Micromachines

20 pages, 3856 KiB

Open AccessArticle

Formulation of a Ceramic Ink for 3D Inkjet Printing

by Dennis Graf, Judith Jung and Thomas Hanemann

Micromachines 2021, 12(9), 1136; https://doi.org/10.3390/mi12091136 - 21 Sep 2021

Cited by 7 | Viewed by 3940

Due to its multi-material capabilities, 3D inkjet printing allows for the fabrication of components with functional elements which may significantly reduce the production steps. The potential to print electronics requires jettable polymer-ceramic composites for thermal management. In this study, a respective material was [...] Read more.

Due to its multi-material capabilities, 3D inkjet printing allows for the fabrication of components with functional elements which may significantly reduce the production steps. The potential to print electronics requires jettable polymer-ceramic composites for thermal management. In this study, a respective material was formulated by functionalizing submicron alumina particles by 3-(trimethoxysilyl)propylmethacrylate (MPS) and suspending them in a mixture of the oligourethane Genomer 4247 with two acrylate functionalities and a volatile solvent. Ink jetting tests were performed, as well as thermal conductance and mechanical property measurements. The material met the strict requirements of the printing technology, showing viscosities of around 16 mPa·s as a liquid. After solidification, it exhibited a ceramic content of 50 vol%, with a thermal conductance of 1 W/(m·K). The resulting values reflect the physical possibilities within the frame of the allowed tolerances set by the production method. Full article

(This article belongs to the Special Issue Recent Advances in Inkjet Technology)

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11 pages, 1300 KiB

Open AccessArticle

Simple Fabrication of Solid-State Nanopores on a Carbon Film

by Natsumi Takai, Kan Shoji, Tei Maki and Ryuji Kawano

Micromachines 2021, 12(9), 1135; https://doi.org/10.3390/mi12091135 - 21 Sep 2021

Cited by 4 | Viewed by 3076

Abstract

Solid-state nanopores are widely used as a platform for stochastic nanopore sensing because they can provide better robustness, controllable pore size, and higher integrability than biological nanopores. However, the fabrication procedures, including thin film preparation and nanopore formation, require advanced micro-and nano-fabrication techniques. [...] Read more.

Solid-state nanopores are widely used as a platform for stochastic nanopore sensing because they can provide better robustness, controllable pore size, and higher integrability than biological nanopores. However, the fabrication procedures, including thin film preparation and nanopore formation, require advanced micro-and nano-fabrication techniques. Here, we describe the simple fabrication of solid-state nanopores in a commercially available material: a flat thin carbon film-coated micro-grid for a transmission electron microscope (TEM). We attempted two general methods for nanopore fabrication in the carbon film. The first method was a scanning TEM (STEM) electron beam method. Nanopores were fabricated by irradiating a focused electron beam on the carbon membrane on micro-grids, resulting in the production of nanopores with pore diameters ranging from 2 to 135 nm. The second attempt was a dielectric breakdown method. In this method, nanopores were fabricated by applying a transmembrane voltage of 10 or 30 V through the carbon film on micro-grids. As a result, nanopores with pore diameters ranging from 3.7 to 1345 nm were obtained. Since these nanopores were successfully fabricated in the commercially available carbon thin film using readily available devices, we believe that these solid-state nanopores offer great utility in the field of nanopore research. Full article

(This article belongs to the Special Issue Frontiers in Micromachines in Japan)

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13 pages, 5229 KiB

Open AccessArticle

Design and Fabrication of a Low-Cost Thermopile Infrared Detector

by Ting Liang, Yihao Guan, Cheng Lei, Xuezhan Wu, Yuehang Bai, Jijun Xiong and Lei Qi

Micromachines 2021, 12(9), 1134; https://doi.org/10.3390/mi12091134 - 21 Sep 2021

Cited by 6 | Viewed by 3340

Abstract

In this paper, we design and optimize a low-cost, closed-film structure of a microelectromechanical systems (MEMS) thermopile infrared detector. By optimizing the circular arrangement of thermocouple strips and the thermal isolation design of the cold end to pursue a higher temperature difference, in [...] Read more.

In this paper, we design and optimize a low-cost, closed-film structure of a microelectromechanical systems (MEMS) thermopile infrared detector. By optimizing the circular arrangement of thermocouple strips and the thermal isolation design of the cold end to pursue a higher temperature difference, in addition to eliminating the absorption region, silicon nitride is deposited on the whole device surface as a passivated absorption layer. This reduces the cost while maintaining the voltage response and is suitable for mass production. The optimized detector had a 22.6% improvement in the response rate to 34.2 V/W, a detection rate of 1.02 × 10⁸ cm·Hz^1/2/W, and a response time of 26.9 ms. The design optimization of this detector provides a reference for further development of IR detectors. Full article

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16 pages, 22031 KiB

Open AccessArticle

Three-Phase Six-Level Multilevel Voltage Source Inverter: Modeling and Experimental Validation

by Sheikh Tanzim Meraj, Nor Zaihar Yahaya, Kamrul Hasan, Molla Shahadat Hossain Lipu, Ammar Masaoud, Sawal Hamid Md Ali, Aini Hussain, Muhammad Murtadha Othman and Farhan Mumtaz

Micromachines 2021, 12(9), 1133; https://doi.org/10.3390/mi12091133 - 21 Sep 2021

Cited by 16 | Viewed by 3487

Abstract

This research proposes a three-phase six-level multilevel inverter depending on twelve-switch three-phase Bridge and multilevel DC-link. The proposed architecture increases the number of voltage levels with less power components than conventional inverters such as the flying capacitor, cascaded H-bridge, diode-clamped and other recently [...] Read more.

This research proposes a three-phase six-level multilevel inverter depending on twelve-switch three-phase Bridge and multilevel DC-link. The proposed architecture increases the number of voltage levels with less power components than conventional inverters such as the flying capacitor, cascaded H-bridge, diode-clamped and other recently established multilevel inverter topologies. The multilevel DC-link circuit is constructed by connecting three distinct DC voltage supplies, such as single DC supply, half-bridge and full-bridge cells. The purpose of both full-bridge and half-bridge cells is to provide a variable DC voltage with a common voltage step to the three-phase bridge’s mid-point. A vector modulation technique is also employed to achieve the desired output voltage waveforms. The proposed inverter can operate as a six-level or two-level inverter, depending on the magnitude of the modulation indexes. To guarantee the feasibility of the proposed configuration, the proposed inverter’s prototype is developed, and the experimental results are provided. The proposed inverter showed good performance with high efficiency of 97.59% following the IEEE 1547 standard. The current harmonics of the proposed inverter was also minimized to only 5.8%. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Sustainable Energy Conversion)

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13 pages, 3427 KiB

Open AccessArticle

A Neural Network Approach towards Generalized Resistive Switching Modelling

by Guilherme Carvalho, Maria Pereira, Asal Kiazadeh and Vítor Grade Tavares

Micromachines 2021, 12(9), 1132; https://doi.org/10.3390/mi12091132 - 21 Sep 2021

Cited by 1 | Viewed by 2223

Abstract

Resistive switching behaviour has been demonstrated to be a common characteristic to many materials. In this regard, research teams to date have produced a plethora of different devices exhibiting diverse behaviour, but when system design is considered, finding a ‘one-model-fits-all’ solution can be [...] Read more.

