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Micromachines, Volume 15, Issue 1 (January 2024) – 166 articles

Cover Story (view full-size image): For drug development, microfluidic devices are important for long-term experiments using organoids and tissues. While the devices extend culture duration, microbubbles often form inside and damage and starve the cells on the organoids and tissues. A microbubble removal method using negative pressure from the devices composed of polydimethylsiloxane (PDMS) has been reported. However, negative pressure is applied to entire devices, and this affects the cells in the device. In this study, a local microbubble removal method was developed using a device with thin PDMS sidewalls. The thin sidewalls counterbalanced the negative and atmospheric pressures, thereby localizing the negative pressure near the negatively pressurized chamber. Microbubbles were removed only near the chamber, whereas those away from the chamber were not removed. View this paper
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14 pages, 3557 KiB  
Article
A High-Accuracy RC Time Constant Auto-Tuning Scheme for Integrated Continuous-Time Filters
by Gang Jin, Hao Wu, Yue Yin, Lei Zheng and Yiqi Zhuang
Micromachines 2024, 15(1), 166; https://doi.org/10.3390/mi15010166 - 22 Jan 2024
Viewed by 866
Abstract
The reliability of the resistor-capacitor (RC) time constant of a continuous-time (CT) filter has long been an obstacle with integrated circuits. Due to process and temperature variations in complementary metal-oxide semiconductor (CMOS) technology, the absolute value of the RC time constant may vary [...] Read more.
The reliability of the resistor-capacitor (RC) time constant of a continuous-time (CT) filter has long been an obstacle with integrated circuits. Due to process and temperature variations in complementary metal-oxide semiconductor (CMOS) technology, the absolute value of the RC time constant may vary over ±50%, which is a big issue for many integrated continuous-time analog circuits. This study proposes an on-chip RC time constant auto-tuning scheme. The proposed scheme is based on the discrete master–slave auto-tuning concept. Considering the limitations in conventional works, a higher tuning accuracy is achieved by adopting two techniques: firstly, parasitic capacitance cancelation is proposed to eliminate the effects caused by parasitic capacitance; secondly, symmetric comparison is introduced to minimize the influence of the DC offset of the comparator. A successive approximation procedure is applied to improve the tuning speed. The proposed auto-tuning scheme has been validated in 55 nm CMOS technology with a fourth-order active-RC low-pass filter under PVT variations and 60 mV input offset voltage. The average tuning error is 2.21%, and the maximum error is 3.67%. The tuning error of the proposed scheme is considerably lower than the conventional scheme. Full article
(This article belongs to the Special Issue High-Reliability Semiconductor Devices and Integrated Circuits)
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20 pages, 9586 KiB  
Article
Gradient-Pattern Micro-Grooved Wicks Fabricated by the Ultraviolet Nanosecond Laser Method and Their Enhanced Capillary Performance
by Guanghan Huang, Jiawei Liao, Chao Fan, Shuang Liu, Wenjie Miao, Yu Zhang, Shiwo Ta, Guannan Yang and Chengqiang Cui
Micromachines 2024, 15(1), 165; https://doi.org/10.3390/mi15010165 - 22 Jan 2024
Viewed by 973
Abstract
Capillary-gradient wicks can achieve fast or directional liquid transport, but they face fabrication challenges by traditional methods in terms of precise patterns. Laser processing is a potential solution due to its high pattern accuracy, but there are a few studies on laser-processed capillary-gradient [...] Read more.
Capillary-gradient wicks can achieve fast or directional liquid transport, but they face fabrication challenges by traditional methods in terms of precise patterns. Laser processing is a potential solution due to its high pattern accuracy, but there are a few studies on laser-processed capillary-gradient wicks. In this paper, capillary step-gradient micro-grooved wicks (CSMWs) were fabricated by an ultraviolet nanosecond pulsed laser, and their capillary performance was studied experimentally. The CSMWs could be divided into three regions with a decreasing capillary radius. The equilibrium rising height of the CSMWs was enhanced by 124% compared to the non-gradient parallel wick. Different from the classical Lucas–Washburn model describing a uniform non-gradient wick, secondary capillary acceleration was observed in the negative gradient direction of the CSMWs. With the increase in laser power and the decrease in scanning speed, the capillary performance was promoted, and the optimal laser processing parameters were 4 W-10 mm/s. The laser-enhanced capillary performance was attributed to the improved hydrophilicity and reduced capillary radius, which resulted from the increased surface roughness, protrusion morphology, and deep-narrow V-shaped grooves induced by the high energy density of the laser. Our study demonstrates that ultraviolet pulsed laser processing is a highly efficient and low-cost method for fabricating high-performance capillary gradient wicks. Full article
(This article belongs to the Special Issue Heat Transfer and Fluid Flow in Microstructures)
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23 pages, 9828 KiB  
Review
Split-Gate: Harnessing Gate Modulation Power in Thin-Film Electronics
by Subin Lee, Yeong Jae Kim and Hocheon Yoo
Micromachines 2024, 15(1), 164; https://doi.org/10.3390/mi15010164 - 22 Jan 2024
Viewed by 988
Abstract
With the increase in electronic devices across various applications, there is rising demand for selective carrier control. The split-gate consists of a gate electrode divided into multiple parts, allowing for the independent biasing of electric fields within the device. This configuration enables the [...] Read more.
With the increase in electronic devices across various applications, there is rising demand for selective carrier control. The split-gate consists of a gate electrode divided into multiple parts, allowing for the independent biasing of electric fields within the device. This configuration enables the potential formation of both p- and n-channels by injecting holes and electrons owing to the presence of the two gate electrodes. Applying voltage to the split-gate allows for the control of the Fermi level and, consequently, the barrier height in the device. This facilitates band bending in unipolar transistors and allows ambipolar transistors to operate as if unipolar. Moreover, the split-gate serves as a revolutionary tool to modulate the contact resistance by controlling the barrier height. This approach enables the precise control of the device by biasing the partial electric field without limitations on materials, making it adaptable for various applications, as reported in various types of research. However, the gap length between gates can affect the injection of the electric field for the precise control of carriers. Hence, the design of the gap length is a critical element for the split-gate structure. The primary investigation in this review is the introduction of split-gate technology applied in various applications by using diverse materials, the methods for forming the split-gate in each device, and the operational mechanisms under applied voltage conditions. Full article
(This article belongs to the Special Issue Organic Semiconductors and Devices)
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13 pages, 7685 KiB  
Article
Self-Assembled Nanotubes Based on Chiral H8-BINOL Modified with 1,2,3-Triazole to Recognize Bi3+ Efficiently by ICT Mechanism
by Jisheng Tao, Fang Guo, Yue Sun, Xiaoxia Sun and Yu Hu
Micromachines 2024, 15(1), 163; https://doi.org/10.3390/mi15010163 - 22 Jan 2024
Viewed by 818
Abstract
A novel fluorescent “off” probe R-β-D-1 containing a 1,2,3-triazole moiety was obtained by the Click reaction with azidoglucose using H8-BINOL as a substrate, and the structure was characterized by 1H NMR and 13C NMR and ESI-MS analysis. [...] Read more.
