Induced Glomerular Leakage
Micromachines 2018, 9(5), 228; https://doi.org/10.3390/mi9050228
Received: 13 April 2018 / Revised: 1 May 2018 / Accepted: 3 May 2018 / Published: 10 May 2018
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Abstract
Transmembrane pressure across the glomerular filter barrier may underlie renal failure. However, studies of renal failure have been difficult owing to a lack of in vitro models to capture the transmembrane pressure in a controlled approach. Here we report a microfluidic platform of
[...] Read more.
Transmembrane pressure across the glomerular filter barrier may underlie renal failure. However, studies of renal failure have been difficult owing to a lack of in vitro models to capture the transmembrane pressure in a controlled approach. Here we report a microfluidic platform of podocyte culture to investigate transmembrane pressure induced glomerular leakage. Podocytes, the glomerular epithelial cells essential for filtration function, were cultivated on a porous membrane supplied with transmembrane pressure ΔP. An anodic aluminum oxide membrane with collagen coating was used as the porous membrane, and the filtration function was evaluated using dextrans of different sizes. The results show that dextran in 20 kDa and 70 kDa can penetrate the podocyte membrane, whereas dextran in 500 kDa was blocked until ΔP ≥ 60 mmHg, which resembles the filtration function when ΔP was in the range of a healthy kidney (ΔP < 60 mmHg) as well as the hypertension-induced glomerular leakage (ΔP ≥ 60 mmHg). Additionally, analysis showed that synaptopodin and actin were also downregulated when ΔP > 30 mmHg, indicating that the dysfunction of renal filtration is correlated with the reduction of synaptopodin expression and disorganized actin cytoskeleton. Taking together, our microfluidic platform enables the investigation of transmembrane pressure in glomerular filter membrane, with potential implications for drug development in the future. Full article
(This article belongs to the Special Issue Microfluidic Devices for Healthcare and Environment Monitoring)
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Open AccessArticle Electroosmotic Flow in Microchannel with Black Silicon Nanostructures
Micromachines 2018, 9(5), 229; https://doi.org/10.3390/mi9050229
Received: 2 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
PDF Full-text (4264 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Although electroosmotic flow (EOF) has been applied to drive fluid flow in microfluidic chips, some of the phenomena associated with it can adversely affect the performance of certain applications such as electrophoresis and ion preconcentration. To minimize the undesirable effects, EOF can be
[...] Read more.
Although electroosmotic flow (EOF) has been applied to drive fluid flow in microfluidic chips, some of the phenomena associated with it can adversely affect the performance of certain applications such as electrophoresis and ion preconcentration. To minimize the undesirable effects, EOF can be suppressed by polymer coatings or introduction of nanostructures. In this work, we presented a novel technique that employs the Dry Etching, Electroplating and Molding (DEEMO) process along with reactive ion etching (RIE), to fabricate microchannel with black silicon nanostructures (prolate hemispheroid-like structures). The effect of black silicon nanostructures on EOF was examined experimentally by current monitoring method, and numerically by finite element simulations. The experimental results showed that the EOF velocity was reduced by 13 ± 7%, which is reasonably close to the simulation results that predict a reduction of approximately 8%. EOF reduction is caused by the distortion of local electric field at the nanostructured surface. Numerical simulations show that the EOF velocity decreases with increasing nanostructure height or decreasing diameter. This reveals the potential of tuning the etching process parameters to generate nanostructures for better EOF suppression. The outcome of this investigation enhances the fundamental understanding of EOF behavior, with implications on the precise EOF control in devices utilizing nanostructured surfaces for chemical and biological analyses. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle Development of a Fully Flexible Sheet-Type Tactile Display Based on Electrovibration Stimulus
Micromachines 2018, 9(5), 230; https://doi.org/10.3390/mi9050230
Received: 8 April 2018 / Revised: 5 May 2018 / Accepted: 7 May 2018 / Published: 11 May 2018
PDF Full-text (6383 KB) | HTML Full-text | XML Full-text
Abstract
Tactile displays have been extensively studied for several decades. However, owing to their bulkiness and stiffness, it has been difficult to integrate these displays with information devices to enable tactile communication between the devices and their users. This paper proposes a novel sheet-type
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Tactile displays have been extensively studied for several decades. However, owing to their bulkiness and stiffness, it has been difficult to integrate these displays with information devices to enable tactile communication between the devices and their users. This paper proposes a novel sheet-type electrovibration tactile display that consists of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate conductive layers and an insulation layer of polydimethylsiloxane. The tactile display is sufficiently thin and flexible for attaching onto various surfaces. In this study, the tactile display was micro-fabricated and characterized through experiments. The experimental results indicated that the tactile display exhibited good durability under bending and that it could present various tactile sensations depending on the type of voltage waveform. In addition, the effect of using a combination of electrovibration and thermal stimuli was also demonstrated. The sheet-type display was attached onto a Peltier element; the thinness of the structure enabled the display to conform to the element and ensure good heat transfer. In the experiment, subjects were asked to scan the display with their fingertips. The results showed that multiple tactile stimuli were also successfully perceived by the subjects. Full article
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Open AccessArticle Acceleration Sensitivity in Bulk-Extensional Mode, Silicon-Based MEMS Oscillators
Micromachines 2018, 9(5), 233; https://doi.org/10.3390/mi9050233
Received: 31 March 2018 / Revised: 8 May 2018 / Accepted: 9 May 2018 / Published: 12 May 2018
PDF Full-text (6922 KB) | HTML Full-text | XML Full-text
Abstract
Acceleration sensitivity in silicon bulk-extensional mode oscillators is studied in this work, and a correlation between the resonator alignment to different crystalline planes of silicon and the observed acceleration sensitivity is established. It is shown that the oscillator sensitivity to the applied vibration
[...] Read more.
