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Micromachines, Volume 14, Issue 6 (June 2023) – 182 articles

Cover Story (view full-size image): Currently, an urgent need in the field of wearable electronics is the development of flexible sensors that can be attached to the human body to monitor various physiological indicators and movements. In this work, we propose a method for forming an electrically conductive network of multi-walled carbon nanotubes (MWCNT) in a matrix of silicone elastomers to make stretchable sensors that are sensitive to mechanical strain. The high electrical and sensitivity characteristics of the sensors made it possible to fabricate a smart gesture recognition sensor system based on these elements, with a recognition accuracy of ~94%. The obtained results offer great prospects for the application of flexible CNT sensors in intelligent wearable devices (IWDs) for medical and industrial applications. View this paper
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10 pages, 2281 KiB  
Article
A Ku-Band Broadband Stacked FET Power Amplifier Using 0.15 μm GaAs pHEMT
by Jiaxuan Li, Yang Yuan, Bin Yuan, Jingxin Fan, Jialong Zeng and Zhongjun Yu
Micromachines 2023, 14(6), 1276; https://doi.org/10.3390/mi14061276 - 20 Jun 2023
Viewed by 1168
Abstract
To meet the application requirements of broadband radar systems for broadband power amplifiers, a Ku-band broadband power amplifier (PA) microwave monolithic integrated circuit (MMIC) based on a 0.15 µm gallium arsenide (GaAs) high-electron-mobility transistor (HEMT) technology is proposed in this paper. In this [...] Read more.
To meet the application requirements of broadband radar systems for broadband power amplifiers, a Ku-band broadband power amplifier (PA) microwave monolithic integrated circuit (MMIC) based on a 0.15 µm gallium arsenide (GaAs) high-electron-mobility transistor (HEMT) technology is proposed in this paper. In this design, the advantages of the stacked FET structure in the broadband PA design are illustrated by theoretical derivation. The proposed PA uses a two-stage amplifier structure and a two-way power synthesis structure to achieve high-power gain and high-power design, respectively. The fabricated power amplifier was tested under continuous wave conditions, and the test results showed a peak power of 30.8 dBm at 16 GHz. At 15 to 17.5 GHz, the output power was above 30 dBm with a PAE of more than 32%. The fractional bandwidth of the 3 dB output power was 30%. The chip area was 3.3 × 1.2 mm2 and included input and output test pads. Full article
(This article belongs to the Special Issue Recent Advances in Microwave Components and Devices)
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17 pages, 6906 KiB  
Article
Fixed-Diamond Abrasive Wire-Saw Cutting Force Modeling Based on Changes in Contact Arc Lengths
by Lie Liang, Shujuan Li, Kehao Lan, Jiabin Wang and Ruijiang Yu
Micromachines 2023, 14(6), 1275; https://doi.org/10.3390/mi14061275 - 20 Jun 2023
Cited by 1 | Viewed by 1899
Abstract
Monocrystalline silicon is widely used in the semiconductor market, but its hard and brittle physical properties make processing difficult. Fixed-diamond abrasive wire-saw (FAW) cutting is currently the most commonly used cutting method for hard and brittle materials due to advantages such as narrow [...] Read more.
Monocrystalline silicon is widely used in the semiconductor market, but its hard and brittle physical properties make processing difficult. Fixed-diamond abrasive wire-saw (FAW) cutting is currently the most commonly used cutting method for hard and brittle materials due to advantages such as narrow cutting seams, low pollution, low cutting force and simple cutting process. During the process of cutting a wafer, the contact between the part and the wire is curved, and the arc length changes during the cutting process. This paper establishes a model of contact arc length by analyzing the cutting system. At the same time, a model of the random distribution of abrasive particles is established to solve the cutting force during the cutting process, using iterative algorithms to calculate cutting forces and chip surface saw marks. The error between the experiment and simulation of the average cutting force in the stable stage is less than 6%, and the errors with respect to the central angle and curvature of the saw arc on the wafer surface are less than 5% between the experiment and simulation. The relationship between the bow angle, contact arc length and cutting parameters is studied using simulations. The results show that the variation trend of the bow angle and contact arc length is consistent, increasing with an increase in the part feed rate and decreasing with an increase in the wire velocity. Full article
(This article belongs to the Section D:Materials and Processing)
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13 pages, 5147 KiB  
Article
Metal–Phenolic Film Coated Quartz Crystal Microbalance as a Selective Sensor for Methanol Detection in Alcoholic Beverages
by Karekin D. Esmeryan, Yuliyan Lazarov, Teodor Grakov, Yulian I. Fedchenko, Lazar G. Vergov and Stefan Staykov
Micromachines 2023, 14(6), 1274; https://doi.org/10.3390/mi14061274 - 20 Jun 2023
Cited by 1 | Viewed by 1189
Abstract
The facile real-time monitoring of methyl content in fermented beverages is of fundamental significance in the alcohol and restaurant industry, since as little as 4 mL of methanol entering the blood may cause intoxication or blindness. So far, the practical applicability of available [...] Read more.
The facile real-time monitoring of methyl content in fermented beverages is of fundamental significance in the alcohol and restaurant industry, since as little as 4 mL of methanol entering the blood may cause intoxication or blindness. So far, the practical applicability of available methanol sensors, including the piezoresonance analogs, is somewhat limited to laboratory use due to the complexity and bulkiness of the measuring equipment involving multistep procedures. This article introduces a hydrophobic metal–phenolic film-coated quartz crystal microbalance (MPF-QCM) as a novel streamlined detector of methanol in alcoholic drinks. Unlike other QCM-based alcohol sensors, our device operates under saturated vapor pressure conditions, permitting rapid detection of methyl fractions up to seven times below the tolerable levels in spirits (e.g., whisky) while effectively suppressing the cross-sensitivity to interfering chemical compounds such as water, petroleum ether or ammonium hydroxide. Furthermore, the good surface adhesion of metal–phenolic complexes endows the MPF-QCM with superior long-term stability, contributing to the repeatable and reversible physical sorption of the target analytes. These features, combined with the lack of mass flow controllers, valves and connecting pipes delivering the gas mixture, outline the likelihood for future design of a portable MPF-QCM prototype suitable to point-of-use analysis in drinking establishments. Full article
(This article belongs to the Special Issue MEMS Sensors: Fabrication and Application)
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45 pages, 14359 KiB  
Review
MXene-Based Nanocomposites for Piezoelectric and Triboelectric Energy Harvesting Applications
by Durga Prasad Pabba, Mani Satthiyaraju, Ananthakumar Ramasdoss, Pandurengan Sakthivel, Natarajan Chidhambaram, Shanmugasundar Dhanabalan, Carolina Venegas Abarzúa, Mauricio J. Morel, Rednam Udayabhaskar, Ramalinga Viswanathan Mangalaraja, Radhamanohar Aepuru, Sathish-Kumar Kamaraj, Praveen Kumar Murugesan and Arun Thirumurugan
Micromachines 2023, 14(6), 1273; https://doi.org/10.3390/mi14061273 - 20 Jun 2023
Cited by 5 | Viewed by 3358
Abstract
Due to its superior advantages in terms of electronegativity, metallic conductivity, mechanical flexibility, customizable surface chemistry, etc., 2D MXenes for nanogenerators have demonstrated significant progress. In order to push scientific design strategies for the practical application of nanogenerators from the viewpoints of the [...] Read more.