A novel fluorescent “off” probe R-β-D-1 containing a 1,2,3-triazole moiety was obtained by the Click reaction with azidoglucose using H8-BINOL as a substrate, and the structure was characterized by 1H NMR and 13C NMR and ESI-MS analysis. The fluorescence properties of R-β-D-1 in methanol were investigated, and it was found that R-β-D-1 could be selectively fluorescently quenched by Bi3+ in the recognition of 19 metal ions and basic cations. The recognition process of Bi3+ by R-β-D-1 was also investigated by fluorescence spectroscopy, SEM, AFM, etc. The complex pattern of R-β-D-1 with Bi3+ was determined by Job’s curve as 1 + 1, and the binding constant Ka of R-β-D-1 and Bi3+ was valued by the Benesi–Hildebrand equation as 1.01 × 104 M−1, indicating that the binding force of R-β-D-1 and Bi3+ was medium. The lowest detection limit (LOD) of the self-assembled H8-BINOL derivative for Bi3+ was up to 0.065 µM. The mechanism for the recognition of Bi3+ by the sensor R-β-D-1 may be the intramolecular charge transfer effect (ICT), which was attributed to the fact that the N-3 of the triazole readily serves as an electron acceptor while the incorporation of Bi3+ serves as an electron donor, and the two readily undergo coordination leading to the quenching of fluorescence. The recognition mechanism and recognition site could be verified by DFT calculation and CDD (Charge Density Difference). Full article
(This article belongs to the Special Issue Miniaturized Chemical Sensors)
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11 pages, 2602 KiB  
Article
Interface Hardness Analysis of between IN625 and CoCrMo Manufactured by Pulsed Wave Laser Powder Bed Fusion
by Zhiong Sheng Hoo, Zhongmin Xiao, Liming Yao, Bozhong Jing, Chuanjie Jin and Chao Tang
Micromachines 2024, 15(1), 162; https://doi.org/10.3390/mi15010162 - 21 Jan 2024
Viewed by 1004
Abstract
The nuclear and petrochemical industries often require multi-metal parts that are corrosion-resistant, heat-resistant, and possess high strength to enhance equipment safety and reduce downtime. Additive manufacturing technology enables the rapid and flexible processing of multi-metal parts to meet these stringent demands. This study [...] Read more.
The nuclear and petrochemical industries often require multi-metal parts that are corrosion-resistant, heat-resistant, and possess high strength to enhance equipment safety and reduce downtime. Additive manufacturing technology enables the rapid and flexible processing of multi-metal parts to meet these stringent demands. This study is aimed at investigating the interface hardness between CoCrMo/IN625 to determine optimal processing parameters that can be utilized in manufacturing reliable and durable multi-metal parts. The result indicates that when the volumetric energy density, Ev, is at or below 20 J/mm3, microfluidic forces are unable to sufficiently diffuse between the two metals, leading to insufficient diffusion, and the high hardness CoCrMo acts as a support, resulting in a significantly higher interface hardness. As Ev increases, intense recoil pressure within the microfluidic forces disrupts the melt pool, allowing for full diffusion between the two metals. The fully diffused high-hardness CoCrMo has been diluted by the low-hardness IN625, thus reducing the interface hardness. Considering the interface hardness, strength, and printing efficiency (time and energy consumption), we recommend a range of 35 J/mm3 < Ev ≤ 75 J/mm3. In this range, the average values for interface hardness and tensile strength of the samples are approximately 382 HV and 903 MPa, respectively. Full article
(This article belongs to the Special Issue Future Prospects of Additive Manufacturing)
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14 pages, 6061 KiB  
Article
Non-Contact Current Sensing System Based on the Giant Magnetoimpedance Effect of CoFeNiSiB Amorphous Ribbon Meanders
by Zhen Yang, Zhenbao Wang, Mengyu Liu and Xuecheng Sun
Micromachines 2024, 15(1), 161; https://doi.org/10.3390/mi15010161 - 21 Jan 2024
Cited by 2 | Viewed by 922
Abstract
A sensitive non-contact sensing system based on the CoFeNiSiB amorphous ribbon giant magnetoimpedance (GMI) effect is proposed for current testing. The sensing system consists of a GMI probe, a sinusoidal current generator, a voltage follower, a preamplifier, a low-pass filter, and a peak [...] Read more.
A sensitive non-contact sensing system based on the CoFeNiSiB amorphous ribbon giant magnetoimpedance (GMI) effect is proposed for current testing. The sensing system consists of a GMI probe, a sinusoidal current generator, a voltage follower, a preamplifier, a low-pass filter, and a peak detector. Four different GMI probes derived from amorphous ribbon meanders are designed and fabricated through MEMS processes. GMI probes were driven by a 10 MHz, 5 mA AC current. A permanent magnet was used to provide a bias magnetic field for the probe. The effect of the bias magnetic field on the output DC voltage was investigated. This non-contact current sensing system exhibits good sensitivity and linearity at a bias magnetic field Hbias = 15 Oe. The sensitivity can reach up to 24.2 mV/A in the ±1.5 A range. Full article
(This article belongs to the Special Issue Magnetic Sensor Chips and Applications)
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13 pages, 2581 KiB  
Article
Integrated Microfluidic Chip Technology for Copper Ion Detection Using an All-Solid-State Ion-Selective Electrode
by Wenpin Zhang, Shuangquan Wang, Dugang Kang, Zhi Xiong, Yong Huang, Lin Ma, Yun Liu, Wei Zhao, Shouliang Chen and Yi Xu
Micromachines 2024, 15(1), 160; https://doi.org/10.3390/mi15010160 - 21 Jan 2024
Viewed by 866
Abstract
This study involved the preparation of an all-solid-state ion-selective electrode (ASS-ISE) with copper and a poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT/PSS) conversion layer through electrode deposition. The morphology of the PEDOT/PSS film was characterized, and the performance of the copper ion-selective film was optimized. [...] Read more.
This study involved the preparation of an all-solid-state ion-selective electrode (ASS-ISE) with copper and a poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT/PSS) conversion layer through electrode deposition. The morphology of the PEDOT/PSS film was characterized, and the performance of the copper ion-selective film was optimized. Additionally, a microfluidic chip for the ASS-ISE with copper was designed and prepared. An integrated microfluidic chip test system with an ASS-ISE was developed using a self-constructed potential detection device. The accuracy of the system was validated through comparison testing with atomic absorption spectrophotometry (AAS). The experimental findings indicate that the relative standard deviation (RSD) of the integrated ASS-ISE with the copper microfluidic chip test system is 4.54%, as compared to the industry standard method. This value complies with the stipulated requirement of an RSD ≤ 5% in DL/T 955-2016. Full article
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13 pages, 14158 KiB  
Article
Flexible Symmetric-Defection Antenna with Bending and Thermal Insensitivity for Miniaturized UAV
by Xueli Nan, Tongtong Kang, Zhonghe Zhang, Xin Wang, Jiale Zhang, Yusheng Lei, Libo Gao, Jianli Cui and Hongcheng Xu
Micromachines 2024, 15(1), 159; https://doi.org/10.3390/mi15010159 - 21 Jan 2024
Viewed by 996
Abstract
Flexible conformal-enabled antennas have great potential for various developable surface-built unmanned aerial vehicles (UAVs) due to their superior mechanical compliance as well as maintaining excellent electromagnetic features. However, it remains a challenge that the antenna holds bending and thermal insensitivity to negligibly shift [...] Read more.
