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Micromachines, Volume 13, Issue 8 (August 2022) – 208 articles

Cover Story (view full-size image): Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF). Spatter behavior has an intrinsic correlation with the forming quality because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes more severe in the fabrication of large-sized parts during multi-beam L-PBF. Therefore, investigations of spatter generation and countermeasures have become more urgent. Although much research has provided insights into the melt pool, microstructure, and mechanical property, reviews of spatter in L-PBF are still limited. This work reviews the literature on the in situ detection, generation, effects, and countermeasures of spatter in L-PBF. It is expected to pave the way toward a novel generation of highly efficient and intelligent L-PBF systems. View this paper
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41 pages, 14677 KiB  
Review
A Review of Spatter in Laser Powder Bed Fusion Additive Manufacturing: In Situ Detection, Generation, Effects, and Countermeasures
by Zheng Li, Hao Li, Jie Yin, Yan Li, Zhenguo Nie, Xiangyou Li, Deyong You, Kai Guan, Wei Duan, Longchao Cao, Dengzhi Wang, Linda Ke, Yang Liu, Ping Zhao, Lin Wang, Kunpeng Zhu, Zhengwen Zhang, Liang Gao and Liang Hao
Micromachines 2022, 13(8), 1366; https://doi.org/10.3390/mi13081366 - 22 Aug 2022
Cited by 53 | Viewed by 7319
Abstract
Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes [...] Read more.
Spatter is an inherent, unpreventable, and undesired phenomenon in laser powder bed fusion (L-PBF) additive manufacturing. Spatter behavior has an intrinsic correlation with the forming quality in L-PBF because it leads to metallurgical defects and the degradation of mechanical properties. This impact becomes more severe in the fabrication of large-sized parts during the multi-laser L-PBF process. Therefore, investigations of spatter generation and countermeasures have become more urgent. Although much research has provided insights into the melt pool, microstructure, and mechanical property, reviews of spatter in L-PBF are still limited. This work reviews the literature on the in situ detection, generation, effects, and countermeasures of spatter in L-PBF. It is expected to pave the way towards a novel generation of highly efficient and intelligent L-PBF systems. Full article
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12 pages, 2449 KiB  
Article
Manufacturing of Ultra-Thin X-ray-Compatible COC Microfluidic Devices for Optimal In Situ Macromolecular Crystallography Experiments
by Ramakrishna Vasireddi, Antonin Gardais and Leonard M. G. Chavas
Micromachines 2022, 13(8), 1365; https://doi.org/10.3390/mi13081365 - 22 Aug 2022
Cited by 4 | Viewed by 2074
Abstract
Cyclic-olefin-copolymer (COC)-based microfluidic devices are increasingly becoming the center of highly valuable research for in situ X-ray measurements due to their compatibility with X-rays, biological compounds, chemical resistance, optical properties, low cost, and simplified handling. COC microfluidic devices present potential solutions to challenging [...] Read more.
Cyclic-olefin-copolymer (COC)-based microfluidic devices are increasingly becoming the center of highly valuable research for in situ X-ray measurements due to their compatibility with X-rays, biological compounds, chemical resistance, optical properties, low cost, and simplified handling. COC microfluidic devices present potential solutions to challenging biological applications such as protein binding, folding, nucleation, growth kinetics, and structural changes. In recent years, the techniques applied to manufacturing and handling these devices have capitalized on enormous progress toward small-scale sample probing. Here, we describe the new and innovative design aspects, fabrication, and experimental implementation of low-cost and micron-sized X-ray-compatible microfluidic sample environments that address diffusion-based crystal formation for crystallographic characterization. The devices appear fully compatible with crystal growth and subsequent X-ray diffraction experiments, resulting in remarkably low background data recording. The results highlighted in this research demonstrate how the engineered microfluidic devices allow the recording of accurate crystallographic data at room temperature and structure determination at high resolution. Full article
(This article belongs to the Section E:Engineering and Technology)
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12 pages, 6298 KiB  
Article
Enabling Intelligent IoTs for Histopathology Image Analysis Using Convolutional Neural Networks
by Mohammed H. Alali, Arman Roohi, Shaahin Angizi and Jitender S. Deogun
Micromachines 2022, 13(8), 1364; https://doi.org/10.3390/mi13081364 - 22 Aug 2022
Cited by 2 | Viewed by 1500
Abstract
Medical imaging is an essential data source that has been leveraged worldwide in healthcare systems. In pathology, histopathology images are used for cancer diagnosis, whereas these images are very complex and their analyses by pathologists require large amounts of time and effort. On [...] Read more.
Medical imaging is an essential data source that has been leveraged worldwide in healthcare systems. In pathology, histopathology images are used for cancer diagnosis, whereas these images are very complex and their analyses by pathologists require large amounts of time and effort. On the other hand, although convolutional neural networks (CNNs) have produced near-human results in image processing tasks, their processing time is becoming longer and they need higher computational power. In this paper, we implement a quantized ResNet model on two histopathology image datasets to optimize the inference power consumption. We analyze classification accuracy, energy estimation, and hardware utilization metrics to evaluate our method. First, the original RGB-colored images are utilized for the training phase, and then compression methods such as channel reduction and sparsity are applied. Our results show an accuracy increase of 6% from RGB on 32-bit (baseline) to the optimized representation of sparsity on RGB with a lower bit-width, i.e., <8:8>. For energy estimation on the used CNN model, we found that the energy used in RGB color mode with 32-bit is considerably higher than the other lower bit-width and compressed color modes. Moreover, we show that lower bit-width implementations yield higher resource utilization and a lower memory bottleneck ratio. This work is suitable for inference on energy-limited devices, which are increasingly being used in the Internet of Things (IoT) systems that facilitate healthcare systems. Full article
(This article belongs to the Special Issue Hardware-Friendly Machine Learning and Its Applications)
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22 pages, 3473 KiB  
Review
Modular Microfluidics: Current Status and Future Prospects
by Xiaochen Lai, Mingpeng Yang, Hao Wu and Dachao Li
Micromachines 2022, 13(8), 1363; https://doi.org/10.3390/mi13081363 - 22 Aug 2022
Cited by 17 | Viewed by 3359
Abstract
This review mainly studies the development status, limitations, and future directions of modular microfluidic systems. Microfluidic technology is an important tool platform for scientific research and plays an important role in various fields. With the continuous development of microfluidic applications, conventional monolithic microfluidic [...] Read more.