Acceleration sensitivity in silicon bulk-extensional mode oscillators is studied in this work, and a correlation between the resonator alignment to different crystalline planes of silicon and the observed acceleration sensitivity is established. It is shown that the oscillator sensitivity to the applied vibration is significantly lower when the silicon-based lateral-extensional mode resonator is aligned to the <110> plane compared to when the same resonator is aligned to <100>. A finite element model is developed that is capable of predicting the resonance frequency variation when a distributed load (i.e., acceleration) is applied to the resonator. Using this model, the orientation-dependent nature of acceleration sensitivity is confirmed, and the effect of material nonlinearity on the acceleration sensitivity is also verified. A thin-film piezoelectric-on-substrate platform is chosen for the implementation of resonators. Approximately, one order of magnitude higher acceleration sensitivity is measured for oscillators built with a resonator aligned to the <100> plane versus those with a resonator aligned to the <110> plane (an average of ~5.66 × 10−8 (1/g) vs. ~3.66 × 10−9 (1/g), respectively, for resonators on a degenerately n-type doped silicon layer). Full article
(This article belongs to the Special Issue Micro-Resonators: The Quest for Superior Performance)
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Open AccessArticle Side-Group Effect on Electron Transport of Single Molecular Junctions
Micromachines 2018, 9(5), 234; https://doi.org/10.3390/mi9050234
Received: 23 April 2018 / Revised: 9 May 2018 / Accepted: 10 May 2018 / Published: 13 May 2018
PDF Full-text (2581 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this article, we have investigated the influence of the nitro side-group on the single molecular conductance of pyridine-based molecules by scanning tunneling microscopy break junction. Single molecular conductance of 4,4′-bipyridine (BPY), 3-nitro-4-(pyridin-4-yl)pyridine (BPY-N), and 3-nitro-4-(3-nitropyridin-4-yl)pyridine (BPY-2N) were measured by contact with Au
[...] Read more.
In this article, we have investigated the influence of the nitro side-group on the single molecular conductance of pyridine-based molecules by scanning tunneling microscopy break junction. Single molecular conductance of 4,4′-bipyridine (BPY), 3-nitro-4-(pyridin-4-yl)pyridine (BPY-N), and 3-nitro-4-(3-nitropyridin-4-yl)pyridine (BPY-2N) were measured by contact with Au electrodes. For the BPY molecular junction, two sets of conductance were found with values around 10−3.1 G0 (high G) and 10−3.7 G0 (low G). The addition of nitro side-group(s) onto the pyridine ring resulted in lower conductance of 10−3.8 G0 for BPY-N and 10−3.9 G0 for BPY-2N, respectively, which can be attributed to the twist angle of two pyridine rings. Moreover, the steric hindrance of nitro group(s) also affects the contacting configuration of electrode-molecule-electrode. As a consequence, only one set of conductance value was observed for BPY-N and BPY-2N. Our work clearly shows the important role of side-groups on the electron transport of single-molecule junctions. Full article
(This article belongs to the Special Issue Atomic and Molecular Junction for Molecular Electronic Devices)
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Open AccessCommunication Assembly and Connection of Micropatterned Single Neurons for Neuronal Network Formation
Micromachines 2018, 9(5), 235; https://doi.org/10.3390/mi9050235
Received: 6 April 2018 / Revised: 4 May 2018 / Accepted: 7 May 2018 / Published: 15 May 2018
PDF Full-text (2431 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Engineering of neuronal network geometry by micropatterning technology is a key future technology for creating artificial brains on a chip. However, engineering of network geometry at the single-cell-level with functional morphology (axon/dendrite) and connectivity (synapses) is still challenging. Here, we describe a method
[...] Read more.