Due to its superior advantages in terms of electronegativity, metallic conductivity, mechanical flexibility, customizable surface chemistry, etc., 2D MXenes for nanogenerators have demonstrated significant progress. In order to push scientific design strategies for the practical application of nanogenerators from the viewpoints of the basic aspect and recent advancements, this systematic review covers the most recent developments of MXenes for nanogenerators in its first section. In the second section, the importance of renewable energy and an introduction to nanogenerators, major classifications, and their working principles are discussed. At the end of this section, various materials used for energy harvesting and frequent combos of MXene with other active materials are described in detail together with the essential framework of nanogenerators. In the third, fourth, and fifth sections, the materials used for nanogenerators, MXene synthesis along with its properties, and MXene nanocomposites with polymeric materials are discussed in detail with the recent progress and challenges for their use in nanogenerator applications. In the sixth section, a thorough discussion of the design strategies and internal improvement mechanisms of MXenes and the composite materials for nanogenerators with 3D printing technologies are presented. Finally, we summarize the key points discussed throughout this review and discuss some thoughts on potential approaches for nanocomposite materials based on MXenes that could be used in nanogenerators for better performance. Full article
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14 pages, 6592 KiB  
Article
Optical Design of a Miniaturized 10× Periscope Zoom Lens for Smartphones
by Wen-Shing Sun, Yi-Hong Liu and Chuen-Lin Tien
Micromachines 2023, 14(6), 1272; https://doi.org/10.3390/mi14061272 - 20 Jun 2023
Viewed by 2838
Abstract
The size of the optical zoom system is important in smartphone camera design, especially as it governs the thickness of the smartphone. We present the optical design of a miniaturized 10× periscope zoom lens for smartphones. To achieve the desired level of miniaturization, [...] Read more.
The size of the optical zoom system is important in smartphone camera design, especially as it governs the thickness of the smartphone. We present the optical design of a miniaturized 10× periscope zoom lens for smartphones. To achieve the desired level of miniaturization, the conventional zoom lens can be replaced with a periscope zoom lens. In addition to this change in the optical design, the quality of the optical glass, which also affects the performance of the lens, must be considered. With advancements in the optical glass manufacturing process, aspheric lenses are becoming more widely used. In this study, aspheric lenses are incorporated into a design for a 10× optical zoom lens with a lens thickness of less than 6.5 mm and an eight-megapixel image sensor. Furthermore, tolerance analysis is carried out to prove its manufacturability. Full article
(This article belongs to the Special Issue Micro-Optics Devices)
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14 pages, 3773 KiB  
Article
Progress of Edge-Emitting Diode Lasers Based on Coupled-Waveguide Concept
by Lili Han, Zhaowei Wang, Nikita Yu. Gordeev, Mikhail V. Maximov, Xiansheng Tang, Artem A. Beckman, Grigoriy O. Kornyshov, Alexey S. Payusov, Yuri M. Shernyakov, Alexey E. Zhukov, Kuilong Li, Ruizhan Zhai, Zhongqing Jia, He Yang and Wei Zhang
Micromachines 2023, 14(6), 1271; https://doi.org/10.3390/mi14061271 - 20 Jun 2023
Cited by 1 | Viewed by 1379
Abstract
Semiconductor lasers have developed rapidly with the steady growth of the global laser market. The use of semiconductor laser diodes is currently considered to be the most advanced option for achieving the optimal combination of efficiency, energy consumption, and cost parameters of high-power [...] Read more.
Semiconductor lasers have developed rapidly with the steady growth of the global laser market. The use of semiconductor laser diodes is currently considered to be the most advanced option for achieving the optimal combination of efficiency, energy consumption, and cost parameters of high-power solid-state and fiber lasers. In this work, an approach for optical mode engineering in planar waveguides is investigated. The approach referred to as Coupled Large Optical Cavity (CLOC) is based on the resonant optical coupling between waveguides and allows the selection of high-order modes. The state-of-art of the CLOC operation is reviewed and discussed. We apply the CLOC concept in our waveguide design strategy. The results in both numerical simulation and experiment show that the CLOC approach can be considered a simple and cost-efficient solution for improving diode laser performance. Full article
(This article belongs to the Special Issue Integrated Photonics and Optoelectronics)
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15 pages, 45677 KiB  
Article
Mathematical Modeling and Experimental Study of Cutting Force for Cutting Hard and Brittle Materials in Fixed Abrasive Trepanning Drill
by Ruijiang Yu, Shujuan Li, Zhengkang Zou and Lie Liang
Micromachines 2023, 14(6), 1270; https://doi.org/10.3390/mi14061270 - 19 Jun 2023
Cited by 1 | Viewed by 1135
Abstract
Hard and brittle materials have excellent physical and mechanical performance, which are widely applied in the fields of microelectronics and optoelectronics. However, deep-hole machining of hard and brittle materials is very difficult and inefficient due to the high hardness and brittleness of these [...] Read more.
Hard and brittle materials have excellent physical and mechanical performance, which are widely applied in the fields of microelectronics and optoelectronics. However, deep-hole machining of hard and brittle materials is very difficult and inefficient due to the high hardness and brittleness of these materials. To improve the quality and efficiency of deep-hole machining of hard and brittle materials, according to the brittle crack fracture removal mechanism of hard and brittle materials and the cutting model of the trepanning cutter, an analytical cutting force prediction model of hard and brittle materials processed using a trepanning cutter is established. This experimental study of K9 optical glass machining shows that as the feeding rate increase, the cutting force increase, and as the spindle speed increase, the cutting force decrease. By comparing and verifying the theoretical and experimental values, the average errors of axial force and torque are 5.0% and 6.7%, respectively, and the maximum error is 14.9%. This paper analyzes the reasons for the errors. The results indicate that the cutting force theoretical model can be used to predict the axial force and torque of machining hard and brittle materials under the same conditions, which provides a theory for optimizing machining process parameters. Full article
(This article belongs to the Section D:Materials and Processing)
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9 pages, 4749 KiB  
Communication
A Miniature Multi-Functional Photoacoustic Probe
by Riqiang Lin, Jiaming Zhang, Wen Gao, Xiatian Wang, Shengmiao Lv, Kwok-Ho Lam and Xiaojing Gong
Micromachines 2023, 14(6), 1269; https://doi.org/10.3390/mi14061269 - 19 Jun 2023
Cited by 1 | Viewed by 1217
Abstract
Photoacoustic technology is a promising tool to provide morphological and functional information in biomedical research. To enhance the imaging efficiency, the reported photoacoustic probes have been designed coaxially involving complicated optical/acoustic prisms to bypass the opaque piezoelectric layer of ultrasound transducers, but this [...] Read more.
