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Micromachines
Special Issues
Micro and Smart Devices and Systems, 2nd Edition
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Micro and Smart Devices and Systems, 2nd Edition

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "E：Engineering and Technology".

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 36782

Special Issue Editors

Dr. Hong Ding

E-Mail Website
Guest Editor
Department of NanoEngineering, University of California San Diego, La Jolla, CA 92093, USA
Interests: MEMS sensors; ultrasound; soft actuators; flexible electronics
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Jin Xie

E-Mail Website
Guest Editor
The State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou 310027, China
Interests: MEMS sensors and actuators; micromachined ultrasonic transducers; resonators
Special Issues, Collections and Topics in MDPI journals
Dr. Zebing Mao

E-Mail Website
Guest Editor
Department of Mechanical Engineering, School of Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan
Interests: functional fluids; soft actuators and sensors; Belousov–Zhabotinsky (BZ) gel; machining and MEMS; microfluidics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Micro and smart devices and systems (solid/fluidic actuators and sensors, flexible electronics, functional fluids, MEMS, microfluidics, wearable devices, self-actuation/sensing and self-power systems, self-oscillating and smart hydrogels, intelligent control systems, lenses, origami batteries, fuel cells, etc.) are becoming popular in various fields of robotics, telecommunications, chemistry, and biology. In addition, these smart devices and systems help us to improve our quality of life and are beneficial for our understanding of insects and animals in Nature. The above devices are made of either rigid or soft materials with special mechanical and electrical properties, which have a large influence on their robustness and stability and can show some intelligent and smart characteristics. However, it is not easy to fully understand their working principles and integrate several components to a smart and intelligent system. Accordingly, relevant topics for this Special Issue include, but are not limited to:

  • Novel design, modeling, fabrication, and assembly of micro and smart devices and systems based on various actuation and sensing methods of electric, thermal, light, magnetic, chemical reaction, acoustic, etc.
  • Smart and intelligent soft solid and fluidic robots, actuators and sensors, microfluidics, batteries, etc.
  • Theory and modeling of complex nonlinear phenomena relating to micro and smart devices and systems.
  • New developments and applications of all types of micro and smart devices and systems.

We look forward to receiving your submissions!

Dr. Hong Ding
Prof. Dr. Jin Xie
Dr. Zebing Mao
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (21 papers)

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11 pages, 2239 KiB  
Article
An Effective Resistive-Type Alcohol Vapor Sensor Using One-Step Facile Nanoporous Anodic Alumina
by Chen-Kuei Chung and Chin-An Ku
Micromachines 2023, 14(7), 1330; https://doi.org/10.3390/mi14071330 - 29 Jun 2023
Cited by 2 | Viewed by 1019
Abstract
With the increases in work environment regulations restricting alcohol to 1000 ppm, and in drink-driving laws, testing for alcohol with a simple method is a crucial issue. Conventional alcohol sensors based on sulfide, metal oxide, boron nitride or graphene oxide have a detection [...] Read more.
With the increases in work environment regulations restricting alcohol to 1000 ppm, and in drink-driving laws, testing for alcohol with a simple method is a crucial issue. Conventional alcohol sensors based on sulfide, metal oxide, boron nitride or graphene oxide have a detection limit in the range of 50–1000 ppm but have disadvantages of complicated manufacture and longer processing times. A recent portable alcohol meter based on semiconductor material using conductivity or chemistry measurements still has the problem of a complex and lengthy manufacturing process. In this paper, a simple and effective resistive-type alcohol vapor sensor using one-step anodic aluminum oxide (AAO) is proposed. The nanoporous AAO was produced in one-step by anodizing low-purity AA1050 at room temperature of 25 °C, which overcame the traditional high-cost and lengthy process at low temperature of anodization and etching from high-purity aluminum. The highly specific surface area of AAO has benefits for good sensing performance, especially as a humidity or alcohol vapor sensor. With the resistance measurement method, alcohol vapor concentration of 0, 100, 300, 500, 700 and 1000 ppm correspond to mean resistances of 8524 Ω, 8672 Ω, 9121 Ω, 9568 Ω, 10,243 Ω, and 11,045 Ω, respectively, in a linear relationship. Compared with other materials for detecting alcohol vapor, the AAO resistive sensor has advantages of fast and simple manufacturing with good detection limits for practical applications. The resistive-type alcohol vapor-sensing mechanism is described with respect to the resistivity of the test substance and the pore morphology of AAO. In a human breath test, the AAO sensor can quickly distinguish whether the subject is drinking, with normal breath response of −30% to −40% and −20% to −30% response after drinking 50 mL of wine of 25% alcohol. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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14 pages, 3616 KiB  
Article
Water Management Capacity of Metal Foam Flow Field for PEMFC under Flooding Situation
by Lingjiang Chen, Zichen Wang, Chuanfu Sun, Hui Zhu, Yuzhen Xia, Guilin Hu and Baizeng Fang
Micromachines 2023, 14(6), 1224; https://doi.org/10.3390/mi14061224 - 10 Jun 2023
Cited by 1 | Viewed by 1193
Abstract
Porous metal foam with complex opening geometry has been used as a flow field to enhance the distribution of reactant gas and the removal of water in polymer electrolyte membrane fuel cells. In this study, the water management capacity of a metal foam [...] Read more.