Engineering of neuronal network geometry by micropatterning technology is a key future technology for creating artificial brains on a chip. However, engineering of network geometry at the single-cell-level with functional morphology (axon/dendrite) and connectivity (synapses) is still challenging. Here, we describe a method for controlling the axon and dendrite morphology of single primary-cultured neurons and assembling a neural circuit using mobile microplates. The microplates enabled morphological control of neurons by their shapes and bringing their ends into contact caused the formation of physical connections. Functional synapse formation at the connection was indicated by immunostaining of synapse-related proteins and intracellular Ca2+ imaging of neural activity. We believe that the method will be useful in engineering neural circuits with selected neurons and defined morphology. Full article
(This article belongs to the Special Issue State-of-the-Art Lab-on-a-Chip Technology in Japan)
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Open AccessArticle Decoupling Research of a Novel Three-Dimensional Force Flexible Tactile Sensor Based on an Improved BP Algorithm
Micromachines 2018, 9(5), 236; https://doi.org/10.3390/mi9050236
Received: 26 March 2018 / Revised: 10 May 2018 / Accepted: 11 May 2018 / Published: 14 May 2018
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Abstract
Decoupling research on flexible tactile sensors play a very important role in the intelligent robot skin and tactile-sensing fields. In this paper, an efficient machine learning method based on the improved back-propagation (BP) algorithm is proposed to decouple the mapping relationship between the
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Decoupling research on flexible tactile sensors play a very important role in the intelligent robot skin and tactile-sensing fields. In this paper, an efficient machine learning method based on the improved back-propagation (BP) algorithm is proposed to decouple the mapping relationship between the resistances of force-sensitive conductive pillars and three-dimensional forces for the 6 × 6 novel flexible tactile sensor array. Tactile-sensing principles and numerical experiments are analyzed. The tactile sensor array model accomplishes the decomposition of the force components by its delicate structure, and avoids direct interference among the electrodes of the sensor array. The force components loaded on the tactile sensor are decoupled with a very high precision from the resistance signal by the improved BP algorithm. The decoupling results show that the k-cross validation (k-CV) algorithm is a highly effective method to improve the decoupling precision of force components for the novel tactile sensor. The large dataset with the k-CV method obtains a better decoupling accuracy of the force components than the small dataset. All of the decoupling results are fairly good, and they indicate that the improved BP model with a strong non-linear approaching ability has an efficient and valid performance in decoupling force components for the tactile sensor. Full article
(This article belongs to the Special Issue Tactile Sensing for Soft Robotics and Wearables)
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Open AccessArticle Fabrication and Characterization of Inhomogeneous Curved Artificial Compound Eye
Micromachines 2018, 9(5), 238; https://doi.org/10.3390/mi9050238
Received: 2 April 2018 / Revised: 27 April 2018 / Accepted: 14 May 2018 / Published: 15 May 2018
PDF Full-text (2919 KB) | HTML Full-text | XML Full-text
Abstract
Compared with the conventional compound eye processing method, a new fabrication method—namely, a mold casting method—was presented. This method is simple, low-cost, easy to implement, and can be reused. A bionic compound eye array model with 61 ommatidia arranged inhomogeneously onto a curved
[...] Read more.
Compared with the conventional compound eye processing method, a new fabrication method—namely, a mold casting method—was presented. This method is simple, low-cost, easy to implement, and can be reused. A bionic compound eye array model with 61 ommatidia arranged inhomogeneously onto a curved surface was fabricated. The curved surface had a radius of 9 mm and a thickness of 0.5 mm. The margin imaging quality was improved significantly by the analysis of light beam focus and the optical imaging properties of the fabricated compound eye. The sub-image of each ommatidium had a high resolution. There was 5% error between the collecting spot brightness and simulation analysis results, which proved that the production method is feasible. Full article
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Open AccessArticle An Organic Flexible Artificial Bio-Synapses with Long-Term Plasticity for Neuromorphic Computing
Micromachines 2018, 9(5), 239; https://doi.org/10.3390/mi9050239
Received: 19 April 2018 / Revised: 10 May 2018 / Accepted: 11 May 2018 / Published: 15 May 2018
PDF Full-text (12076 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Artificial synapses, with synaptic plasticity, are the key components of constructing the neuromorphic computing system and mimicking the bio-synaptic function. Traditional synaptic devices are based on silicon and inorganic materials, while organic electronics can open up new opportunities for flexible devices. Here, a
[...] Read more.
Artificial synapses, with synaptic plasticity, are the key components of constructing the neuromorphic computing system and mimicking the bio-synaptic function. Traditional synaptic devices are based on silicon and inorganic materials, while organic electronics can open up new opportunities for flexible devices. Here, a flexible artificial synaptic device with an organic functional layer was proposed. The organic device showed good switching behaviors such as ON/OFF ratio over 100 at low operation voltages. The set and reset voltages were lower than 0.5 V and −0.25 V, respectively. The long-term plasticity, spike-timing-dependent plasticity learning rules (STDP), and forgetting function were emulated using the device. The retention times of the excitatory and inhibitory post-synaptic currents were both longer than 60 s. The long-term plasticity was repeatable without noticeable degradation after the application of five voltage pulse cycles to the top electrode. These results indicate that our organic flexible device has the potential to be applied in bio-inspired neuromorphic systems. Full article
(This article belongs to the Special Issue Flexible Electronics: Fabrication and Ubiquitous Integration)
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Open AccessArticle How Hydrogen Dielectric Strength Forces the Work Voltage in the Electric Discharge Machining
Micromachines 2018, 9(5), 240; https://doi.org/10.3390/mi9050240
Received: 9 April 2018 / Revised: 9 May 2018 / Accepted: 11 May 2018 / Published: 15 May 2018
PDF Full-text (935 KB) | HTML Full-text | XML Full-text
Abstract
An electro-thermal model based on the Joule heating effect is proposed to simulate a single discharge in an electric discharge machining process. Normally, the dielectric strength of the hydrocarbons oil is approximately 20 MV/m, but it varies with both the thickness of the
[...] Read more.
