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A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 44762

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Dr. Cheng-Hsin Chuang

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Guest Editor

Institute of Medical Science and Technology, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
Interests: impedance-based biosensor; printed electronics; tactile sensor; wire-based metal 3D printing
Special Issues, Collections and Topics in MDPI journals

Prof. Yi Chiu

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Guest Editor

Department of Electrical and Computer Engineering, National Chiao Tung University, Hsin Chu, Taiwan
Interests: CMOS MEMS; energy harvesting; micro sensors

Special Issue Information

Dear Colleagues,

The 2020 International Conference on Smart Sensors (ICSS) will be held on 22–23 June 2020 at National Sun Yat-sen University, Kaohsiung, Taiwan (http://www.icsstw.org/ICSS_2020). As with last year, the conference is a joint event of the 25th Symposium of Association for Chemical Sensors in Taiwan and the 23nd Nano Engineering and Microsystem Technology Conference.

This Special Issue will publish both selected papers from ICSS 2020 and external papers. The topics to be covered include but are not limited to:

A. Chemical Sensors
Electrochemical sensors
Optical sensors
Semiconductor and electric sensors

B. Biosensors
Nanomaterial, enzyme-based or cell-based biosensors
Immunosensors for the clinic, food, environment, drugs, etc.
DNA or RNA-related biosensors for the clinic, food, environment, drugs, etc.

C. Microfluidics for Medical Applications
Lab-on-a-chip microdevices
Portable and emerging microfluidics technologies
Medical application techniques classified by clinical Subjects

D. MEMS and NEMS Fabrication
Material and device characterization
Mechanical/physical sensors and microsystems
Micro- and nanoengineering

E. Microfluidics
Micro and nano fluidic devices and systems
Microfluidics for separations, reactions, and synthesis
Fundamentals in microfluidics

F. Applied MEMS and Applied Microfluidics
Energy harvesting/power/RF/optical/acoustic MEMS
BioMEMS and integrated microfluidic platforms
Enabling technologies for IoT applications

We encourage both original research papers and comprehensive review articles to be submitted to this Special Issue.

Prof. Cheng-Hsin Chuang
Prof. Yi Chiu
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 (11 papers)

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Research

12 pages, 3301 KiB

Open AccessArticle

Smart Fall Detection Framework Using Hybridized Video and Ultrasonic Sensors

by Feng-Shuo Hsu, Tang-Chen Chang, Zi-Jun Su, Shin-Jhe Huang and Chien-Chang Chen

Micromachines 2021, 12(5), 508; https://doi.org/10.3390/mi12050508 - 1 May 2021

Cited by 5 | Viewed by 2953

Abstract

Fall accidents can cause severe impacts on the physical health and the quality of life of those who suffer limb diseases or injuries, the elderly, and their caregivers. Moreover, the later the accident is discovered, the lower the chance of recovery of the injured one. In order to detect accidents earlier, we propose a data-driven human fall detection framework. By combining the sensing mechanism of a commercialized webcam and an ultrasonic sensor array, we develop a probability model for automatic human fall monitoring. The webcam and ultrasonic array respectively collect the transverse and longitudinal time-series signals from a moving subject, and then these signals are assembled as a three-dimensional (3D) movement trajectory map. We also use two different detection-tracking algorithms for recognizing the tracked subjects. The mean height of the subjects is 164.2 ± 12 cm. Based on the data density functional theory (DDFT), we use the 3D motion data to estimate the cluster numbers and their cluster boundaries. We also employ the Gaussian mixture model as the DDFT kernel. Then, we utilize those features to build a probabilistic model of human falling. The model visually exhibits three possible states of human motions: normal motion, transition, and falling. The acceptable detection accuracy and the small model size reveals the feasibility of the proposed hybridized platform. The time from starting the alarm to an actual fall is on average about 0.7 s in our platform. The proposed sensing mechanisms offer 90% accuracy, 90% sensitivity, and 95% precision in the data validation. Then these vital results validate that the proposed framework has comparable performance to the contemporary methods. Full article