This review mainly studies the development status, limitations, and future directions of modular microfluidic systems. Microfluidic technology is an important tool platform for scientific research and plays an important role in various fields. With the continuous development of microfluidic applications, conventional monolithic microfluidic chips show more and more limitations. A modular microfluidic system is a system composed of interconnected, independent modular microfluidic chips, which are easy to use, highly customizable, and on-site deployable. In this paper, the current forms of modular microfluidic systems are classified and studied. The popular fabrication techniques for modular blocks, the major application scenarios of modular microfluidics, and the limitations of modular techniques are also discussed. Lastly, this review provides prospects for the future direction of modular microfluidic technologies. Full article
(This article belongs to the Special Issue Physics in Micro/Nano Devices: From Fundamental to Application)
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13 pages, 2696 KiB  
Article
Acoustic Manipulation of Intraocular Particles
by Ari Leshno, Avraham Kenigsberg, Heli Peleg-Levy, Silvia Piperno, Alon Skaat and Hagay Shpaisman
Micromachines 2022, 13(8), 1362; https://doi.org/10.3390/mi13081362 - 21 Aug 2022
Cited by 2 | Viewed by 2397
Abstract
Various conditions cause dispersions of particulate matter to circulate inside the anterior chamber of a human eye. These dispersed particles might reduce visual acuity or promote elevation of intraocular pressure (IOP), causing secondary complications such as particle related glaucoma, which is a major [...] Read more.
Various conditions cause dispersions of particulate matter to circulate inside the anterior chamber of a human eye. These dispersed particles might reduce visual acuity or promote elevation of intraocular pressure (IOP), causing secondary complications such as particle related glaucoma, which is a major cause of blindness. Medical and surgical treatment options are available to manage these complications, yet preventive measures are not currently available. Conceptually, manipulating these dispersed particles in a way that reduces their negative impact could prevent these complications. However, as the eye is a closed system, manipulating dispersed particles in it is challenging. Standing acoustic waves have been previously shown to be a versatile tool for manipulation of bioparticles from nano-sized extracellular vesicles up to millimeter-sized organisms. Here we introduce for the first time a novel method utilizing standing acoustic waves to noninvasively manipulate intraocular particles inside the anterior chamber. Using a cylindrical acoustic resonator, we show ex vivo manipulation of pigmentary particles inside porcine eyes. We study the effect of wave intensity over time and rule out temperature changes that could damage tissues. Optical coherence tomography and histologic evaluations show no signs of damage or any other side effect that could be attributed to acoustic manipulation. Finally, we lay out a clear pathway to how this technique can be used as a non-invasive tool for preventing secondary glaucoma. This concept has the potential to control and arrange intraocular particles in specific locations without causing any damage to ocular tissue and allow aqueous humor normal outflow which is crucial for maintaining proper IOP levels. Full article
(This article belongs to the Special Issue Recent Advances in Acoustofluidics)
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16 pages, 4163 KiB  
Article
Effect of the Deposition Time on the Structural, 3D Vertical Growth, and Electrical Conductivity Properties of Electrodeposited Anatase–Rutile Nanostructured Thin Films
by Moisés do Amaral Amâncio, Yonny Romaguera-Barcelay, Robert Saraiva Matos, Marcelo Amanajás Pires, Ariamna María Dip Gandarilla, Marcus Valério Botelho do Nascimento, Francisco Xavier Nobre, Ştefan Ţălu, Henrique Duarte da Fonseca Filho and Walter Ricardo Brito
Micromachines 2022, 13(8), 1361; https://doi.org/10.3390/mi13081361 - 21 Aug 2022
Cited by 1 | Viewed by 1314
Abstract
TiO2 time-dependent electrodeposited thin films were synthesized using an electrophoretic apparatus. The XRD analysis revealed that the films could exhibit a crystalline structure composed of ~81% anatase and ~6% rutile after 10 s of deposition, with crystallite size of 15 nm. AFM [...] Read more.
TiO2 time-dependent electrodeposited thin films were synthesized using an electrophoretic apparatus. The XRD analysis revealed that the films could exhibit a crystalline structure composed of ~81% anatase and ~6% rutile after 10 s of deposition, with crystallite size of 15 nm. AFM 3D maps showed that the surfaces obtained between 2 and 10 s of deposition exhibit strong topographical irregularities with long-range and short-range correlations being observed in different surface regions, a trend also observed by the Minkowski functionals. The height-based ISO, as well as specific surface microtexture parameters, showed an overall decrease from 2 to 10 s of deposition, showing a subtle decrease in the vertical growth of the films. The surfaces were also mapped to have low spatial dominant frequencies, which is associated with the similar roughness profile of the films, despite the overall difference in vertical growth observed. The electrical conductivity measurements showed that despite the decrease in topographical roughness, the films acquired a thickness capable of making them increasingly insulating from 2 to 10 s of deposition. Thus, our results prove that the deposition time used during the electrophoretic experiment consistently affects the films’ structure, morphology, and electrical conductivity. Full article
(This article belongs to the Special Issue Recent Advances in Thin Film Electronic Devices)
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12 pages, 1822 KiB  
Article
Integrated Amplitude and Phase Monitor for Micro-Actuators
by Sandra Nicole Manosalvas-Kjono, Ronald Quan and Olav Solgaard
Micromachines 2022, 13(8), 1360; https://doi.org/10.3390/mi13081360 - 20 Aug 2022
Cited by 2 | Viewed by 1730
Abstract
Micro-actuators driven on resonance maximize reach and speed; however, due to their sensitivity to environmental factors (e.g., temperature and air pressure), the amplitude and phase response must be monitored to achieve an accurate actuator position. We introduce an MEMS (microelectromechanical system) amplitude and [...] Read more.