Flexible conformal-enabled antennas have great potential for various developable surface-built unmanned aerial vehicles (UAVs) due to their superior mechanical compliance as well as maintaining excellent electromagnetic features. However, it remains a challenge that the antenna holds bending and thermal insensitivity to negligibly shift resonant frequency during conformal attachment and aerial flight, respectively. Here, we report a flexible symmetric-defection antenna (FSDA) with bending and thermal insensitivity. By engraving a symmetric defection on the reflective ground, the radiated unit attached to the soft polydimethylsiloxane (PDMS) makes the antenna resonate at the ISM microwave band (resonant frequency = 2.44 GHz) and conformal with a miniaturized UAV. The antenna is also insensitive to both the bending-conformal attachment (20 mm < r < 70 mm) and thermal radiation (20~100 °C) due to the symmetric peripheral-current field along the defection and the low-change thermal effect of the PDMS, respectively. Therefore, the antenna in a non-bending state almost keeps the same impedance matching and radiation when it is attached to a cylinder-back of a UAV. The flexible antenna with bending and thermal insensitivity will pave the way for more conformal or wrapping applications. Full article
(This article belongs to the Special Issue Flexible and Wearable Sensors, 3rd Edition)
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16 pages, 5553 KiB  
Article
A Computational Evaluation of Minimum Feature Size in Projection Two-Photon Lithography for Rapid Sub-100 nm Additive Manufacturing
by Rushil Pingali, Harnjoo Kim and Sourabh K. Saha
Micromachines 2024, 15(1), 158; https://doi.org/10.3390/mi15010158 - 21 Jan 2024
Viewed by 1023
Abstract
Two-photon lithography (TPL) is a laser-based additive manufacturing technique that enables the printing of arbitrarily complex cm-scale polymeric 3D structures with sub-micron features. Although various approaches have been investigated to enable the printing of fine features in TPL, it is still challenging to [...] Read more.
Two-photon lithography (TPL) is a laser-based additive manufacturing technique that enables the printing of arbitrarily complex cm-scale polymeric 3D structures with sub-micron features. Although various approaches have been investigated to enable the printing of fine features in TPL, it is still challenging to achieve rapid sub-100 nm 3D printing. A key limitation is that the physical phenomena that govern the theoretical and practical limits of the minimum feature size are not well known. Here, we investigate these limits in the projection TPL (P-PTL) process, which is a high-throughput variant of TPL, wherein entire 2D layers are printed at once. We quantify the effects of the projected feature size, optical power, exposure time, and photoinitiator concentration on the printed feature size through finite element modeling of photopolymerization. Simulations are performed rapidly over a vast parameter set exceeding 10,000 combinations through a dynamic programming scheme, which is implemented on high-performance computing resources. We demonstrate that there is no physics-based limit to the minimum feature sizes achievable with a precise and well-calibrated P-TPL system, despite the discrete nature of illumination. However, the practically achievable minimum feature size is limited by the increased sensitivity of the degree of polymer conversion to the processing parameters in the sub-100 nm regime. The insights generated here can serve as a roadmap towards fast, precise, and predictable sub-100 nm 3D printing. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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12 pages, 1637 KiB  
Article
Analysis of Nanowire pn-Junction with Combined Current–Voltage, Electron-Beam-Induced Current, Cathodoluminescence, and Electron Holography Characterization
by Nicklas Anttu, Elisabetta Maria Fiordaliso, José Cano Garcia, Giuliano Vescovi and David Lindgren
Micromachines 2024, 15(1), 157; https://doi.org/10.3390/mi15010157 - 20 Jan 2024
Viewed by 1097
Abstract
We present the characterization of a pn-junction GaAs nanowire. For the characterization, current–voltage, electron-beam-induced current, cathodoluminescence, and electron holography measurements are used. We show that by combining information from these four methods, in combination with drift-diffusion modelling, we obtain a detailed picture of [...] Read more.
We present the characterization of a pn-junction GaAs nanowire. For the characterization, current–voltage, electron-beam-induced current, cathodoluminescence, and electron holography measurements are used. We show that by combining information from these four methods, in combination with drift-diffusion modelling, we obtain a detailed picture of how the nanowire pn-junction is configured and how the recombination lifetime varies axially in the nanowire. We find (i) a constant doping concentration and 600 ps recombination lifetime in the n segment at the top part of the nanowire; (ii) a 200–300 nm long gradient in the p doping next to the pn-junction; and (iii) a strong gradient in the recombination lifetime on the p side, with 600 ps lifetime at the pn-junction, which drops to 10 ps at the bottom of the p segment closest to the substrate. We recommend such complementary characterization with multiple methods for nanowire-based optoelectronic devices. Full article
(This article belongs to the Special Issue III-V Optoelectronics and Semiconductor Process Technology)
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11 pages, 2100 KiB  
Article
Highly Responsive Gate-Controlled p-GaN/AlGaN/GaN Ultraviolet Photodetectors with a High-Transmittance Indium Tin Oxide Gate
by Zhanfei Han, Xiangdong Li, Hongyue Wang, Yuebo Liu, Weitao Yang, Zesheng Lv, Meng Wang, Shuzhen You, Jincheng Zhang and Yue Hao
Micromachines 2024, 15(1), 156; https://doi.org/10.3390/mi15010156 - 20 Jan 2024
Viewed by 910
Abstract
This work presents highly responsive gate-controlled p-GaN/AlGaN/GaN ultraviolet photodetectors (UVPDs) on Si substrates with a high-transmittance ITO gate. The two-dimensional electron gas (2DEG) in the quantum well of the polarized AlGaN/GaN heterojunction was efficiently depleted by the p-GaN gate, leading to a high [...] Read more.
This work presents highly responsive gate-controlled p-GaN/AlGaN/GaN ultraviolet photodetectors (UVPDs) on Si substrates with a high-transmittance ITO gate. The two-dimensional electron gas (2DEG) in the quantum well of the polarized AlGaN/GaN heterojunction was efficiently depleted by the p-GaN gate, leading to a high photo-to-dark current ratio (PDCR) of 3.2 × 105. The quantum wells of the p-GaN/AlGaN and AlGaN/GaN heterojunctions can trap the holes and electrons excited by the UV illumination, thus efficiently triggering a photovoltaic effect and photoconductive effect, separately. Furthermore, the prepared photodetectors allow flexible adjustment of the static bias point, making it adaptable to different environments. Compared to traditional thin-film semi-transparent Ni/Au gates, indium tin oxide (ITO) exhibits higher transmittance. Under 355 nm illumination, the photodetector exhibited a super-high responsivity exceeding 3.5 × 104 A/W, and it could even exceed 106 A/W under 300 nm illumination. The well-designed UVPD combines both the advantages of the high-transmittance ITO gate and the structure of the commercialized p-GaN/AlGaN/GaN high-electron-mobility transistors (HEMTs), which opens a new possibility of fabricating large-scale, low-cost, and high-performance UVPDs in the future. Full article
(This article belongs to the Special Issue III-Nitride Materials in Electronic and Photonic Devices)
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10 pages, 3800 KiB  
Article
Implementation of Highly Reliable Contacts for RF MEMS Switches
by Lili Jiang, Lifeng Wang, Xiaodong Huang, Zhen Huang and Min Huang
Micromachines 2024, 15(1), 155; https://doi.org/10.3390/mi15010155 - 20 Jan 2024
Viewed by 1006
Abstract
A contact is the key structure of RF MEMS (Radio Frequency Microelectromechanical System) switches, which has a direct impact on the switch’s electrical and mechanical properties. In this paper, the implementation of highly reliable contacts for direct-contact RF MEMS switches is provided. As [...] Read more.