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

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14 pages, 6498 KiB

Open AccessArticle

Persistent Effect Test and Internal Microscopic Monitoring for PEM Water Electrolyzer

by Chi-Yuan Lee, Chia-Hung Chen, Guo-Bin Jung, Yu-Xiang Zheng and Yi-Cheng Liu

Micromachines 2021, 12(5), 494; https://doi.org/10.3390/mi12050494 - 27 Apr 2021

Cited by 5 | Viewed by 2545

Abstract

As the environmental considerations rise all over the world and under the drive of renewable energy policy, the society of hydrogen energy will come out gradually in the future. The proton exchange membrane water electrolyzer (PEMWE) is a very good hydrogen generator, characterized by low cost, high efficiency and zero emission of greenhouse gases. In this study, the micro temperature, humidity, flow, pressure, voltage, and current sensors were successfully integrated on a 50 μm thick Polyimide (PI) substrate by using micro-electro-mechanical systems (MEMS) technology. After the optimal design and process optimization of the flexible 6-in-1 microsensor, it was embedded in the PEMWE for a 500-h persistent effect test and internal real-time microscopic monitoring. Full article

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

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9 pages, 3733 KiB

Open AccessArticle

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

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

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

Cited by 1 | Viewed by 2775

Abstract

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

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

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27 pages, 12612 KiB

Open AccessArticle

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

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

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

Cited by 20 | Viewed by 4139

Abstract

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

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

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20 pages, 37936 KiB

Open AccessArticle

Competitive Real-Time Near Infrared (NIR) Vein Finder Imaging Device to Improve Peripheral Subcutaneous Vein Selection in Venipuncture for Clinical Laboratory Testing

by Mark D. Francisco, Wen-Fan Chen, Cheng-Tang Pan, Ming-Cheng Lin, Zhi-Hong Wen, Chien-Feng Liao and Yow-Ling Shiue

Micromachines 2021, 12(4), 373; https://doi.org/10.3390/mi12040373 - 30 Mar 2021

Cited by 24 | Viewed by 9103

Abstract

In this study, near-infrared (NIR) technology was utilized to develop a low-cost real-time near infrared (NIR) guiding device for cannulation. A portable device that can be used by medical practitioners and also by students for their skills development training in performing cannulation. Methods. First, is the development of a reflectance type optical vein finder using three (3) light emitting diode (LED) lights with 960 nm wavelength, complementary metal-oxide-semiconductor-infrared (CMOS-IR) sensor camera with 1920 × 1080 UXGA (1080P), IR filter set for the given wavelength, and an open-source image processing software. Second, is the actual in-vitro human testing in two sites: the arm and dorsal hand of 242 subjects. The following parameters were included, such as gender, age, mass index (BMI), and skin tone. In order to maximize the assessment process towards the device, the researchers included the arm circumference. This augmented subcutaneous vein imaging study using the develop vein finder device compared the difference in the captured vein images through visual and digital imaging approaches. The human testing was performed in accordance with the ethical standards of the Trinity University of Asia—Institutional Ethics Review Committee (TUA—IERC). Results. The NIR imaging system of the developed vein finder in this study showed its capability as an efficient guiding device through real-time vein pattern recognition, for both sites. Improved captured vein images were observed, having 100% visibility of vein patterns on the dorsal hand site. Fourteen (5.79%) out of 242 subjects reported non-visible peripheral subcutaneous veins in the arm sites. Conclusions. The developed vein finder device with the NIR technology and reflected light principle with low-energy consumption was efficient for real-time peripheral subcutaneous vein imaging without the application of a tourniquet. This might be utilized as a guiding device in locating the vein for the purpose of cannulation, at a very low cost as compared to the commercially available vein finders. Moreover, it may be used as an instructional device for student training in performing cannulation. Full article

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

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20 pages, 6180 KiB

Open AccessArticle

Design of Customize Interbody Fusion Cages of Ti64ELI with Gradient Porosity by Selective Laser Melting Process

by Cheng-Tang Pan, Che-Hsin Lin, Ya-Kang Huang, Jason S. C. Jang, Hsuan-Kai Lin, Che-Nan Kuo, De-Yao Lin and Jacob C. Huang