Micro-actuators driven on resonance maximize reach and speed; however, due to their sensitivity to environmental factors (e.g., temperature and air pressure), the amplitude and phase response must be monitored to achieve an accurate actuator position. We introduce an MEMS (microelectromechanical system) amplitude and phase monitor (MAPM) with a signal-to-noise ratio of 51 dB and 11.0 kHz bandwidth, capable of simultaneously driving and sensing the movement of 1D and 2D electrostatically driven micro-actuators without modifying the chip or its packaging. The operational principle is to electromechanically modulate the amplitude of a high-frequency signal with the changing capacitance of the micro-actuator. MAPM operation is characterized and verified by simultaneously measuring the amplitude and phase frequency response of commercial micromirrors. We demonstrate that the MAPM circuitry is insensitive to complex relationships between capacitance and position of the MEMS actuators, and it is capable of giving real-time read-out of the micromirror motion. Our measurements also reveal and quantify observations of phase drift and crosstalk in 2D resonant operation. Measurements of phase changes over time under normal operation also verify the need for phase monitoring. The open-loop, high-sensitivity position sensor enables detailed characterization of dynamic micro-actuator behavior, leading to new insights and new types of operation, including improved control of nonlinear motion. Full article
(This article belongs to the Special Issue Optical MEMS, Volume III)
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15 pages, 3489 KiB  
Article
Pressure-Driven Perfusion System to Control, Multiplex and Recirculate Cell Culture Medium for Organs-on-Chips
by Mees N. S. de Graaf, Aisen Vivas, Andries D. van der Meer, Christine L. Mummery and Valeria V. Orlova
Micromachines 2022, 13(8), 1359; https://doi.org/10.3390/mi13081359 - 20 Aug 2022
Cited by 9 | Viewed by 3752
Abstract
Organ-on-chip (OoC) devices are increasingly used to mimic the tissue microenvironment of cells in intact organs. This includes microchannels to mimic, for example, fluidic flow through blood vessels. Present methods for controlling microfluidic flow in these systems rely on gravity, rocker systems or [...] Read more.
Organ-on-chip (OoC) devices are increasingly used to mimic the tissue microenvironment of cells in intact organs. This includes microchannels to mimic, for example, fluidic flow through blood vessels. Present methods for controlling microfluidic flow in these systems rely on gravity, rocker systems or external pressure pumps. For many purposes, pressure pumps give the most consistent flow profiles, but they are not well-suited for high throughput as might be required for testing drug responses. Here, we describe a method which allows for multiplexing of microfluidic channels in OoC devices plus the accompanying custom software necessary to run the system. Moreover, we show the approach is also suitable for recirculation of culture medium, an essential cost consideration when expensive culture reagents are used and are not “spent” through uptake by the cells during transient unidirectional flow. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2022)
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22 pages, 4301 KiB  
Review
Rubbing-Assisted Approach for Fabricating Oriented Nanobiomaterials
by Yadong Chai, Yanni Zhou and Motohiro Tagaya
Micromachines 2022, 13(8), 1358; https://doi.org/10.3390/mi13081358 - 20 Aug 2022
Cited by 1 | Viewed by 1710
Abstract
The highly-oriented structures in biological tissues play an important role in determining the functions of the tissues. In order to artificially fabricate oriented nanostructures similar to biological tissues, it is necessary to understand the oriented mechanism and invent the techniques for controlling the [...] Read more.
The highly-oriented structures in biological tissues play an important role in determining the functions of the tissues. In order to artificially fabricate oriented nanostructures similar to biological tissues, it is necessary to understand the oriented mechanism and invent the techniques for controlling the oriented structure of nanobiomaterials. In this review, the oriented structures in biological tissues were reviewed and the techniques for producing highly-oriented nanobiomaterials by imitating the oriented organic/inorganic nanocomposite mechanism of the biological tissues were summarized. In particular, we introduce a fabrication technology for the highly-oriented structure of nanobiomaterials on the surface of a rubbed polyimide film that has physicochemical anisotropy in order to further form the highly-oriented organic/inorganic nanocomposite structures based on interface interaction. This is an effective technology to fabricate one-directional nanobiomaterials by a biomimetic process, indicating the potential for wide application in the biomedical field. Full article
(This article belongs to the Section D:Materials and Processing)
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10 pages, 3015 KiB  
Article
Multilayer Soft Photolithography Fabrication of Microfluidic Devices Using a Custom-Built Wafer-Scale PDMS Slab Aligner and Cost-Efficient Equipment
by Trieu Nguyen, Tanoy Sarkar, Tuan Tran, Sakib M. Moinuddin, Dipongkor Saha and Fakhrul Ahsan
Micromachines 2022, 13(8), 1357; https://doi.org/10.3390/mi13081357 - 20 Aug 2022
Cited by 12 | Viewed by 3940
Abstract
We present a robust, low-cost fabrication method for implementation in multilayer soft photolithography to create a PDMS microfluidic chip with features possessing multiple height levels. This fabrication method requires neither a cleanroom facility nor an expensive UV exposure machine. The central part of [...] Read more.