An electro-thermal model based on the Joule heating effect is proposed to simulate a single discharge in an electric discharge machining process. Normally, the dielectric strength of the hydrocarbons oil is approximately 20 MV/m, but it varies with both the thickness of the film and its decomposition. After the breakdown, the hydrocarbon oil has an average dielectric strength value of 2 MV/m. This value is close to the dielectric strength of the hydrogen, which is the main gas that results from the hydrocarbon oil decomposition, at temperatures between 6000 K and 9000 K. Therefore, the electric discharge occurs in a hydrogen atmosphere that imposes both the discharge gap and the work voltage. A 200 V voltage is associated to a 100 μm discharge gap, leading to a 20 V work voltage. Therefore, the 3 V work voltage control corresponds to approximately 15 μm. In other words, the increase of the discharge gap originates other discharge during the discharge pulse. The work voltage control, together with the multiple discharge method, is taken into account. The 100 μm discharge gap corresponds to the higher value of the transitory discharge gap that over evaluates the material removal and the tool wear rates. The results of the numerical simulations are validated with experimental data. Full article
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Open AccessArticle Hysteresis Compensation and Sliding Mode Control with Perturbation Estimation for Piezoelectric Actuators
Micromachines 2018, 9(5), 241; https://doi.org/10.3390/mi9050241
Received: 28 March 2018 / Revised: 11 May 2018 / Accepted: 15 May 2018 / Published: 16 May 2018
PDF Full-text (1987 KB) | HTML Full-text | XML Full-text
Abstract
Based on the background of atomic force microscope (AFM) driven by piezoelectric actuators (PEAs), this paper proposes a sliding mode control coupled with an inverse Bouc–Wen (BW) hysteresis compensator to improve the positioning performance of PEAs. The intrinsic hysteresis and creep characteristics degrade
[...] Read more.
Based on the background of atomic force microscope (AFM) driven by piezoelectric actuators (PEAs), this paper proposes a sliding mode control coupled with an inverse Bouc–Wen (BW) hysteresis compensator to improve the positioning performance of PEAs. The intrinsic hysteresis and creep characteristics degrade the performance of the PEA and cause accuracy loss. Although creep effect can be eliminated by the closed-loop control approach, hysteresis effects need to be compensated and alleviated by hysteresis compensators. For the purpose of dealing with the estimation errors, unmodeled vibration, and disturbances, a sliding mode control with perturbation estimation (SMCPE) method is adopted to enhance the performance and robustness of the system. In order to validate the feasibility and performance of the proposed method, experimental studies are carried out, and the results show that the proposed controller performs better than a proportional-integral-derivative (PID) controller at 1 and 2 Hz, reducing error to 1.2% and 1.4%, respectively. Full article
(This article belongs to the Section Micro-/Nano-system and Technology)
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Open AccessArticle Micromachined Planar Supercapacitor with Interdigital Buckypaper Electrodes
Micromachines 2018, 9(5), 242; https://doi.org/10.3390/mi9050242
Received: 25 April 2018 / Revised: 11 May 2018 / Accepted: 12 May 2018 / Published: 16 May 2018
PDF Full-text (3429 KB) | HTML Full-text | XML Full-text
Abstract
In this work, a flexible micro-supercapacitor with interdigital planar buckypaper electrodes is presented. A simple fabrication process involving vacuum filtration method and SU-8 molding techniques is proposed to fabricate in-plane interdigital buckypaper electrodes on a membrane filter substrate. The proposed process exhibits excellent
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In this work, a flexible micro-supercapacitor with interdigital planar buckypaper electrodes is presented. A simple fabrication process involving vacuum filtration method and SU-8 molding techniques is proposed to fabricate in-plane interdigital buckypaper electrodes on a membrane filter substrate. The proposed process exhibits excellent flexibility for future integration of the micro-supercapacitors (micro-SC) with other electronic components. The device’s maximum specific capacitance measured using cyclic voltammetry was 107.27 mF/cm2 at a scan rate of 20 mV/s. The electrochemical stability was investigated by measuring the performance of charge-discharge at different discharge rates. Devices with different buckypaper electrode thicknesses were also fabricated and measured. The specific capacitance of the proposed device increased linearly with the buckypaper electrode thickness. The measured leakage current was approximately 9.95 µA after 3600 s. The device exhibited high cycle stability, with 96.59% specific capacitance retention after 1000 cycles. A Nyquist plot of the micro-SC was also obtained by measuring the impedances with frequencies from 1 Hz to 50 kHz; it indicated that the equivalent series resistance value was approximately 18 Ω. Full article
(This article belongs to the Special Issue Atomic Scale Materials for Electronic and Photonic Devices)
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Open AccessArticle Energy Harvesting Combat Boot for Satellite Positioning
Micromachines 2018, 9(5), 244; https://doi.org/10.3390/mi9050244
Received: 3 April 2018 / Revised: 7 May 2018 / Accepted: 11 May 2018 / Published: 17 May 2018
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Abstract
Most portable electronic devices are power-limited by battery capacity, and recharging these batteries often interrupts the user’s experience with the device. The product presented in this paper provides an alternative to powering portables by converting regular human walking motion to electricity. The device
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Most portable electronic devices are power-limited by battery capacity, and recharging these batteries often interrupts the user’s experience with the device. The product presented in this paper provides an alternative to powering portables by converting regular human walking motion to electricity. The device harvests electric power using air bulbs, distributed in the sole of a shoe to drive a series of micro-turbines connected to small DC motors. The number and position of air bulbs is optimized to harvest the maximum airflow from each foot-strike. The system is designed to continuously drive the micro-turbines by utilizing both outflow and inflow from the air bulbs. A prototype combat boot was fitted on the right foot of a 75 kg test subject, and produced an average continuous power on the order of 10 s of mW over a 22 Ω load during walking at 3.0 mph. This combat boot provides enough electric power to a passive GPS tracker that periodically relays geographical coordinates to a smartphone via satellite without battery replacement. Full article