Resistive switching behaviour has been demonstrated to be a common characteristic to many materials. In this regard, research teams to date have produced a plethora of different devices exhibiting diverse behaviour, but when system design is considered, finding a ‘one-model-fits-all’ solution can be quite difficult, or even impossible. However, it is in the interest of the community to achieve more general modelling tools for design that allows a quick model update as devices evolve. Laying the grounds with such a principle, this paper presents an artificial neural network learning approach to resistive switching modelling. The efficacy of the method is demonstrated firstly with two simulated devices and secondly with a

4 {μ m}^{2}

amorphous IGZO device. For the amorphous IGZO device, a normalized root-mean-squared error (NRMSE) of 5.66 × 10⁻³ is achieved with a

[2, 50, 50, 1]

network structure, representing a good balance between model complexity and accuracy. A brief study on the number of hidden layers and neurons and its effect on network performance is also conducted with the best NRMSE reported at 4.63 × 10⁻³. The low error rate achieved in both simulated and real-world devices is a good indicator that the presented approach is flexible and can suit multiple device types. Full article

(This article belongs to the Special Issue Amorphous Oxide Semiconductor-Based Memristive Devices and Thin-Film Transistors)

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15 pages, 13445 KiB

Open AccessArticle

Electric Field-Driven Liquid Metal Droplet Generation and Direction Manipulation

by Jinwon Jeong, Sangkug Chung, Jeong-Bong Lee and Daeyoung Kim

Micromachines 2021, 12(9), 1131; https://doi.org/10.3390/mi12091131 - 20 Sep 2021

Cited by 7 | Viewed by 4543

Abstract

A gallium-based liquid metal got high attention recently, due to the excellent material properties that are useful in various research areas. We report here on electric field-induced liquid metal droplet generation and falling direction manipulation. The well-analyzed electro-hydrodynamic method is a selectable way [...] Read more.

A gallium-based liquid metal got high attention recently, due to the excellent material properties that are useful in various research areas. We report here on electric field-induced liquid metal droplet generation and falling direction manipulation. The well-analyzed electro-hydrodynamic method is a selectable way to control the liquid metal, as the liquid metal is conductive. The electric field-induced liquid metal manipulation can be affected by the flow rate (0.05~0.2 mL/min), voltage (0~7 kV), and distance (15 and 30 mm) between electrodes, which changes the volume of the electric field-induced generated liquid metal droplet and the number of the generated droplets. When the electric field intensity increases or the flow rate increases, the generated droplet volume decreases, and the number of droplets increases. With the highest voltage of 7 kV with 15 mm between electrodes at the 0.2 mL/min flow rate, the lowest volume and the largest number of the generated droplets for 10 s were ~10 nL and 541, respectively. Additionally, we controlled the direction of the generated droplet by changing the electric field. The direction of the liquid metal droplet was controlled with the maximum angle of ~12°. Moreover, we exhibited a short circuit demonstration by controlling the volume or falling direction of the generated liquid metal droplet with an applied electric field. Full article

(This article belongs to the Special Issue Multifunctional Liquid Metal and Its Applications)

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14 pages, 28774 KiB

Open AccessArticle

Electromagnetic Vibration Energy Harvester with Tunable Resonance Frequency Based on Stress Modulation of Flexible Springs

by Yunjia Li, Chenyuan Zhou, Qi Cao, Xinyi Wang, Dayong Qiao and Kai Tao

Micromachines 2021, 12(9), 1130; https://doi.org/10.3390/mi12091130 - 20 Sep 2021

Cited by 12 | Viewed by 2509

Abstract

This paper presents a compact electromagnetic vibrational energy harvester (EVEH) with tunable resonance frequency. The resonance frequency of the EVEH is tuned by adjusting the axial stress in the flexible polymeric springs, which is realized by physically pulling and pushing the springs. The [...] Read more.

This paper presents a compact electromagnetic vibrational energy harvester (EVEH) with tunable resonance frequency. The resonance frequency of the EVEH is tuned by adjusting the axial stress in the flexible polymeric springs, which is realized by physically pulling and pushing the springs. The stress tuning functionality is realized with a compact structure with small volume. The total frequency tuning range of the proposed EVEH is 56 Hz (74–130 Hz), which is 64% of the natural resonance frequency of the EVEH (88 Hz). It is found that the tensile stress increases the resonance frequency of the EVEH, while the compressive stress firstly reduces the resonance frequency and then increases the resonance frequency due to buckling. Full article

(This article belongs to the Special Issue Smart Devices and Systems for Vibration Sensing and Energy Harvesting)

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11 pages, 3045 KiB

Open AccessArticle

Optimization of the Fluidic-Based Assembly for Three-Dimensional Construction of Multicellular Hydrogel Micro-Architecture in Mimicking Hepatic Lobule-like Tissues

by Qian Liang, Yaozhen Hou, Fei Meng and Huaping Wang

Micromachines 2021, 12(9), 1129; https://doi.org/10.3390/mi12091129 - 20 Sep 2021

Viewed by 2008

Abstract

Three-dimensional (3D) assembly of microstructures encapsulating co-cultured multiple cells can highly recapitulate the in vivo tissues, which has a great prospect in tissue engineering and regenerative medicine. In order to fully mimic the in vivo architecture, the hydrogel microstructure needs to be designed [...] Read more.

Three-dimensional (3D) assembly of microstructures encapsulating co-cultured multiple cells can highly recapitulate the in vivo tissues, which has a great prospect in tissue engineering and regenerative medicine. In order to fully mimic the in vivo architecture, the hydrogel microstructure needs to be designed into a special shape and spatially organized without damage, which is very challenging because of its limited mechanical properties. Here, we propose a 3D assembly method for the construction of liver lobule-like microstructures (a mimetic gear-like microstructure of liver lobule) through the local fluidic interaction. Although the method has been proven and is known as the consensual means for constructing 3D cellular models, it is still challenging to improve the assembly efficiency and the assembly success rate by adjusting the fluidic force of non-contact lifting and stacking. To improve the assembly efficiency and the assembly success rate, a fluidic simulation model is proposed based on the mechanism of the interaction between the microstructures and the fluid. By computing the simulation model, we found three main parameters that affect the assembly process; they are the velocity of the microflow, the tilt angle of the manipulator and the spacing between the microstructures and the manipulator. Compared with our previous work, the assembly efficiency was significantly improved 63.8% by using the optimized parameters of the model for assembly process, and the assembly success rate was improved from 98% to 99.5%. With the assistance of the assembly simulation, the luminal 3D micromodels of liver tissue show suitable bioactivity and biocompatibility after long-term hepatocytes culture. We anticipate that our method will be capable of improving the efficiency of the microstructures assembly to regenerate more complex multicellular constructs with unprecedented possibilities for future tissue engineering applications. Full article

