Micromachines

28 pages, 5806 KB

Open AccessFeature PaperEditor’s ChoiceReview

Optical-Trapping Laser Techniques for Characterizing Airborne Aerosol Particles and Its Application in Chemical Aerosol Study

by Aimable Kalume, Chuji Wang and Yong-Le Pan

Micromachines 2021, 12(4), 466; https://doi.org/10.3390/mi12040466 - 20 Apr 2021

Cited by 14 | Viewed by 6992

Abstract

We present a broad assessment on the studies of optically-trapped single airborne aerosol particles, particularly chemical aerosol particles, using laser technologies. To date, extensive works have been conducted on ensembles of aerosols as well as on their analogous bulk samples, and a decent [...] Read more.

We present a broad assessment on the studies of optically-trapped single airborne aerosol particles, particularly chemical aerosol particles, using laser technologies. To date, extensive works have been conducted on ensembles of aerosols as well as on their analogous bulk samples, and a decent general description of airborne particles has been drawn and accepted. However, substantial discrepancies between observed and expected aerosols behavior have been reported. To fill this gap, single-particle investigation has proved to be a unique intersection leading to a clear representation of microproperties and size-dependent comportment affecting the overall aerosol behavior, under various environmental conditions. In order to achieve this objective, optical-trapping technologies allow holding and manipulating a single aerosol particle, while offering significant advantages such as contactless handling, free from sample collection and preparation, prevention of contamination, versatility to any type of aerosol, and flexibility to accommodation of various analytical systems. We review spectroscopic methods that are based on the light-particle interaction, including elastic light scattering, light absorption (cavity ring-down and photoacoustic spectroscopies), inelastic light scattering and emission (Raman, laser-induced breakdown, and laser-induced fluorescence spectroscopies), and digital holography. Laser technologies offer several benefits such as high speed, high selectivity, high accuracy, and the ability to perform in real-time, in situ. This review, in particular, discusses each method, highlights the advantages and limitations, early breakthroughs, and recent progresses that have contributed to a better understanding of single particles and particle ensembles in general. Full article

(This article belongs to the Special Issue Optical Trapping and Manipulation: From Fundamentals to Applications, Volume II)

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29 pages, 2944 KB

Open AccessReview

Tethered and Untethered 3D Microactuators Fabricated by Two-Photon Polymerization: A Review

by Zhaoxin Lao, Neng Xia, Shijie Wang, Tiantian Xu, Xinyu Wu and Li Zhang

Micromachines 2021, 12(4), 465; https://doi.org/10.3390/mi12040465 - 20 Apr 2021

Cited by 50 | Viewed by 8029

Abstract

Microactuators, which can transform external stimuli into mechanical motion at microscale, have attracted extensive attention because they can be used to construct microelectromechanical systems (MEMS) and/or microrobots, resulting in extensive applications in a large number of fields such as noninvasive surgery, targeted delivery, [...] Read more.

Microactuators, which can transform external stimuli into mechanical motion at microscale, have attracted extensive attention because they can be used to construct microelectromechanical systems (MEMS) and/or microrobots, resulting in extensive applications in a large number of fields such as noninvasive surgery, targeted delivery, and biomedical machines. In contrast to classical 2D MEMS devices, 3D microactuators provide a new platform for the research of stimuli-responsive functional devices. However, traditional planar processing techniques based on photolithography are inadequate in the construction of 3D microstructures. To solve this issue, researchers have proposed many strategies, among which 3D laser printing is becoming a prospective technique to create smart devices at the microscale because of its versatility, adjustability, and flexibility. Here, we review the recent progress in stimulus-responsive 3D microactuators fabricated with 3D laser printing depending on different stimuli. Then, an outlook of the design, fabrication, control, and applications of 3D laser-printed microactuators is propounded with the goal of providing a reference for related research. Full article

(This article belongs to the Special Issue Micro/Nano Robotics: A Theme Issue in Honor of Professor Toshio Fukuda)

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26 pages, 17295 KB

Open AccessArticle

Investigation on GaN HEMTs Based Three-Phase STATCOM with Hybrid Control Scheme

by Chao-Tsung Ma and Zhen-Huang Gu

Micromachines 2021, 12(4), 464; https://doi.org/10.3390/mi12040464 - 20 Apr 2021

Cited by 1 | Viewed by 2837

Abstract

The modern trend of decarbonization has encouraged intensive research on renewable energy (RE)-based distributed power generation (DG) and smart grid, where advanced electronic power interfaces are necessary for connecting the generator with power grids and various electrical systems. On the other hand, modern [...] Read more.

The modern trend of decarbonization has encouraged intensive research on renewable energy (RE)-based distributed power generation (DG) and smart grid, where advanced electronic power interfaces are necessary for connecting the generator with power grids and various electrical systems. On the other hand, modern technologies such as Industry 4.0 and electrical vehicles (EV) have higher requirements for power converters than that of conventional applications. Consequently, the enhancement of power interfaces will play an important role in the future power generation and distribution systems as well as various industrial applications. It has been discovered that wide-bandgap (WBG) switching devices such as gallium nitride (GaN) high electron mobility transistors (HEMTs) and silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) offer considerable potential for outperforming conventional silicon (Si) switching devices in terms of breakdown voltage, high temperature capability, switching speed, and conduction losses. This paper investigates the performance of a 2kVA three-phase static synchronous compensator (STATCOM) based on a GaN HEMTs-based voltage-source inverter (VSI) and a neural network-based hybrid control scheme. The proportional-integral (PI) controllers along with a radial basis function neural network (RBFNN) controller for fast reactive power control are designed in synchronous reference frame (SRF). Both simulation and hardware implementation are conducted. Results confirm that the proposed RBFNN assisted hybrid control scheme yields excellent dynamic performance in terms of various reactive power tracking control of the GaN HEMTs-based three-phase STATCOM system. Full article

(This article belongs to the Special Issue GaN-Based Semiconductor Devices)

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13 pages, 3100 KB

Open AccessArticle

Studying the Bulk and Contour Ice Nucleation of Water Droplets via Quartz Crystal Microbalances

by Karekin Dikran Esmeryan and Nikolay Ivanov Stoimenov

Micromachines 2021, 12(4), 463; https://doi.org/10.3390/mi12040463 - 20 Apr 2021

Cited by 4 | Viewed by 2945

Abstract

Due to the stochastic and time-dependent character of the ice embryo formation and growth (i.e., a process that can be analyzed statistically, but cannot be predicted precisely), the heterogeneous ice nucleation on atmospheric aerosols or macroscopic solid surfaces is still shrouded in mystery, [...] Read more.