(This article belongs to the Special Issue Microsystems for Power, Energy, and Actuation)
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Open AccessArticle Improved Morphological Filter Based on Variational Mode Decomposition for MEMS Gyroscope De-Noising
Micromachines 2018, 9(5), 246; https://doi.org/10.3390/mi9050246
Received: 19 April 2018 / Revised: 13 May 2018 / Accepted: 15 May 2018 / Published: 17 May 2018
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Abstract
An adaptive multi-scale method based on the combination generalized morphological filter (CGMF) is presented for de-noising of the output signal from a MEMS gyroscope. A variational mode decomposition is employed to decompose the original signal into multi-scale modes. After choosing a length selection
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An adaptive multi-scale method based on the combination generalized morphological filter (CGMF) is presented for de-noising of the output signal from a MEMS gyroscope. A variational mode decomposition is employed to decompose the original signal into multi-scale modes. After choosing a length selection for the structure element (SE), the adaptive multi-scale CGMF method reduces the noise corresponding to the different modes, after which a reconstruction of the de-noised signal is obtained. From an analysis of the effect of de-noising, the main advantages of the present method are that it: (i) effectively overcomes deficiencies arising from data deviation compared with conventional morphological filters (MFs); (ii) effectively targets the different components of noise and provides efficacy in de-noising, not only primarily eliminating noise but also smoothing the waveform; and (iii) solves the problem of SE-length selection for a MF and produces feasible formulae of indicators such as the power spectral entropy and root mean square error for mode evaluations. Compared with the other current signal processing methods, the method proposed owns a simpler construction with a reasonable complexity, and it can offer better noise suppression effect. Experiments demonstrate the applicability and feasibility of the de-noising algorithm. Full article
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Open AccessArticle Micro Droplet Formation towards Continuous Nanoparticles Synthesis
Micromachines 2018, 9(5), 248; https://doi.org/10.3390/mi9050248 (registering DOI)
Received: 26 April 2018 / Revised: 12 May 2018 / Accepted: 15 May 2018 / Published: 18 May 2018
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Abstract
In this paper, micro droplets are generated in a microfluidic focusing contactor and then they move sequentially in a free-flowing mode (no wall contact). For this purpose, two different micro-flow glass devices (hydrophobic and hydrophilic) were used. During the study, the influence of
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In this paper, micro droplets are generated in a microfluidic focusing contactor and then they move sequentially in a free-flowing mode (no wall contact). For this purpose, two different micro-flow glass devices (hydrophobic and hydrophilic) were used. During the study, the influence of the flow rate of the water phase and the oil phase on the droplet size and size distribution was investigated. Moreover, the influence of the oil phase viscosity on the droplet size was analyzed. It was found that the size and size distribution of the droplets can be controlled simply by the aqueous phase flow rate. Additionally, 2D simulations to determine the droplet size were performed and compared with the experiment. Full article
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Open AccessArticle Motion Constraints and Vanishing Point Aided Land Vehicle Navigation
Micromachines 2018, 9(5), 249; https://doi.org/10.3390/mi9050249 (registering DOI)
Received: 15 April 2018 / Revised: 12 May 2018 / Accepted: 17 May 2018 / Published: 20 May 2018
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Abstract
In the typical Inertial Navigation System (INS)/ Global Navigation Satellite System (GNSS) setup for ground vehicle navigation, measures should be taken to maintain the performance when there are GNSS signal outages. Usually, aiding sensors are utilized to reduce the INS drift. A full
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In the typical Inertial Navigation System (INS)/ Global Navigation Satellite System (GNSS) setup for ground vehicle navigation, measures should be taken to maintain the performance when there are GNSS signal outages. Usually, aiding sensors are utilized to reduce the INS drift. A full motion constraint model is developed allowing the online calibration of INS frame with respect to (w.r.t) the motion frame. To obtain better heading and lateral positioning performance, we propose to use of vanishing point (VP) observations of parallel lane markings from a single forward-looking camera to aid the INS. In the VP module, the relative attitude of the camera w.r.t the road frame is derived from the VP coordinates. The state-space model is developed with augmented vertical attitude error state. Finally, the VP module is added to a modified motion constrains module in the Extended Kalman filter (EKF) framework. Simulations and real-world experiments have shown the validity of VP-based method and improved heading and cross-track position accuracy compared with the solution without VP. The proposed method can work jointly with conventional visual odometry to aid INS for better accuracy and robustness. Full article
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Review

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Open AccessReview Integrated Electromechanical Transduction Schemes for Polymer MEMS Sensors
Micromachines 2018, 9(5), 197; https://doi.org/10.3390/mi9050197
Received: 9 February 2018 / Revised: 13 April 2018 / Accepted: 16 April 2018 / Published: 24 April 2018
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Abstract
Polymer Micro ElectroMechanical Systems (MEMS) have the potential to constitute a powerful alternative to silicon-based MEMS devices for sensing applications. Although the use of commercial photoresists as structural material in polymer MEMS has been widely reported, the integration of functional polymer materials as