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

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11 pages, 1941 KiB

Open AccessArticle

Fabrication of Formalin-Fixed, Paraffin-Embedded (FFPE) Circulating Tumor Cell (CTC) Block Using a Hydrogel Core-Mediated Method

by Tae Hee Lee, Young Jun Kim, Woo Sun Rou and Hyuk Soo Eun

Micromachines 2021, 12(9), 1128; https://doi.org/10.3390/mi12091128 - 20 Sep 2021

Cited by 3 | Viewed by 7247

Abstract

Circulating tumor cells (CTCs) are extremely low-frequency cells in the bloodstream. As those cells have detached from the primary tumor tissues and it circulates throughout the whole body, they are considered as promising diagnostic biomarkers for clinical application. However, the analysis of CTC [...] Read more.

Circulating tumor cells (CTCs) are extremely low-frequency cells in the bloodstream. As those cells have detached from the primary tumor tissues and it circulates throughout the whole body, they are considered as promising diagnostic biomarkers for clinical application. However, the analysis of CTC is often restricted due to their rarity and heterogeneity, as well as their short-term presence. Here we proposed formalin-fixed, paraffin-embedded (FFPE) CTC block method, in combination manner with the hydrogel core-mediated CTC accumulation and conventional paraffin tissue block preparation. The hydrogel core specifically captures and releases cancer cells with high efficiency with an immunoaffinity manner. An additional shell structure protects the isolated cancer cells during the FFPE CTC block preparation process. The fabricated FFPE CTC block was sectioned and cytopathologically investigated just the same way as the conventional tissue block. Our results demonstrate that rare cells such as CTCs can also be prepared for FFPE cell blocks and shows great promise for cytopathological CTC studies. Full article

(This article belongs to the Special Issue Micro/Nanotechnologies for Liquid Biopsy)

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15 pages, 3886 KiB

Open AccessArticle

Investigation on Design Theory and Performance Analysis of Vacuum Capacitive Micromachined Ultrasonic Transducer

by Xiao Huang, Hongliang Wang and Lijun Yu

Micromachines 2021, 12(9), 1127; https://doi.org/10.3390/mi12091127 - 19 Sep 2021

Cited by 5 | Viewed by 3202

Abstract

The capacitive micromachined ultrasonic transducer (CMUT), as a new acoustic-electric conversion element, has a promising application prospect. In this paper, the structure of the vacuum capacitive micromachined ultrasonic transducer is presented, and its performance-influencing factors are investigated. Firstly, the influencing factors of the [...] Read more.

The capacitive micromachined ultrasonic transducer (CMUT), as a new acoustic-electric conversion element, has a promising application prospect. In this paper, the structure of the vacuum capacitive micromachined ultrasonic transducer is presented, and its performance-influencing factors are investigated. Firstly, the influencing factors of the performance parameters of the vacuum CMUT are analyzed theoretically based on the circular plate model and flat plate capacitance model, and the design principles of the structural parameters of the CMUT cell are proposed. Then, the finite element simulation software COMSOL Multiphysics is used to construct CMUT cell models with different membrane materials, membrane shapes, membrane radius thicknesses, and cavity heights for simulation verification. The results show that both the membrane parameters and the cavity heights affect the performance parameters of the Vacuum CMUT. In order to improve the efficiency of the CMUT, materials with low bending stiffness should be selected, and the filling factor of the membrane should be increased. In order to achieve high-transmission sound pressure, a smaller radius thickness and a larger cavity height should be selected. To achieve high reception sensitivity, a larger membrane radius thickness and a smaller cavity height should be selected. In order to obtain high fractional bandwidth, a larger membrane radius thickness should be selected. The results of this paper provide a basis for the design of Vacuum CMUT cell structure. Full article

(This article belongs to the Special Issue Advances in MEMS Theory and Applications)

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14 pages, 3752 KiB

Open AccessArticle

Large-Scale Lever-Based Triboelectric Nanogenerator for Sensing Lateral Vibration and Wrist or Finger Bending for Controlling Shooting Game

by Inkyum Kim, Tae Young Ahn and Daewon Kim

Micromachines 2021, 12(9), 1126; https://doi.org/10.3390/mi12091126 - 18 Sep 2021

Cited by 2 | Viewed by 2301

Abstract

With advances in internet of things technology and fossil fuel depletion, energy harvesting has emerged rapidly as a means of supplying small electronics with electricity. As a method of enhancing the electrical output of the triboelectric nanogenerator, specialized for harvesting mechanical energy, structural [...] Read more.

With advances in internet of things technology and fossil fuel depletion, energy harvesting has emerged rapidly as a means of supplying small electronics with electricity. As a method of enhancing the electrical output of the triboelectric nanogenerator, specialized for harvesting mechanical energy, structural modification to amplify the input force is receiving attention due to the limited input energy level. In this research, a lever structure was employed for delivering the amplified input force to a triboelectric nanogenerator. With structural optimization of a 2.5 cm : 5 cm distance ratio of the first and second parts using two lever structures, the highest electrical outputs were achieved: a V_OC of 51.03 V, current density of 3.34 mA m⁻², and power density of 73.5 mW m⁻² at 12 MΩ in the second part. As applications of this triboelectric generator, a vertical vibration sensor and a wearable reloading trigger in a gun shooting game were demonstrated. The possibility for a wearable finger bending sensor with low-level input was checked using a minimized device. Enhanced low-detection limit with amplified input force from the structural advantage of this lever-based triboelectric nanogenerator device can expand its applicability to the mechanical trigger for wearable electronics. Full article

(This article belongs to the Section E：Engineering and Technology)

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18 pages, 5427 KiB

Open AccessArticle

Cavitation Dynamics and Inertial Cavitation Threshold of Lipid Coated Microbubbles in Viscoelastic Media with Bubble–Bubble Interactions

by Dui Qin, Qingqin Zou, Shuang Lei, Wei Wang and Zhangyong Li

Micromachines 2021, 12(9), 1125; https://doi.org/10.3390/mi12091125 - 18 Sep 2021

Cited by 23 | Viewed by 3632

Abstract

Encapsulated microbubbles combined with ultrasound have been widely utilized in various biomedical applications; however, the bubble dynamics in viscoelastic medium have not been completely understood. It involves complex interactions of coated microbubbles with ultrasound, nearby microbubbles and surrounding medium. Here, a comprehensive model [...] Read more.