Due to the stochastic and time-dependent character of the ice embryo formation and growth (i.e., a process that can be analyzed statistically, but cannot be predicted precisely), the heterogeneous ice nucleation on atmospheric aerosols or macroscopic solid surfaces is still shrouded in mystery, regardless of the extremely active research and exponential progress within this scientific field. For instance, whether the icing appears from outside-in or inside-out is a subject of intense controversy, with practicability in designing passive icephobic coatings or improving the effectiveness of the cryopreservation technologies. Here, we propose an artful technique for quantitative analysis of the different modes of water freezing using super-nonwettable soot-coated quartz crystal microbalances (QCMs). To achieve this goal, a set of 5 MHz QCMs are loaded one at a time with a 50 μL droplet, whose bulk or contour solidification is detected in real-time. The obtained experimental results show that our sensor devices recognize explicitly if the ice nuclei form predominantly at the liquid–solid interface or spread along the droplet’s entire outer shell by triggering individual reproducible responses in terms of the direction of signal evolution in time. Our results may serve as a foundation for the future incorporation of QCM devices in different freezing assays, where gaining information about the ice adhesion forces and ice layer’s thickness is mandatory. Full article

(This article belongs to the Section A：Physics)

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20 pages, 16028 KB

Open AccessArticle

An Investigation of Flow Patterns and Mixing Characteristics in a Cross-Shaped Micromixer within the Laminar Regime

by Shuai Yuan, Bingyan Jiang, Tao Peng, Qiang Li and Mingyong Zhou

Micromachines 2021, 12(4), 462; https://doi.org/10.3390/mi12040462 - 20 Apr 2021

Cited by 22 | Viewed by 4219

Abstract

A fast mixing is critical for subsequent practical development of microfluidic devices, which are often used for assays in the detection of reagents and samples. The present work sets up computational fluid dynamics simulations to explore the flow characteristic and mixing mechanism of [...] Read more.

A fast mixing is critical for subsequent practical development of microfluidic devices, which are often used for assays in the detection of reagents and samples. The present work sets up computational fluid dynamics simulations to explore the flow characteristic and mixing mechanism of fluids in cross-shaped mixers within the laminar regime. First, the effects of increasing an operating parameter on local mixing quality along the microchannels are investigated. It is found that sufficient diffusion cannot occur even though the concentration gradient is large at a high Reynolds number. Meanwhile, a method for calculating local mixing efficiency is also characterized. The mixing efficiency varies exponentially with the flow distance. Second, in order to optimize the cross-shaped mixer, the effects of design parameters, namely aspect ratio, mixing angle and blockage, on mixing quality are captured and the visualization of velocity and concentration distribution are demonstrated. The results show that the aspect ratio and the blockage play an important role in accelerating the mixing process. They can improve the mixing efficiency by increasing the mass transfer area and enhancing the chaotic advection, respectively. In contrast, the inflow angle that affects dispersion length is not an effective parameter. Besides, the surface roughness, which makes the disturbance of fluid flow by roughness more obvious, is considered. Three types of rough elements bring benefits for enhancing mixing quality due to the convection induced by the lateral velocity. Full article

(This article belongs to the Special Issue Micro-Reaction Engineering)

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13 pages, 3118 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Switchable Transducers in GaN MEMS Resonators: Performance Comparison and Analysis

by Imtiaz Ahmed and Dana Weinstein

Micromachines 2021, 12(4), 461; https://doi.org/10.3390/mi12040461 - 19 Apr 2021

Cited by 4 | Viewed by 3903

Abstract

This work presents a comprehensive comparison of switchable electromechanical transducers in an AlN/GaN heterostructure toward the goal of reconfigurable RF building blocks in next-generation ad hoc radios. The transducers’ inherent switching was achieved by depleting a 2D electron gas (2DEG) channel, allowing an [...] Read more.

This work presents a comprehensive comparison of switchable electromechanical transducers in an AlN/GaN heterostructure toward the goal of reconfigurable RF building blocks in next-generation ad hoc radios. The transducers’ inherent switching was achieved by depleting a 2D electron gas (2DEG) channel, allowing an RF signal launched by interdigital transducers (IDTs) to effectively excite the symmetric (S_o) Lamb mode of vibration in the piezoelectric membrane. Different configurations for applying DC bias to the channel for electromechanical actuation in the piezoelectric are discussed. Complete suppression of the mechanical mode was achieved with the transducers in the OFF state. Equivalent circuit models were developed to extract parameters from measurements by fitting in both ON and OFF states. This is the first time that an extensive comparative study of the performance of different switchable transducers in their ON/OFF state is presented along with frequency scaling of the resonant mode. The switchable transducer with Ohmic IDTs and a Schottky control gate showed superior performance among the designs under consideration. Full article

(This article belongs to the Special Issue Nitrides and Carbides MEMS/NEMS)

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16 pages, 3159 KB

Open AccessArticle

An Investigation of the High-Frequency Ultrasonic Vibration-Assisted Cutting of Steel Optical Moulds

by Canbin Zhang, Chifai Cheung, Benjamin Bulla and Chenyang Zhao

Micromachines 2021, 12(4), 460; https://doi.org/10.3390/mi12040460 - 19 Apr 2021

Cited by 16 | Viewed by 3747

Abstract

Ultrasonic vibration-assisted cutting (UVAC) has been regarded as a promising technology to machine difficult-to-machine materials such as tungsten carbide, optical glass, and hardened steel in order to achieve superfinished surfaces. To increase vibration stability to achieve optical surface quality of a workpiece, a [...] Read more.

Ultrasonic vibration-assisted cutting (UVAC) has been regarded as a promising technology to machine difficult-to-machine materials such as tungsten carbide, optical glass, and hardened steel in order to achieve superfinished surfaces. To increase vibration stability to achieve optical surface quality of a workpiece, a high-frequency ultrasonic vibration-assisted cutting system with a vibration frequency of about 104 kHz is used to machine spherical optical steel moulds. A series of experiments are conducted to investigate the effect of machining parameters on the surface roughness of the workpiece including nominal cutting speed, feed rate, tool nose radius, vibration amplitude, and cutting geometry. This research takes into account the effects of the constantly changing contact point on the tool edge with the workpiece induced by the cutting geometry when machining a spherical steel mould. The surface morphology and surface roughness at different regions on the machined mould, with slope degrees (SDs) of 0°, 5°, 10°, and 15°, were measured and analysed. The experimental results show that the arithmetic roughness

S_{a}

of the workpiece increases gradually with increasing slope degree. By using optimised cutting parameters, a constant surface roughness

S_{a}

of 3 nm to 4 nm at different slope degrees was achieved by the applied high-frequency UVAC technique. This study provides guidance for ultra-precision machining of steel moulds with great variation in slope degree in the pursuit of optical quality on the whole surface. Full article

(This article belongs to the Special Issue Advances in Ultra-Precision Machining Technology and Applications)

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10 pages, 3810 KB

Open AccessArticle

CSRR-SICW High Sensitivity High Temperature Sensor Based on Si₃N₄ Ceramics

by Shujing Su, Ting Ren, Lili Zhang and Fujia Xu

Micromachines 2021, 12(4), 459; https://doi.org/10.3390/mi12040459 - 19 Apr 2021

Cited by 7 | Viewed by 2696

Abstract

A new type of wireless passive, high sensitivity, high temperature sensor was designed to meet the real-time temperature test in the harsh aero-engine environment. The sensor consists of a complementary split ring resonator and a substrate integrated circular waveguide (CSRR-SICW) structure and is [...] Read more.