We present a robust, low-cost fabrication method for implementation in multilayer soft photolithography to create a PDMS microfluidic chip with features possessing multiple height levels. This fabrication method requires neither a cleanroom facility nor an expensive UV exposure machine. The central part of the method stays on the alignment of numerous PDMS slabs on a wafer-scale instead of applying an alignment for a photomask positioned right above a prior exposure layer using a sophisticated mask aligner. We used a manual XYZR stage attached to a vacuum tweezer to manipulate the top PDMS slab. The bottom PDMS slab sat on a rotational stage to conveniently align with the top part. The movement of the two slabs was observed by a monocular scope with a coaxial light source. As an illustration of the potential of this system for fast and low-cost multilayer microfluidic device production, we demonstrate the microfabrication of a 3D microfluidic chaotic mixer. A discussion on another alternative method for the fabrication of multiple height levels is also presented, namely the micromilling approach. Full article
(This article belongs to the Special Issue Microfluidics in Analytical Chemistry)
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40 pages, 27383 KiB  
Review
A Focused Review on the Flexible Wearable Sensors for Sports: From Kinematics to Physiologies
by Lei Liu and Xuefeng Zhang
Micromachines 2022, 13(8), 1356; https://doi.org/10.3390/mi13081356 - 20 Aug 2022
Cited by 11 | Viewed by 3767
Abstract
As an important branch of wearable electronics, highly flexible and wearable sensors are gaining huge attention due to their emerging applications. In recent years, the participation of wearable devices in sports has revolutionized the way to capture the kinematical and physiological status of [...] Read more.
As an important branch of wearable electronics, highly flexible and wearable sensors are gaining huge attention due to their emerging applications. In recent years, the participation of wearable devices in sports has revolutionized the way to capture the kinematical and physiological status of athletes. This review focuses on the rapid development of flexible and wearable sensor technologies for sports. We identify and discuss the indicators that reveal the performance and physical condition of players. The kinematical indicators are mentioned according to the relevant body parts, and the physiological indicators are classified into vital signs and metabolisms. Additionally, the available wearable devices and their significant applications in monitoring these kinematical and physiological parameters are described with emphasis. The potential challenges and prospects for the future developments of wearable sensors in sports are discussed comprehensively. This review paper will assist both athletic individuals and researchers to have a comprehensive glimpse of the wearable techniques applied in different sports. Full article
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10 pages, 3713 KiB  
Communication
A Compact MIMO Antenna with Improved Isolation for ISM, Sub-6 GHz, and WLAN Application
by Batchingis Bayarzaya, Niamat Hussain, Wahaj Abbas Awan, Md. Abu Sufian, Anees Abbas, Domin Choi, Jaemin Lee and Nam Kim
Micromachines 2022, 13(8), 1355; https://doi.org/10.3390/mi13081355 - 20 Aug 2022
Cited by 21 | Viewed by 2373
Abstract
This paper presents a compact two-element MIMO antenna with improved isolation for triple-band applications. The antenna consists of two radiating elements with the shared ground plane and a novel decoupling structure. Each antenna element has three stubs with different lengths, which work as [...] Read more.
This paper presents a compact two-element MIMO antenna with improved isolation for triple-band applications. The antenna consists of two radiating elements with the shared ground plane and a novel decoupling structure. Each antenna element has three stubs with different lengths, which work as quarter-wavelength monopoles to give a triple-band operation. The decoupling system is made by etching various slots in an inverted H-shape stub attached to two quarter-circles at its lower ends. The simulated and measured results show that the antenna operates (|S11| < −10 dB) at the key frequency bands of 2.4 GHz (2.29–2.47 GHz), 3.5 GHz (3.34–3.73 GHz), and 5.5 GHz (4.57–6.75 GHz) with a stable gain and radiation patterns. Moreover, the MIMO antenna shows good isolation characteristics. The isolation is more than 20 dB, the envelope correlation coefficient is <0.003, and diversity gain is 9.98 dB, within the frequency band of interest. Furthermore, the MIMO antenna has a compact size of 48 mm × 31 mm × 1.6 mm. These features of the proposed antenna make it a suitable candidate for I.S.M., 5G sub-6 GHz, and WLAN applications. Full article
(This article belongs to the Special Issue Microwave Antennas: From Fundamental Research to Applications)
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16 pages, 5193 KiB  
Article
Design and Fabrication of Millimeter-Wave Frequency-Tunable Metamaterial Absorber Using MEMS Cantilever Actuators
by Myungjin Chung, Heijun Jeong, Yong-Kweon Kim, Sungjoon Lim and Chang-Wook Baek
Micromachines 2022, 13(8), 1354; https://doi.org/10.3390/mi13081354 - 20 Aug 2022
Cited by 7 | Viewed by 2052
Abstract
In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced [...] Read more.
In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced MEMS cantilever array having initial out-of-plane deflections, and the cantilevers were electrostatically actuated to generate a capacitance change. The dimensional parameters of the absorber were determined via impedance matching using a full electromagnetic simulation. The designed absorber was fabricated on a glass wafer with surface micromachining processes using a photoresist sacrificial layer and the oxygen-plasma-ashing process to release the cantilevers. The performance of the fabricated absorber was experimentally validated using a waveguide measurement setup. The absorption frequency shifted down according to the applied DC (direct current) bias voltage from 28 GHz in the initial off state to 25.5 GHz in the pull-down state with the applied voltage of 15 V. The measured reflection coefficients at those frequencies were −5.68 dB and −33.60 dB, corresponding to the peak absorptivity rates of 72.9 and 99.9%, respectively. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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12 pages, 2583 KiB  
Article
A Piezoelectric Heterostructure Scavenging Mechanical Energy from Human Foot Strikes
by Wei He
Micromachines 2022, 13(8), 1353; https://doi.org/10.3390/mi13081353 - 20 Aug 2022
Cited by 3 | Viewed by 1298
Abstract
This paper presents a piezoelectric heterostructure for extracting mechanical energy from human foot strikes based on the impact of a moving block on the tips of the piezoelectric unimorph cantilevers. The use of the magnetic springs allows low-frequency and high-amplitude movements of the [...] Read more.