Porous metal foam with complex opening geometry has been used as a flow field to enhance the distribution of reactant gas and the removal of water in polymer electrolyte membrane fuel cells. In this study, the water management capacity of a metal foam flow field is experimentally investigated by polarization curve tests and electrochemical impedance spectroscopy measurements. Additionally, the dynamic behavior of water at the cathode and anode under various flooding situations is examined. It is found that obvious flooding phenomena are observed after water addition both into the anode and cathode, which are alleviated during a constant-potential test at 0.6 V. Greater abilities of anti-flooding and mass transfer and higher current densities are found as the same amount of water is added at the anode. No diffusion loop is depicted in the impedance plots although a 58.3% flow volume is occupied by water. The maximum current density of 1.0 A cm−2 and the lowest Rct around 17 mΩ cm2 are obtained at the optimum state after 40 and 50 min of operation as 2.0 and 2.5 g of water are added, respectively. The porous metal pores store a certain amount of water to humidify the membrane and achieve an internal “self-humidification” function. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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13 pages, 29350 KiB  
Article
Thermal Energy Harvesting from Slow Variations in Environmental Temperatures
by Joshua Curry, Nick Harris and Neil White
Micromachines 2023, 14(6), 1202; https://doi.org/10.3390/mi14061202 - 06 Jun 2023
Cited by 2 | Viewed by 1169
Abstract
With the Internet of Things expanding to more locations across our planet, power becomes the main factor affecting device longevity. There is a need for more novel energy harvesting systems that are able to power remote devices for sustained periods. This publication presents [...] Read more.
With the Internet of Things expanding to more locations across our planet, power becomes the main factor affecting device longevity. There is a need for more novel energy harvesting systems that are able to power remote devices for sustained periods. This publication presents one such device. Based on a novel actuator that utilises off-the-shelf gas mixtures to generate a variable force from temperature change, this publication presents a device capable of generating up to 150mJ per diurnal temperature cycle; this is enough electrical energy to send up to three LoRaWAN transmissions per day using slowly changing environmental temperatures. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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13 pages, 4113 KiB  
Article
Modal-Transition-Induced Valleys of K2 in Piezoelectric Bilayer Laterally Vibrating Resonators
by Zihao Xie, Jiabao Sun and Jin Xie
Micromachines 2023, 14(5), 1022; https://doi.org/10.3390/mi14051022 - 10 May 2023
Viewed by 1034
Abstract
Piezoelectric Laterally Vibrating Resonators (LVRs) have attracted significant attention as a potential technology for next-generation wafer-level multi-band filters. Piezoelectric bilayer structures such as Thin-film Piezoelectric-on-Silicon (TPoS) LVRs which aim to increase the quality factor (Q) or aluminum nitride and silicon dioxide [...] Read more.
Piezoelectric Laterally Vibrating Resonators (LVRs) have attracted significant attention as a potential technology for next-generation wafer-level multi-band filters. Piezoelectric bilayer structures such as Thin-film Piezoelectric-on-Silicon (TPoS) LVRs which aim to increase the quality factor (Q) or aluminum nitride and silicon dioxide (AlN/SiO2) composite membrane for thermal compensation have been proposed. However, limited studies have investigated the detailed behaviors of the electromechanical coupling factor (K2) of these piezoelectric bilayer LVRs. Herein, AlN/Si bilayer LVRs are selected as an example, we observed notable degenerative valleys in K2 at specific normalized thicknesses using two-dimensional finite element analysis (FEA), which has not been reported in the previous studies of bilayer LVRs. Moreover, the bilayer LVRs should be designed away from the valleys to minimize the reduction in K2. Modal-transition-induced mismatch between electric and strain fields of AlN/Si bilayer LVRs are investigated to interpret the valleys from energy considerations. Furthermore, the impact of various factors, including electrode configurations, AlN/Si thickness ratios, the Number of Interdigitated Electrode (IDT) Fingers (NFs), and IDT Duty Factors (DFs), on the observed valleys and K2 are analyzed. These results can provide guidance for the designs of piezoelectric LVRs with bilayer structure, especially for LVRs with a moderate K2 and low thickness ratio. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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27 pages, 8994 KiB  
Article
Design and Implementation of an Integrated Control Scheme for GaN-Based Multiple Power Converters
by Chao-Tsung Ma and Bing-Hong Yao
Micromachines 2023, 14(4), 833; https://doi.org/10.3390/mi14040833 - 11 Apr 2023
Cited by 2 | Viewed by 1295
Abstract
In response to the rapid changes in the international energy environment, developing renewable energy (RE)-based distributed generation (DG) and various smart micro-grid systems is crucial for creating a robust electric power grid and new energy industries. In this aspect, there is an urgent [...] Read more.