A contact is the key structure of RF MEMS (Radio Frequency Microelectromechanical System) switches, which has a direct impact on the switch’s electrical and mechanical properties. In this paper, the implementation of highly reliable contacts for direct-contact RF MEMS switches is provided. As a soft metal material, gold has the advantages of low contact resistance, high chemical stability, and mature process preparation, so it is chosen as the metal material for the beam structure as well as the contacts of the switch. However, a Pt film is used in the bottom contact area to enhance the reliability of the contact. Three kinds of contacts with various shapes are fabricated using different processes. Particularly, a circular-shaped contact is obtained by dry/wet combined processes. The detailed fabrication process of the contacts as well as the Pt film on the bottom contact area are given. The experimental test shows that the contact shape has little effect on the RF performance of the switches. However, the circular contact shows better reliability than other contacts and can work well even after 1.2 × 109 cycles. Full article
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14 pages, 3803 KiB  
Article
Preparation and Characterization of Multielement Composite Oxide Nanomaterials Containing Ce, Zr, Y, and Yb via Continuous Hydrothermal Flow Synthesis
by Qingyun Li, Zihua Wang and Xuezhong Wang
Micromachines 2024, 15(1), 154; https://doi.org/10.3390/mi15010154 - 20 Jan 2024
Viewed by 775
Abstract
The synthesis of multielement composite oxide nanomaterials containing Ce, Zr, Y, and Yb was investigated using a micro confined jet mixer reactor operated in continuous mode under supercritical water conditions. The obtained nanoparticles were characterized using ICP-AES, SEM-EDS, FTIR, Raman spectroscopy, XRD, and [...] Read more.
The synthesis of multielement composite oxide nanomaterials containing Ce, Zr, Y, and Yb was investigated using a micro confined jet mixer reactor operated in continuous mode under supercritical water conditions. The obtained nanoparticles were characterized using ICP-AES, SEM-EDS, FTIR, Raman spectroscopy, XRD, and TEM. All samples exhibited a uniform particle shape and a narrow particle size distribution. An analysis of the d-spacing results using selected electron area diffraction (SAED) patterns confirmed the production of cubic-phase crystals. A BET test was employed to determine the specific surface area of the prepared nanoparticles. OSC and TPR techniques were utilized to characterize the oxygen storage capacity and reduction performance of the obtained samples, with an analysis conducted to determine how the different proportions of elements affected the performance of multielement mixed oxides. The ionic conductivity of multielement composite oxide was measured using alternating current impedance spectroscopy (EIS), and the impact of Y, Ce, and Yb on the electrolyte material’s ionic conductivity was analyzed. Full article
(This article belongs to the Special Issue Functional Materials and Microdevices)
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28 pages, 17616 KiB  
Article
Novel Bidirectional Output Ytterbium-Doped High Power Fiber Lasers: From Continuous to Quasi-Continuous
by Lingfa Zeng, Xinyi Ding, Jiaqi Liu, Xiaolin Wang, Yun Ye, Hanshuo Wu, Peng Wang, Xiaoming Xi, Hanwei Zhang, Chen Shi, Fengjie Xi and Xiaojun Xu
Micromachines 2024, 15(1), 153; https://doi.org/10.3390/mi15010153 - 20 Jan 2024
Viewed by 731
Abstract
Traditional ytterbium-doped high-power fiber lasers generally use a unidirectional output structure. To reduce the cost and improve the efficiency of the fiber laser, we propose a bidirectional output fiber laser (BOFL). The BOFL has many advantages over that of the traditional unidirectional output [...] Read more.
Traditional ytterbium-doped high-power fiber lasers generally use a unidirectional output structure. To reduce the cost and improve the efficiency of the fiber laser, we propose a bidirectional output fiber laser (BOFL). The BOFL has many advantages over that of the traditional unidirectional output fiber laser (UOFL) and has a wide application in the industrial field. In theory, the model of the BOFL is established, and a comparison of the nonlinear effect in the traditional UOFL and the BOFL is studied. Experimentally, high-power continuous wave (CW) and quasi-continuous wave (QCW) BOFLs are demonstrated. In the continuous laser, we first combine the BOFL with the oscillating amplifying integrated structure, and a near-single-mode bidirectional 2 × 4 kW output with a total power of above 8 kW is demonstrated. Then, with the simple BOFL, a CW bidirectional 2 × 5 kW output with a total power of above 10 kW is demonstrated. By means of pump source modulation, a QCW BOFL is developed, and the output of a near-single mode QCW laser with a peak output of 2 × 4.5 kW with a total peak power of more than 9 kW is realized. Both CW and QCW output BOFL are the highest powers reported at present. Full article
(This article belongs to the Special Issue Fiber Lasers and Applications)
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13 pages, 6120 KiB  
Article
Influence of Femtosecond Laser Surface Modification on Tensile Properties of Titanium Alloy
by Kai Zhou, Xiaoyuan Nie, Xingbang Che, Han Xiao, Xuwen Wang, Junming Liao, Xu Wu, Can Yang and Chunbo Li
Micromachines 2024, 15(1), 152; https://doi.org/10.3390/mi15010152 - 19 Jan 2024
Viewed by 767
Abstract
Titanium alloy components often experience damage from impact loads during usage, which makes improving the mechanical properties of TC4 titanium alloys crucial. This paper investigates the influence of laser scanning irradiation on the tensile properties of thin titanium alloy sheets. Results indicate that [...] Read more.
Titanium alloy components often experience damage from impact loads during usage, which makes improving the mechanical properties of TC4 titanium alloys crucial. This paper investigates the influence of laser scanning irradiation on the tensile properties of thin titanium alloy sheets. Results indicate that the tensile strength of thin titanium alloy sheets exhibits a trend of initial increase followed by a decrease. Different levels of enhancement are observed in the elongation at break of a cross-section. Optimal improvement in the elongation at break is achieved when the laser fluence is around 8 J/cm2, while the maximum increase in tensile strength occurs at approximately 10 J/cm2. Using femtosecond laser surface irradiation, this study compares the maximum enhancement in the tensile strength of titanium alloy base materials, which is approximately 8.54%, and the maximum increase in elongation at break, which reaches 25.61%. In addition, the results verify that cracks in tensile fractures of TC4 start from the middle, while laser-induced fracture cracks occur from both ends. Full article
(This article belongs to the Section D:Materials and Processing)
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16 pages, 4258 KiB  
Article
Droplet Motion Driven by Liquid Dielectrophoresis in the Low-Frequency Range
by Sarah Günther-Müller, Raschid Azizy and Steffen Strehle
Micromachines 2024, 15(1), 151; https://doi.org/10.3390/mi15010151 - 19 Jan 2024
Viewed by 749
Abstract
Electrohydrodynamic wetting manipulation plays a major role in modern microfluidic technologies such as lab-on-a-chip applications and digital microfluidics. Liquid dielectrophoresis (LDEP) is a common driving mechanism, which induces hydrodynamic motion in liquids by the application of nonhomogeneous electrical fields. Among strategies to analyze [...] Read more.