This paper presents a piezoelectric heterostructure for extracting mechanical energy from human foot strikes based on the impact of a moving block on the tips of the piezoelectric unimorph cantilevers. The use of the magnetic springs allows low-frequency and high-amplitude movements of the device. The piezoelectric unimorph cantilevers deform under a human foot strike on the pedal, and the piezoelectric elements in d31-mode produce output voltages. An analysis was conducted, and the working principle was stated. A prototype was fabricated to validate the feasibility of the proposed design. The experimental results show that the generated RMS voltage increases with human walking (running) speed. At the walking speed of 6 km/h, an average power of 36.26 μW is produced across a matching resistive load of 4 MΩ with an initial separating distance of 9 mm. Improvements of the device are possible, allowing an increase in the average power by increasing the number of piezoelectric unimorph cantilevers and using the piezoelectric materials with higher piezoelectric constants. Full article
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13 pages, 13332 KiB  
Article
Optimization of Microchannels and Application of Basic Activation Functions of Deep Neural Network for Accuracy Analysis of Microfluidic Parameter Data
by Feroz Ahmed, Masashi Shimizu, Jin Wang, Kenji Sakai and Toshihiko Kiwa
Micromachines 2022, 13(8), 1352; https://doi.org/10.3390/mi13081352 - 20 Aug 2022
Cited by 4 | Viewed by 1890
Abstract
The fabrication of microflow channels with high accuracy in terms of the optimization of the proposed designs, minimization of surface roughness, and flow control of microfluidic parameters is challenging when evaluating the performance of microfluidic systems. The use of conventional input devices, such [...] Read more.
The fabrication of microflow channels with high accuracy in terms of the optimization of the proposed designs, minimization of surface roughness, and flow control of microfluidic parameters is challenging when evaluating the performance of microfluidic systems. The use of conventional input devices, such as peristaltic pumps and digital pressure pumps, to evaluate the flow control of such parameters cannot confirm a wide range of data analysis with higher accuracy because of their operational drawbacks. In this study, we optimized the circular and rectangular-shaped microflow channels of a 100 μm microfluidic chip using a three-dimensional simulation tool, and analyzed concentration profiles of different regions of the microflow channels. Then, we applied a deep learning (DL) algorithm for the dense layers of the rectified linear unit (ReLU), Leaky ReLU, and Swish activation functions to train and test 1600 experimental and interpolation of data samples which obtained from the microfluidic chip. Moreover, using the same DL algorithm, we configured three models for each of these three functions by changing the internal middle layers of these models. As a result, we obtained a total of 9 average accuracy values of ReLU, Leaky ReLU, and Swish functions for a defined threshold value of 6×105 using the trial-and-error method. We applied single-to-five-fold cross-validation technique of deep neural network to avoid overfitting and reduce noises from data-set to evaluate better average accuracy of data of microfluidic parameters. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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16 pages, 5642 KiB  
Article
Research on Temperature Compensation of Multi-Channel Pressure Scanner Based on an Improved Cuckoo Search Optimizing a BP Neural Network
by Huan Wang, Qinghua Zeng, Zongyu Zhang and Hongfu Wang
Micromachines 2022, 13(8), 1351; https://doi.org/10.3390/mi13081351 - 19 Aug 2022
Cited by 6 | Viewed by 1581
Abstract
A multi-channel pressure scanner is an essential tool for measuring and acquiring various pressure parameters in aerospace applications. It is important to note, however, that the pressure sensor of each of these channels will drift significantly with the increase in the temperature range [...] Read more.
A multi-channel pressure scanner is an essential tool for measuring and acquiring various pressure parameters in aerospace applications. It is important to note, however, that the pressure sensor of each of these channels will drift significantly with the increase in the temperature range of the pressure measurement, and the output voltage of each of these channels will show nonlinear characteristics, which will constrain the improvements in the accuracy of the measurement. In the regression fitting process, it is difficult to fit nonlinear data with the traditional least-squares method, which leaves pressure measurement accuracy unsatisfactory. A temperature compensation method based on an improved cuckoo search optimizing a BP neural network for a multi-channel pressure scanner is proposed in this paper to improve pressure measurement accuracy in a wide temperature range. Using the chaotic simplex algorithm, we first improved the cuckoo search algorithm, then optimized the connection weights and thresholds of the BP neural network, and finally constructed an experimental calibration system to investigate the temperature compensation of the multi-channel pressure scanning valves in the −40 °C to 60 °C temperature range. The compensation test results show that the algorithm has a better compensation effect and is more suitable for the temperature compensation of multi-channel pressure scanners than the traditional least-squares method and the standard RBF and BP neural networks. The maximum full-scale error of all 32 channels is 0.02% FS (full-scale error) and below, which realizes its high-accuracy multi-point pressure measurement in a wide temperature range. Full article
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9 pages, 2805 KiB  
Article
3200 ppi Matrix-Addressable Blue MicroLED Display
by Meng-Chyi Wu, Ming-Che Chung and Cheng-Yeu Wu
Micromachines 2022, 13(8), 1350; https://doi.org/10.3390/mi13081350 - 19 Aug 2022
Cited by 7 | Viewed by 2589
Abstract
In this article, an active matrix (AM) micro light-emitting diode (MicroLED) display with a resolution of 1920 × 1080 and a high pixel density of 3200 pixels per inch (ppi) is reported. The single pixel with a diameter of 5 μm on the [...] Read more.