Photoacoustic technology is a promising tool to provide morphological and functional information in biomedical research. To enhance the imaging efficiency, the reported photoacoustic probes have been designed coaxially involving complicated optical/acoustic prisms to bypass the opaque piezoelectric layer of ultrasound transducers, but this has led to bulky probes and has hindered the applications in limited space. Though the emergence of transparent piezoelectric materials helps to save effort on the coaxial design, the reported transparent ultrasound transducers were still bulky. In this work, a miniature photoacoustic probe with an outer diameter of 4 mm was developed, in which an acoustic stack was made with a combination of transparent piezoelectric material and a gradient-index lens as a backing layer. The transparent ultrasound transducer exhibited a high center frequency of ~47 MHz and a −6 dB bandwidth of 29.4%, which could be easily assembled with a pigtailed ferrule of a single-mode fiber. The multi-functional capability of the probe was successfully validated through experiments of fluid flow sensing and photoacoustic imaging. Full article
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8 pages, 3948 KiB  
Article
Design and Manufacture of Polarization-Independent 3D SOI Vertical Optical Coupler
by Shengtao Yu, Xiaoyu Li and Chengqun Gui
Micromachines 2023, 14(6), 1268; https://doi.org/10.3390/mi14061268 - 18 Jun 2023
Viewed by 1174
Abstract
An optical coupler is a key input/output (I/O) device in a photonic integrated circuit (PIC), which plays the role of light-source import and modulated light output. In this research, a vertical optical coupler consisting of a concave mirror and a half-cone edge taper [...] Read more.
An optical coupler is a key input/output (I/O) device in a photonic integrated circuit (PIC), which plays the role of light-source import and modulated light output. In this research, a vertical optical coupler consisting of a concave mirror and a half-cone edge taper was designed. We optimized the structure of mirror curvature and taper through finite-difference-time-domain (FDTD) and ZEMAX simulation to achieve mode matching between SMF (single-mode fiber) and the optical coupler. The device was fabricated via laser-direct-writing 3D lithography, dry etching and deposition on a 3.5 µm silicon-on-insulator (SOI) platform. The test results show that the overall loss of the coupler and its connected waveguide at 1550 nm was 1.11 dB in transverse-electric (TE) mode and 2.25 dB in transverse-magnetic (TM) mode. Full article
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17 pages, 10362 KiB  
Article
Injection of Viscous Micro-Droplet via Nozzle-Driven Piezoelectric Micro-Jet and Its Performance Control Method
by Ti-Yuan Shan, Xiao-Sheng Wu, Yuan-Wen Hu, Xin-Di Lin and Dan-Feng Sun
Micromachines 2023, 14(6), 1267; https://doi.org/10.3390/mi14061267 - 18 Jun 2023
Viewed by 1355
Abstract
The inkjet printing technology based on piezoelectric micro-jets can effectively realize the efficient and high-precision processing of special-shaped structures. In this work, a nozzle-driven piezoelectric micro-jet device is proposed, and its structure and micro-jet process are described. ANSYS two-phase, two-way fluid–structure coupling simulation [...] Read more.
The inkjet printing technology based on piezoelectric micro-jets can effectively realize the efficient and high-precision processing of special-shaped structures. In this work, a nozzle-driven piezoelectric micro-jet device is proposed, and its structure and micro-jet process are described. ANSYS two-phase, two-way fluid–structure coupling simulation analysis is carried out, and the mechanism of the piezoelectric micro-jet is described in detail. The effects of voltage amplitude, input signal frequency, nozzle diameter and oil viscosity on the injection performance of the proposed device are studied, and a set of effective control methods is summarized. The correctness of the piezoelectric micro-jet mechanism and the feasibility of the proposed nozzle-driven piezoelectric micro-jet device are proved by experiments, and an injection performance test is carried out. The experimental results are consistent with the ANSYS simulation results, which confirms the correctness of the experiment. Finally, the stability and superiority of the proposed device are verified via comparation experiments. Full article
(This article belongs to the Special Issue Front Researches of Micro/Nano Sensors and Actuators)
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14 pages, 10703 KiB  
Article
Optical Logic Gates Based on Z-Shaped Silicon Waveguides at 1.55 μm
by Amer Kotb, Kyriakos E. Zoiros, Antonios Hatziefremidis and Chunlei Guo
Micromachines 2023, 14(6), 1266; https://doi.org/10.3390/mi14061266 - 18 Jun 2023
Cited by 4 | Viewed by 1145
Abstract
In the last ten years, silicon photonics has made considerable strides in terms of device functionality, performance, and circuit integration for a variety of practical uses, including communication, sensing, and information processing. In this work, we theoretically demonstrate a complete family of all-optical [...] Read more.
In the last ten years, silicon photonics has made considerable strides in terms of device functionality, performance, and circuit integration for a variety of practical uses, including communication, sensing, and information processing. In this work, we theoretically demonstrate a complete family of all-optical logic gates (AOLGs), including XOR, AND, OR, NOT, NOR, NAND, and XNOR, through finite-difference-time-domain simulations using compact silicon-on-silica optical waveguides that operate at 1.55 μm. Three slots, grouped in the shape of the letter Z, make up the suggested waveguide. The function of the target logic gates is based on constructive and destructive interferences that result from the phase difference experienced by the launched input optical beams. These gates are evaluated against the contrast ratio (CR) by investigating the impact of key operating parameters on this metric. The obtained results indicate that the proposed waveguide can realize AOLGs at a higher speed of 120 Gb/s with better CRs compared to other reported designs. This suggests that AOLGs could be realized in an affordable manner and with improved outcomes to enable the satisfaction of the current and future requirements of lightwave circuits and systems that critically rely on AOLGs as core building elements. Full article
(This article belongs to the Special Issue Novel Silicon-Based Optoelectronic Devices)
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17 pages, 7839 KiB  
Article
Research on Intelligent Wheelchair Attitude-Based Adjustment Method Based on Action Intention Recognition
by Jianwei Cui, Zizheng Huang, Xiang Li, Linwei Cui, Yucheng Shang and Liyan Tong
Micromachines 2023, 14(6), 1265; https://doi.org/10.3390/mi14061265 - 17 Jun 2023
Cited by 2 | Viewed by 1266
Abstract
At present, research on intelligent wheelchairs mostly focuses on motion control, while research on attitude-based adjustment is relatively insufficient. The existing methods for adjusting wheelchair posture generally lack collaborative control and good human–machine collaboration. This article proposes an intelligent wheelchair posture-adjustment method based [...] Read more.