Electrohydrodynamic wetting manipulation plays a major role in modern microfluidic technologies such as lab-on-a-chip applications and digital microfluidics. Liquid dielectrophoresis (LDEP) is a common driving mechanism, which induces hydrodynamic motion in liquids by the application of nonhomogeneous electrical fields. Among strategies to analyze droplet movement, systematic research on the influence of different frequencies under AC voltage is missing. In this paper, we therefore present a first study covering the motion characteristics of LDEP-driven droplets of the dielectric liquids ethylene glycol and glycerol carbonate in the driving voltage frequency range from 50 Hz to 1600 Hz. A correlation between the switching speed of LDEP-actuated droplets in a planar electrode configuration and the frequency of the applied voltage is shown. Hereby, motion times of different-sized droplets could be reduced by up to a factor of 5.3. A possible excitation of the droplets within their range of eigenfrequencies is investigated using numerical calculations. The featured fluidic device is designed using larger-sized electrodes rather than typical finger or strip electrodes, which are commonly employed in LDEP devices. The influence of the electrode shape is considered simulatively by studying the electric field gradients. Full article
(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)
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15 pages, 4244 KiB  
Article
Compressive Behavior of Some Balls Manufactured by 3D Printing from Ceramic–Polymer Composite Materials
by Adelina Hrițuc, Vasile Ermolai, Andrei Marius Mihalache, Liviu Andrușcă, Oana Dodun, Gheorghe Nagîț, Marius Andrei Boca and Laurențiu Slătineanu
Micromachines 2024, 15(1), 150; https://doi.org/10.3390/mi15010150 - 19 Jan 2024
Cited by 1 | Viewed by 774
Abstract
It is known that ceramic–polymer composite materials can be used to manufacture spherical bodies in the category of balls. Since balls are frequently subjected to compression loads, the paper presents some research results on the compression behavior of balls made of ceramic composite [...] Read more.
It is known that ceramic–polymer composite materials can be used to manufacture spherical bodies in the category of balls. Since balls are frequently subjected to compression loads, the paper presents some research results on the compression behavior of balls made of ceramic composite materials with a polymer matrix. The mathematical model of the pressure variation inside the balls highlights the existence of maximum values in the areas of contact with other parts. Experimental research was carried out on balls with a diameter of 20 mm, manufactured by 3D printing from four ceramic–polymer composite materials with a polymer matrix: pottery clay, terracotta, concrete, and granite. The same ceramic–polymer composite material was used, but different dyes were added to it. A gravimetric analysis revealed similar behavior of the four materials upon controlled heating. Through the mathematical processing of the experimental results obtained by compression tests, empirical mathematical models of the power-type function type were determined. These models highlight the influence exerted by different factors on the force at which the initiation of cracks in the ball materials occurs. The decisive influence of the infill factor on the size of the force at which the cracking of the balls begins was found. Full article
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19 pages, 4315 KiB  
Article
Hardware Trojan Attacks on the Reconfigurable Interconnections of Field-Programmable Gate Array-Based Convolutional Neural Network Accelerators and a Physically Unclonable Function-Based Countermeasure Detection Technique
by Jia Hou, Zichu Liu, Zepeng Yang and Chen Yang
Micromachines 2024, 15(1), 149; https://doi.org/10.3390/mi15010149 - 19 Jan 2024
Cited by 1 | Viewed by 1063
Abstract
Convolutional neural networks (CNNs) have demonstrated significant superiority in modern artificial intelligence (AI) applications. To accelerate the inference process of CNNs, reconfigurable CNN accelerators that support diverse networks are widely employed for AI systems. Given the ubiquitous deployment of these AI systems, there [...] Read more.
Convolutional neural networks (CNNs) have demonstrated significant superiority in modern artificial intelligence (AI) applications. To accelerate the inference process of CNNs, reconfigurable CNN accelerators that support diverse networks are widely employed for AI systems. Given the ubiquitous deployment of these AI systems, there is a growing concern regarding the security of CNN accelerators and the potential attacks they may face, including hardware Trojans. This paper proposes a hardware Trojan designed to attack a crucial component of FPGA-based CNN accelerators: the reconfigurable interconnection network. Specifically, the hardware Trojan alters the data paths during activation, resulting in incorrect connections in the arithmetic circuit and consequently causing erroneous convolutional computations. To address this issue, the paper introduces a novel detection technique based on physically unclonable functions (PUFs) to safeguard the reconfigurable interconnection network against hardware Trojan attacks. Experimental results demonstrate that by incorporating a mere 0.27% hardware overhead to the accelerator, the proposed hardware Trojan can degrade the inference accuracy of popular neural network architectures, including LeNet, AlexNet, and VGG, by a significant range of 8.93% to 86.20%. The implemented arbiter-PUF circuit on a Xilinx Zynq XC7Z100 platform successfully detects the presence and location of hardware Trojans in a reconfigurable interconnection network. This research highlights the vulnerability of reconfigurable CNN accelerators to hardware Trojan attacks and proposes a promising detection technique to mitigate potential security risks. The findings underscore the importance of addressing hardware security concerns in the design and deployment of AI systems utilizing FPGA-based CNN accelerators. Full article
(This article belongs to the Section E:Engineering and Technology)
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11 pages, 1566 KiB  
Article
Effect of α″-Ti Martensitic Phase Formation on Plasticity in Ti–Fe–Sn Ultrafine Eutectic Composites
by Deva Prasaad Neelakandan, Wonhyeong Kim, Barton C. Prorok, Elham Mirkoohi, Dong-Joo Kim, Peter K. Liaw, Gian Song and Chanho Lee
Micromachines 2024, 15(1), 148; https://doi.org/10.3390/mi15010148 - 19 Jan 2024
Viewed by 772
Abstract
Extensive research has been conducted on Ti–Fe–Sn ultrafine eutectic composites due to their high yield strength, compared to conventional microcrystalline alloys. The unique microstructure of ultrafine eutectic composites, which consists of the ultrafine-grained lamella matrix with the formation of primary dendrites, leads to [...] Read more.