In this article, an active matrix (AM) micro light-emitting diode (MicroLED) display with a resolution of 1920 × 1080 and a high pixel density of 3200 pixels per inch (ppi) is reported. The single pixel with a diameter of 5 μm on the MicroLED array exhibits excellent characteristics, including a forward voltage of 2.8 V at 4.4 μA, an ideality factor of 1.7 in the forward bias of 2–3 V, an extremely low leakage current of 131 fA at −10 V, an external quantum efficiency of 6.5%, and a wall-plug efficiency of 6.6% at 10.2 A/cm2, a light output power of 28.3 μW and brightness of 1.6 × 105 cd/m2 (nits) at 1 mA. The observed blue shift in the electroluminent peak wavelength is only 6.6 nm from 441.2 nm to 434.6 nm with increasing the current from 5 μA to 1 mA (from 10 to 5 × 103 A/cm2). Through flip-chip bonding technology, the 1920 × 1080 bottom-emitting MicroLED display through the backside of a sapphire substrate can demonstrate high-resolution graphic images. Full article
(This article belongs to the Special Issue Micro-Light Emitting Diode: From Chips to Applications)
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17 pages, 1234 KiB  
Review
Diagnosis Methods for COVID-19: A Systematic Review
by Renata Maia, Violeta Carvalho, Bernardo Faria, Inês Miranda, Susana Catarino, Senhorinha Teixeira, Rui Lima, Graça Minas and João Ribeiro
Micromachines 2022, 13(8), 1349; https://doi.org/10.3390/mi13081349 - 19 Aug 2022
Cited by 18 | Viewed by 3871
Abstract
At the end of 2019, the coronavirus appeared and spread extremely rapidly, causing millions of infections and deaths worldwide, and becoming a global pandemic. For this reason, it became urgent and essential to find adequate tests for an accurate and fast diagnosis of [...] Read more.
At the end of 2019, the coronavirus appeared and spread extremely rapidly, causing millions of infections and deaths worldwide, and becoming a global pandemic. For this reason, it became urgent and essential to find adequate tests for an accurate and fast diagnosis of this disease. In the present study, a systematic review was performed in order to provide an overview of the COVID-19 diagnosis methods and tests already available, as well as their evolution in recent months. For this purpose, the Science Direct, PubMed, and Scopus databases were used to collect the data and three authors independently screened the references, extracted the main information, and assessed the quality of the included studies. After the analysis of the collected data, 34 studies reporting new methods to diagnose COVID-19 were selected. Although RT-PCR is the gold-standard method for COVID-19 diagnosis, it cannot fulfill all the requirements of this pandemic, being limited by the need for highly specialized equipment and personnel to perform the assays, as well as the long time to get the test results. To fulfill the limitations of this method, other alternatives, including biological and imaging analysis methods, also became commonly reported. The comparison of the different diagnosis tests allowed to understand the importance and potential of combining different techniques, not only to improve diagnosis but also for a further understanding of the virus, the disease, and their implications in humans. Full article
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15 pages, 6507 KiB  
Article
Rapid and Sensitive Electrochemical Assay of Cefditoren with MWCNT/Chitosan NCs/Fe2O3 as a Nanosensor
by Nida Aydogdu, Goksu Ozcelikay and Sibel A. Ozkan
Micromachines 2022, 13(8), 1348; https://doi.org/10.3390/mi13081348 - 19 Aug 2022
Cited by 2 | Viewed by 1336
Abstract
In this research, a glassy carbon electrode (GCE) modified by MWCNT/chitosan NCs/Fe2O3 was prepared for the determination of the cephalosporin antibiotic cefditoren (CFT) using adsorptive stripping differential pulse and cyclic voltammetry techniques. The effects of pH, the scan rate, the [...] Read more.
In this research, a glassy carbon electrode (GCE) modified by MWCNT/chitosan NCs/Fe2O3 was prepared for the determination of the cephalosporin antibiotic cefditoren (CFT) using adsorptive stripping differential pulse and cyclic voltammetry techniques. The effects of pH, the scan rate, the deposition potential, the accumulation time, and modification agents on the determination of CFT were analyzed. The results showed that the modified electrode significantly increased the oxidation peak current of CFT. Under optimized conditions, the MWCNT/chitosan NCs/Fe2O3/GCE nanosensor exhibited a linear response between 0.2 µM and 10 µM toward CFT. The limit of detection and quantification were determined to be 1.65 nM and 5.50 nM, respectively. Model drugs (cefdinir, cefpodoxime, cephalexin, and ceftazidime compounds) were used to enlighten the CFT oxidation mechanism. Moreover, the nanosensor was used to analyze CFT in a pharmaceutical dosage form and commercial deproteinated human serum samples. The accuracy of these methods was proven in the recovery studies, with values of 96.98 and 98.62% for the pharmaceutical dosage form and commercial deproteinated human serum sample, respectively. Full article
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11 pages, 5219 KiB  
Article
Tuning Axial Resolution Independent of Lateral Resolution in a Computational Imaging System Using Bessel Speckles
by Vijayakumar Anand
Micromachines 2022, 13(8), 1347; https://doi.org/10.3390/mi13081347 - 19 Aug 2022
Cited by 10 | Viewed by 1625
Abstract
Speckle patterns are formed by random interferences of mutually coherent beams. While speckles are often considered as unwanted noise in many areas, they also formed the foundation for the development of numerous speckle-based imaging, holography, and sensing technologies. In the recent years, artificial [...] Read more.