Encapsulated microbubbles combined with ultrasound have been widely utilized in various biomedical applications; however, the bubble dynamics in viscoelastic medium have not been completely understood. It involves complex interactions of coated microbubbles with ultrasound, nearby microbubbles and surrounding medium. Here, a comprehensive model capable of simulating the complex bubble dynamics was developed via taking the nonlinear viscoelastic behaviors of the shells, the bubble–bubble interactions and the viscoelasticity of the surrounding medium into account simultaneously. For two interacting lipid-coated bubbles with different initial radii in viscoelastic media, it exemplified that the encapsulating shell, the inter-bubble interactions and the medium viscoelasticity would noticeably suppress bubble oscillations. The inter-bubble interactions exerted a much stronger suppressing effect on the small bubble within the parameters examined in this paper, which might result from a larger radiated pressure acting on the small bubble due to the inter-bubble interactions. The lipid shells make the microbubbles exhibit two typical asymmetric dynamic behaviors (i.e., compression or expansion dominated oscillations), which are determined by the initial surface tension of the bubbles. Accordingly, the inertial cavitation threshold decreases as the initial surface tension increases, but increases as the shell elasticity and viscosity increases. Moreover, with the distance between bubbles decreasing and/or the initial radius of the large bubble increasing, the oscillations of the small bubble decrease and the inertial cavitation threshold increases gradually due to the stronger suppression effects caused by the enhanced bubble–bubble interactions. Additionally, increasing the elasticity and/or viscosity of the surrounding medium would also dampen bubble oscillations and result in a significant increase in the inertial cavitation threshold. This study may contribute to both encapsulated microbubble-associated ultrasound diagnostic and emerging therapeutic applications. Full article

(This article belongs to the Special Issue Microbubbles for Ultrasound Therapy)

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13 pages, 4282 KiB

Open AccessArticle

Design of a Single-Material Complex Structure Anthropomorphic Robotic Hand

by Li Tian, Jianmin Zheng, Nadia Magnenat Thalmann, Hanhui Li, Qifa Wang, Jialin Tao and Yiyu Cai

Micromachines 2021, 12(9), 1124; https://doi.org/10.3390/mi12091124 - 18 Sep 2021

Cited by 11 | Viewed by 3911

Abstract

In the field of robotic hand design, soft body and anthropomorphic design are two trends with a promising future. Designing soft body anthropomorphic robotic hands with human-like grasping ability, but with a simple and reliable structure, is a challenge that still has not [...] Read more.

In the field of robotic hand design, soft body and anthropomorphic design are two trends with a promising future. Designing soft body anthropomorphic robotic hands with human-like grasping ability, but with a simple and reliable structure, is a challenge that still has not been not fully solved. In this paper, we present an anatomically correct robotic hand 3D model that aims to realize the human hand’s functionality using a single type of 3D-printable material. Our robotic hand 3D model is combined with bones, ligaments, tendons, pulley systems, and tissue. We also describe the fabrication method to rapidly produce our robotic hand in 3D printing, wherein all parts are made by elastic 50 A (shore durometer) resin. In the experimental section, we show that our robotic hand has a similar motion range to a human hand with substantial grasping strength and compare it with the latest other designs of anthropomorphic robotic hands. Our new design greatly reduces the fabrication cost and assembly time. Compared with other robotic hand designs, we think our robotic hand may induce a new approach to the design and production of robotic hands as well as other related mechanical structures. Full article

(This article belongs to the Special Issue 3D Printed Actuators)

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16 pages, 3965 KiB

Open AccessArticle

Process Optimization of Silver Nanoparticle Synthesis and Its Application in Mercury Detection

by Lung-Ming Fu, Jia-Hong Hsu, Ming-Kuei Shih, Chang-Wei Hsieh, Wei-Jhong Ju, Yu-Wei Chen, Bao-Hong Lee and Chih-Yao Hou

Micromachines 2021, 12(9), 1123; https://doi.org/10.3390/mi12091123 - 18 Sep 2021

Cited by 35 | Viewed by 8587

Abstract

Silver nanoparticles (AgNPs) have stable reactivity and excellent optical absorption properties. They can be applied in various industries, such as environmental protection, biochemical engineering, and analyte monitoring. However, synthesizing AgNPs and determining their appropriate dosage as a coloring substance are difficult tasks. In [...] Read more.

Silver nanoparticles (AgNPs) have stable reactivity and excellent optical absorption properties. They can be applied in various industries, such as environmental protection, biochemical engineering, and analyte monitoring. However, synthesizing AgNPs and determining their appropriate dosage as a coloring substance are difficult tasks. In this study, to optimize the process of AgNP synthesis and obtain a simple detection method for trace mercury in the environment, we evaluate several factors—including the reagent addition sequence, reaction temperature, reaction time, the pH of the solution, and reagent concentration—considering the color intensity and purity of AgNPs as the reaction optimization criteria. The optimal process for AgNP synthesis is as follows: Mix 10 mM of silver nitrate with trisodium citrate in a hot water bath for 10 min; then, add 10 mM of sodium borohydride to produce the AgNPs and keep stirring for 2 h; finally, adjust the pH to 12 to obtain the most stable products. For AgNP-based mercury detection, the calibration curve of mercury over the concentration range of 0.1–2 ppb exhibits good linearity (R² > 0.99). This study provides a stable and excellent AgNP synthesis technique that can improve various applications involving AgNP-mediated reactions and has the potential to be developed as an alternative to using expensive detection equipment and to be applied for the detection of mercury in food. Full article

(This article belongs to the Special Issue Microfluidic-Based Approaches for Detection in Water and Food Samples)

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17 pages, 1955 KiB

Open AccessReview

Recapitulating the Cancer Microenvironment Using Bioprinting Technology for Precision Medicine

by Jisoo Kim, Jinah Jang and Dong-Woo Cho

Micromachines 2021, 12(9), 1122; https://doi.org/10.3390/mi12091122 - 17 Sep 2021

Cited by 8 | Viewed by 3392

Abstract

The complex and heterogenous nature of cancer contributes to the development of cancer cell drug resistance. The construction of the cancer microenvironment, including the cell–cell interactions and extracellular matrix (ECM), plays a significant role in the development of drug resistance. Traditional animal models [...] Read more.