At present, research on intelligent wheelchairs mostly focuses on motion control, while research on attitude-based adjustment is relatively insufficient. The existing methods for adjusting wheelchair posture generally lack collaborative control and good human–machine collaboration. This article proposes an intelligent wheelchair posture-adjustment method based on action intention recognition by studying the relationship between the force changes on the contact surface between the human body and the wheelchair and the action intention. This method is applied to a multi-part adjustable electric wheelchair, which is equipped with multiple force sensors to collect pressure information from various parts of the passenger’s body. The upper level of the system converts the pressure data into the form of a pressure distribution map, extracts the shape features using the VIT deep learning model, identifies and classifies them, and ultimately identifies the action intentions of the passengers. Based on different action intentions, the electric actuator is controlled to adjust the wheelchair posture. After testing, this method can effectively collect the body pressure data of passengers, with an accuracy of over 95% for the three common intentions of lying down, sitting up, and standing up. The wheelchair can adjust its posture based on the recognition results. By adjusting the wheelchair posture through this method, users do not need to wear additional equipment and are less affected by the external environment. The target function can be achieved with simple learning, which has good human–machine collaboration and can solve the problem of some people having difficulty adjusting the wheelchair posture independently during wheelchair use. Full article
(This article belongs to the Special Issue Assistive Robots)
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25 pages, 9679 KiB  
Article
Thermo-Mechanical Fluid–Structure Interaction Numerical Modelling and Experimental Validation of MEMS Electrothermal Actuators for Aqueous Biomedical Applications
by Thomas Sciberras, Marija Demicoli, Ivan Grech, Bertram Mallia, Pierluigi Mollicone and Nicholas Sammut
Micromachines 2023, 14(6), 1264; https://doi.org/10.3390/mi14061264 - 17 Jun 2023
Cited by 2 | Viewed by 979
Abstract
Recent developments in MEMS technologies have made such devices attractive for use in applications that involve precision engineering and scalability. In the biomedical industry, MEMS devices have gained popularity in recent years for use as single-cell manipulation and characterisation tools. A niche application [...] Read more.
Recent developments in MEMS technologies have made such devices attractive for use in applications that involve precision engineering and scalability. In the biomedical industry, MEMS devices have gained popularity in recent years for use as single-cell manipulation and characterisation tools. A niche application is the mechanical characterisation of single human red blood cells, which may exhibit certain pathological conditions that impart biomarkers of quantifiable magnitude that are potentially detectable via MEMS devices. Such applications come with stringent thermal and structural specifications wherein the potential device candidates must be able to function with no exceptions. This work presents a state-of-the-art numerical modelling methodology that is capable of accurately predicting MEMS device performance in various media, including aqueous ones. The method is strongly coupled in nature, whereby thermal as well as structural degrees of freedom are transferred to and from finite element and finite volume solvers at every iteration. This method therefore provides MEMS design engineers with a reliable tool that can be used in design and development stages and helps to avoid total reliability on experimental testing. The proposed numerical model is validated via a series of physical experiments. Four MEMS electrothermal actuators with cascaded V-shaped drivers are presented. With the use of the newly proposed numerical model as well as the experimental testing, the MEMS devices’ suitability for biomedical applications is confirmed. Full article
(This article belongs to the Special Issue MEMS Microgrippers and Their Applications)
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16 pages, 11610 KiB  
Article
Comparison of Surface Morphology and Tool Wear in the Machining of Ti-6Al-4V Alloys with Uncoated and TiAlN Tools under Dry, Minimum Quantity Lubrication, Flood Cooling, and Low-Temperature Spray Jet Cooling Conditions
by Jinfu Zhao, Zhanqiang Liu, Zipeng Gong, Annan Liu, Yukui Cai, Bing Wang, Qinghua Song, Xiaoliang Liang, Yanbin Zhang, Zhicheng Zhang and Haiyang Ji
Micromachines 2023, 14(6), 1263; https://doi.org/10.3390/mi14061263 - 17 Jun 2023
Cited by 2 | Viewed by 1077
Abstract
TiAlN-coated carbide tools have been used to machine Ti-6Al-4V alloys in aviation workshops. However, the effect of TiAlN coating on surface morphology and tool wear in the processing of Ti-6Al-4V alloys under various cooling conditions has not been reported in the public published [...] Read more.
TiAlN-coated carbide tools have been used to machine Ti-6Al-4V alloys in aviation workshops. However, the effect of TiAlN coating on surface morphology and tool wear in the processing of Ti-6Al-4V alloys under various cooling conditions has not been reported in the public published literature. In our current research, turning experiments of Ti-6Al-4V with uncoated and TiAlN tools under dry, MQL, flood cooling, and cryogenic spray jet cooling conditions were carried out. The machined surface roughness and tool life were selected as the two main quantitative indexes for estimating the effects of TiAlN coating on the cutting performance of Ti-6Al-4V under various cooling conditions. The results showed that TiAlN coating makes it hard to improve the machined surface roughness and tool wear of a cutting titanium alloy at a low speed of 75 m/min compared to that achieved by uncoated tools. The TiAlN tools presented excellent tool life in turning Ti-6Al-4V at a high speed of 150 m/min compared to that achieved by uncoated tools. From the perspective of obtaining finished surface roughness and superior tool life in high-speed turning Ti-6Al-4V, the selection of TiAlN tools is feasible and reasonable under the cryogenic spray jet cooling condition. The dedicative results and conclusions of this research could guide the optimized selection of cutting tools in machining Ti-6Al-4V for the aviation industry. Full article
(This article belongs to the Special Issue High-Quality Surface Integrity of Ultra-Precision Machining)
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10 pages, 2582 KiB  
Article
SiC Electrochemical Sensor Validation for Alzheimer Aβ42 Antigen Detection
by Brayan Montero-Arevalo, Bianca I. Seufert, Mohammad S. Hossain, Evans Bernardin, Arash Takshi, Stephen E. Saddow and Norelli Schettini
Micromachines 2023, 14(6), 1262; https://doi.org/10.3390/mi14061262 - 16 Jun 2023
Cited by 1 | Viewed by 1640
Abstract
Alzheimer’s disease (AD) is a neurodegenerative disease with only late-stage detection; thus, diagnosis is made when it is no longer possible to treat the disease, only its symptoms. Consequently, this often leads to caregivers who are the patient’s relatives, which adversely impacts the [...] Read more.