In response to the rapid changes in the international energy environment, developing renewable energy (RE)-based distributed generation (DG) and various smart micro-grid systems is crucial for creating a robust electric power grid and new energy industries. In this aspect, there is an urgent need to develop hybrid power systems suitable for coexistent AC and DC power grids, integrated by high-performance wide ban gap (WBG) semiconductor-based power conversion interfaces and advanced operating and control strategies. Due to the intrinsic feature of variation in RE-based power generation, the design and integration of energy storage devices, real-time regulation of power flow, and intelligent energy control schemes are key technologies for further promoting DG systems and micro-grids. This paper investigates an integrated control scheme for multiple GaN-based power converters in a small- to medium-capacity, grid-connected, and RE-based power system. This is the first time that a complete design case demonstrating three GaN-based power converters with different control functions integrated with a single digital signal processor (DSP) chip to achieve a reliable, flexible, cost effective, and multifunctional power interface for renewable power generation systems is presented. The system studied includes a photovoltaic (PV) generation unit, a battery energy storage unit, a grid-connected single-phase inverter, and a power grid. Based on system operation condition and the state of charge (SOC) of the energy storage unit, two typical operating modes and advanced power control functions are developed with a fully digital and coordinated control scheme. Hardware of the GaN-based power converters and digital controllers are designed and implemented. The feasibility and effectiveness of the designed controllers and overall performance of the proposed control scheme are verified with results from simulation and experimental tests on a 1-kVA small-scale hardware system. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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14 pages, 3890 KiB  
Article
Comparison of Illumination Methods for Flow-Through Optofluidic Biosensors
by Matthew Hamblin, Joel Wright, Holger Schmidt and Aaron R. Hawkins
Micromachines 2023, 14(4), 723; https://doi.org/10.3390/mi14040723 - 24 Mar 2023
Viewed by 912
Abstract
Optofluidic biosensors have become an important medical diagnostic tool because they allow for rapid, high-sensitivity testing of small samples compared to standard lab testing. For these devices, the practicality of use in a medical setting depends heavily on both the sensitivity of the [...] Read more.
Optofluidic biosensors have become an important medical diagnostic tool because they allow for rapid, high-sensitivity testing of small samples compared to standard lab testing. For these devices, the practicality of use in a medical setting depends heavily on both the sensitivity of the device and the ease of alignment of passive chips to a light source. This paper uses a model previously validated by comparison to physical devices to compare alignment, power loss, and signal quality for windowed, laser line, and laser spot methods of top-down illumination. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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11 pages, 5974 KiB  
Article
Polarization-Dependent Coding Metasurface with Switchable Transmission and RCS Reduction Bands
by Hamza Asif Khan, Chenxi Huang, Qiang Xiao and Syed Muzahir Abbas
Micromachines 2023, 14(1), 78; https://doi.org/10.3390/mi14010078 - 28 Dec 2022
Cited by 6 | Viewed by 1890
Abstract
In this article, a coding metasurface is specifically designed to switch transmission and reflection functionalities between two different frequency bands for linearly polarized waves within wide incidence angles. A metasurface consists of four metallic patterns, where the middle two structures are inserted to [...] Read more.
In this article, a coding metasurface is specifically designed to switch transmission and reflection functionalities between two different frequency bands for linearly polarized waves within wide incidence angles. A metasurface consists of four metallic patterns, where the middle two structures are inserted to ensure effective performance of transmission and reflection, while the top and bottom patterns are designed based on simultaneously controlling the reflection phase for both polarization states. It has been experimentally demonstrated that the proposed metasurface can convert a transmission band into a complete reflection band (meanwhile, the reflection band is translated into a complete transmission band) by changing the incident polarization state. Highly efficient transmission and reflection characteristics have been achieved from 21.1 to 24.5 GHz as well as from 33.3 to 38.3 GHz, whereas more than 10 dB radar cross-section (RCS) reduction has also been obtained for both TE and TM modes in their respective reflection bands. The performance of the proposed metasurface is well sustained up to 40° oblique incidence. This work will help to open a new aspect in metasurfaces to manipulate the electromagnetic waves at preferable frequency bands to achieve desirable functionalities. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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30 pages, 9506 KiB  
Article
Characterization of Multilayer Coupling Based on Square Complementary Split Ring Resonator for Multiport Device Implementation
by Eduardo Jarauta, Juan Carlos Iriarte and Francisco Falcone
Micromachines 2023, 14(1), 68; https://doi.org/10.3390/mi14010068 - 27 Dec 2022
Cited by 1 | Viewed by 1325
Abstract
The advent of context-aware environments and related applications demands a high degree of connectivity, with new spectral bands and related radio resource management functionalities in the current 5G bands and foreseen in future 6G wireless communication systems. This, in turn, poses new challenges [...] Read more.