The complex and heterogenous nature of cancer contributes to the development of cancer cell drug resistance. The construction of the cancer microenvironment, including the cell–cell interactions and extracellular matrix (ECM), plays a significant role in the development of drug resistance. Traditional animal models used in drug discovery studies have been associated with feasibility issues that limit the recapitulation of human functions; thus, in vitro models have been developed to reconstruct the human cancer system. However, conventional two-dimensional and three-dimensional (3D) in vitro cancer models are limited in their ability to emulate complex cancer microenvironments. Advances in technologies, including bioprinting and cancer microenvironment reconstruction, have demonstrated the potential to overcome some of the limitations of conventional models. This study reviews some representative bioprinted in vitro models used in cancer research, particularly fabrication strategies for modeling and consideration of essential factors needed for the reconstruction of the cancer microenvironment. In addition, we highlight recent studies that applied such models, including application in precision medicine using advanced bioprinting technologies to fabricate biomimetic cancer models. Furthermore, we discuss current challenges in 3D bioprinting and suggest possible strategies to construct in vitro models that better mimic the pathophysiology of the cancer microenvironment for application in clinical settings. Full article

(This article belongs to the Special Issue Advanced Biofabrication Technologies)

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11 pages, 1286 KiB

Open AccessArticle

Fabrication of Microparticles with Front–Back Asymmetric Shapes Using Anisotropic Gelation

by Dongkyu Lee, Hiroyuki Kitahata and Hiroaki Ito

Micromachines 2021, 12(9), 1121; https://doi.org/10.3390/mi12091121 - 17 Sep 2021

Cited by 5 | Viewed by 2594

Abstract

Droplet-based microfluidics is a powerful tool for producing monodispersed micrometer-sized droplets with controlled sizes and shapes; thus, it has been widely applied in diverse fields from fundamental science to industries. Toward a simpler method for fabricating microparticles with front–back asymmetry in their shapes, [...] Read more.

Droplet-based microfluidics is a powerful tool for producing monodispersed micrometer-sized droplets with controlled sizes and shapes; thus, it has been widely applied in diverse fields from fundamental science to industries. Toward a simpler method for fabricating microparticles with front–back asymmetry in their shapes, we studied anisotropic gelation of alginate droplets, which occurs inside a flow-focusing microfluidic device. In the proposed method, sodium alginate (NaAlg) aqueous phase fused with a calcium chloride (

{CaCl}_{2}

) emulsion dispersed in the organic phase just before the aqueous phase breaks up into the droplets. The fused droplet with a front–back asymmetric shape was generated, and the asymmetric shape was kept after geometrical confinement by a narrow microchannel was removed. The shape of the fused droplet depended on the size of prefused NaAlg aqueous phase and a

{CaCl}_{2}

emulsion, and the front–back asymmetry appeared in the case of the smaller emulsion size. The analysis of the velocity field inside and around the droplet revealed that the stagnation point at the tip of the aqueous phase also played an important role. The proposed mechanism will be potentially applicable as a novel fabrication technique of microparticles with asymmetric shapes. Full article

(This article belongs to the Special Issue Advances in Microfluidics for Quantifying Cell Mechanics and Biotransport)

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16 pages, 9842 KiB

Open AccessArticle

Investigation on the Electrochemical Deposition of Nanocrystalline Zinc with Cationic Polyacrylamide (CPAM)-ZnSO₄ Electrolyte

by Xiaolei Chen, Jiasen Chen, Jiajun Zhu, Tianyu Cai and Zhongning Guo

Micromachines 2021, 12(9), 1120; https://doi.org/10.3390/mi12091120 - 17 Sep 2021

Cited by 4 | Viewed by 2189

Abstract

The electrochemical deposition of nanocrystalline zinc has high potential to deposit zinc coatings, which have improved wear and corrosion properties compared to conventional coating methods. Conventionally, two or more additives are used in the electrolyte for the formation nanocrystalline zinc; these electrolyte components [...] Read more.

The electrochemical deposition of nanocrystalline zinc has high potential to deposit zinc coatings, which have improved wear and corrosion properties compared to conventional coating methods. Conventionally, two or more additives are used in the electrolyte for the formation nanocrystalline zinc; these electrolyte components are complex, and their maintenance is inconvenient, making it unstable and not suitable for industrial scale production. This paper proposes an electrochemical deposition technique for nanocrystalline zinc using a ZnSO₄ solution with cationic polyacrylamide (CPAM) as the unique additive. The results reveal that the cationic degree of CPAM has a significant influence on the deposition process and that the cationic degree of 20% enhances the electrolyte conductivity and improves the density of the deposited coating. The concentration of CPAM affects the electrolyte viscosity and conductivity. CPAM with a concentration of 20 g/L could simultaneously improve the electrolyte conductivity and maintain the viscosity at a low value, which promotes the formation of a bright deposited coating with a grain size of 87 nm. Additionally, the current density affects the grain structure of the deposited coating. With a current density of 0.5 A/dm², a dense coating with lamellar grains and a grain size of 54.5 nm was obtained, which has, and the surface roughness was reduced to 0.162 μm. Moreover, the corrosion resistant property of the deposited coating was also improved. Full article

(This article belongs to the Section D：Materials and Processing)

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17 pages, 6820 KiB

Open AccessArticle

Cutting Performance of Randomly Distributed Active Abrasive Grains in Gear Honing Process

by Yang Gao, Fuwei Wang, Yuan Liang, Jiang Han, Jie Su, Yu Tong and Lin Liu

Micromachines 2021, 12(9), 1119; https://doi.org/10.3390/mi12091119 - 17 Sep 2021

Cited by 7 | Viewed by 2576

Abstract

In power gear honing, the random distribution of abrasive grains on the tooth surface of the honing wheel is the main factor that influences the machining performance of high-quality hardened gears. In order to investigate the micro-edge cutting performance of the active abrasive [...] Read more.

In power gear honing, the random distribution of abrasive grains on the tooth surface of the honing wheel is the main factor that influences the machining performance of high-quality hardened gears. In order to investigate the micro-edge cutting performance of the active abrasive grains on the workpiece gear, the real honing process is simplified into a micro-edge cutting model with random distribution of active abrasive grains in the cells of the meshing area by obtaining the random distribution states such as the position, orientation and quantity of the honing wheel teeth. The results show that although the active abrasive grains are distributed at different locations, they all experience three types of material removal—slip rubbing, plowing and cutting—allowing the gear honing process to have the combined machining characteristics of grinding, lapping and polishing. The active abrasive grains in first contact produce high honing force, high material removal efficiency and poor surface roughness on the machined workpiece, while the latter ones have the opposite effects. The dislocation angle affects the chip shape and chip discharging direction, and the highest honing force and material removal efficiency is achieved with a dislocation angle of 135°. The higher the number of active abrasive grains in a given contact area, the higher the material removal efficiency. Full article

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10 pages, 1301 KiB

Open AccessArticle

Three-Dimensional Finite Element Analysis and Characterization of Quasi-Surface Acoustic Wave Resonators

by Wen Chen, Linwei Zhang, Shangshu Yang, Wenhan Jia, Songsong Zhang, Yuandong Gu, Liang Lou and Guoqiang Wu

Micromachines 2021, 12(9), 1118; https://doi.org/10.3390/mi12091118 - 17 Sep 2021

Cited by 2 | Viewed by 2372

Abstract

In this work, three-dimensional finite element analysis (3D FEA) of quasi-surface acoustic wave (QSAW) resonators with high accuracy is reported. The QSAW resonators consist of simple molybdenum (Mo) interdigitated transducers (IDT) on solidly mounted stacked layers of AlN/Mo/Si. Different to the SAW resonators [...] Read more.