A new type of wireless passive, high sensitivity, high temperature sensor was designed to meet the real-time temperature test in the harsh aero-engine environment. The sensor consists of a complementary split ring resonator and a substrate integrated circular waveguide (CSRR-SICW) structure and is based on high temperature resistant Si₃N₄ ceramic as the substrate material. Temperature is measured by real-time monitoring of the resonant frequency of the sensor. In addition, the ambient temperature affects the dielectric constant of the dielectric substrate, and the resonant frequency of the sensor is determined by the dielectric constant, so the function relationship between temperature and resonant frequency can be established. The experimental results show that the resonant frequency of the sensor decreases from 11.3392 GHz to 11.0648 GHz in the range of 50–1000 °C. The sensitivity is 123 kHz/°C and 417 kHz/°C at 50–450 °C and 450–1000 °C, respectively, and the average test sensitivity is 289 kHz/°C. Compared with previously reported high temperature sensors, the average test sensitivity is approximately doubled, and the test sensitivity at 450–1000 °C is approximately three times higher. Therefore, the proposed high sensitivity sensor has promising prospects for high temperature measurement. Full article

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7 pages, 2179 KB

Open AccessArticle

Rapid Fabrication of Large-Area Concave Microlens Array on ZnSe

by Fan Zhang, Qing Yang, Hao Bian, Xun Hou and Feng Chen

Micromachines 2021, 12(4), 458; https://doi.org/10.3390/mi12040458 - 19 Apr 2021

Cited by 9 | Viewed by 2734

Abstract

A rapid and single-step method for the fabrication of a zinc selenide (ZnSe) concave microlens array through the high-speed line-scanning of a femtosecond laser pulse is presented. Approximately 1.1 million microlenses, with minimized volume and high transparency at wavelengths between approximately 0.76–20 μm [...] Read more.

A rapid and single-step method for the fabrication of a zinc selenide (ZnSe) concave microlens array through the high-speed line-scanning of a femtosecond laser pulse is presented. Approximately 1.1 million microlenses, with minimized volume and high transparency at wavelengths between approximately 0.76–20 μm were fabricated within 36 min. More importantly, the size of the microlenses can be controlled by adjusting the laser power. Their high-quality infrared optical performance was also demonstrated. This method holds great promise for the development of ZnSe-based micro-optical devices. Full article

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15 pages, 2747 KB

Open AccessArticle

Multi-Directional Universal Energy Harvesting Ball

by Ryan G. Hall and Reza Rashidi

Micromachines 2021, 12(4), 457; https://doi.org/10.3390/mi12040457 - 19 Apr 2021

Cited by 4 | Viewed by 3960

Abstract

This paper discusses the development of a multi-directional, universal, electromagnetic energy harvester. The device is a ball consisting of two parts: a rigid spherical core with internal tubes, coils and magnets, and a flexible silicone-based shell holding a carrier fluid. The multi-directional aspect [...] Read more.

This paper discusses the development of a multi-directional, universal, electromagnetic energy harvester. The device is a ball consisting of two parts: a rigid spherical core with internal tubes, coils and magnets, and a flexible silicone-based shell holding a carrier fluid. The multi-directional aspect of the design comes from the device’s spherical shape. The harvester generates energy when subject to compressive force, by moving fluid through a tube, pushing a permanently magnetized ball through a coil wound around the tube. A combination of 3-D printed PLA plastic and molded silicone was used to produce a prototype. The energy harvester can be utilized in applications where there is an oscillating compression and it is not limited to certain applications due to its universal ball shape. It was tested at five different frequencies between 4–15 Hz on its four different outer sides producing electricity at a range of 17 to 44 mV. Full article

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9 pages, 3733 KB

Open AccessArticle

Evaporation of Ti/Cr/Ti Multilayer on Flexible Polyimide and Its Application for Strain Sensor

by Yu-Jen Hsiao, Ru-Li Lin, Hwi-Ming Wang and Cheng-Zhe Cai

Micromachines 2021, 12(4), 456; https://doi.org/10.3390/mi12040456 - 19 Apr 2021

Cited by 1 | Viewed by 3513

Abstract

A flexible Ti/Cr/Ti multilayer strain gauge have been successfully developed based on polyimide substrate. The pure Ti metal strain gauge have shown the hysteresis phenomenon at the relationship between resistance and strain during tensile test. The experimental results of multilayer strain gauge show [...] Read more.

A flexible Ti/Cr/Ti multilayer strain gauge have been successfully developed based on polyimide substrate. The pure Ti metal strain gauge have shown the hysteresis phenomenon at the relationship between resistance and strain during tensile test. The experimental results of multilayer strain gauge show that adding Cr interlayer can improve the recovery and stability of the sensing electrode. When the interlayer Cr thickness was increased from 0 to 70 nm, the resistance decreased from 27 to 8.8 kΩ. The gauge factor (GF) value also decreased from 4.24 to 2.31 with the increase in the thickness of Cr interlayer from 30 to 70 nm, and the hysteresis phenomenon disappeared gradually. The multilayer Ti/Cr/Ti film has feasible application for strain sensor. Full article

(This article belongs to the Special Issue Smart Sensors 2020)

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20 pages, 5288 KB

Open AccessArticle

Micro-Hole Generation by High-Energy Pulsed Bessel Beams in Different Transparent Materials

by Valeria V. Belloni, Monica Bollani, Shane M. Eaton, Paolo Di Trapani and Ottavia Jedrkiewicz

Micromachines 2021, 12(4), 455; https://doi.org/10.3390/mi12040455 - 18 Apr 2021

Cited by 11 | Viewed by 4188

Abstract

Micro-drilling transparent dielectric materials by using non-diffracting beams impinging orthogonally to the sample can be performed without scanning the beam position along the sample thickness. In this work, the laser micromachining process, based on the combination of picosecond pulsed Bessel beams with the [...] Read more.