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Polymer Micro ElectroMechanical Systems (MEMS) have the potential to constitute a powerful alternative to silicon-based MEMS devices for sensing applications. Although the use of commercial photoresists as structural material in polymer MEMS has been widely reported, the integration of functional polymer materials as electromechanical transducers has not yet received the same amount of interest. In this context, we report on the design and fabrication of different electromechanical schemes based on polymeric materials ensuring different transduction functions. Piezoresistive transduction made of carbon nanotube-based nanocomposites with a gauge factor of 200 was embedded within U-shaped polymeric cantilevers operating either in static or dynamic modes. Flexible resonators with integrated piezoelectric transduction were also realized and used as efficient viscosity sensors. Finally, piezoelectric-based organic field effect transistor (OFET) electromechanical transduction exhibiting a record sensitivity of over 600 was integrated into polymer cantilevers and used as highly sensitive strain and humidity sensors. Such advances in integrated electromechanical transduction schemes should favor the development of novel all-polymer MEMS devices for flexible and wearable applications in the future. Full article
(This article belongs to the Special Issue Polymer Based MEMS and Microfabrication)
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Open AccessReview Particle Manipulation by Optical Forces in Microfluidic Devices
Micromachines 2018, 9(5), 200; https://doi.org/10.3390/mi9050200
Received: 29 March 2018 / Revised: 18 April 2018 / Accepted: 20 April 2018 / Published: 24 April 2018
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Abstract
Since the pioneering work of Ashkin and coworkers, back in 1970, optical manipulation gained an increasing interest among the scientific community. Indeed, the advantages and the possibilities of this technique are unsubtle, allowing for the manipulation of small particles with a broad spectrum
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Since the pioneering work of Ashkin and coworkers, back in 1970, optical manipulation gained an increasing interest among the scientific community. Indeed, the advantages and the possibilities of this technique are unsubtle, allowing for the manipulation of small particles with a broad spectrum of dimensions (nanometers to micrometers size), with no physical contact and without affecting the sample viability. Thus, optical manipulation rapidly found a large set of applications in different fields, such as cell biology, biophysics, and genetics. Moreover, large benefits followed the combination of optical manipulation and microfluidic channels, adding to optical manipulation the advantages of microfluidics, such as a continuous sample replacement and therefore high throughput and automatic sample processing. In this work, we will discuss the state of the art of these optofluidic devices, where optical manipulation is used in combination with microfluidic devices. We will distinguish on the optical method implemented and three main categories will be presented and explored: (i) a single highly focused beam used to manipulate the sample, (ii) one or more diverging beams imping on the sample, or (iii) evanescent wave based manipulation. Full article
(This article belongs to the Special Issue Optical Manipulation of Cells: Strategies and Devices)
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Open AccessReview Recent Microdevice-Based Aptamer Sensors
Micromachines 2018, 9(5), 202; https://doi.org/10.3390/mi9050202
Received: 7 April 2018 / Revised: 19 April 2018 / Accepted: 21 April 2018 / Published: 25 April 2018
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Abstract
Since the systematic evolution of ligands by exponential enrichment (SELEX) method was developed, aptamers have made significant contributions as bio-recognition sensors. Microdevice systems allow for low reagent consumption, high-throughput of samples, and disposability. Due to these advantages, there has been an increasing demand
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Since the systematic evolution of ligands by exponential enrichment (SELEX) method was developed, aptamers have made significant contributions as bio-recognition sensors. Microdevice systems allow for low reagent consumption, high-throughput of samples, and disposability. Due to these advantages, there has been an increasing demand to develop microfluidic-based aptasensors for analytical technique applications. This review introduces the principal concepts of aptasensors and then presents some advanced applications of microdevice-based aptasensors on several platforms. Highly sensitive detection techniques, such as electrochemical and optical detection, have been integrated into lab-on-a-chip devices and researchers have moved towards the goal of establishing point-of-care diagnoses for target analyses. Full article
(This article belongs to the Special Issue State-of-the-Art Lab-on-a-Chip Technology in Japan)
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Open AccessReview Applications of Laser Welding in Dentistry: A State-of-the-Art Review
Micromachines 2018, 9(5), 209; https://doi.org/10.3390/mi9050209
Received: 28 March 2018 / Revised: 23 April 2018 / Accepted: 25 April 2018 / Published: 28 April 2018
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Abstract
The dental industry without lasers is inconceivable right now. This captivating technology has outlasted other possible alternative technologies applied in dentistry in the past due to its precision, accuracy, minimal invasive effect as well as faster operating time. Other alternatives such as soldering,
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The dental industry without lasers is inconceivable right now. This captivating technology has outlasted other possible alternative technologies applied in dentistry in the past due to its precision, accuracy, minimal invasive effect as well as faster operating time. Other alternatives such as soldering, resistance (spot) welding, plasma (torch) welding, and single pulse tungsten inert gas welding have their pros and cons; nevertheless, laser welding remains the most suitable option so far for dental application. This paper attempts to give an insight into the laser principle and types of lasers used for dental purposes, types of dental alloys used by the dentist, and effect of laser parameters on prosthesis/implants. It is apparent from the literature review that laser assisted dental welding will continue to grow and will become an unparalleled technology for dental arena. Full article
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Open AccessReview Single-Molecule Tethered Particle Motion: Stepwise Analyses of Site-Specific DNA Recombination
Micromachines 2018, 9(5), 216; https://doi.org/10.3390/mi9050216
Received: 15 March 2018 / Revised: 25 April 2018 / Accepted: 28 April 2018 / Published: 3 May 2018
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Abstract
Tethered particle motion/microscopy (TPM) is a biophysical tool used to analyze changes in the effective length of a polymer, tethered at one end, under changing conditions. The tether length is measured indirectly by recording the Brownian motion amplitude of a bead attached to