The advent of context-aware environments and related applications demands a high degree of connectivity, with new spectral bands and related radio resource management functionalities in the current 5G bands and foreseen in future 6G wireless communication systems. This, in turn, poses new challenges in the implementation of wireless transceivers and radiating systems, in terms of device integration, miniaturization and element isolation, among others. High-performance miniature devices are presented and studied in this work, aided by metamaterial-inspired complementary resonators. A single particle is used to build a single layer, double layer, double frequency resonators and power dividers. A complete characterization of each equivalent circuit is also analyzed, showing great agreement between analytical circuit models and full-wave electromagnetic simulations. By adding more particles, different diplexers and triplexers in the multi-layer configuration are proposed. The flexibility in the design is the key advantage, as all devices are easily tunable and the output lines can be built in different layers, enabling frequency scalability from RF to millimeter wave ranges. Nevertheless, they are only a sample of all possible combinations of devices that can be designed for integration in future wireless communication systems. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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13 pages, 3392 KiB  
Article
Effect of Polyvinylpolypyrrolidone Surfactant on Characteristics of Iron-Oxide Nanoparticles Synthesized by Using Recycled Waste Permanent Magnets
by Sung-Jei Hong, Ajin Jo, Sang Hyeok Hong, Byeong Jun Kim, Young Sung Kim, Suwon Yang and Jae-Yong Lee
Micromachines 2022, 13(11), 2020; https://doi.org/10.3390/mi13112020 - 19 Nov 2022
Cited by 1 | Viewed by 996
Abstract
In this study, iron oxide nanoparticles (FeOx NPs) were synthesized by using Fe solution recycled from NdFeB permanent magnet scrap. Furthermore, the effect of polyvinylpolypyrrolidone (PVP) as a surfactant on the characteristics of the FeOx NPs was investigated. Firstly, Fe solution [...] Read more.
In this study, iron oxide nanoparticles (FeOx NPs) were synthesized by using Fe solution recycled from NdFeB permanent magnet scrap. Furthermore, the effect of polyvinylpolypyrrolidone (PVP) as a surfactant on the characteristics of the FeOx NPs was investigated. Firstly, Fe solution was prepared by using 10% H2SO4 solution and Na2SO4 salt. In addition, three reducing agent solutions were prepared by dissolving PVP in 0.5 M NH4OH solution in distilled (D.I.) water with concentrations of 0 wt%, 1 wt%, and 2 wt%, respectively. Each reducing agent solution was added dropwise into the Fe solution to precipitate three precursors of FeOx NPs, and they were heat-treated at 400 °C to prepare three FeOx NPs samples, P0, P1, and P2. In X-ray diffractometer (XRD) analysis, diffraction peaks of P0 sample are consistent with the Fe3O4 with (311) preferred orientation. The XRD peak shifted from Fe3O4 to Fe2O3 structure as PVP concentration increased, and the crystal structure of P2 sample was transformed to Fe2O3 with (104) preferred orientation. Brunauer, Emmett, and Teller (BET) specific surface area increased in proportional to PVP concentration. HRTEM observation also supported the tendency; the particle size of the P0 sample was less than 40 nm, and particle size decreased as PVP concentration increased, leading to the particle size of the P2 sample being less than 20 nm in width. In addition, particle morphology started to be transformed from particle to rod shape as PVP concentration increased and, in the P2 sample, all the morphology of particles was transformed to a rod shape. Magnetic properties analysis revealed that the P0 sample exhibited the highest value of magnetic moment, 65.6 emu/g, and the magnetic moment was lowered in the P1 sample, and the P2 sample exhibited the lowest value of magnetic moment, 2.4 emu/g. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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13 pages, 21112 KiB  
Article
A Tuneable Pressure-Based Energy Harvester for Powering the Environmental Internet of Things
by Joshua Curry, Nick Harris and Neil White
Micromachines 2022, 13(11), 1973; https://doi.org/10.3390/mi13111973 - 14 Nov 2022
Cited by 1 | Viewed by 1050
Abstract
As the internet of things expands to more remote locations, solutions are required for long-term remote powering of environmental sensing devices. In this publication, a device is presented which utilises the slow-moving diurnal temperature change present in many natural environments to produce electrical [...] Read more.