Extensive research has been conducted on Ti–Fe–Sn ultrafine eutectic composites due to their high yield strength, compared to conventional microcrystalline alloys. The unique microstructure of ultrafine eutectic composites, which consists of the ultrafine-grained lamella matrix with the formation of primary dendrites, leads to high strength and desirable plasticity. A lamellar structure is known for its high strength with limited plasticity, owing to its interface-strengthening effect. Thus, extensive efforts have been conducted to induce the lamellar structure and control the volume fraction of primary dendrites to enhance plasticity by tailoring the compositions. In this study, however, it was found that not only the volume fraction of primary dendrites but also the morphology of dendrites constitute key factors in inducing excellent ductility. We selected three compositions of Ti–Fe–Sn ultrafine eutectic composites, considering the distinct volume fractions and morphologies of β-Ti dendrites based on the Ti–Fe–Sn ternary phase diagram. As these compositions approach quasi-peritectic reaction points, the α-Ti martensitic phase forms within the primary β-Ti dendrites due to under-cooling effects. This pre-formation of the α-Ti martensitic phase effectively governs the growth direction of β-Ti dendrites, resulting in the development of round-shaped primary dendrites during the quenching process. These microstructural evolutions of β-Ti dendrites, in turn, lead to an improvement in ductility without a significant compromise in strength. Hence, we propose that fine-tuning the composition to control the primary dendrite morphology can be a highly effective alloy design strategy, enabling the attainment of greater macroscopic plasticity without the typical ductility and strength trade-off. Full article
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11 pages, 3730 KiB  
Article
Breakdown Characteristics of GaN DMISFETs Fabricated via Mg, Si and N Triple Ion Implantation
by Tohru Nakamura, Michitaka Yoshino, Toru Toyabe and Akira Yasuda
Micromachines 2024, 15(1), 147; https://doi.org/10.3390/mi15010147 - 18 Jan 2024
Viewed by 857
Abstract
Mg-ion-implanted layers in a GaN substrate after annealing were investigated. Implanted Mg atoms precipitated along the edges of crystal defects were observed using 3D-APT. The breakdown characteristics of a GaN double-diffused vertical MISFET (DMISFET) fabricated via triple ion implantation are presented. A DMISFET [...] Read more.
Mg-ion-implanted layers in a GaN substrate after annealing were investigated. Implanted Mg atoms precipitated along the edges of crystal defects were observed using 3D-APT. The breakdown characteristics of a GaN double-diffused vertical MISFET (DMISFET) fabricated via triple ion implantation are presented. A DMISFET with Si-ion-implanted source regions was formed in Mg-ion-implanted p-base regions, which were isolated from adjacent devices by N-ion-implanted edge termination regions. A threshold voltage of −0.5 V was obtained at a drain voltage of 0.5 V for the fabricated vertical MISFET with an estimated Mg surface concentration of 5 × 1018 cm−3. The maximum drain current and maximum transconductance in a saturation region of Vds = 100 V were 2.8 mA/mm and 0.5 mS/mm at a gate voltage of 15 V, respectively. The breakdown voltage in the off-state was 417 V. The breakdown points were determined by the boundary regions between the N- and Mg-implanted regions. By improving heat annealing methods, ion-implanted GaN DMISFETs can be a promising candidate for future high-voltage and high-power applications. Full article
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12 pages, 2951 KiB  
Article
Highly Transparent Red Organic Light-Emitting Diodes with AZO/Ag/AZO Multilayer Electrode
by Dongwoon Lee, Min Seok Song, Yong Hyeok Seo, Won Woo Lee, Young Woo Kim, Minseong Park, Ye Ji Shin, Sang Jik Kwon, Yongmin Jeon and Eou-Sik Cho
Micromachines 2024, 15(1), 146; https://doi.org/10.3390/mi15010146 - 18 Jan 2024
Cited by 1 | Viewed by 980
Abstract
Free-form factor optoelectronics is becoming more important for various applications. Specifically, flexible and transparent optoelectronics offers the potential to be adopted in wearable devices in displays, solar cells, or biomedical applications. However, current transparent electrodes are limited in conductivity and flexibility. This study [...] Read more.
Free-form factor optoelectronics is becoming more important for various applications. Specifically, flexible and transparent optoelectronics offers the potential to be adopted in wearable devices in displays, solar cells, or biomedical applications. However, current transparent electrodes are limited in conductivity and flexibility. This study aims to address these challenges and explore potential solutions. For the next-generation transparent conductive electrode, Al-doped zinc oxide (AZO) and silver (AZO/Ag/AZO) deposited by in-line magnetron sputtering without thermal treatment was investigated, and this transparent electrode was used as a transparent organic light-emitting diode (OLED) anode to maximize the transparency characteristics. The experiment and simulation involved adjusting the thickness of Ag and AZO and OLED structure to enhance the transmittance and device performance. The AZO/Ag/AZO with Ag of 12 nm and AZO of 32 nm thickness achieved the results of the highest figure of merit (FOM) (Φ550 = 4.65 mΩ−1) and lowest roughness. The full structure of transparent OLED (TrOLED) with AZO/Ag/AZO anode and Mg:Ag cathode reached 64.84% transmittance at 550 nm, and 300 cd/m2 at about 4 V. The results demonstrate the feasibility of adopting flexible substrates, such as PET, without the need for thermal treatment. This research provides valuable insights into the development of transparent and flexible electronic devices. Full article
(This article belongs to the Special Issue Organic Semiconductors and Devices)
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11 pages, 8072 KiB  
Article
A Study on the Surface Quality and Damage Properties of Single-Crystal Silicon Using Different Post-Treatment Processes
by Wei Li, Fangyuan Zha, Bo Fu, Yanglong Li, Jiazhu Duan and Ziyou Zhou
Micromachines 2024, 15(1), 145; https://doi.org/10.3390/mi15010145 - 17 Jan 2024
Viewed by 828
Abstract
Detecting subsurface defects in optical components has always been challenging. This study utilizes laser scattering and photothermal weak absorption techniques to detect surface and subsurface nano-damage precursors of single-crystal silicon components. Based on laser scattering and photothermal weak absorption techniques, we successfully establish [...] Read more.
Detecting subsurface defects in optical components has always been challenging. This study utilizes laser scattering and photothermal weak absorption techniques to detect surface and subsurface nano-damage precursors of single-crystal silicon components. Based on laser scattering and photothermal weak absorption techniques, we successfully establish the relationship between damage precursors and laser damage resistance. The photothermal absorption level is used as an important parameter to measure the damage resistance threshold of optical elements. Single-crystal silicon elements are processed and post-processed optimally. This research employs dry etching and wet etching techniques to effectively eliminate damage precursors from optical components. Additionally, detection techniques are utilized to comprehensively characterize these components, resulting in the successful identification of optimal damage precursor removal methods for various polishing types of single-crystal silicon components. Consequently, this method efficiently enhances the damage thresholds of optical components. Full article
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18 pages, 3758 KiB  
Article
Miniaturization of CRISPR/Cas12-Based DNA Sensor Array by Non-Contact Printing
by Hiroki Shigemori, Satoshi Fujita, Eiichi Tamiya and Hidenori Nagai
Micromachines 2024, 15(1), 144; https://doi.org/10.3390/mi15010144 - 17 Jan 2024
Viewed by 1209
Abstract
DNA microarrays have been applied for comprehensive genotyping, but remain a drawback in complicated operations. As a solution, we previously reported the solid-phase collateral cleavage (SPCC) system based on the clustered regularly interspaced short palindromic repeat/CRISPR-associated protein 12 (CRISPR/Cas12). Surface-immobilized Cas12-CRISPR RNA (crRNA) [...] Read more.