Micro-drilling transparent dielectric materials by using non-diffracting beams impinging orthogonally to the sample can be performed without scanning the beam position along the sample thickness. In this work, the laser micromachining process, based on the combination of picosecond pulsed Bessel beams with the trepanning technique, is applied to different transparent materials. We show the possibility to create through-apertures with diameter on the order of tens of micrometers, on dielectric samples with different thermal and mechanical characteristics as well as different thicknesses ranging from two hundred to five hundred micrometers. Advantages and drawbacks of the application of this technique to different materials such as glass, polymer, or diamond are highlighted by analyzing the features, the morphology, and the aspect-ratio of the through-holes generated. Alternative Bessel beam drilling configurations, and the possibility of optimization of the quality of the aperture at the output sample/air interface is also discussed in the case of glass. Full article

(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)

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13 pages, 3971 KB

Open AccessArticle

Soft Tooling-Friendly Inductive Mold Heating—A Novel Concept

by Tobias Vieten, Davide Zanin, Andrea Knöller, Thomas Litwin, Wolfgang Eberhardt and André Zimmermann

Micromachines 2021, 12(4), 454; https://doi.org/10.3390/mi12040454 - 17 Apr 2021

Cited by 1 | Viewed by 2966

Abstract

In order to economize injection molded prototypes, additive manufacturing of, e.g., curable plastics based tools, can be employed, which is known as soft tooling. However, one disadvantage of such tools is that the variothermal process, which is needed to produce polymeric parts with [...] Read more.

In order to economize injection molded prototypes, additive manufacturing of, e.g., curable plastics based tools, can be employed, which is known as soft tooling. However, one disadvantage of such tools is that the variothermal process, which is needed to produce polymeric parts with small features, can lead to a shorter lifespan of the tooling due to its thermally impaired material properties. Here, a novel concept is proposed, which allows to locally heat the mold cavity via induction to circumvent the thermal impairment of the tooling material. The developed fabrication process consists of additive manufacturing of the tooling, PVD coating the mold cavity with an adhesion promoting layer and a seed layer, electroplating of a ferromagnetic metal layer, and finally patterning the metal layer via laser ablation to enhance the quality and efficiency of the energy transfer as well as the longevity by geometric measures. This process chain is investigated on 2D test specimens to find suitable fabrication parameters, backed by adhesion tests as well as environmental and induction tests. The results of these investigations serve as proof of concept and form the base for the investigation of such induction layers in actual soft tooling cavities. Full article

(This article belongs to the Special Issue Soft Tooling — Polymer Additive Manufacturing Applied to Injection Moulding Process Chains)

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13 pages, 5918 KB

Open AccessArticle

CPW-Fed Flexible Ultra-Wideband Antenna for IoT Applications

by Sharadindu Gopal Kirtania, Bachir Adham Younes, Abdul Rakib Hossain, Tutku Karacolak and Praveen Kumar Sekhar

Micromachines 2021, 12(4), 453; https://doi.org/10.3390/mi12040453 - 17 Apr 2021

Cited by 57 | Viewed by 6419

Abstract

In this article, an inkjet-printed circular-shaped monopole ultra-wideband (UWB) antenna with an inside-cut feed structure was implemented on a flexible polyethylene terephthalate (PET) substrate. The coplanar waveguide (CPW)-fed antenna was designed using ANSYS high-frequency structural simulator (HFSS), which operates at 3.04–10.70 GHz and [...] Read more.

In this article, an inkjet-printed circular-shaped monopole ultra-wideband (UWB) antenna with an inside-cut feed structure was implemented on a flexible polyethylene terephthalate (PET) substrate. The coplanar waveguide (CPW)-fed antenna was designed using ANSYS high-frequency structural simulator (HFSS), which operates at 3.04–10.70 GHz and 15.18–18 GHz (upper

K_{u}

band) with a return loss < −10 dB and a VSWR < 2. The antenna, with the dimensions of 47 mm × 25 mm × 0.135 mm, exhibited omnidirectional radiation characteristics over the entire impedance bandwidth, with an average peak gain of 3.94 dBi. The simulated antenna structure was in good agreement with the experiment’s measured results under flat and bending conditions, making it conducive for flexible and wearable Internet of things (IoT) applications. Full article

(This article belongs to the Special Issue Flexible Antennas and Devices)

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27 pages, 12612 KB

Open AccessArticle

Flexible Piezoresistive Tactile Sensor Based on Polymeric Nanocomposites with Grid-Type Microstructure

by Da-Huei Lee, Cheng-Hsin Chuang, Muhammad Omar Shaikh, Yong-Syuan Dai, Shao-Yu Wang, Zhi-Hong Wen, Chung-Kun Yen, Chien-Feng Liao and Cheng-Tang Pan

Micromachines 2021, 12(4), 452; https://doi.org/10.3390/mi12040452 - 16 Apr 2021

Cited by 29 | Viewed by 5456

Abstract

Piezoresistive tactile sensors made using nanocomposite polymeric materials have been shown to possess good flexibility, electrical performance, and sensitivity. However, the sensing performance, especially in the low-pressure range, can be significantly improved by enabling uniform dispersion of the filler material and utilization of [...] Read more.

Piezoresistive tactile sensors made using nanocomposite polymeric materials have been shown to possess good flexibility, electrical performance, and sensitivity. However, the sensing performance, especially in the low-pressure range, can be significantly improved by enabling uniform dispersion of the filler material and utilization of effective structural designs that improve the tactile sensing performance. In this study, a novel flexible piezoresistive tactile sensor with a grid-type microstructure was fabricated using polymer composites comprising multi-walled carbon nanotubes (MWCNTs) as the conductive filler and polydimethylsiloxane (PDMS) as the polymeric matrix. The research focused on improving the tactile sensor performance by enabling uniform dispersion of filler material and optimizing sensor design and structure. The doping weight ratio of MWCNTs in PDMS varied from 1 wt.% to 10 wt.% using the same grid structure-sensing layer (line width, line spacing, and thickness of 1 mm). The sensor with a 7 wt.% doping ratio had the most stable performance, with an observed sensitivity of 6.821 kPa⁻¹ in the lower pressure range of 10–20 kPa and 0.029 kPa⁻¹ in the saturation range of 30–200 kPa. Furthermore, the dimensions of the grid structure were optimized and the relationship between grid structure, sensitivity, and sensing range was correlated. The equation between pressure and resistance output was derived to validate the principle of piezoresistance. For the grid structure, dimensions with line width, line spacing, and thickness of 1, 1, and 0.5 mm were shown to have the most stable and improved response. The observed sensitivity was 0.2704 kPa⁻¹ in the lower pressure range of 50–130 kPa and 0.0968 kPa⁻¹ in the saturation range of 140–200 kPa. The piezoresistive response, which was mainly related to the quantum tunneling effect, can be optimized based on the dopant concentration and the grid microstructure. Furthermore, the tactile sensor showed a repeatable response, and the accuracy was not affected by temperature changes in the range of 10 to 40 °C and humidity variations from 50 to 80%. The maximum error fluctuation was about 5.6% with a response delay time of about 1.6 ms when cyclic loading tests were performed under a normal force of 1 N for 10,200 cycles. Consequently, the proposed tactile sensor shows practical feasibility for a wide range of wearable technologies and robotic applications such as touch detection and grasping. Full article

(This article belongs to the Special Issue Smart Sensors 2020)

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10 pages, 2468 KB

Open AccessArticle

High-Performance CVD Bilayer MoS₂ Radio Frequency Transistors and Gigahertz Mixers for Flexible Nanoelectronics

by Qingguo Gao, Chongfu Zhang, Kaiqiang Yang, Xinjian Pan, Zhi Zhang, Jianjun Yang, Zichuan Yi, Feng Chi and Liming Liu

Micromachines 2021, 12(4), 451; https://doi.org/10.3390/mi12040451 - 16 Apr 2021

Cited by 12 | Viewed by 4293

Abstract

Two-dimensional (2D) MoS₂ have attracted tremendous attention due to their potential applications in future flexible high-frequency electronics. Bilayer MoS₂ exhibits the advantages of carrier mobility when compared with monolayer mobility, thus making the former more suitable for use in future flexible [...] Read more.