As the internet of things expands to more remote locations, solutions are required for long-term remote powering of environmental sensing devices. In this publication, a device is presented which utilises the slow-moving diurnal temperature change present in many natural environments to produce electrical energy. This device utilises a novel actuator which harnesses temperature-dependent phase change to provide a variable force output, and this is combined with energy storage and release apparatus to convert the output force into electrical energy. Appropriate modelling is utilised to identify parameters for system tuning, and a final proof-of-concept solution is constructed and demonstrated to generate up to 10 mJ per 24 h period. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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11 pages, 4961 KiB  
Article
Design and High-Resolution Analysis of an Efficient Periodic Split-and-Recombination Microfluidic Mixer
by Xiannian Zhang, Zhenwei Qian, Mengcheng Jiang, Wentao Li, Yanyi Huang and Yongfan Men
Micromachines 2022, 13(10), 1720; https://doi.org/10.3390/mi13101720 - 12 Oct 2022
Viewed by 1526
Abstract
We developed a highly efficient passive mixing device based on a split-and-recombine (SAR) configuration. This micromixer was constructed by simply bonding two identical microfluidic periodical open-trench patterns face to face. The structure parameters of periodical units were optimized through numerical simulation to facilitate [...] Read more.
We developed a highly efficient passive mixing device based on a split-and-recombine (SAR) configuration. This micromixer was constructed by simply bonding two identical microfluidic periodical open-trench patterns face to face. The structure parameters of periodical units were optimized through numerical simulation to facilitate the mixing efficiency. Despite the simplicity in design and fabrication, it provided rapid mixing performance in both experiment and simulation conditions. To better illustrate the mixing mechanism, we developed a novel scheme to achieve high-resolution confocal imaging of serial channel cross-sections to accurately characterize the mixing details and performance after each SAR cycle. Using fluorescent IgG as an indicator, nearly complete mixing was achieved using only four SAR cycles in an aqueous solution within a device’s length of less than 10 mm for fluids with a Péclet number up to 8.7 × 104. Trajectory analysis revealed that each SAR cycle transforms the input fluids using three synergetic effects: rotation, combination, and stretching to increase the interfaces exponentially. Furthermore, we identified that the pressure gradients in the parallel plane of the curved channel induced vertical convection, which is believed to be the driving force underlying these effects to accelerate the mixing process. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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14 pages, 3399 KiB  
Article
Development of Pressure Sensor Based Wearable Pulse Detection Device for Radial Pulse Monitoring
by Shihang Wang, Zhinan Zhang, Zhijian Chen, Deqing Mei and Yancheng Wang
Micromachines 2022, 13(10), 1699; https://doi.org/10.3390/mi13101699 - 09 Oct 2022
Cited by 5 | Viewed by 2503
Abstract
Wearable pulse detection devices can be used for daily human healthcare monitoring; however, the relatively poor flexibility and low sensitivity of the pulse detection devices are hindering the scrutiny of pulse information during pulse diagnosis of different pulse positions. This paper developed a [...] Read more.
Wearable pulse detection devices can be used for daily human healthcare monitoring; however, the relatively poor flexibility and low sensitivity of the pulse detection devices are hindering the scrutiny of pulse information during pulse diagnosis of different pulse positions. This paper developed a novel and wearable pulse detection device based on three flexible pressure sensors using synthetic graphene and silver composites as the pressure sensing material. The structural design of the pulse detection device is firstly presented; the core component of pressure sensors is using the sawtooth protrusions to convert pressure induced by radial pulse vibrations into localized deformation of graphene composites. The fabricated pulse detection device is characterized by high pressure sensing performance, including relatively high sensitivity (8.65% kPa−1), broad sensing range (12 kPa), and good dynamic response with a response time of about 100 ms. Then, the pulse detection device is worn on a human wrist to detect the pulses from three pulse positions, namely, ‘Cun’, ‘Guan’, and ‘Chi’, and the results demonstrated the capability of using our device to detect pulse signals. The physical conditions of the subject, such as arterial stiffness index, can be further analyzed through the characteristics of the acquired pulse signals, demonstrating the potential application of using wearable pulse detection devices for human health monitoring. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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23 pages, 4440 KiB  
Article
Effects of Side Profile on Acoustic Streaming by Oscillating Microstructures in Channel
by Lin Lin, Haojie Dang, Rongxin Zhu, Ying Liu and Hui You
Micromachines 2022, 13(9), 1439; https://doi.org/10.3390/mi13091439 - 31 Aug 2022
Cited by 4 | Viewed by 1457
Abstract
In microchannels, microstructure-induced acoustic streaming can be achieved at low frequencies, providing simple platforms for biomedicine and microfluidic manipulation. Nowadays, microstructures are generally fabricated by photolithography or soft photolithography. Existing studies mainly focused on the projection plane, while ignoring the side profile including [...] Read more.