DNA microarrays have been applied for comprehensive genotyping, but remain a drawback in complicated operations. As a solution, we previously reported the solid-phase collateral cleavage (SPCC) system based on the clustered regularly interspaced short palindromic repeat/CRISPR-associated protein 12 (CRISPR/Cas12). Surface-immobilized Cas12-CRISPR RNA (crRNA) can directly hybridize target double-stranded DNA (dsDNA) and subsequently produce a signal via the cleavage of single-stranded DNA (ssDNA) reporter immobilized on the same spot. Therefore, SPCC-based multiplex dsDNA detection can be performed easily. This study reports the miniaturization of SPCC-based spots patterned by a non-contact printer and its performance in comprehensive genotyping on a massively accumulated array. Initially, printing, immobilization, and washing processes of Cas12–crRNA were established to fabricate the non-contact-patterned SPCC-based sensor array. A target dsDNA concentration response was obtained based on the developed sensor array, even with a spot diameter of 0.64 ± 0.05 mm. Also, the limit of detection was 572 pM, 531 pM, and 3.04 nM with 40, 20, and 10 nL-printing of Cas12–crRNA, respectively. Furthermore, the sensor array specifically detected three dsDNA sequences in one-pot multiplexing; therefore, the feasibility of comprehensive genotyping was confirmed. These results demonstrate that our technology can be miniaturized as a CRISPR/Cas12-based microarray by using non-contact printing. In the future, the non-contact-patterned SPCC-based sensor array can be applied as an alternative tool to DNA microarrays. Full article
(This article belongs to the Section B1: Biosensors)
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21 pages, 11882 KiB  
Article
Radiation Detector Front-End Readout Chip with Nonbinary Successive Approximation Register Analog-to-Digital Converter for Wearable Healthcare Monitoring Applications
by Hsuan-Lun Kuo and Shih-Lun Chen
Micromachines 2024, 15(1), 143; https://doi.org/10.3390/mi15010143 - 17 Jan 2024
Viewed by 750
Abstract
A 16-channel front-end readout chip for a radiation detector is designed for portable or wearable healthcare monitoring applications. The proposed chip reads the signal of the radiation detector and converts it into digital serial-out data by using a nonbinary successive approximation register (SAR) [...] Read more.
A 16-channel front-end readout chip for a radiation detector is designed for portable or wearable healthcare monitoring applications. The proposed chip reads the signal of the radiation detector and converts it into digital serial-out data by using a nonbinary successive approximation register (SAR) analog-to-digital converter (ADC) that has a 1-MS/s sampling rate and 10-b resolution. The minimum-to-maximum differential and integral nonlinearity are measured as −0.32 to 0.33 and −0.43 to 0.37 least significant bits, respectively. The signal-to-noise-and-distortion ratio and effective number of bits are 57.41 dB and 9.24 bits, respectively, for an input frequency of 500 kHz and a sampling rate of 1 MS/s. The SAR ADC has a 38.9-fJ/conversion step figure of merit at the sampling rate of 1 MS/s. The proposed chip can read input signals with peak currents ranging from 20 to 750 μA and convert the analog signal into a 10-bit serial-output digital signal. The input dynamic range is 2–75 pC. The resolution of the peak current is 208.3 nA. The chip, which has an area of 1.444 mm × 10.568 mm, is implemented using CMOS 0.18-μm 1P6M technology, and the power consumption of each channel is 19 mW. This design is suitable for wearable devices, especially biomedical devices. Full article
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17 pages, 4852 KiB  
Article
A Novel Compact Broadband Quasi-Twisted Branch Line Coupler Based on a Double-Layered Microstrip Line
by Fayyadh H. Ahmed, Rola Saad and Salam K. Khamas
Micromachines 2024, 15(1), 142; https://doi.org/10.3390/mi15010142 - 17 Jan 2024
Viewed by 789
Abstract
A novel quasi-twisted miniaturized wideband branch line coupler (BLC) is proposed. The design is based on bisecting the conventional microstrip line BLC transversely and folding bisected sections on double-layered substrates with a common ground plane in between. The input and output terminals, each [...] Read more.
A novel quasi-twisted miniaturized wideband branch line coupler (BLC) is proposed. The design is based on bisecting the conventional microstrip line BLC transversely and folding bisected sections on double-layered substrates with a common ground plane in between. The input and output terminals, each with a length of λg/4, and the pair of quarter-wavelength horizontal parallel arms are converted into a Z-shaped meandered microstrip line in the designed structure. Conversely, the pair of quarter-wavelength vertical arms are halved into two lines and transformed into a periodically loaded slow-wave structure. The bisected parts of the BLC are placed on the opposite side of the doubled-layer substrate and connected through four vias passing through the common ground plane. This technique enabled a compact BLC size of 6.4 × 18 mm2, which corresponds to a surface area miniaturization by ~50% as compared to the classical BLC size of 10 × 23 mm2 at 6 GHz. Moreover, the attained relative bandwidth is 73.9% (4.6–10 GHz) for S11, S33, S21, and the phase difference between outputs (∠S21 − ∠S41). However, if a coupling parameter (S41) of up to −7.5 dB is considered, then the relative bandwidth reduces to 53.9% (4.6–10 GHz) for port 1 as the input. Similarly, for port 3 as the input, the obtained bandwidth is 75.8% (4.5–10 GHz) for S33, S11, S43, and the phase difference between outputs (∠S43 − ∠S23). Likewise, this bandwidth reduces to 56% (4.5–8 GHz) when a coupling parameter (S23) of up to −7.5 dB is considered. In contrast, the relative bandwidth for the ordinary BLC is 41% at the same resonant frequency. The circuit is constructed on a double-layered low-cost FR4 substrate with a relative permittivity of 4.3 and a loss tangent of 0.025. An isolation of −13 dB was realized in both S13 and S31 demonstrating an excellent performance. The transmission coefficients between input/output ports S21, S41, S23, and S43 are between −3.1 dB to −3.5 dB at a frequency of 6 GHz. Finally, the proposed BLC provides phase differences between output ports of 90.5° and 94.8° at a frequency of 6 GHz when the input ports 1 and 3 are excited, respectively. The presented design offers the potential of being utilized as a unit cell for building a Butler matrix (BM) for sub-6 GHz 5G beamforming networks. Full article
(This article belongs to the Special Issue Recent Advances in Electromagnetic Devices)
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10 pages, 1209 KiB  
Article
Micromotors of MnO2 for the Recovery of Microplastics
by Oscar Cervantes, Claudia Valtierra-Montiel, Laura Sampedro-Plata, Norberto Casillas, Nieves Menendez and Pilar Herrasti
Micromachines 2024, 15(1), 141; https://doi.org/10.3390/mi15010141 - 17 Jan 2024
Viewed by 1086
Abstract
Plastics, primarily microplastics, are among the greatest pollutants in aquatic environments. Their removal and/or degradation in these environments are crucial to ensure an optimal future of these ecosystems. In this work, MnO2 particles were synthesized and characterized for the removal of polystyrene [...] Read more.
Plastics, primarily microplastics, are among the greatest pollutants in aquatic environments. Their removal and/or degradation in these environments are crucial to ensure an optimal future of these ecosystems. In this work, MnO2 particles were synthesized and characterized for the removal of polystyrene microplastics as a model. MnO2 catalyzes the peroxide reaction, resulting in the formation of oxygen bubbles that propel the pollutants to the surface, achieving removal efficiencies of up to 80%. To achieve this, hydrothermal synthesis was employed using various methods. Parameters such as MnO2, pH, microplastics, and H2O2 concentrations were varied to determine the optimal conditions for microplastics recovering. The ideal conditions for a low microplastic concentrations (10 mg L−1) are 0.2 g L−1 MnO2, 1.6% of H2O2 and 0.01 triton as a surfactant. In these conditions, the micromotors can recover approximately 80% of 300 nm sized polystyrene microplastic within 40 min. Full article
(This article belongs to the Special Issue Fundamentals and Catalytic Applications of Oxide-Based Materials)
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12 pages, 4533 KiB  
Article
Air Gap Fiber Bragg Grating for Simultaneous Strain and Temperature Measurement
by Fuling Yang, Kehui Zhu, Xiaoyi Yu, Tianze Liu, Ke Lu, Zelong Wang and Yan Li
Micromachines 2024, 15(1), 140; https://doi.org/10.3390/mi15010140 - 16 Jan 2024
Viewed by 914
Abstract
We propose an air gap fiber Bragg grating (g-FBG) sensor that can measure strain and temperature simultaneously. The sensor is made by aligning two fiber Bragg gratings (FBGs), and an air gap exists between these two sub-gratings. This sensor’s architecture allows it to [...] Read more.