Two-dimensional (2D) MoS₂ have attracted tremendous attention due to their potential applications in future flexible high-frequency electronics. Bilayer MoS₂ exhibits the advantages of carrier mobility when compared with monolayer mobility, thus making the former more suitable for use in future flexible high-frequency electronics. However, there are fewer systematical studies of chemical vapor deposition (CVD) bilayer MoS₂ radiofrequency (RF) transistors on flexible polyimide substrates. In this work, CVD bilayer MoS₂ RF transistors on flexible substrates with different gate lengths and gigahertz flexible frequency mixers were constructed and systematically studied. The extrinsic cutoff frequency (f_T) and maximum oscillation frequency (f_max) increased with reducing gate lengths. From transistors with a gate length of 0.3 μm, we demonstrated an extrinsic f_T of 4 GHz and f_max of 10 GHz. Furthermore, statistical analysis of 14 flexible MoS₂ RF transistors is presented in this work. The study of a flexible mixer demonstrates the dependence of conversion gain versus gate voltage, LO power and input signal frequency. These results present the potential of CVD bilayer MoS₂ for future flexible high-frequency electronics. Full article

(This article belongs to the Special Issue Electronic Devices and Circuits Based on 2D Materials)

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12 pages, 48261 KB

Open AccessArticle

The Influence of Blade Type and Feeding Force during Resin Bonded Dentin Specimen Preparation on the Microtensile Bond Strength Test

by Apinya Limvisitsakul, Suppason Thitthaweerat and Pisol Senawongse

Micromachines 2021, 12(4), 450; https://doi.org/10.3390/mi12040450 - 16 Apr 2021

Viewed by 2328

Abstract

This paper presents the effect of blade type and feeding force during resin-bonded dentin specimen preparation on the microtensile bond strength (μTBS) test. Forty resin-bonded flat middle dentin specimens were divided into four groups. The specimens of each group were sectioned according to [...] Read more.

This paper presents the effect of blade type and feeding force during resin-bonded dentin specimen preparation on the microtensile bond strength (μTBS) test. Forty resin-bonded flat middle dentin specimens were divided into four groups. The specimens of each group were sectioned according to type of blade and feeding force as follows: fine grit/20 N, fine grit/40 N, medium grit/20 N, and medium grit/40 N to obtain resin-dentin sticks with a cross-sectional area of 1.0 mm². Four sticks from the center of each tooth were subjected to the μTBS test. Five remaining sticks of each group were selected for surface topography observation under a scanning electron microscope (SEM). As a result, the bond strength of the medium-grit group was higher than that of the fine-grit group (p < 0.001), whereas the feeding force had no influence on bond strength values (p = 0.648). From the SEM, sticks prepared with the fine-grit blade showed a smoother surface integrity and fewer defects on the specimen edges in comparison with the sticks prepared with the medium-grit blade. The grit type of the blade is one of the considerable factors that may affect the bond strength and the surface integrity of resin-dentin specimens for microtensile testing. Full article

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17 pages, 8883 KB

Open AccessArticle

Application of Machine Learning Algorithm on MEMS-Based Sensors for Determination of Helmet Wearing for Workplace Safety

by Yan Hao Tan, Agarwal Hitesh and King Ho Holden Li

Micromachines 2021, 12(4), 449; https://doi.org/10.3390/mi12040449 - 16 Apr 2021

Cited by 13 | Viewed by 3917

Abstract

Appropriate use of helmets as industrial personal protective gear is a long-standing challenge. The dilemma for any user wearing a helmet is thermal discomfort versus the chances of head injuries while not wearing it. Applying helmet microclimate psychrometry, we propose a logistic regression- [...] Read more.

Appropriate use of helmets as industrial personal protective gear is a long-standing challenge. The dilemma for any user wearing a helmet is thermal discomfort versus the chances of head injuries while not wearing it. Applying helmet microclimate psychrometry, we propose a logistic regression- (LR) based machine learning (ML) algorithm coupled with low-cost and readily available MEMS sensors to determine if a helmet was worn (W) or not worn (NW) by a human user. Experiment runs involving human subject (S) and mannequin experiment control (C) groups were conducted across no mask (NM) and mask (M) conditions. Only ambient-microclimate humidity difference (AMHD) was a feasible parameter for helmet wearing determination with 71 to 85% goodness of fit, 72 to 76% efficacy, and distinction from control group. Ambient-microclimate humidity difference’s rate of change (AMHDROC) had high correlation to helmet wearing and removal initiations and was quantitatively better in all measures. However, its feasibility was doubtful for continuous use beyond 1 min due to plateauing AMHD response. Experiments with control groups and temperature measurement showed invariant response to helmet worn or not worn with goodness of fit and efficacy consolidation to 50%. Results showed the algorithm can make helmet-wearing determinations with combination of analysis and use of data that was individually authentic and non-identifiable. This is an improvement as compared to state of the art skin-contact mechanisms and image analytics methods in enabling safety enhancements through data-driven worker safety ownership. Full article

(This article belongs to the Special Issue Artificial Intelligence on MEMS/Microdevices/Microsystems)

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19 pages, 3936 KB

Open AccessArticle

Control of Spring Softening and Hardening in the Squared Daisy

by Mathieu Gratuze, Abdul-Hafiz Alameh, Seyedfakhreddin Nabavi and Frederic Nabki

Micromachines 2021, 12(4), 448; https://doi.org/10.3390/mi12040448 - 16 Apr 2021

Cited by 4 | Viewed by 3198

Abstract

Nonlinear, mechanical microelectromechanical system (MEMS) resonating structures exhibit large displacement and a relatively broad operating bandwidth. These unique features make them particularly of interest for the development of MEMS actuators and sensors. In this work, a mechanical MEMS structure allowing the designer to [...] Read more.