In microchannels, microstructure-induced acoustic streaming can be achieved at low frequencies, providing simple platforms for biomedicine and microfluidic manipulation. Nowadays, microstructures are generally fabricated by photolithography or soft photolithography. Existing studies mainly focused on the projection plane, while ignoring the side profile including microstructure’s sidewall and channel’s upper wall. Based on the perturbation theory, the article focuses on the effect of microstructure’s sidewall errors caused by machining and the viscous dissipation of upper wall on the streaming. We discovered that the side profile parameters, particularly the gap (gap g between the top of the structure and the upper wall of the channel), have a significant impact on the maximum velocity, mode, and effective area of the streaming.To broaden the applicability, we investigated boundary layer thickness parameters including frequency and viscosity. Under different thickness parameters, the effects of side profile parameters on the streaming are similar. But the maximum streaming velocity is proportional to the frequency squared and inversely proportional to the viscosity. Besides, the ratio factor θ of the maximum streaming velocity to the vibration velocity is affected by the side profile parameter gap g and sidewall profile angle α. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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13 pages, 13332 KiB  
Article
Optimization of Microchannels and Application of Basic Activation Functions of Deep Neural Network for Accuracy Analysis of Microfluidic Parameter Data
by Feroz Ahmed, Masashi Shimizu, Jin Wang, Kenji Sakai and Toshihiko Kiwa
Micromachines 2022, 13(8), 1352; https://doi.org/10.3390/mi13081352 - 20 Aug 2022
Cited by 4 | Viewed by 1915
Abstract
The fabrication of microflow channels with high accuracy in terms of the optimization of the proposed designs, minimization of surface roughness, and flow control of microfluidic parameters is challenging when evaluating the performance of microfluidic systems. The use of conventional input devices, such [...] Read more.
The fabrication of microflow channels with high accuracy in terms of the optimization of the proposed designs, minimization of surface roughness, and flow control of microfluidic parameters is challenging when evaluating the performance of microfluidic systems. The use of conventional input devices, such as peristaltic pumps and digital pressure pumps, to evaluate the flow control of such parameters cannot confirm a wide range of data analysis with higher accuracy because of their operational drawbacks. In this study, we optimized the circular and rectangular-shaped microflow channels of a 100 μm microfluidic chip using a three-dimensional simulation tool, and analyzed concentration profiles of different regions of the microflow channels. Then, we applied a deep learning (DL) algorithm for the dense layers of the rectified linear unit (ReLU), Leaky ReLU, and Swish activation functions to train and test 1600 experimental and interpolation of data samples which obtained from the microfluidic chip. Moreover, using the same DL algorithm, we configured three models for each of these three functions by changing the internal middle layers of these models. As a result, we obtained a total of 9 average accuracy values of ReLU, Leaky ReLU, and Swish functions for a defined threshold value of 6×10−5 using the trial-and-error method. We applied single-to-five-fold cross-validation technique of deep neural network to avoid overfitting and reduce noises from data-set to evaluate better average accuracy of data of microfluidic parameters. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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14 pages, 3473 KiB  
Article
Investigation of an Electrochromic Device Based on Ammonium Metatungstate-Iron (II) Chloride Electrochromic Liquid
by Sifan Kong, Guanguang Zhang, Muyun Li, Rihui Yao, Chenxiao Guo, Honglong Ning, Jianzhi Zhang, Ruiqiang Tao, Haoyang Yan and Xubing Lu
Micromachines 2022, 13(8), 1345; https://doi.org/10.3390/mi13081345 - 19 Aug 2022
Cited by 6 | Viewed by 2202
Abstract
Even though electrochromism has been around for more than 50 years, it still has several issues. Multi-layered films, high manufacturing costs, and a short lifetime are present in existing electrochromic devices. We demonstrate a unique high-performance device with a basic structure and no [...] Read more.