Alzheimer’s disease (AD) is a neurodegenerative disease with only late-stage detection; thus, diagnosis is made when it is no longer possible to treat the disease, only its symptoms. Consequently, this often leads to caregivers who are the patient’s relatives, which adversely impacts the workforce along with severely diminishing the quality of life for all involved. It is, therefore, highly desirable to develop a fast, effective and reliable sensor to enable early-stage detection in an attempt to reverse disease progression. This research validates the detection of amyloid-beta 42 (Aβ42) using a Silicon Carbide (SiC) electrode, a fact that is unprecedented in the literature. Aβ42 is considered a reliable biomarker for AD detection, as reported in previous studies. To validate the detection with a SiC-based electrochemical sensor, a gold (Au) electrode-based electrochemical sensor was used as a control. The same cleaning, functionalization and Aβ1–28 antibody immobilization steps were used on both electrodes. Sensor validation was carried out by means of Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) aiming to detect an 0.5 µg·mL−142 concentration in 0.1 M buffer solution as a proof of concept. A repeatable peak directly related to the presence of Aβ42 was observed, indicating that a fast SiC-based electrochemical sensor was constructed and may prove to be a useful approach for the early detection of AD. Full article
(This article belongs to the Special Issue Biosensors for Biomedical and Environmental Applications)
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11 pages, 4859 KiB  
Article
Comparison of Robot-Assisted and Manual Cannula Insertion in Simulated Big-Bubble Deep Anterior Lamellar Keratoplasty
by Yinzheng Zhao, Anne-Marie Jablonka, Niklas A. Maierhofer, Hessam Roodaki, Abouzar Eslami, Mathias Maier, Mohammad Ali Nasseri and Daniel Zapp
Micromachines 2023, 14(6), 1261; https://doi.org/10.3390/mi14061261 - 16 Jun 2023
Cited by 1 | Viewed by 832
Abstract
This study aimed to compare the efficacy of robot-assisted and manual cannula insertion in simulated big-bubble deep anterior lamellar keratoplasty (DALK). Novice surgeons with no prior experience in performing DALK were trained to perform the procedure using manual or robot-assisted techniques. The results [...] Read more.
This study aimed to compare the efficacy of robot-assisted and manual cannula insertion in simulated big-bubble deep anterior lamellar keratoplasty (DALK). Novice surgeons with no prior experience in performing DALK were trained to perform the procedure using manual or robot-assisted techniques. The results showed that both methods could generate an airtight tunnel in the porcine cornea, and result in successful generation of a deep stromal demarcation plane representing sufficient depth reached for big-bubble generation in most cases. However, the combination of intraoperative OCT and robotic assistance received a significant increase in the depth of achieved detachment in non-perforated cases, comprising a mean of 89% as opposed to 85% of the cornea in manual trials. This research suggests that robot-assisted DALK may offer certain advantages over manual techniques, particularly when used in conjunction with intraoperative OCT. Full article
(This article belongs to the Special Issue Assistive Robots)
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14 pages, 3736 KiB  
Article
Numerical Investigation of Transonic Flow-Induced Spontaneous Condensation in Micro-Ejector Nozzles
by Yu Han, Xiaodong Wang, Wei Wang, Yuan Xien Lee and Ao Li
Micromachines 2023, 14(6), 1260; https://doi.org/10.3390/mi14061260 - 16 Jun 2023
Cited by 1 | Viewed by 980
Abstract
Micro-cooling systems are compact refrigeration systems widely applicable in microchemical analysis, biomedicine, and microelectromechanical systems (MEMS). These systems rely on the use of micro-ejectors to achieve precise, fast, and reliable flow and temperature control. However, the efficiency of micro-cooling systems is hindered by [...] Read more.
Micro-cooling systems are compact refrigeration systems widely applicable in microchemical analysis, biomedicine, and microelectromechanical systems (MEMS). These systems rely on the use of micro-ejectors to achieve precise, fast, and reliable flow and temperature control. However, the efficiency of micro-cooling systems is hindered by spontaneous condensation occurring downstream of the nozzle throat and within the nozzle itself, impacting the performance of the micro-ejector. A micro-scale ejector mathematical model describing wet steam flow was simulated to investigate the steam condensation phenomenon and its influence on flow, incorporating equations for liquid phase mass fraction and droplet number density transfer. The simulation results of wet vapor flow and ideal gas flow were compared and analyzed. The findings revealed that the pressure at the micro-nozzle outlet exceeded predictions based on the ideal gas assumption, while the velocity fell below it. These discrepancies indicated that condensation of the working fluid reduces the pumping capacity and the efficiency of the micro-cooling system. Furthermore, simulations explored the impact of inlet pressure and temperature conditions on spontaneous condensation within the nozzle. The results demonstrated that the properties of the working fluid directly influence transonic flow condensation, underscoring the importance of selecting appropriate working fluid parameters for nozzle design to ensure nozzle stability and optimal micro-ejector operation. Full article
(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)
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29 pages, 5579 KiB  
Review
A Review of Phase-Change Materials and Their Potential for Reconfigurable Intelligent Surfaces
by Randy Matos and Nezih Pala
Micromachines 2023, 14(6), 1259; https://doi.org/10.3390/mi14061259 - 16 Jun 2023
Cited by 4 | Viewed by 2702
Abstract
Phase-change materials (PCMs) and metal-insulator transition (MIT) materials have the unique feature of changing their material phase through external excitations such as conductive heating, optical stimulation, or the application of electric or magnetic fields, which, in turn, results in changes to their electrical [...] Read more.
Phase-change materials (PCMs) and metal-insulator transition (MIT) materials have the unique feature of changing their material phase through external excitations such as conductive heating, optical stimulation, or the application of electric or magnetic fields, which, in turn, results in changes to their electrical and optical properties. This feature can find applications in many fields, particularly in reconfigurable electrical and optical structures. Among these applications, the reconfigurable intelligent surface (RIS) has emerged as a promising platform for both wireless RF applications as well as optical ones. This paper reviews the current, state-of-the-art PCMs within the context of RIS, their material properties, their performance metrics, some applications found in the literature, and how they can impact the future of RIS. Full article
(This article belongs to the Section E:Engineering and Technology)
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13 pages, 3959 KiB  
Article
Saturation-Induced Phase Error Compensation Method Using Complementary Phase
by Yingying Wan, Yiping Cao, Min Xu and Tao Tang
Micromachines 2023, 14(6), 1258; https://doi.org/10.3390/mi14061258 - 16 Jun 2023
Cited by 2 | Viewed by 1007
Abstract
Intensity saturation can induce phase error and, thus, measurement error in fringe projection profilometry. To reduce saturation-induced phase errors, a compensation method is developed. The mathematical model of saturation-induced phase errors is analyzed for N-step phase-shifting profilometry, and the phase error is [...] Read more.