In this work, three-dimensional finite element analysis (3D FEA) of quasi-surface acoustic wave (QSAW) resonators with high accuracy is reported. The QSAW resonators consist of simple molybdenum (Mo) interdigitated transducers (IDT) on solidly mounted stacked layers of AlN/Mo/Si. Different to the SAW resonators operating in the piezoelectric substrates, the reported resonators are operating in the QSAW mode, since the IDT-excited Rayleigh waves not only propagate in the thin piezoelectric layer of AlN, but also penetrate the Si substrate. Compared with the commonly used two-dimensional (2D) FEA approach, the 3D FEA method reported in this work shows high accuracy, in terms of the resonant frequency, temperature coefficient of frequency (

T C F

), effective coupling coefficient (

k_{e f f}^{2}

) and frequency response. The fabricated QSAW resonator has demonstrated a

k_{e f f}^{2}

of 0.291%, series resonant frequency of 422.50 MHz, and

T C F

of −23.418 ppm/°C in the temperature range between 30 °C and 150 °C, for the design of wavelength at 10.4

μ

m. The measurement results agree well with the simulations. Moreover, the QSAW resonators are more mechanically robust than lamb wave devices and can be integrated with silicon-based film bulk acoustic resonator (FBAR) devices to offer multi-frequency function in a single chip. Full article

(This article belongs to the Special Issue Physical Microelectromechanical Systems (MEMS): Design, Modeling, Fabrication, and Characterization)

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10 pages, 2227 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micro-Prism Patterned Remote Phosphor Film for Enhanced Luminous Efficiency and Color Uniformity of Phosphor-Converted Light-Emitting Diodes

by Jiadong Yu, Shudong Yu, Ting Fu and Yong Tang

Micromachines 2021, 12(9), 1117; https://doi.org/10.3390/mi12091117 - 17 Sep 2021

Cited by 3 | Viewed by 2723

Abstract

In this work, we propose micro-prism patterned remote phosphor (RP) films to enhance both luminous efficiency and color uniformity (CU) of remote phosphor-converted light-emitting diodes (rpc-LEDs) simultaneously. On the incident surface of the RP film, one micro-prism film is used to extract backward [...] Read more.

In this work, we propose micro-prism patterned remote phosphor (RP) films to enhance both luminous efficiency and color uniformity (CU) of remote phosphor-converted light-emitting diodes (rpc-LEDs) simultaneously. On the incident surface of the RP film, one micro-prism film is used to extract backward light by double reflection. On the exit surface, the other micro-prism film is adopted to retain blue light inside the RP film, thus enhancing the phosphor excitation. Experimental results show that double prism-patterned RP (DP-RP) film configuration shows a luminous flux of 55.16 lm, which is 45.1% higher than that of RP film configuration at 300 mA. As regards the CU, the DP-RP film configuration reduces the angular CIE-x and CIE-y standard variations by 68% and 69.32%, respectively, compared with the pristine device. Moreover, the DP-RP film configuration shows excellent color stability under varying driving currents. Since micro-prism films can be easily fabricated by a roll-to-roll process, the micro-prism patterned RP film can be an alternative to a conventional RP layer to enable the practical application of rpc-LEDs. Full article

(This article belongs to the Special Issue Microsystem for Electronic Devices)

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10 pages, 3265 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

P-Doped Carbon Quantum Dots with Antibacterial Activity

by Shuiqin Chai, Lijia Zhou, Shuchen Pei, Zhiyuan Zhu and Bin Chen

Micromachines 2021, 12(9), 1116; https://doi.org/10.3390/mi12091116 - 16 Sep 2021

Cited by 42 | Viewed by 5206

Abstract

It is a major challenge to effectively inhibit microbial pathogens in the treatment of infectious diseases. Research on the application of nanomaterials as antibacterial agents has evidenced their great potential for the remedy of infectious disease. Among these nanomaterials, carbon quantum dots (CQDs) [...] Read more.

It is a major challenge to effectively inhibit microbial pathogens in the treatment of infectious diseases. Research on the application of nanomaterials as antibacterial agents has evidenced their great potential for the remedy of infectious disease. Among these nanomaterials, carbon quantum dots (CQDs) have attracted much attention owing to their unique optical properties and high biosafety. In this work, P-doped CQDs were prepared by simple hydrothermal treatment of m-aminophenol and phosphoric acid with fluorescence emission at 501 nm when excited at 429 nm. The P-doped CQDs showed effective antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The minimal inhibitory concentrations (MICs) of P-doped CQD were 1.23 mg/mL for E. coli and 1.44 mg/mL for S. aureus. Furthermore, the morphologies of E. coli cells were damaged and S. aureus became irregular when treated with the P-doped CQDs. The results of zeta potential analysis demonstrated that the P-doped CQDs inhibit antibacterial activity and destroy the structure of bacteria by electronic interaction. In combination, the results of this study indicate that the as-prepared P-doped CQDs can be a promising candidate for the treatment of bacterial infections. Full article

(This article belongs to the Special Issue Flexible Sensors and Actuators for Biomedicine)

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16 pages, 5295 KiB

Open AccessArticle

Real-Time Built-In Self-Test of MEMS Gyroscope Based on Quadrature Error Signal

by Rui Feng, Jiong Wang, Wei Qiao, Fu Wang, Ming Zhou, Xinglian Shang, Lei Yu, Liuhui Zhou and Shuwen Guo

Micromachines 2021, 12(9), 1115; https://doi.org/10.3390/mi12091115 - 16 Sep 2021

Cited by 5 | Viewed by 3423

Abstract

In high-reliability applications, the health condition of the MEMS gyroscope needs to be known in real time to ensure that the system does not fail due to the wrong output signal. Because the MEMS gyroscope self-test based on the principle of electrostatic force [...] Read more.

In high-reliability applications, the health condition of the MEMS gyroscope needs to be known in real time to ensure that the system does not fail due to the wrong output signal. Because the MEMS gyroscope self-test based on the principle of electrostatic force cannot be performed during the working state. We propose that by monitoring the quadrature error signal of the MEMS gyroscope in real time, an online self-test of the MEMS gyroscope can be realized. The correlation between the gyroscope’s quadrature error amplitude signal and the gyroscope scale factor and bias was theoretically analyzed. Based on the sixteen-sided cobweb-like MEMS gyroscope, the real-time built-in self-test (BIST) method of the MEMS gyroscope based on the quadrature error signal was verified. By artificially setting the control signal of the gyroscope to zero, we imitated several scenarios where the gyroscope malfunctioned. Moreover, a mechanical impact table was used to impact the gyroscope. After a 6000 g shock, the gyroscope scale factor, bias, and quadrature error amplitude changed by −1.02%, −5.76%, and −3.74%, respectively, compared to before the impact. The gyroscope failed after a 10,000 g impact, and the quadrature error amplitude changed −99.82% compared to before the impact. The experimental results show that, when the amplitude of the quadrature error signal seriously deviates from the original value, it can be determined that the gyroscope output signal is invalid. Full article

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

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14 pages, 7155 KiB

Open AccessArticle

Anisotropy Characterization of Metallic Lens Structures

by Yosef T. Aladadi and Majeed A. S. Alkanhal

Micromachines 2021, 12(9), 1114; https://doi.org/10.3390/mi12091114 - 16 Sep 2021

Cited by 1 | Viewed by 1824

Abstract

This paper presents a full electromagnetic (EM) characterization of metallic lenses. The method is based on the utilization of free-space transmission and reflection coefficients to accurately obtain lenses’ tensorial EM parameters. The applied method reveals a clear anisotropic behavior with a full tensorial [...] Read more.