Even though electrochromism has been around for more than 50 years, it still has several issues. Multi-layered films, high manufacturing costs, and a short lifetime are present in existing electrochromic devices. We demonstrate a unique high-performance device with a basic structure and no solid electrochromic sheets in this work. In this device, the electrolyte layer is also avoided. The device uses an electrochromic solution prepared from a mixture of ammonium metatungstate and iron (II) chloride solution as a functional layer with reversible redox properties. The tungstate ions on the electrode surface are reduced when the device is colored, and the Fe2+ on the electrode surface is oxidized on another electrode surface. The generated Fe3+ in the mixed functional layer oxidizes the previously reduced tungstate ions as the device fades. We determined the ΔT (transmittance modulation) and response time among ammonium metatungstate ratios, iron (II) chloride ratios, and driven current density using DOE (design of experiment) trials. Using 0.175 mol/L ammonium metatungstate and 0.30 mol/L iron (II) chloride, a device with outstanding ΔT (more than 57% at 700 nm), a short response time (less than 10 s), and high coloring efficiency (160.04 cm2/C at 700 nm) is demonstrated. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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11 pages, 3478 KiB  
Article
Ti3C2Tx MXene-Polymeric Strain Sensor with Huge Gauge Factor for Body Movement Detection
by Wei Xian Rebecca Leong, Adel Mohammed Al-Dhahebi, Mohamad Radzi Ahmad and Mohamed Shuaib Mohamed Saheed
Micromachines 2022, 13(8), 1302; https://doi.org/10.3390/mi13081302 - 12 Aug 2022
Cited by 6 | Viewed by 1923
Abstract
In this work, a composite strain sensor is fabricated by synthesizing MXene and deposition of polypyrrole on top of the flexible electrospun PVDF nanofibers. The fabricated sensor exhibits a conductive network constructed with MXene and polypyrrole of microcracks network structure, demonstrating its strain [...] Read more.
In this work, a composite strain sensor is fabricated by synthesizing MXene and deposition of polypyrrole on top of the flexible electrospun PVDF nanofibers. The fabricated sensor exhibits a conductive network constructed with MXene and polypyrrole of microcracks network structure, demonstrating its strain sensing properties. The presence of these microcracks serves as mechanical weak points, which leads to sensitivity enhancement, while the electrospun fiber substrate act as a cushion for strain loading under large deformations. The as-prepared MXene@Polypyrrole PVDF sensor has a gauge factor range of 78–355 with a sensing range between 0–100%. Besides strain deformations, the sensor can operate in torsional deformation and human motion, indicating the sensor’s potential as a wearable health monitoring device. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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23 pages, 6113 KiB  
Article
Stripline Multilayer Devices Based on Complementary Split Ring Resonators
by Eduardo Jarauta and Francisco Falcone
Micromachines 2022, 13(8), 1190; https://doi.org/10.3390/mi13081190 - 28 Jul 2022
Cited by 1 | Viewed by 1684
Abstract
A new analytic design for multilayer stripline devices in planar circuit technology is presented. The Complementary Split Ring Resonator (CSRR) is used as a sub-wavelength resonant particle, which provides high-Q resonances in a compact size. The electromagnetic field distribution achieved along the stripline [...] Read more.
A new analytic design for multilayer stripline devices in planar circuit technology is presented. The Complementary Split Ring Resonator (CSRR) is used as a sub-wavelength resonant particle, which provides high-Q resonances in a compact size. The electromagnetic field distribution achieved along the stripline enables enhanced excitation of the resonators. An optimal solution for multilayer power dividers is presented, in a configuration in which each output is obtained in different layers and also in a different layer than the input line. The solution is expanded to design different devices, such as diplexers, resonators, and multi-frequency resonators, leading to vertical filters. As the resonances are achieved by stacking resonators, the effective circuit footprint is very compact. The proposed devices can be implemented in a volumetric chip fashion, allowing integration with planar transmission line circuits and flexible output connection placement. A complete analysis of the different devices is proposed, extracting and verifying their equivalent circuit models. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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Review

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23 pages, 1945 KiB  
Review
A Review on Electrohydrodynamic (EHD) Pump
by Yanhong Peng, Dongze Li, Xiaoyan Yang, Zisu Ma and Zebing Mao
Micromachines 2023, 14(2), 321; https://doi.org/10.3390/mi14020321 - 26 Jan 2023
Cited by 12 | Viewed by 3648
Abstract
In recent years, functional fluidic and gas electrohydrodynamic (EHD) pumps have received considerable attention due to their remarkable features, such as simple structure, quiet operation, and energy-efficient utilization. EHD pumps can be applied in various industrial applications, including flow transfer, thermal management, and [...] Read more.