Intensity saturation can induce phase error and, thus, measurement error in fringe projection profilometry. To reduce saturation-induced phase errors, a compensation method is developed. The mathematical model of saturation-induced phase errors is analyzed for N-step phase-shifting profilometry, and the phase error is approximately N-folder of the frequency of the projected fringe. Additional N-step phase-shifting fringe patterns with initial phase-shift π/N are projected for generating a complementary phase map. The final phase map is obtained by averaging the original phase map extracted from the original fringe patterns and the complementary phase map, and then the phase error can be canceled out. Both simulations and experiments demonstrated that the proposed method can substantially reduce the saturation-induced phase error and realize accurate measurements for a highly dynamic range of scenarios. Full article
(This article belongs to the Special Issue Three-Dimensional Display Technologies)
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13 pages, 7148 KiB  
Article
Microdroplet PCR in Microfluidic Chip Based on Constant Pressure Regulation
by Luyang Duanmu, Yuanhua Yu and Xiangkai Meng
Micromachines 2023, 14(6), 1257; https://doi.org/10.3390/mi14061257 - 15 Jun 2023
Viewed by 1572
Abstract
A device and method for the constant pressure regulation of microdroplet PCR in microfluidic chips are developed to optimize for the microdroplet movement, fragmentation, and bubble generation in microfluidic chips. In the developed device, an air source device is adopted to regulate the [...] Read more.
A device and method for the constant pressure regulation of microdroplet PCR in microfluidic chips are developed to optimize for the microdroplet movement, fragmentation, and bubble generation in microfluidic chips. In the developed device, an air source device is adopted to regulate the pressure in the chip, such that microdroplet generation and PCR amplification without bubbles can be achieved. In 3 min, the sample in 20 μL will be distributed into nearly 50,000 water-in-oil droplets exhibiting a diameter of about 87 μm, and the microdroplet will be subjected to a close arrangement in the chip without air bubbles. The device and chip are adopted to quantitatively detect human genes. As indicated by the experimental results, a good linear relationship exists between the detection signal and DNA concentration ranging from 101 to 105 copies/μL (R2 = 0.999). The microdroplet PCR devices based on constant pressure regulation chips exhibit a wide variety of advantages (e.g., achieving high pollution resistance, microdroplet fragmentation and integration avoidance, reducing human interference, and standardizing results). Thus, microdroplet PCR devices based on constant pressure regulation chips have promising applications for nucleic acid quantification. Full article
(This article belongs to the Topic Advances in Microfluidics and Lab on a Chip Technology)
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18 pages, 6283 KiB  
Article
A Low-Noise Interface ASIC for MEMS Disk Resonator Gyroscope
by Wenbo Zhang, Liang Yin, Yihang Wang, Risheng Lv, Haifeng Zhang, Weiping Chen, Xiaowei Liu and Qiang Fu
Micromachines 2023, 14(6), 1256; https://doi.org/10.3390/mi14061256 - 15 Jun 2023
Viewed by 1343
Abstract
This paper proposes a low-noise interface application-specific integrated circuit (ASIC) for a microelectromechanical systems (MEMS) disk resonator gyroscope (DRG) which operates in force-to-rebalance (FTR) mode. The ASIC employs an analog closed-loop control scheme which incorporates a self-excited drive loop, a rate loop and [...] Read more.
This paper proposes a low-noise interface application-specific integrated circuit (ASIC) for a microelectromechanical systems (MEMS) disk resonator gyroscope (DRG) which operates in force-to-rebalance (FTR) mode. The ASIC employs an analog closed-loop control scheme which incorporates a self-excited drive loop, a rate loop and a quadrature loop. A ΣΔ modulator and a digital filter are also contained in the design to digitize the analog output besides the control loops. The clocks for the modulator and digital circuits are both generated by the self-clocking circuit, which avoids the requirement of additional quartz crystal. A system-level noise model is established to determine the contribution of each noise source in order to reduce the noise at the output. A noise optimization solution suitable for chip integration is proposed based on system-level analysis, which can effectively avoid the effects of the 1/f noise of the PI amplifier and the white noise of the feedback element. A performance of 0.0075°/√h angle random walk (ARW) and 0.038°/h bias instability (BI) is achieved using the proposed noise optimization method. The ASIC is fabricated in a 0.35 μm process with a die area of 4.4 mm × 4.5 mm and power consumption of 50 mW. Full article
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15 pages, 5944 KiB  
Article
Three-Dimensional Integrated Fan-Out Wafer-Level Package Micro-Bump Electromigration Study
by Wenchao Tian, Ran Gao, Lin Gu, Haoyue Ji and Liming Zhou
Micromachines 2023, 14(6), 1255; https://doi.org/10.3390/mi14061255 - 15 Jun 2023
Cited by 2 | Viewed by 1330
Abstract
To meet the demands for miniaturization and multi-functional and high-performance electronics applications, the semiconductor industry has shifted its packaging approach to multi-chip vertical stacking. Among the advanced packaging technologies for high-density interconnects, the most persistent factor affecting their reliability is the electromigration (EM) [...] Read more.
To meet the demands for miniaturization and multi-functional and high-performance electronics applications, the semiconductor industry has shifted its packaging approach to multi-chip vertical stacking. Among the advanced packaging technologies for high-density interconnects, the most persistent factor affecting their reliability is the electromigration (EM) problem on the micro-bump. The operating temperature and the operating current density are the main factors affecting the EM phenomenon. Therefore, when a micro-bump structure is in the electrothermal environment, the EM failure mechanism of the high-density integrated packaging structure must be studied. To investigate the relationship between loading conditions and EM failure time in micro-bump structures, this study established an equivalent model of the vertical stacking structure of fan-out wafer-level packages. Then, the electrothermal interaction theory was used to carry out numerical simulations in an electrothermal environment. Finally, the MTTF equation was invoked, with Sn63Pb37 as the bump material, and the relationship between the operating environment and EM lifetime was investigated. The results showed that the current aggregation was the location where the bump structure was most susceptible to EM failure. The accelerating effect of the temperature on the EM failure time was more obvious at a current density of 3.5 A/cm2, which was 27.51% shorter than 4.5 A/cm2 at the same temperature difference. When the current density exceeded 4.5 A/cm2, the change in the failure time was not obvious, and the maximum critical value of the micro-bump failure was 4 A/cm2~4.5 A/cm2. Full article
(This article belongs to the Section A:Physics)
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14 pages, 4880 KiB  
Article
Dual-Band and Wideband Bandpass Filters Using Coupled Lines and Tri-Stepped Impedance Stubs
by Abdullah J. Alazemi
Micromachines 2023, 14(6), 1254; https://doi.org/10.3390/mi14061254 - 14 Jun 2023
Cited by 2 | Viewed by 1093
Abstract
In this paper, two bandpass filters—one with a dual-band response and the other with a wideband response—were designed, implemented, and experimented with. The filters are based on the novel combination of series coupled lines and tri-stepped impedance stubs. However, coupled lines along with [...] Read more.