Micromachines 2021, 12(3), 307; https://doi.org/10.3390/mi12030307 - 15 Mar 2021

Cited by 12 | Viewed by 6127

Abstract

Intervertebral fusion surgery for spinal trauma, degeneration, and deformity correction is a major vertebral reconstruction operation. For most cages, the stiffness of the cage is high enough to cause stress concentration, leading to a stress shielding effect between the vertebral bones and the cages. The stress shielding effect affects the outcome after the reconstruction surgery, easily causing damage and leading to a higher risk of reoperation. A porous structure for the spinal fusion cage can effectively reduce the stiffness to obtain more comparative strength for the surrounding tissue. In this study, an intervertebral cage with a porous gradation structure was designed for Ti64ELI alloy powders bonded by the selective laser melting (SLM) process. The medical imaging software InVesalius and 3D surface reconstruction software Geomagic Studio 12 (Raindrop Geomagic Inc., Morrisville, NC, USA) were utilized to establish the vertebra model, and ANSYS Workbench 16 (Ansys Inc., Canonsburg, PA, USA) simulation software was used to simulate the stress and strain of the motions including vertical body-weighted compression, flexion, extension, lateral bending, and rotation. The intervertebral cage with a hollow cylinder had porosity values of 80–70–60–70–80% (from center to both top side and bottom side) and had porosity values of 60–70–80 (from outside to inside). In addition, according to the contact areas between the vertebras and cages, the shape of the cages can be custom-designed. The cages underwent fatigue tests by following ASTM F2077-17. Then, mechanical property simulations of the cages were conducted for a comparison with the commercially available cages from three companies: Zimmer (Zimmer Biomet Holdings, Inc., Warsaw, IN, USA), Ulrich (Germany), and B. Braun (Germany). The results show that the stress and strain distribution of the cages are consistent with the ones of human bone, and show a uniform stress distribution, which can reduce stress concentration. Full article

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

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11 pages, 4683 KiB

Open AccessArticle

Design and Application of MEMS-Based Hall Sensor Array for Magnetic Field Mapping

by Chia-Yen Lee, Yu-Ying Lin, Chung-Kang Kuo and Lung-Ming Fu

Micromachines 2021, 12(3), 299; https://doi.org/10.3390/mi12030299 - 12 Mar 2021

Cited by 4 | Viewed by 4919

Abstract

A magnetic field measurement system based on an array of Hall sensors is proposed. The sensors are fabricated using conventional microelectromechanical systems (MEMS) techniques and consist of a P-type silicon substrate, a silicon dioxide isolation layer, a phosphide-doped cross-shaped detection zone, and gold signal leads. When placed within a magnetic field, the interaction between the local magnetic field produced by the working current and the external magnetic field generates a measurable Hall voltage from which the strength of the external magnetic field is then derived. Four Hall sensors are fabricated incorporating cross-shaped detection zones with an identical aspect ratio (2.625) but different sizes (S, M, L, and XL). For a given working current, the sensitivities and response times of the four devices are found to be almost the same. However, the offset voltage increases with the increasing size of the detection zone. A 3 × 3 array of sensors is assembled into a 3D-printed frame and used to determine the magnetic field distributions of a single magnet and a group of three magnets, respectively. The results show that the constructed 2D magnetic field contour maps accurately reproduce both the locations of the individual magnets and the distributions of the magnetic fields around them. Full article

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

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10 pages, 1857 KiB

Open AccessArticle

Detection of Candida albicans Using a Manufactured Electrochemical Sensor

by Prakhar Dutta, Yi-Jung Lu, Han-Yu Hsieh, Tyng-Yuh Lee, Yi-Tzu Lee, Chao-Min Cheng and Yu-Jui Fan

Micromachines 2021, 12(2), 166; https://doi.org/10.3390/mi12020166 - 8 Feb 2021

Cited by 10 | Viewed by 3190

Abstract

Candida albicans is a commensal fungus that is responsible for a lot of nosocomial infections in immunocompromised people. Cell culture is currently the predominant method for diagnosing candidiasis, but it is time consuming. In this study, we developed a rapid screen procedure by devising a method for detecting C. albicans with the use of electrochemical sensors. Through this experiment, we propose a method for the detection of C. albicans in the system through the use of personal glucose meters. The hemicellulase was used to break down the cell wall of C. albicans to glucose and oligo, which can be detected by a glucose meter. The spiked samples were prepared suspending C. albicans in urine and serum, demonstrating the feasibility of the developed method in a real situation. Full article

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

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11 pages, 4978 KiB

Open AccessArticle

Flexible Five-in-One Microsensor for Real-Time Wireless Microscopic Diagnosis inside Electric Motorcycle Fuel Cell Stack Range Extender

by Chi-Yuan Lee, Chia-Hung Chen, Ti-Ju Lee, John-Shong Cheong, Yi-Cheng Liu and Yu-Chun Chen