This paper presents a full electromagnetic (EM) characterization of metallic lenses. The method is based on the utilization of free-space transmission and reflection coefficients to accurately obtain lenses’ tensorial EM parameters. The applied method reveals a clear anisotropic behavior with a full tensorial directional permittivity and permeability and noticeably dispersive permeability and wave impedance. This method yields accurate values for the effective refractive index, wave impedance, permittivity, and permeability, unlike those obtained by simple methods such as the eigenmode method. These correct cell parameters affect their lens performance, as manifested in a clear level of anisotropy, impedance matching, and losses. The effect of anisotropy caused by oblique incidence on the performance and operation of lens designs is illustrated in a lens design case. Full article

(This article belongs to the Special Issue Advanced Photonics and Metamaterials)

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43 pages, 14947 KiB

Open AccessReview

A Review of the Methods of Modeling Multi-Phase Flows within Different Microchannels Shapes and Their Applications

by Awatef Abidi, Amir Ahmadi, Mojtaba Enayati, S. Mohammad Sajadi, Hooman Yarmand, Arslan Ahmed and Goshtasp Cheraghian

Micromachines 2021, 12(9), 1113; https://doi.org/10.3390/mi12091113 - 16 Sep 2021

Cited by 18 | Viewed by 5242

Abstract

In industrial processes, the microtechnology concept refers to the operation of small devices that integrate the elements of operational and reaction units to save energy and space. The advancement of knowledge in the field of microfluidics has resulted in fabricating devices with different [...] Read more.

In industrial processes, the microtechnology concept refers to the operation of small devices that integrate the elements of operational and reaction units to save energy and space. The advancement of knowledge in the field of microfluidics has resulted in fabricating devices with different applications in micro and nanoscales. Micro- and nano-devices can provide energy-efficient systems due to their high thermal performance. Fluid flow in microchannels and microstructures has been widely considered by researchers in the last two decades. In this paper, a review study on fluid flow within microstructures is performed. The present study aims to present the results obtained in previous studies on this type of system. First, different types of flows in microchannels are examined. The present article will then review previous articles and present a general summary in each section. Then, the multi-phase flows inside the microchannels are discussed, and the flows inside the micropumps, microturbines, and micromixers are evaluated. According to the literature review, it is found that the use of microstructures enhances energy efficiency. The results of previous investigations revealed that the use of nanofluids as a working fluid in microstructures improves energy efficiency. Previous studies have demonstrated special attention to the design aspects of microchannels and micro-devices compared to other design strategies to improve their performance. Finally, general concluding remarks are presented, and the existing challenges in the use of these devices and suggestions for future investigations are presented. Full article

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12 pages, 4270 KiB

Open AccessArticle

Impacts of Crystal Quality on Carrier Recombination and Spin Dynamics in (110)-Oriented GaAs/AlGaAs Multiple Quantum Wells at Room Temperature

by Satoshi Iba, Ryogo Okamoto, Koki Obu, Yuma Obata and Yuzo Ohno

Micromachines 2021, 12(9), 1112; https://doi.org/10.3390/mi12091112 - 16 Sep 2021

Cited by 2 | Viewed by 2332

Abstract

We have systematically investigated the structural properties, carrier lifetimes, namely, photoluminescence (PL) lifetimes (τ_PL), and electron spin relaxation times (τ_s) in (110) GaAs/AlGaAs multiple quantum wells (MQWs) by using time-resolved PL measurements. The MQWs were grown by [...] Read more.

We have systematically investigated the structural properties, carrier lifetimes, namely, photoluminescence (PL) lifetimes (τ_PL), and electron spin relaxation times (τ_s) in (110) GaAs/AlGaAs multiple quantum wells (MQWs) by using time-resolved PL measurements. The MQWs were grown by molecular beam epitaxy within a wide range of the growth temperature T_g (430–600 °C) and a high V/III flux ratio using As₂. At 530 °C < T_g < 580 °C, we found that the quality of the heterointerfaces is significantly improved, resulting in τ_PL~40 ns at RT, one order of magnitude longer than those reported so far. Long τ_s (~6 ns) is also observed at RT. Full article

(This article belongs to the Special Issue Spin-Photonic Devices and Its Applications)

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11 pages, 5320 KiB

Open AccessArticle

Poly (Ethylene Glycol) Methyl Ether Methacrylate-Based Hydrogel and Cerium(IV) Oxide Nanoparticles as Ophthalmic Lens Material

by Min-Jae Lee, Seon-Young Park and A-Young Sung

Micromachines 2021, 12(9), 1111; https://doi.org/10.3390/mi12091111 - 16 Sep 2021

Cited by 5 | Viewed by 2912

Abstract

The functional hydrogel lens containing 2-hydroxyethylmethacrylate (HEMA) was manufactured by thermal polymerization. The physical properties of the produced hydrogel lens were measured and analyzed. In this study, HEMA, ethylene glycol dimethacrylate (EGDMA), and azobisisobutyronitrile (AIBN) were used for thermal copolymerization. Additionally, poly (ethylene [...] Read more.

The functional hydrogel lens containing 2-hydroxyethylmethacrylate (HEMA) was manufactured by thermal polymerization. The physical properties of the produced hydrogel lens were measured and analyzed. In this study, HEMA, ethylene glycol dimethacrylate (EGDMA), and azobisisobutyronitrile (AIBN) were used for thermal copolymerization. Additionally, poly (ethylene glycol) methyl ether methacrylate (PEGMEMA), 3-(Triethoxysilyl) propyl isocyanate (TEPI), and cerium(Ⅳ) oxide nanoparticles were used as additives to make a functional hydrogel lens. The mixture was heated at 100 °C for 90 min to produce the hydrogel ophthalmic lens by the cast mold method. The resulting physical properties showed that the water content and refractive index of the sample were in the ranges of 38.06~42.11% and 1.426~1.436, respectively. The addition of cerium oxide nanoparticles lowered the contact angle and allowed the hydrogel lens to block UV light. The tensile strength was also improved by 52.13% through cerium oxide nanoparticles, and up to 123.4% by using TEPI. Based on the results of this study, the produced ophthalmic lens is suitable for durable, UV-blocking high-performance lenses. Full article

(This article belongs to the Special Issue Nano Korea 2021)

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12 pages, 3984 KiB

Open AccessArticle

Influence of Lubricant Environment on Machined Surface Quality in Single-Point Diamond Turning of Ferrous Metal

by Menghua Zhou, Jianpeng Wang and Guoqing Zhang

Micromachines 2021, 12(9), 1110; https://doi.org/10.3390/mi12091110 - 15 Sep 2021

Cited by 6 | Viewed by 2331

Abstract

In the field of single-point diamond turning (SPDT), machining ferrous metal is an important research topic with promising application. For SPDT of ferrous metal, the influence of lubricant on the workpiece surface morphology remains to be studied. In this study, three lubricant machining [...] Read more.