In this paper, two bandpass filters—one with a dual-band response and the other with a wideband response—were designed, implemented, and experimented with. The filters are based on the novel combination of series coupled lines and tri-stepped impedance stubs. However, coupled lines along with tri-stepped impedance open stubs (TSIOSs) give a third-order dual passband response. The advantage of dual-band filters using coupled lines and TSIOSs is that they have wide passbands that are close together and separated by a single transmission zero. In contrast, the inclusion of tri-stepped impedance short-circuited stubs (TSISSs) instead of TSIOSs provides a fifth-order wide passband response. The advantage of wideband bandpass filters using coupled lines and TSISSs is that they have a very good selectivity factor. Theoretical analysis was carried out to validate both filter configurations. The tested bandpass filter using coupled lines and TSIOS units had two close wide passbands operating at 0.92 and 1.52 GHz center frequencies, respectively. The dual-band bandpass filter was implemented to operate in GSM and GPS applications. The first passband had a 3 dB fractional bandwidth (FBW) of 38.04%, while the second passband had a 3 dB FBW of 22.36%. The experimental result of the wideband bandpass filter (with coupled lines and TSISS units) had a center frequency of 1.51 GHz with a 3 dB fractional bandwidth of 62.91% and a selectivity factor of 0.90. A good congruence was demonstrated between the full-wave simulated and tested results for both filters. Full article
(This article belongs to the Special Issue Microwave Passive Components)
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34 pages, 6074 KiB  
Review
A Review of Fingerprint Sensors: Mechanism, Characteristics, and Applications
by Yirong Yu, Qiming Niu, Xuyang Li, Jianshe Xue, Weiguo Liu and Dabin Lin
Micromachines 2023, 14(6), 1253; https://doi.org/10.3390/mi14061253 - 14 Jun 2023
Cited by 4 | Viewed by 6757
Abstract
Identification technology based on biometrics is a branch of research that employs the unique individual traits of humans to authenticate identity, which is the most secure method of identification based on its exceptional high dependability and stability of human biometrics. Common biometric identifiers [...] Read more.
Identification technology based on biometrics is a branch of research that employs the unique individual traits of humans to authenticate identity, which is the most secure method of identification based on its exceptional high dependability and stability of human biometrics. Common biometric identifiers include fingerprints, irises, and facial sounds, among others. In the realm of biometric recognition, fingerprint recognition has gained success with its convenient operation and fast identif ication speed. Different fingerprint collecting techniques, which supply fingerprint information for fingerprint identification systems, have attracted a significant deal of interest in authentication technology regarding fingerprint identification systems. This work presents several fingerprint acquisition techniques, such as optical capacitive and ultrasonic, and analyzes acquisition types and structures. In addition, the pros and drawbacks of various sensor types, as well as the limits and benefits of optical, capacitive, and ultrasonic kinds, are discussed. It is the necessary stage for the application of the Internet of Things (IoT). Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors and Actuators, 2nd Edition)
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21 pages, 3029 KiB  
Article
Research on Pedestrian Indoor Positioning Based on Two-Step Robust Adaptive Cubature Kalman Filter with Smartphone MEMS Sensors
by Jijun Geng, Xuexiang Yu, Congcong Wu and Guoqing Zhang
Micromachines 2023, 14(6), 1252; https://doi.org/10.3390/mi14061252 - 14 Jun 2023
Viewed by 1016
Abstract
With the development of location-based service (LBS), indoor positioning based on pedestrian dead reckoning (PDR) has become a hot research topic. Smartphones are becoming more popular for indoor positioning. This paper proposes a two-step robust-adaptive-cubature Kalman filter (RACKF) algorithm based on smartphone micro-electro-mechanical-system [...] Read more.
With the development of location-based service (LBS), indoor positioning based on pedestrian dead reckoning (PDR) has become a hot research topic. Smartphones are becoming more popular for indoor positioning. This paper proposes a two-step robust-adaptive-cubature Kalman filter (RACKF) algorithm based on smartphone micro-electro-mechanical-system (MEMS) sensor fusion for indoor positioning. To estimate pedestrian heading, a quaternion-based robust-adaptive-cubature Kalman filter algorithm is proposed. Firstly, the model noise parameters are adaptively corrected based on the fading-memory-weighting method and the limited-memory-weighting method. The memory window of the limited-memory-weighting algorithm is modified based on the characteristics of pedestrian walking. Secondly, an adaptive factor is constructed based on the partial state inconsistency to overcome filtering-model deviation and abnormal disturbances. Finally, to identify and control the measurement outliers, the robust factor based on maximum-likelihood estimation is introduced into the filtering to enhance the robustness of heading estimation and support more robust dynamic-position estimation. In addition, based on the accelerometer information, a nonlinear model is constructed and the empirical model is used to estimate the step length. Combining heading and step length, the two-step robust-adaptive-cubature Kalman filter is proposed to improve the pedestrian-dead-reckoning method, which enhances the adaptability and robustness of the algorithm and further improves the accuracy of the plane-position solution. The adaptive factor based on the prediction residual and the robust factor based on the maximum-likelihood estimation are introduced into the filter to improve the adaptability and robustness of the filter, reduce the positioning error, and improve the accuracy of the pedestrian-dead-reckoning method. Three different smartphones are used to validate the proposed algorithm in an indoor environment. Additionally, the experimental results confirm the algorithm’s effectiveness. From the results of the three smartphones, the root mean square error (RMSE) of the indoor-positioning results obtained by the proposed method is about 1.3–1.7 m. Full article
(This article belongs to the Special Issue Advances in MEMS Theory and Applications, 2nd Edition)
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11 pages, 4591 KiB  
Article
Design of a Novel Compact Bandpass Filter Based on Low-Cost Through-Silicon-Via Technology
by Hai Dong, Yingtao Ding, Han Wang, Xingling Pan, Mingrui Zhou and Ziyue Zhang
Micromachines 2023, 14(6), 1251; https://doi.org/10.3390/mi14061251 - 14 Jun 2023
Cited by 1 | Viewed by 1211
Abstract
Three-dimensional (3D) integration based on through-silicon-via (TSV) technology provides a solution to the miniaturization of electronic systems. In this paper, novel integrated passive devices (IPDs) including capacitor, inductor, and bandpass filter are designed by employing TSV structures. For lower manufacturing costs, polyimide (PI) [...] Read more.