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Tethered particle motion/microscopy (TPM) is a biophysical tool used to analyze changes in the effective length of a polymer, tethered at one end, under changing conditions. The tether length is measured indirectly by recording the Brownian motion amplitude of a bead attached to the other end. In the biological realm, DNA, whose interactions with proteins are often accompanied by apparent or real changes in length, has almost exclusively been the subject of TPM studies. TPM has been employed to study DNA bending, looping and wrapping, DNA compaction, high-order DNA–protein assembly, and protein translocation along DNA. Our TPM analyses have focused on tyrosine and serine site-specific recombinases. Their pre-chemical interactions with DNA cause reversible changes in DNA length, detectable by TPM. The chemical steps of recombination, depending on the substrate and the type of recombinase, may result in a permanent length change. Single molecule TPM time traces provide thermodynamic and kinetic information on each step of the recombination pathway. They reveal how mechanistically related recombinases may differ in their early commitment to recombination, reversibility of individual steps, and in the rate-limiting step of the reaction. They shed light on the pre-chemical roles of catalytic residues, and on the mechanisms by which accessory proteins regulate recombination directionality. Full article
(This article belongs to the Special Issue Micro Technologies for Single Molecule Manipulation and Detection)
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Open AccessReview Controlled Mechanical Motions of Microparticles in Optical Tweezers
Micromachines 2018, 9(5), 232; https://doi.org/10.3390/mi9050232
Received: 15 April 2018 / Revised: 5 May 2018 / Accepted: 9 May 2018 / Published: 12 May 2018
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Abstract
Optical tweezers, formed by a highly focused laser beam, have intriguing applications in biology and physics. Inspired by molecular rotors, numerous optical beams and artificial particles have been proposed to build optical tweezers trapping microparticles, and extensive experiences have been learned towards constructing
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Optical tweezers, formed by a highly focused laser beam, have intriguing applications in biology and physics. Inspired by molecular rotors, numerous optical beams and artificial particles have been proposed to build optical tweezers trapping microparticles, and extensive experiences have been learned towards constructing precise, stable, flexible and controllable micromachines. The mechanism of interaction between particles and localized light fields is quite different for different types of particles, such as metal particles, dielectric particles and Janus particles. In this article, we present a comprehensive overview of the latest development on the fundamental and application of optical trapping. The emphasis is placed on controllable mechanical motions of particles, including rotation, translation and their mutual coupling under the optical forces and torques created by a wide variety of optical tweezers operating on different particles. Finally, we conclude by proposing promising directions for future research. Full article
(This article belongs to the Special Issue Optical Manipulation of Cells: Strategies and Devices)
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Open AccessReview Nanostructure-Enabled and Macromolecule-Grafted Surfaces for Biomedical Applications
Micromachines 2018, 9(5), 243; https://doi.org/10.3390/mi9050243
Received: 15 April 2018 / Revised: 11 May 2018 / Accepted: 16 May 2018 / Published: 17 May 2018
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Abstract
Advances in nanotechnology and nanomaterials have enabled the development of functional biomaterials with surface properties that reduce the rate of the device rejection in injectable and implantable biomaterials. In addition, the surface of biomaterials can be functionalized with macromolecules for stimuli-responsive purposes to
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Advances in nanotechnology and nanomaterials have enabled the development of functional biomaterials with surface properties that reduce the rate of the device rejection in injectable and implantable biomaterials. In addition, the surface of biomaterials can be functionalized with macromolecules for stimuli-responsive purposes to improve the efficacy and effectiveness in drug release applications. Furthermore, macromolecule-grafted surfaces exhibit a hierarchical nanostructure that mimics nanotextured surfaces for the promotion of cellular responses in tissue engineering. Owing to these unique properties, this review focuses on the grafting of macromolecules on the surfaces of various biomaterials (e.g., films, fibers, hydrogels, and etc.) to create nanostructure-enabled and macromolecule-grafted surfaces for biomedical applications, such as thrombosis prevention and wound healing. The macromolecule-modified surfaces can be treated as a functional device that either passively inhibits adverse effects from injectable and implantable devices or actively delivers biological agents that are locally based on proper stimulation. In this review, several methods are discussed to enable the surface of biomaterials to be used for further grafting of macromolecules. In addition, we review surface-modified films (coatings) and fibers with respect to several biomedical applications. Our review provides a scientific update on the current achievements and future trends of nanostructure-enabled and macromolecule-grafted surfaces in biomedical applications. Full article
(This article belongs to the Special Issue Biomedical Applications of Nanotechnology and Nanomaterials)
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Open AccessReview Manipulation of Biological Cells Using a Robot-Aided Optical Tweezers System
Micromachines 2018, 9(5), 245; https://doi.org/10.3390/mi9050245
Received: 16 April 2018 / Revised: 15 May 2018 / Accepted: 15 May 2018 / Published: 17 May 2018
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Abstract
This article reviews the autonomous manipulation strategies of biological cells utilizing optical tweezers, mainly including optical direct and indirect manipulation strategies. The typical and latest achievements in the optical manipulation of cells are presented, and the existing challenges for autonomous optical manipulation of