Nonlinear, mechanical microelectromechanical system (MEMS) resonating structures exhibit large displacement and a relatively broad operating bandwidth. These unique features make them particularly of interest for the development of MEMS actuators and sensors. In this work, a mechanical MEMS structure allowing the designer to determine the type of nonlinearity, that is, softening or hardening, based on its anchor scheme is presented. Effects of the excitation signal on the behavior of the proposed MEMS in the frequency domain are investigated. In this regard, a comprehensive experimental comparison among the nonlinear behaviors of softening and hardening has been conducted. To reduce the hysteresis effect to a minimum, an excitation approach, which is a pulsed sweep in frequency with a discrete resolution, is presented. The maximal velocity, quality factor, bandwidth, and resonant frequency of these two types of nonlinear MEMS resonators are compared under three different types of excitation. Finally, it is shown that the performance and characteristics extracted from nonlinear mechanical MEMS resonating structures are highly dependent on the excitation method. Hence, in the present case, the apparent performances of the MEMS resonator can increase by up to 150% or decrease by up to 21%, depending on the excitation approaches. This implies the necessity of a standardized testing methodology for nonlinear MEMS resonators for given end applications. Full article

(This article belongs to the Special Issue Integrated MEMS Resonators)

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14 pages, 3728 KB

Open AccessArticle

Hydrogel Surface-Modified Polyurethane Copolymer Film with Water Permeation Resistance and Biocompatibility for Implantable Biomedical Devices

by Hey In Jeong, Dae Hyeok An, Jun Woo Lim, Taehoon Oh, Hojin Lee, Sung-Min Park, Jae Hyun Jeong and Jae Woo Chung

Micromachines 2021, 12(4), 447; https://doi.org/10.3390/mi12040447 - 16 Apr 2021

Cited by 5 | Viewed by 4009

Abstract

To use implantable biomedical devices such as electrocardiograms and neurostimulators in the human body, it is necessary to package them with biocompatible materials that protect the internal electronic circuits from the body’s internal electrolytes and moisture without causing foreign body reactions. Herein, we [...] Read more.

To use implantable biomedical devices such as electrocardiograms and neurostimulators in the human body, it is necessary to package them with biocompatible materials that protect the internal electronic circuits from the body’s internal electrolytes and moisture without causing foreign body reactions. Herein, we describe a hydrogel surface-modified polyurethane copolymer film with concurrent water permeation resistance and biocompatibility properties for application to an implantable biomedical device. To achieve this, hydrophobic polyurethane copolymers comprising hydrogenated poly(ethylene-co-butylene) (HPEB) and aliphatic poly(carbonate) (PC) were synthesized and their hydrophobicity degree and mechanical properties were adjusted by controlling the copolymer composition ratio. When 10 wt% PC was introduced, the polyurethane copolymer exhibited hydrophobicity and water permeation resistance similar to those of HPEB; however, with improved mechanical properties. Subsequently, a hydrophilic poly(vinyl pyrrolidone) (PVP) hydrogel layer was formed on the surface of the polyurethane copolymer film by Fenton reaction using an initiator and crosslinking agent and the effect of the initiator and crosslinking agent immobilization time, PVP concentration and crosslinking agent concentration on the hydrogel properties were investigated. Finally, MTT assay showed that the hydrogel surface-modified polyurethane copolymer film displays excellent biocompatibility. Full article

(This article belongs to the Special Issue Smart Implants)

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12 pages, 2604 KB

Open AccessArticle

Development of Highly Sensitive Immunosensor for Detection of Staphylococcus aureus Based on AuPdPt Trimetallic Nanoparticles Functionalized Nanocomposite

by En Han, Yun Zhang, Jianrong Cai and Xinai Zhang

Micromachines 2021, 12(4), 446; https://doi.org/10.3390/mi12040446 - 16 Apr 2021

Cited by 16 | Viewed by 3267

Abstract

The rapid and sensitive detection of Staphylococcus aureus (S. aureus) is essential to ensure food safety and protect humans from foodborne diseases. In this study, a sensitive and facile electrochemical immunosensor using AuPdPt trimetallic nanoparticles functionalized multi-walled carbon nanotubes (MWCNTs-AuPdPt) as [...] Read more.

The rapid and sensitive detection of Staphylococcus aureus (S. aureus) is essential to ensure food safety and protect humans from foodborne diseases. In this study, a sensitive and facile electrochemical immunosensor using AuPdPt trimetallic nanoparticles functionalized multi-walled carbon nanotubes (MWCNTs-AuPdPt) as the signal amplification platform was designed for the label-free detection of S. aureus. The nanocomposite of MWCNTs-AuPdPt was prepared by an in situ growth method of loading AuPdPt trimetallic nanoparticles on the surface of MWCNTs. The synthesized MWCNTs-AuPdPt featured good conductivity and superior catalytic performance for hydrogen peroxide. The nanocomposite of MWCNTs-AuPdPt with good biocompatibility and high specific surface area was further functionalized by anti-S. aureus antibodies. The immobilized antibodies could efficiently capture S. aureus to the modified electrode by an immune reaction, which resulted in the change of catalytic current intensity to realize the sensitive detection of S. aureus. The designed immunosensor could detect S. aureus in a linear range from 1.1 × 10² to 1.1 × 10⁷ CFU mL⁻¹ with a low detection limit of 39 CFU mL⁻¹. Additionally, the proposed immunosensor was successfully applied to determine S. aureus in actual samples with acceptable results. This strategy provided a promising platform for highly sensitive determination of S. aureus and other pathogens in food products. Full article

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11 pages, 4609 KB

Open AccessArticle

Understanding the Leakage Mechanisms and Breakdown Limits of Vertical GaN-on-Si p⁺n⁻n Diodes: The Road to Reliable Vertical MOSFETs

by Kalparupa Mukherjee, Carlo De Santi, Matteo Buffolo, Matteo Borga, Shuzhen You, Karen Geens, Benoit Bakeroot, Stefaan Decoutere, Andrea Gerosa, Gaudenzio Meneghesso, Enrico Zanoni and Matteo Meneghini

Micromachines 2021, 12(4), 445; https://doi.org/10.3390/mi12040445 - 16 Apr 2021

Cited by 14 | Viewed by 4850

Abstract

This work investigates p⁺n⁻n GaN-on-Si vertical structures, through dedicated measurements and TCAD simulations, with the ultimate goal of identifying possible strategies for leakage and breakdown optimization. First, the dominant leakage processes were identified through temperature-dependent current–voltage characterization. Second, the [...] Read more.

This work investigates p⁺n⁻n GaN-on-Si vertical structures, through dedicated measurements and TCAD simulations, with the ultimate goal of identifying possible strategies for leakage and breakdown optimization. First, the dominant leakage processes were identified through temperature-dependent current–voltage characterization. Second, the breakdown voltage of the diodes was modelled through TCAD simulations based on the incomplete ionization of Mg in the p⁺ GaN layer. Finally, the developed simulation model was utilized to estimate the impact of varying the p-doping concentration on the design of breakdown voltage; while high p-doped structures are limited by the critical electric field at the interface, low p-doping designs need to contend with possible depletion of the entire p-GaN region and the consequent punch-through. A trade-off on the value of p-doping therefore exists to optimize the breakdown. Full article

(This article belongs to the Special Issue GaN-Based Semiconductor Devices)

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17 pages, 10859 KB

Open AccessArticle

Design, Fabrication, and Testing of a Novel 3D 3-Fingered Electrothermal Microgripper with Multiple Degrees of Freedom

by Guoning Si, Liangying Sun, Zhuo Zhang and Xuping Zhang

Micromachines 2021, 12(4), 444; https://doi.org/10.3390/mi12040444 - 15 Apr 2021

Cited by 18 | Viewed by 3128

Abstract

This paper presents the design, fabrication, and testing of a novel three-dimensional (3D) three-fingered electrothermal microgripper with multiple degrees of freedom (multi DOFs). Each finger of the microgripper is composed of a V-shaped electrothermal actuator providing one DOF, and a 3D U-shaped electrothermal [...] Read more.