Micromachines 2021, 12(2), 103; https://doi.org/10.3390/mi12020103 - 21 Jan 2021

Cited by 2 | Viewed by 1904

Abstract

The focus of research and development on electric motorcycle range extender are system integration and energy regulation and management but the present fuel cell stack range extender still has defects, such as large volume, heavy weight and high cost. Its volume and weight will have a strong impact on the endurance of electric motorcycle. The bipolar plate takes most volume and weight of a proton exchange membrane fuel cell (PEMFC) stack and it is the key component influencing the overall power density and cost. Therefore, how to thin and lighten the bipolar plate and to enhance the performance and life of PEMFC stack is an urgent research subject to be solved for the moment and will be the key to whether the PEMFC stack range extender can be put in the electric motorcycle or not. In addition, the internal temperature, humidity, flow, voltage and current in the operation of PEMFC stack will influence its performance and life and the overall performance and life of fuel cell stack will be directly influenced by different external operating conditions. As nonuniform distribution of temperature, humidity, flow, voltage and current will occur in various regions inside the fuel cell stack, this study will use micro-electro-mechanical systems (MEMS) technology to develop a flexible five-in-one microsensor, which is embedded in the PEMFC stack range extender for real-time wireless microscopic diagnosis and the reliability test is performed, so that the actual operating condition inside the fuel cell stack range extender can be mastered instantly and correctly and the internal information is fed back instantly, the fuel cell stack range extender control system can be modified to the optimum operating parameters immediately, so as to enhance the performance and prolong the lifetime effectively. Full article

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

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19 pages, 8069 KiB

Open AccessArticle

Measurement of Effects of Different Substrates on the Mechanical Properties of Submicron Titanium Nickel Shape Memory Alloy Thin Film Using the Bulge Test

by Nhat Minh Dang, Zhao-Ying Wang, Ti-Yuan Wu, Tra Anh Khoa Nguyen and Ming-Tzer Lin

Micromachines 2021, 12(1), 85; https://doi.org/10.3390/mi12010085 - 15 Jan 2021

Cited by 4 | Viewed by 2695

Abstract

This study investigated the effects of different substrates on the mechanical properties of Ti-60at%Ni shape memory alloys (SMA). Two types of samples were prepared for this experiment: (1) a Ti-60at%Ni deposited on SiNx, and (2) a Ti-60at%Ni deposited on SiNx/Cr; both had a 600 nm thick film of Ti-60at%Ni. Deposition was done using the physical vapor deposition (PVD) process, and the microstructural changes and crystallization phase changes were observed through scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the TiNi thin film with a Cr adhesion layer had better mechanical properties. The bulge test showed that TiNi thin film with a Cr adhesion had a higher Young’s modulus and lower residual stress. From the thermal cycling experiment, it was found that the Cr adhesion layer buffered the mismatch between TiNi and SiNx. Additionally, the thermal cycling test was also used to measure the thermal expansion coefficient of the films, and the fatigue test showed that the Cr layer significantly improved the fatigue resistance of the TiNi film. Full article

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

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12 pages, 6977 KiB

Open AccessArticle

Internal Microscopic Diagnosis of Accelerated Aging of Proton Exchange Membrane Water Electrolysis Cell Stack

by Chi-Yuan Lee, Chia-Hung Chen, Guo-Bin Jung, Shih-Chun Li and Yi-Zhen Zeng

Micromachines 2020, 11(12), 1078; https://doi.org/10.3390/mi11121078 - 4 Dec 2020

Cited by 7 | Viewed by 2933

Abstract

The hydrogen production reaction of the proton exchange membrane (PEM) water electrolysis cell stack is the reverse reaction of the fuel cell, but the water electrolysis operation requires high pressure, and the high pressure decomposes hydrogen molecules, thus aging or causing failure in the water electrolysis cell stack. In addition, there are five important physical parameters (current, voltage, flow, pressure and temperature) inside the water electrolysis cell stack, which can change the performance and shorten the life of the cell stack. However, the present techniques obtain data only by external simulation or single measurement; they cannot collect the internal real data in operation instantly and accurately. This study discusses the causes for aging or failure, and develops an internal real-time microscopic diagnosis tool for accelerated aging of the PEM water electrolysis cell stack. A flexible integrated (current, voltage, flow, pressure and temperature) microsensor applicable to the inside (high voltage and electrochemical environment) of the PEM water electrolysis cell stack is developed by using micro-electro-mechanical systems (MEMS) technology; it is embedded in the PEM water electrolysis cell stack for microscopic diagnosis of accelerated aging, and 100-h durability and reliability tests are performed. The distribution of important physical parameters inside the PEM water electrolysis cell stack can be measured instantly and accurately, so as to adjust it to the optimal operating conditions, and the local aging and failure problems are discussed. Full article

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

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