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This article reviews the autonomous manipulation strategies of biological cells utilizing optical tweezers, mainly including optical direct and indirect manipulation strategies. The typical and latest achievements in the optical manipulation of cells are presented, and the existing challenges for autonomous optical manipulation of biological cells are also introduced. Moreover, the integrations of optical tweezers with other manipulation tools are presented, which broadens the applications of optical tweezers in the biomedical manipulation areas and will also foster new developments in cell-based physiology and pathology studies, such as cell migration, single cell surgery, and preimplantation genetic diagnosis (PGD). Full article
(This article belongs to the Special Issue Optical Manipulation of Cells: Strategies and Devices)
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Open AccessReview Fluorescent Nanodiamond Applications for Cellular Process Sensing and Cell Tracking
Micromachines 2018, 9(5), 247; https://doi.org/10.3390/mi9050247 (registering DOI)
Received: 30 April 2018 / Revised: 14 May 2018 / Accepted: 15 May 2018 / Published: 18 May 2018
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Abstract
Diamond nanocrystals smaller than 100 nm (nanodiamonds) are now recognized to be highly biocompatible. They can be made fluorescent with perfect photostability by creating nitrogen-vacancy (NV) color centers in the diamond lattice. The resulting fluorescent nanodiamonds (FND) have been used since the late
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Diamond nanocrystals smaller than 100 nm (nanodiamonds) are now recognized to be highly biocompatible. They can be made fluorescent with perfect photostability by creating nitrogen-vacancy (NV) color centers in the diamond lattice. The resulting fluorescent nanodiamonds (FND) have been used since the late 2000s as fluorescent probes for short- or long-term analysis. FND can be used both at the subcellular scale and the single cell scale. Their limited sub-diffraction size allows them to track intracellular processes with high spatio-temporal resolution and high contrast from the surrounding environment. FND can also track the fate of therapeutic compounds or whole cells in the organs of an organism. This review presents examples of FND applications (1) for intra and intercellular molecular processes sensing, also introducing the different potential biosensing applications based on the optically detectable electron spin resonance of NV centers; and (2) for tracking, firstly, FND themselves to determine their biodistribution, and secondly, using FND as cell tracking probes for diagnosis or follow-up purposes in oncology and regenerative medicine. Full article
(This article belongs to the Special Issue Color Centers in Diamond: Fabrication, Devices and Applications)
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Other

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Open AccessPerspective Liquid-Metal Enabled Droplet Circuits
Micromachines 2018, 9(5), 218; https://doi.org/10.3390/mi9050218
Received: 13 April 2018 / Revised: 29 April 2018 / Accepted: 2 May 2018 / Published: 5 May 2018
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Abstract
Conventional electrical circuits are generally rigid in their components and working styles, which are not flexible and stretchable. As an alternative, liquid-metal-based soft electronics offer important opportunities for innovation in modern bioelectronics and electrical engineering. However, their operation in wet environments such as
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Conventional electrical circuits are generally rigid in their components and working styles, which are not flexible and stretchable. As an alternative, liquid-metal-based soft electronics offer important opportunities for innovation in modern bioelectronics and electrical engineering. However, their operation in wet environments such as aqueous solution, biological tissue or allied subjects still encounters many technical challenges. Here, we propose a new conceptual electrical circuit, termed as droplet circuit, to fulfill the special needs described above. Such unconventional circuits are immersed in a solution and composed of liquid metal droplets, conductive ions or wires, such as carbon nanotubes. With specifically-designed topological or directional structures/patterns, the liquid-metal droplets composing the circuit can be discrete and disconnected from each other, while achieving the function of electron transport through conductive routes or the quantum tunneling effect. The conductive wires serve as electron transfer stations when the distance between two separate liquid-metal droplets is far beyond that which quantum tunneling effects can support. The unique advantage of the current droplet circuit lies in the fact that it allows parallel electron transport, high flexibility, self-healing, regulation and multi-point connectivity without needing to worry about the circuit break. This would extend the category of classical electrical circuits into newly emerging areas like realizing room temperature quantum computing, making brain-like intelligence or nerve–machine interface electronics, etc. The mechanisms and potential scientific issues of the droplet circuits are interpreted and future prospects in this direction are outlined. Full article
(This article belongs to the Special Issue Flexible Electronics: Fabrication and Ubiquitous Integration)
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Open AccessLetter Hard-Baked Photoresist as a Sacrificial Layer for Sub-180 °C Surface Micromachining Processes
Micromachines 2018, 9(5), 231; https://doi.org/10.3390/mi9050231
Received: 5 April 2018 / Revised: 30 April 2018 / Accepted: 4 May 2018 / Published: 11 May 2018
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Abstract
This letter proposes a method for utilizing a positive photoresist, Shipley 1805, as a sacrificial layer for sub-180 °C fabrication process flows. In the proposed process, the sacrificial layer is etched at the end to release the structures using a relatively fast wet-etching
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This letter proposes a method for utilizing a positive photoresist, Shipley 1805, as a sacrificial layer for sub-180 °C fabrication process flows. In the proposed process, the sacrificial layer is etched at the end to release the structures using a relatively fast wet-etching technique employing resist remover and a critical point dryer (CPD). This technique allows high etching selectivity over a large number of materials, including silicon-based structural materials such as silicon-carbide, metals such as titanium and aluminum, and cured polymers. This selectivity, as well as the low processing thermal budget, introduces more flexibility in material selection for monolithic integration above complementary metal oxide semiconductor (CMOS) as well as flexible substrates. Full article
(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)
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