This paper presents the design, fabrication, and testing of a novel three-dimensional (3D) three-fingered electrothermal microgripper with multiple degrees of freedom (multi DOFs). Each finger of the microgripper is composed of a V-shaped electrothermal actuator providing one DOF, and a 3D U-shaped electrothermal actuator offering two DOFs in the plane perpendicular to the movement of the V-shaped actuator. As a result, each finger possesses 3D mobilities with three DOFs. Each beam of the actuators is heated externally with the polyimide film. The durability of the polyimide film is tested under different voltages. The static and dynamic properties of the finger are also tested. Experiments show that not only can the microgripper pick and place microobjects, such as micro balls and even highly deformable zebrafish embryos, but can also rotate them in 3D space. Full article

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

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14 pages, 3309 KB

Open AccessArticle

Optimization of a Spin-Orbit Torque Switching Scheme Based on Micromagnetic Simulations and Reinforcement Learning

by Roberto L. de Orio, Johannes Ender, Simone Fiorentini, Wolfgang Goes, Siegfried Selberherr and Viktor Sverdlov

Micromachines 2021, 12(4), 443; https://doi.org/10.3390/mi12040443 - 15 Apr 2021

Cited by 9 | Viewed by 3324

Abstract

Spin-orbit torque memory is a suitable candidate for next generation nonvolatile magnetoresistive random access memory. It combines high-speed operation with excellent endurance, being particularly promising for application in caches. In this work, a two-current pulse magnetic field-free spin-orbit torque switching scheme is combined [...] Read more.

Spin-orbit torque memory is a suitable candidate for next generation nonvolatile magnetoresistive random access memory. It combines high-speed operation with excellent endurance, being particularly promising for application in caches. In this work, a two-current pulse magnetic field-free spin-orbit torque switching scheme is combined with reinforcement learning in order to determine current pulse parameters leading to the fastest magnetization switching for the scheme. Based on micromagnetic simulations, it is shown that the switching probability strongly depends on the configuration of the current pulses for cell operation with sub-nanosecond timing. We demonstrate that the implemented reinforcement learning setup is able to determine an optimal pulse configuration to achieve a switching time in the order of 150 ps, which is 50% shorter than the time obtained with non-optimized pulse parameters. Reinforcement learning is a promising tool to automate and further optimize the switching characteristics of the two-pulse scheme. An analysis of the impact of material parameter variations has shown that deterministic switching can be ensured for all cells within the variation space, provided that the current densities of the applied pulses are properly adjusted. Full article

(This article belongs to the Special Issue Magnetic and Spin Devices)

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15 pages, 4547 KB

Open AccessArticle

Microfluidic Device for the Identification of Biological Sex by Analysis of Latent Fingermark Deposits

by Jamila S. Marshall, Madelyn L. Sita and James P. Landers

Micromachines 2021, 12(4), 442; https://doi.org/10.3390/mi12040442 - 15 Apr 2021

Cited by 3 | Viewed by 3267

Abstract

To date, most research regarding amino acid detection and quantification in fingermarks relies on spectrometric methods. Herein, the Sakaguchi colorimetric test was adapted to a rotationally-driven microfluidic platform and used to detect and quantify arginine in fingermarks deposited by male and female donors. [...] Read more.

To date, most research regarding amino acid detection and quantification in fingermarks relies on spectrometric methods. Herein, the Sakaguchi colorimetric test was adapted to a rotationally-driven microfluidic platform and used to detect and quantify arginine in fingermarks deposited by male and female donors. A red color indicates the presence of arginine in a given sample following the reaction, and the intensity of this color is linearly proportional to the concentration. Objective detection and quantification of arginine were accomplished using image analysis software (freeware) based on this colorimetric result. The mean concentrations obtained in a blind study were 96.4 ± 5.1 µM for samples from female donors and 55.3 ± 5.3 µM for samples from males. These were not statistically different from the literature values of 94.8 µM ± 12.9 µM for females (p = 0.908) and 54.0 ± 12.6 µM for males (p = 0.914), respectively (± SEM in all cases). Conversely, the experimental means from males and female samples were statistically different from each other (p < 0.001). Objective differentiation between male and female fingermark deposits was achieved in a blind study with 93% accuracy. Additionally, the method was compatible both with samples lifted from common surfaces and with magnetically-powdered samples. Full article

(This article belongs to the Section C：Chemistry)

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36 pages, 2624 KB

Open AccessFeature PaperEditor’s ChoiceReview

Review of Design Considerations for Brain-on-a-Chip Models

by Tiffany Cameron, Tanya Bennet, Elyn M. Rowe, Mehwish Anwer, Cheryl L. Wellington and Karen C. Cheung

Micromachines 2021, 12(4), 441; https://doi.org/10.3390/mi12040441 - 15 Apr 2021

Cited by 38 | Viewed by 9577

Abstract

In recent years, the need for sophisticated human in vitro models for integrative biology has motivated the development of organ-on-a-chip platforms. Organ-on-a-chip devices are engineered to mimic the mechanical, biochemical and physiological properties of human organs; however, there are many important considerations when [...] Read more.

In recent years, the need for sophisticated human in vitro models for integrative biology has motivated the development of organ-on-a-chip platforms. Organ-on-a-chip devices are engineered to mimic the mechanical, biochemical and physiological properties of human organs; however, there are many important considerations when selecting or designing an appropriate device for investigating a specific scientific question. Building microfluidic Brain-on-a-Chip (BoC) models from the ground-up will allow for research questions to be answered more thoroughly in the brain research field, but the design of these devices requires several choices to be made throughout the design development phase. These considerations include the cell types, extracellular matrix (ECM) material(s), and perfusion/flow considerations. Choices made early in the design cycle will dictate the limitations of the device and influence the end-point results such as the permeability of the endothelial cell monolayer, and the expression of cell type-specific markers. To better understand why the engineering aspects of a microfluidic BoC need to be influenced by the desired biological environment, recent progress in microfluidic BoC technology is compared. This review focuses on perfusable blood–brain barrier (BBB) and neurovascular unit (NVU) models with discussions about the chip architecture, the ECM used, and how they relate to the in vivo human brain. With increased knowledge on how to make informed choices when selecting or designing BoC models, the scientific community will benefit from shorter development phases and platforms curated for their application. Full article

(This article belongs to the Special Issue Microfluidic Brain-on-a-Chip)

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11 pages, 6332 KB

Open AccessArticle

The Design, Simulation and Fabrication of an Omnidirectional Inertial Switch with Rectangular Suspension Spring

by Wenguo Chen, Rui Wang, Huiying Wang and Shulei Sun

Micromachines 2021, 12(4), 440; https://doi.org/10.3390/mi12040440 - 15 Apr 2021

Cited by 5 | Viewed by 2818

Abstract

An omnidirectional inertial switch with rectangular spring is proposed in this paper, and the prototype has been fabricated by surface micromachining technology. To evaluate the threshold consistency and stability of omnidirectional inertia switch, the stiffness of rectangular suspension springs is analyzed. The simulation [...] Read more.