Three-dimensional (3D) integration based on through-silicon-via (TSV) technology provides a solution to the miniaturization of electronic systems. In this paper, novel integrated passive devices (IPDs) including capacitor, inductor, and bandpass filter are designed by employing TSV structures. For lower manufacturing costs, polyimide (PI) liners are used in the TSVs. The influences of structural parameters of TSVs on the electrical performance of the TSV-based capacitor and inductor are individually evaluated. Moreover, with the topologies of capacitor and inductor elements, a compact third-order Butterworth bandpass filter with a central frequency of 2.4 GHz is developed, and the footprint is only 0.814 mm × 0.444 mm. The simulated 3-dB bandwidth of the filter is 410 MHz, and the fraction bandwidth (FBW) is 17%. Besides, the in-band insertion loss is less than 2.63 dB, and the return loss in the passband is better than 11.4 dB, showing good RF performance. Furthermore, as the filter is fully formed by identical TSVs, it not only features a simple architecture and low cost, but also provides a promising idea for facilitating the system integration and layout camouflaging of radio frequency (RF) devices. Full article
(This article belongs to the Special Issue State-of-the-Art CMOS and MEMS Devices)
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16 pages, 10060 KiB  
Article
1-Bit Transmission-Type Digital Programmable Coding Metasurface with Multi-Functional Beam-Shaping Capability for Ka-Band Applications
by Aqeel Hussain Naqvi, Duc Anh Pham, Syed Imran Hussain Shah and Sungjoon Lim
Micromachines 2023, 14(6), 1250; https://doi.org/10.3390/mi14061250 - 14 Jun 2023
Cited by 2 | Viewed by 1638
Abstract
Digital programmable coding metasurfaces (DPCMs) have recently attracted enormous attention and have been broadly applied, owing to their ability to manipulate electromagnetic (EM) wave behaviours and programmable multi-functionality. Recent DPCM works are divided into reflection and transmission types (R-DPCM and T-DPCM, respectively); however, [...] Read more.
Digital programmable coding metasurfaces (DPCMs) have recently attracted enormous attention and have been broadly applied, owing to their ability to manipulate electromagnetic (EM) wave behaviours and programmable multi-functionality. Recent DPCM works are divided into reflection and transmission types (R-DPCM and T-DPCM, respectively); however, there are only a few reported T-DPCM works in the millimetre-wave spectrum, owing to the difficulty of realising the large-phase controllable range while maintaining low transmission losses with electronic control components. Consequently, most millimetre-wave T-DPCMs are demonstrated only with limited functions in a single design. Additionally, all these designs use high-cost substrate materials that constrain practical applicability, owing to cost-ineffectiveness. Herein, we propose a 1-bit T-DPCM that simultaneously performs three dynamic beam-shaping functions with a single structure for millimetre-wave applications. The proposed structure is completely constructed using low-cost FR-4 materials, and operation of each meta-cell is manipulated using PIN-diodes, thus driving the achievement of multiple effective dynamic functionalities including dual-beam scanning, multi-beam shaping, and orbital-angular-momentum-mode generation. It should be noted that there are no reported millimetre-wave T-DPCMs demonstrating multi-function design, thus showing a gap in the recent literature of millimetre-wave T-DPCMs. Moreover, cost-effectiveness can be significantly enhanced, owing to the construction of the proposed T-DPCM using only low-cost material. Full article
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16 pages, 2250 KiB  
Review
How Practical Are Fiber Supercapacitors for Wearable Energy Storage Applications?
by Parya Teymoory, Jingzhou Zhao and Caiwei Shen
Micromachines 2023, 14(6), 1249; https://doi.org/10.3390/mi14061249 - 14 Jun 2023
Cited by 1 | Viewed by 1373
Abstract
Future wearable electronics and smart textiles face a major challenge in the development of energy storage devices that are high-performing while still being flexible, lightweight, and safe. Fiber supercapacitors are one of the most promising energy storage technologies for such applications due to [...] Read more.
Future wearable electronics and smart textiles face a major challenge in the development of energy storage devices that are high-performing while still being flexible, lightweight, and safe. Fiber supercapacitors are one of the most promising energy storage technologies for such applications due to their excellent electrochemical characteristics and mechanical flexibility. Over the past decade, researchers have put in tremendous effort and made significant progress on fiber supercapacitors. It is now the time to assess the outcomes to ensure that this kind of energy storage device will be practical for future wearable electronics and smart textiles. While the materials, fabrication methods, and energy storage performance of fiber supercapacitors have been summarized and evaluated in many previous publications, this review paper focuses on two practical questions: Are the reported devices providing sufficient energy and power densities to wearable electronics? Are the reported devices flexible and durable enough to be integrated into smart textiles? To answer the first question, we not only review the electrochemical performance of the reported fiber supercapacitors but also compare them to the power needs of a variety of commercial electronics. To answer the second question, we review the general approaches to assess the flexibility of wearable textiles and suggest standard methods to evaluate the mechanical flexibility and stability of fiber supercapacitors for future studies. Lastly, this article summarizes the challenges for the practical application of fiber supercapacitors and proposes possible solutions. Full article
(This article belongs to the Special Issue Micro Supercapacitors for Energy Storage and Power Management)
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3 pages, 174 KiB  
Editorial
Editorial for the Special Issue on Emerging Micro Manufacturing Technologies and Applications
by Nikolaos Tapoglou
Micromachines 2023, 14(6), 1248; https://doi.org/10.3390/mi14061248 - 14 Jun 2023
Viewed by 660
Abstract
In recent years, the field of micromachining has gained a lot of traction owing to the drive towards lightweighting, electrification, and sustainability [...] Full article
(This article belongs to the Special Issue Emerging Micro Manufacturing Technologies and Applications)
20 pages, 5265 KiB  
Article
Optimization of Multiple Reactants in a Membrane-Less Direct Methanol Fuel Cell (DMFC)
by Iesti Hajar Hanapi, Siti Kartom Kamarudin, Azran Mohd Zainoodin, Umi Azmah Hasran and Zulfirdaus Zakaria
Micromachines 2023, 14(6), 1247; https://doi.org/10.3390/mi14061247 - 14 Jun 2023
Cited by 2 | Viewed by 1526
Abstract
Membrane-less fuel cells are a promising power source for portable applications that enable the solving of membrane-related issues, such as water management and high cost, in conventional fuel cells. Apparently, research on this system uses a single electrolyte. This study focused on enhancing [...] Read more.
Membrane-less fuel cells are a promising power source for portable applications that enable the solving of membrane-related issues, such as water management and high cost, in conventional fuel cells. Apparently, research on this system uses a single electrolyte. This study focused on enhancing the performance of membrane-less fuel cells by introducing multiple reactants that are dual electrolytes with hydrogen peroxide (H2O2) and oxygen as oxidants in membrane-less direct methanol fuel cells (DMFC). The conditions tested for the system are (a) acidic, (b) alkaline, (c) dual medium with oxygen as an oxidant, and (d) dual medium and dual oxygen and hydrogen peroxide as an oxidant. Additionally, the effect of fuel utilization on different electrolyte and fuel concentrations was also studied. It was found that the fuel utilization decreases dramatically with the increasing of the fuel concentration, but it improved with the increasing of the electrolyte concentration until 2M. The performance of the dual oxidants in dual-electrolyte membrane-less DMFCs was 15.5 mW cm−2 of the power density achieved before optimization. Later, the system was optimized, and the power density increased to 30 mW cm−2. Finally, this work presented the stability of the cell using the suggested parameters from the optimization process. This study indicated that the performance of the membrane-less DMFC increased for dual electrolytes with mixed oxygen and hydrogen peroxide as oxidants compared to a single electrolyte. Full article
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