Speckle patterns are formed by random interferences of mutually coherent beams. While speckles are often considered as unwanted noise in many areas, they also formed the foundation for the development of numerous speckle-based imaging, holography, and sensing technologies. In the recent years, artificial speckle patterns have been generated with spatially incoherent sources using static and dynamic optical modulators for advanced imaging applications. In this report, a basic study has been carried out with Bessel distribution as the fundamental building block of the speckle pattern (i.e., speckle patterns formed by randomly interfering Bessel beams). In general, Bessel beams have a long focal depth, which in this scenario is counteracted by the increase in randomness enabling tunability of the axial resolution. As a direct imaging method could not be applied when there is more than one Bessel beam, an indirect computational imaging framework has been applied to study the imaging characteristics. This computational imaging process consists of three steps. In the first step, the point spread function (PSF) is calculated, which is the speckle pattern formed by the random interferences of Bessel beams. In the next step, the intensity distribution for an object is obtained by a convolution between the PSF and object function. The object information is reconstructed by processing the PSF and the object intensity distribution using non-linear reconstruction. In the computational imaging framework, the lateral resolution remained a constant, while the axial resolution improved when the randomness in the system was increased. Three-dimensional computational imaging with statistical averaging for different cases of randomness has been synthetically demonstrated for two test objects located at two different distances. The presented study will lead to a new generation of incoherent imaging technologies. Full article
(This article belongs to the Special Issue Non-diffractive Beams for the State of the Art Applications)
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15 pages, 18793 KiB  
Article
Research on Integral Fabrication and Inner Surface Metallization of the High-Frequency Terahertz Hollow-Core Metal Rectangular Waveguide Cavity by a Combined Process Based on Wire Electrochemical Micromachining and Electrochemical Deposition
by Xiaolei Bi and Lingchao Meng
Micromachines 2022, 13(8), 1346; https://doi.org/10.3390/mi13081346 - 19 Aug 2022
Viewed by 1257
Abstract
With the development of fabrication technology for terahertz rectangular cavity devices, the fabrication process of integral terahertz waveguide cavities has received much attention because of its beneficial effect on improving the transmission of terahertz signals. However, smaller feature sizes, higher dimensional accuracy, and [...] Read more.
With the development of fabrication technology for terahertz rectangular cavity devices, the fabrication process of integral terahertz waveguide cavities has received much attention because of its beneficial effect on improving the transmission of terahertz signals. However, smaller feature sizes, higher dimensional accuracy, and more stringent requirements for cavity surface roughness and edge radius make it difficult to manufacture terahertz waveguide cavities with a high operating frequency by using existing micro-manufacturing technology. At the same time, the smaller feature size also makes it more difficult to realize uniform metallization on the inner surface of a terahertz waveguide cavity. In this paper, a new and improved combined manufacturing process based on wire electrochemical micromachining and electrochemical deposition is proposed to realize the integral fabrication and uniform metallization of the inner surface of a high-frequency terahertz metal rectangular waveguide cavity. A detailed description and analysis of this combined process are carried out, together with corresponding experimental investigations. An integral 1.7 THz hollow-core metal rectangular waveguide cavity with an end-face size of 165.9 μm × 88.3 μm, an edge radius of less than 10 μm, an internal bottom surface roughness of less than 0.10 μm, and an internal side surface roughness of less than 0.40 μm was manufactured, and high-quality metallization of its inner surface was also achieved. Full article
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14 pages, 3473 KiB  
Article
Investigation of an Electrochromic Device Based on Ammonium Metatungstate-Iron (II) Chloride Electrochromic Liquid
by Sifan Kong, Guanguang Zhang, Muyun Li, Rihui Yao, Chenxiao Guo, Honglong Ning, Jianzhi Zhang, Ruiqiang Tao, Haoyang Yan and Xubing Lu
Micromachines 2022, 13(8), 1345; https://doi.org/10.3390/mi13081345 - 19 Aug 2022
Cited by 6 | Viewed by 2177
Abstract
Even though electrochromism has been around for more than 50 years, it still has several issues. Multi-layered films, high manufacturing costs, and a short lifetime are present in existing electrochromic devices. We demonstrate a unique high-performance device with a basic structure and no [...] Read more.
Even though electrochromism has been around for more than 50 years, it still has several issues. Multi-layered films, high manufacturing costs, and a short lifetime are present in existing electrochromic devices. We demonstrate a unique high-performance device with a basic structure and no solid electrochromic sheets in this work. In this device, the electrolyte layer is also avoided. The device uses an electrochromic solution prepared from a mixture of ammonium metatungstate and iron (II) chloride solution as a functional layer with reversible redox properties. The tungstate ions on the electrode surface are reduced when the device is colored, and the Fe2+ on the electrode surface is oxidized on another electrode surface. The generated Fe3+ in the mixed functional layer oxidizes the previously reduced tungstate ions as the device fades. We determined the ΔT (transmittance modulation) and response time among ammonium metatungstate ratios, iron (II) chloride ratios, and driven current density using DOE (design of experiment) trials. Using 0.175 mol/L ammonium metatungstate and 0.30 mol/L iron (II) chloride, a device with outstanding ΔT (more than 57% at 700 nm), a short response time (less than 10 s), and high coloring efficiency (160.04 cm2/C at 700 nm) is demonstrated. Full article
(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)
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14 pages, 1760 KiB  
Article
Implementation of a Sponge-Based Flexible Electronic Skin for Safe Human–Robot Interaction
by Kun Yang, Xinkai Xia, Fan Zhang, Huanzhou Ma, Shengbo Sang, Qiang Zhang and Jianlong Ji
Micromachines 2022, 13(8), 1344; https://doi.org/10.3390/mi13081344 - 19 Aug 2022
Cited by 1 | Viewed by 1964
Abstract
In current industrial production, robots have increasingly been taking the place of manual workers. With the improvements in production efficiency, accidents that involve operators occur frequently. In this study, a flexible sensor system was designed to promote the security performance of a collaborative [...] Read more.
In current industrial production, robots have increasingly been taking the place of manual workers. With the improvements in production efficiency, accidents that involve operators occur frequently. In this study, a flexible sensor system was designed to promote the security performance of a collaborative robot. The flexible sensors, which was made by adsorbing graphene into a sponge, could accurately convert the pressure on a contact surface into a numerical signal. Ecoflex was selected as the substrate material for our sensing array so as to enable the sensors to better adapt to the sensing application scenario of the robot arm. A 3D printing mold was used to prepare the flexible substrate of the sensors, which made the positioning of each part within the sensors more accurate and ensured the unity of the sensing array. The sensing unit showed a correspondence between the input force and the output resistance that was in the range of 0–5 N. Our stability and reproducibility experiments indicated that the sensors had a good stability. In addition, a tactile acquisition system was designed to sample the tactile data from the sensor array. Our interaction experiment results showed that the proposed electronic skin could provide an efficient approach for secure human–robot interaction. Full article
(This article belongs to the Special Issue Intelligent Biosensors and Biochips)
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11 pages, 2123 KiB  
Article
Variable Stiffness Conductive Composites by 4D Printing Dual Materials Alternately
by Fei Long, Gaojie Xu, Jing Wang, Yong Ren and Yuchuan Cheng
Micromachines 2022, 13(8), 1343; https://doi.org/10.3390/mi13081343 - 19 Aug 2022
Cited by 2 | Viewed by 1985
Abstract
Materials that can be designed with programmable properties and which change in response to external stimuli are of great importance in numerous fields of soft actuators, involving robotics, drug delivery and aerospace applications. In order to improve the interaction of human and robots, [...] Read more.