An omnidirectional inertial switch with rectangular spring is proposed in this paper, and the prototype has been fabricated by surface micromachining technology. To evaluate the threshold consistency and stability of omnidirectional inertia switch, the stiffness of rectangular suspension springs is analyzed. The simulation result shows that the coupling stiffness of the rectangular spring suspension system in the non-sensitive direction is a little more than that in the sensitive direction, which indicated that the omnidirectional switching system’s stability is reinforced, attributed to the design of rectangular springs. The dynamic response simulation shows that the threshold of the omnidirectional inertial switch using the rectangular suspension spring has high consistency in the horizontal direction. The prototype of an inertial switch is fabricated and tested successfully. The testing results indicate even threshold distribution in the horizontal direction. The threshold acceleration of the designed inertial switch is about 58 g in the X direction and 37 g in the Z direction; the contact time is about 18 μs. Full article

(This article belongs to the Special Issue Micro Inertial Sensors: Calibration Methods, Technologies and Application)

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18 pages, 3381 KB

Open AccessArticle

Identification and Speed Estimation of a Moving Object in an Indoor Application Based on Visible Light Sensing of Retroreflective Foils

by Andreas Peter Weiss and Franz Peter Wenzl

Micromachines 2021, 12(4), 439; https://doi.org/10.3390/mi12040439 - 15 Apr 2021

Cited by 9 | Viewed by 2645

Abstract

Identification and sensing are two of the main tasks a wireless sensor node has to perform in an Internet of Things (IoT) environment. Placing active powered nodes on objects is the most usual approach for the fulfillment of these functions. With the expected [...] Read more.

Identification and sensing are two of the main tasks a wireless sensor node has to perform in an Internet of Things (IoT) environment. Placing active powered nodes on objects is the most usual approach for the fulfillment of these functions. With the expected massive increase of connected things, there are several issues on the horizon that hamper the further deployment of this approach in an energy efficient, sustainable way, like the usage of environmentally hazardous batteries or accumulators, as well as the required electrical energy for their operation. In this work, we propose a novel approach for performing the tasks of identification and sensing, applying visible light sensing (VLS) based on light emitting diode (LED) illumination and utilizing retroreflective foils mounted on a moving object. This low cost hardware is combined with a self-developed, low complex software algorithm with minimal training effort. Our results show that successful identification and sensing of the speed of a moving object can be achieved with a correct estimation rate of 99.92%. The used foils are commercially available and pose no threat to the environment and there is no need for active sensors on the moving object and no requirement of wireless radio frequency communication. All of this is achievable whilst undisturbed illumination is still provided. Full article

(This article belongs to the Special Issue Micro-Nano Science and Engineering)

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15 pages, 3838 KB

Open AccessArticle

Simulation Research of Hydraulic Stepper Drive Technology Based on High Speed On/Off Valves and Miniature Plunger Cylinders

by Hanyu Qiu and Qi Su

Micromachines 2021, 12(4), 438; https://doi.org/10.3390/mi12040438 - 15 Apr 2021

Cited by 11 | Viewed by 3087

Abstract

The technology for stepper drive that can achieve accurate motion in the hydraulic field has always been urgently needed in the industry. This paper proposes a hydraulic stepper drive based on five high speed on/off valves and two miniature plunger cylinders. The stepper [...] Read more.

The technology for stepper drive that can achieve accurate motion in the hydraulic field has always been urgently needed in the industry. This paper proposes a hydraulic stepper drive based on five high speed on/off valves and two miniature plunger cylinders. The stepper drive discretizes the continuous flow medium into fixed small steps through the miniature plunger cylinder and realizes the state control of the drive through the logic action of the high speed on/off valve. This paper improves the current stepper drive and establishes a mathematical model to analyze the error of the drive and calculate the position of the actuator. In addition, through simulation research, the performance parameters such as the single-step step characteristic and pressure characteristic of the stepper drive are studied. The results show that, compared with the technology of current stepper drive, this stepper drive can effectively remove the “post step” phenomenon, greatly improve the stepper accuracy of the stepper drive, and have a more excellent performance. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Flow in Micromachines)

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12 pages, 2727 KB

Open AccessArticle

A New Electrochemical Platform for Dasatinib Anticancer Drug Sensing Using Fe₃O₄-SWCNTs/Ionic Liquid Paste Sensor

by Ali Moghaddam, Hassan Ali Zamani and Hassan Karimi-Maleh

Micromachines 2021, 12(4), 437; https://doi.org/10.3390/mi12040437 - 14 Apr 2021

Cited by 26 | Viewed by 3283

Abstract

A new electrochemical platform was suggested for the sensing of the dasatinib (DA) anticancer drug based on paste electrode modification (PE) amplified with Fe₃O₄-SWCNTs nanocomposite and 1-hexyl-3-methylimidazolium tetrafluoroborate (mim-BF₄⁻). The new platform showed a linear dynamic [...] Read more.

A new electrochemical platform was suggested for the sensing of the dasatinib (DA) anticancer drug based on paste electrode modification (PE) amplified with Fe₃O₄-SWCNTs nanocomposite and 1-hexyl-3-methylimidazolium tetrafluoroborate (mim-BF₄⁻). The new platform showed a linear dynamic range from 0.001–220 µM with a detection limit of 0.7 nM to determine DA at optimal condition. Electrochemical investigation showed that the redox reaction of DA is relative to changing the pH of solution. Moreover, Fe₃O₄-SWCNTs/mim-BF₄⁻/PE has improved the oxidation current of DA about 5.58 times which reduced its oxidation potential by about 120 mV at optimal condition. In the final step, Fe₃O₄-SWCNTs/mim-BF₄⁻/PE was used as an analytical platform to determine the DA in tablets and a dextrose saline spike sample, and the results showed recovery data 99.58–103.6% which confirm the powerful ability of the sensor as an analytical tool to determine the DA in real samples. Full article

(This article belongs to the Special Issue Nanomaterials Modified Electrochemical Sensors)

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