In the field of single-point diamond turning (SPDT), machining ferrous metal is an important research topic with promising application. For SPDT of ferrous metal, the influence of lubricant on the workpiece surface morphology remains to be studied. In this study, three lubricant machining environments were selected to carry out specific control experiments. The machined surface morphology and cutting force in different lubricant machining environments were analyzed. The experiment results showed that the lubricant environment will have significant impacts on the quality of the machined surface morphology of ferrous metal. In the environment of minimum quantity lubrication machining (MQLM-oil), better machined surface quality can be obtained than that in ordinary dry machining (ODM) and high-pressure gas machining (HGM). Furthermore, the cutting force captured in the ODM and HGM environment increased with the increase of the cutting depth, while the cutting force in the MQLM-oil environment remained almost unchanged. That indicates MQLM-oil can suppress the formation of hard particles to improve the machining quality. Full article

(This article belongs to the Special Issue Frontiers in Ultra-Precision Machining)

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9 pages, 21769 KiB

Open AccessArticle

Fluorescence Anisotropy as a Temperature-Sensing Molecular Probe Using Fluorescein

by Puneet Jain, Takuya Aida and Masahiro Motosuke

Micromachines 2021, 12(9), 1109; https://doi.org/10.3390/mi12091109 - 15 Sep 2021

Cited by 7 | Viewed by 2951

Abstract

Fluorescence anisotropy, a technique to study the folding state of proteins or affinity of ligands, is used in this present work as a temperature sensor, to measure the microfluidic temperature field, by adding fluorophore in the liquid. Fluorescein was used as a temperature-sensing [...] Read more.

Fluorescence anisotropy, a technique to study the folding state of proteins or affinity of ligands, is used in this present work as a temperature sensor, to measure the microfluidic temperature field, by adding fluorophore in the liquid. Fluorescein was used as a temperature-sensing probe, while glycerol–aq. ammonia solution was used as a working fluid. Fluorescence anisotropy of fluorescein was measured by varying various parameters. Apart from this, a comparison of fluorescence anisotropy and fluorescence intensity is also performed to demonstrate the validity of anisotropy to be applied in a microfluidic field with non-uniform liquid thickness. Viscosity dependence and temperature dependence on the anisotropy are also clarified; the results indicate an appropriate selection of relation between molecule size and viscosity is important to obtain a large temperature coefficient in anisotropy. Furthermore, a practical calibration procedure of the apparatus constant is proposed. In addition, the potential of temperature imaging is confirmed by the measurement of temperature distribution under focused laser heating. Full article

(This article belongs to the Special Issue Selected Papers from the 11th Symposium on Micro-Nano Science and Technology on Micromachines)

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13 pages, 6564 KiB

Open AccessArticle

Investigation on Bidirectional Pulse Electrochemical Micromachining of Micro Dimples

by Zhouzhi Gu, Xiaolei Chen, Zhongzheng Xu, Zhisen Ye and Guojun Li

Micromachines 2021, 12(9), 1108; https://doi.org/10.3390/mi12091108 - 15 Sep 2021

Cited by 2 | Viewed by 2058

Abstract

Through-mask electrochemical micromachining (TMEMM) is a promising method to prepare micro dimples on the surface of metallic parts. However, the workpiece is machined one by one in traditional TMEMM. This paper introduced bidirectional pulse to TMEMM to improve the machining efficiency. Two masked [...] Read more.

Through-mask electrochemical micromachining (TMEMM) is a promising method to prepare micro dimples on the surface of metallic parts. However, the workpiece is machined one by one in traditional TMEMM. This paper introduced bidirectional pulse to TMEMM to improve the machining efficiency. Two masked workpieces were placed face to face, and connected to the ends of the bidirectional pulse power supply. Along with the change of the pulse direction, the polarities of the two workpieces were interchanged periodically, and micro dimples could be prepared on both workpieces at one time. The simulation and experiment results indicated that with bidirectional pulse mode, micro dimples with same the profile can be prepared on two workpieces at one time, and the dimension of micro dimple was smaller than that with unidirectional pulse mode. In bidirectional pulse current, the pulse frequency and pulse duty cycle played an important role on the preparation of micro dimple. With high pulse frequency and low pulse duty cycle, it is useful to reduce the undercut of micro dimple and improve the machining localization. With the pulse duty cycle of 20% and pulse frequency of 10 kHz, micro dimples with etch factor (EF) of 3 were well prepared on both workpieces surface. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in Materials and Processing 2021)

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11 pages, 27790 KiB

Open AccessArticle

Analysis of Shape Memory Behavior and Mechanical Properties of Shape Memory Polymer Composites Using Thermal Conductive Fillers

by Mijeong Kim, Seongeun Jang, Sungwoong Choi, Junghoon Yang, Jungpil Kim and Duyoung Choi

Micromachines 2021, 12(9), 1107; https://doi.org/10.3390/mi12091107 - 15 Sep 2021

Cited by 14 | Viewed by 3474

Abstract

Shape memory polymers (SMPs) are attracting attention for their use in wearable displays and biomedical materials due to their good biocompatibility and excellent moldability. SMPs also have the advantage of being lightweight with excellent shape recovery due to their low density. However, they [...] Read more.

Shape memory polymers (SMPs) are attracting attention for their use in wearable displays and biomedical materials due to their good biocompatibility and excellent moldability. SMPs also have the advantage of being lightweight with excellent shape recovery due to their low density. However, they have not yet been applied to a wide range of engineering fields because of their inferior physical properties as compared to those of shape memory alloys (SMAs). In this study, we attempt to find optimized shape memory polymer composites. We also investigate the shape memory performance and physical properties according to the filler type and amount of hardener. The shape memory composite was manufactured by adding nanocarbon materials of graphite and non-carbon additives of Cu. The shape-recovery mechanism was compared, according to the type and content of the filler. The shape fixation and recovery properties were analyzed, and the physical properties of the shape recovery composite were obtained through mechanical strength, thermal conductivity and differential scanning calorimetry analysis. Full article

(This article belongs to the Special Issue Nano Korea 2021)

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