In recent years, functional fluidic and gas electrohydrodynamic (EHD) pumps have received considerable attention due to their remarkable features, such as simple structure, quiet operation, and energy-efficient utilization. EHD pumps can be applied in various industrial applications, including flow transfer, thermal management, and actuator drive. In this paper, the authors reviewed the literature surrounding functional fluidic and gas EHD pumps regarding the following aspects: the initial observation of the EHD effect, mathematical modeling, and the choice of pump structure, electrode configuration, and working medium. Based on the review, we present a summary of the development and latest research on EHD pumps. This paper provides a critical analysis of the current limitations of EHD pumps and identifies potential areas for future research. Additionally, the potential application of artificial intelligence in the field of EHD pumps is discussed in the context of its cross-disciplinary nature. Many reviews on EHD pumps focus on rigid pumps, and the contribution of this review is to summarize and analyze soft EHD pumps that have received less attention, thus reducing the knowledge gap. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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18 pages, 3790 KiB  
Review
Zero Bias Operation: Photodetection Behaviors Obtained by Emerging Materials and Device Structures
by Juhyung Seo, Yeong Jae Kim and Hocheon Yoo
Micromachines 2022, 13(12), 2089; https://doi.org/10.3390/mi13122089 - 27 Nov 2022
Cited by 3 | Viewed by 1751
Abstract
Zero-biased photodetectors have desirable characteristics for potentially next-generation devices, including high efficiency, rapid response, and low power operation. In particular, the detector efficiency can be improved simply by changing the electrode contact geometry or morphological structure of materials, which give unique properties such [...] Read more.
Zero-biased photodetectors have desirable characteristics for potentially next-generation devices, including high efficiency, rapid response, and low power operation. In particular, the detector efficiency can be improved simply by changing the electrode contact geometry or morphological structure of materials, which give unique properties such as energy band bending, photo absorbance and electric field distribution. In addition, several combinations of materials enable or disable the operation of selective wavelengths of light detection. Herein, such recent progresses in photodetector operating at zero-bias voltage are reviewed. Considering the advantages and promises of these low-power photodetectors, this review introduces various zero-bias implementations and reviews the key points. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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20 pages, 5426 KiB  
Review
Highly Sensitive Self-Powered Biomedical Applications Using Triboelectric Nanogenerator
by Tapas Kamilya and Jinhyoung Park
Micromachines 2022, 13(12), 2065; https://doi.org/10.3390/mi13122065 - 25 Nov 2022
Cited by 4 | Viewed by 2259
Abstract
The triboelectric nanogenerator (TENG) is a promising research topic for the conversion of mechanical to electrical energy and its application in different fields. Among the various applications, self-powered bio-medical sensing application has become popular. The selection of a wide variety of materials and [...] Read more.
The triboelectric nanogenerator (TENG) is a promising research topic for the conversion of mechanical to electrical energy and its application in different fields. Among the various applications, self-powered bio-medical sensing application has become popular. The selection of a wide variety of materials and the simple design of devices has made it attractive for the applications of real-time self-powered healthcare sensing systems. Human activity is the source of mechanical energy which gets converted to electrical energy by TENG fitted to different body parts for the powering up of the biomedical sensing and detection systems. Among the various techniques, wearable sensing systems developed by TENG have shown their merit in the application of healthcare sensing and detection systems. Some key studies on wearable self-powered biomedical sensing systems based on TENG which have been carried out in the last seven years are summarized here. Furthermore, the key features responsible for the highly sensitive output of the self-powered sensors have been briefed. On the other hand, the challenges that need to be addressed for the commercialization of TENG-based biomedical sensors have been raised in order to develop versatile sensitive sensors, user-friendly devices, and to ensure the stability of the device over changing environments. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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22 pages, 6973 KiB  
Review
Smart Manufacturing Processes of Low-Tortuous Structures for High-Rate Electrochemical Energy Storage Devices
by Chun-Yang Kang and Yu-Sheng Su
Micromachines 2022, 13(9), 1534; https://doi.org/10.3390/mi13091534 - 16 Sep 2022
Cited by 2 | Viewed by 2646
Abstract
To maximize the performance of energy storage systems more effectively, modern batteries/supercapacitors not only require high energy density but also need to be fully recharged within a short time or capable of high-power discharge for electric vehicles and power applications. Thus, how to [...] Read more.
To maximize the performance of energy storage systems more effectively, modern batteries/supercapacitors not only require high energy density but also need to be fully recharged within a short time or capable of high-power discharge for electric vehicles and power applications. Thus, how to improve the rate capability of batteries or supercapacitors is a very important direction of research and engineering. Making low-tortuous structures is an efficient means to boost power density without replacing materials or sacrificing energy density. In recent years, numerous manufacturing methods have been developed to prepare low-tortuous configurations for fast ion transportation, leading to impressive high-rate electrochemical performance. This review paper summarizes several smart manufacturing processes for making well-aligned 3D microstructures for batteries and supercapacitors. These techniques can also be adopted in other advanced fields that require sophisticated structural control to achieve superior properties. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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