We propose an air gap fiber Bragg grating (g-FBG) sensor that can measure strain and temperature simultaneously. The sensor is made by aligning two fiber Bragg gratings (FBGs), and an air gap exists between these two sub-gratings. This sensor’s architecture allows it to form a spectrum with phase-shifted fiber Bragg grating (PSFBG) spectroscopy and Fabry–Perot interference (FPI) spectroscopy. Since the sensitivity of PSFBG and FPI spectra is different for strain and temperature, it is possible to measure both strain and temperature by measuring one of the reflected dips of PSFBG and the interference dip of FPI. The experimental results show that the strain sensitivity is about 11.95 pm/με via the dip wavelength detection of FPI, and the temperature sensitivity is about 9.64 pm/°C via the dip wavelength detection of PSFBG. The g-FBG sensor demonstrates a resolution of approximately ±3.7 με within the strain range of 0 to 1000 με and about ±0.6 °C within the temperature range of 25 °C to 120 °C. The proposed g-FBG sensor, characterized by its simple structure, compact size, and cost-effectiveness, exhibits significant potential in the field of multi-parameter measurements. Full article
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17 pages, 29594 KiB  
Article
Theoretical and Experimental Investigation of Surface Textures in Vibration-Assisted Micro Milling
by Bowen Song, Dawei Zhang, Xiubing Jing, Yingying Ren, Yun Chen and Huaizhong Li
Micromachines 2024, 15(1), 139; https://doi.org/10.3390/mi15010139 - 16 Jan 2024
Cited by 1 | Viewed by 876
Abstract
Vibration-assisted micro milling is a promising technique for fabricating engineered mi-cro-scaled surface textures. This paper presents a novel approach for theoretical modeling of three-dimensional (3D) surface textures produced by vibration-assisted micro milling. The proposed model considers the effects of tool edge geometry, minimum [...] Read more.
Vibration-assisted micro milling is a promising technique for fabricating engineered mi-cro-scaled surface textures. This paper presents a novel approach for theoretical modeling of three-dimensional (3D) surface textures produced by vibration-assisted micro milling. The proposed model considers the effects of tool edge geometry, minimum uncut chip thickness (MUCT), and material elastic recovery. The surface texture formation under different machining parameters is simulated and analyzed through mathematical modeling. Two typical surface morphologies can be generated: wave-type and fish scale-type textures, depending on the phase difference between tool paths. A 2-degrees-of-freedom (2-DOF) vibration stage is also developed to provide vibration along the feed and cross-feed directions during micro-milling process. Micro-milling experiments on copper were carried out to verify the ability to fabricate controlled surface textures using the vibration stage. The simulated and experimentally generated surfaces show good agreement in geometry and dimensions. This work provides an accurate analytical model for vibration-assisted micro-milling surface generation and demonstrates its feasibility for efficient, flexible texturing. Full article
(This article belongs to the Special Issue Research Progress of Ultra-Precision Micro-nano Machining)
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12 pages, 6504 KiB  
Article
Thermal Conductivity Gas Sensors for High-Temperature Applications
by Nikolay Samotaev, Boris Podlepetsky, Mikhail Mashinin, Igor Ivanov, Ivan Obraztsov, Konstantin Oblov and Pavel Dzhumaev
Micromachines 2024, 15(1), 138; https://doi.org/10.3390/mi15010138 - 16 Jan 2024
Cited by 1 | Viewed by 1351
Abstract
This paper describes a fast and flexible microfabrication method for thermal conductivity gas sensors useful in high-temperature applications. The key parts of the sensor, the microheater and the package, were fabricated from glass-coated platinum wire and the combination of laser micromilling (ablation) of [...] Read more.
This paper describes a fast and flexible microfabrication method for thermal conductivity gas sensors useful in high-temperature applications. The key parts of the sensor, the microheater and the package, were fabricated from glass-coated platinum wire and the combination of laser micromilling (ablation) of already-sintered monolithic ceramic materials and thick-film screen-printing technologies. The final thermal conductivity gas sensor was fabricated in the form of a complete MEMS device in a metal ceramic package, which could be used as a compact miniaturized surface-mounted device for soldering to standard PCB. Functional test results of the manufactured sensor are presented, demonstrating their full suitability for gas sensing applications and indicating that the obtained parameters are at a level comparable to those of standard industrially produced sensors. The results of the design and optimization principles of applied methods are discussed with regard to possible wider applications in thermal gas sensor prototyping in the future. The advantage of the developed sensors is their ability to operate in air environments under high temperatures of 900 °C and above. The sensor element material and package metallization were insensitive to oxidation compared with classical sensor-solution-based metal–glass packages and silicone MEMS membranes, which exhibit mechanical stress at temperatures above 700 °C. Full article
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15 pages, 7052 KiB  
Article
High-Performance Multi-Level Grayscale Conversion by Driving Waveform Optimization in Electrowetting Displays
by Wanzhen Xu, Zichuan Yi, Mouhua Jiang, Jiashuai Wang, Zhengxing Long, Liming Liu, Feng Chi, Li Wang and Qiming Wan
Micromachines 2024, 15(1), 137; https://doi.org/10.3390/mi15010137 - 16 Jan 2024
Viewed by 712
Abstract
As a new type of reflective display, electrowetting display (EWD) has excellent dynamic display performance, which is based on polymer coatings. However, there are still some issues which can limit its performance, such as oil backflow and the hysteresis effect which reduces the [...] Read more.
As a new type of reflective display, electrowetting display (EWD) has excellent dynamic display performance, which is based on polymer coatings. However, there are still some issues which can limit its performance, such as oil backflow and the hysteresis effect which reduces the stability and response speed of EWDs. Therefore, an effective driving waveform was proposed to overcome these drawbacks, which consisted of grayscale conversions between low gray levels and high gray levels. In the driving waveform, to stabilize the EWD at any initial grayscale (low gray levels/high gray levels), an exponential function waveform and an AC signal were used. Then, the grayscale conversion was performed by using an AC signal with a switching voltage to quickly achieve the target grayscale. Finally, another AC signal was used to stabilize the EWD at the target grayscale. A set of driving waveforms in grayscale ranging across four levels was designed using this method. According to the experimental results, oil backflow and the hysteresis effect could be effectively attenuated by the proposed driving waveforms. During conversion, the response speed of EWDs was boosted by at least 9.37% compared to traditional driving waveforms. Full article
(This article belongs to the Special Issue Micromachines for Dielectrophoresis, 3rd Edition)
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