Materials that can be designed with programmable properties and which change in response to external stimuli are of great importance in numerous fields of soft actuators, involving robotics, drug delivery and aerospace applications. In order to improve the interaction of human and robots, materials with variable stiffness are introduced to develop their compliance. A variable stiffness composite has been investigated in this paper, which is composed of liquid metals (LMs) and silicone elastomers. The phase changing materials (LMs) have been encapsulated into silicone elastomer by printing the dual materials alternately with three-dimensional direct ink writing. Such composites enable the control over their own stiffness between soft and rigid states through LM effective phase transition. The tested splines demonstrated that the stiffness changes approximately exceeded 1900%, and the storage modulus is 4.75 MPa and 0.2 MPa when LM is rigid and soft, respectively. In the process of heating up, the stretching strain can be enlarged by at least three times, but the load capacity is weakened. At a high temperature, the resistance of the conductive composites changes with the deformation degree, which is expected to be applied in the field of soft sensing actuators. Full article
(This article belongs to the Special Issue Droplet-Based Microfluidics: Design, Fabrication and Applications)
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20 pages, 4593 KiB  
Article
A Novel Design Nomogram for Optimization of Micro Search Coil Magnetometer for Energy Monitoring in Smart Buildings
by Hadi Tavakkoli, Kui Song, Xu Zhao, Mingzheng Duan and Yi-Kuen Lee
Micromachines 2022, 13(8), 1342; https://doi.org/10.3390/mi13081342 - 18 Aug 2022
Cited by 4 | Viewed by 1329
Abstract
In this paper, a new analytical method to achieve the maximum signal-to-noise ratio (SNR) of a micro search coil magnetometer (µSCM) is presented. A planar spiral inductor was utilized to miniaturize conventional bulky search coil magnetometers. First, dimensional analysis was applied [...] Read more.
In this paper, a new analytical method to achieve the maximum signal-to-noise ratio (SNR) of a micro search coil magnetometer (µSCM) is presented. A planar spiral inductor was utilized to miniaturize conventional bulky search coil magnetometers. First, dimensional analysis was applied to identify three dimensionless parameters for the µSCM’s key performance indices (sensitivity (Se), noise, and SNR). The effect of the parameters on the µSCM’s performance was carefully investigated, and a novel 4D nomogram was developed. Furthermore, an SNR analysis considering noise sources of a low-noise amplifier was performed. By combining the results from the nomogram and the effect of the noise sources from the amplifier circuit, optimum values for the dimensionless parameters were calculated. According to the calculation results, the dominant noise source varied with an increase in the track width ratio to the outer diameter. Seven different samples were fabricated by a single-mask lithography process. The sensitivity of 1612 mV/mT was demonstrated at a 50 Hz input magnetic field, which was better than the previous µSCM (Se = 6.5 mV/mT) by more than 2 orders of magnitude. Finally, one of the fabricated µSCMs was employed to measure the online power consumption of a personal computer while different types of software were running. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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16 pages, 4959 KiB  
Article
Visualization and Heat Transfer Performance of Mini-Grooved Flat Heat Pipe Filled with Different Working Fluids
by Fei Xin, Qiang Lyu and Wenchao Tian
Micromachines 2022, 13(8), 1341; https://doi.org/10.3390/mi13081341 - 18 Aug 2022
Cited by 4 | Viewed by 1348
Abstract
Mini-grooved flat heat pipe (MGFHP) possesses the advantages of high compactness, no mechanical component, super thermal conductivity, and excellent temperature uniformity, which can meet the demand for electronic devices efficiently cooling. In this research, visual and heat transfer experiments were performed to investigate [...] Read more.
Mini-grooved flat heat pipe (MGFHP) possesses the advantages of high compactness, no mechanical component, super thermal conductivity, and excellent temperature uniformity, which can meet the demand for electronic devices efficiently cooling. In this research, visual and heat transfer experiments were performed to investigate the flow and thermal characteristics inside the MGFHP. Fluid flow and distribution are observed to be quite different in the MGFHP containing different working fluids, which is affected by the physical properties of working fluid, the surface state of the grooved wick, and limited working space. Additionally, the input heat, working fluid type, filling ratio, and wettability obviously affect the thermal conductivity and temperature uniformity of the MGFHP. The deionized water-filled MGFHP possesses lower thermal resistance and higher heat transfer capacity than anhydrous ethanol or hexane filled MGFHP, especially for the copper oxide MGFHP filled with deionized water with a filling ratio of 1.0. Thermal resistance, maximum temperature, and temperature nonuniformity at the condensation section of deionized water-filled copper oxide MGFHP are lower than those of the original copper MGFHP by 31.1%, 3.7 °C, and 0.11 °C for the anhydrous ethanol filled MGFHP and 34.4%, 3.1 °C, and 0.13 °C for the hexane filled MGFHP, respectively. Full article
(This article belongs to the Special Issue Advanced Packaging for Microsystem Applications)
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13 pages, 455 KiB  
Article
Unconventional Rashba Spin-Orbit Coupling on the Charge Conductance and Spin Polarization of a Ferromagnetic/Insulator/Ferromagnetic Rashba Metal Junction
by Aek Jantayod
Micromachines 2022, 13(8), 1340; https://doi.org/10.3390/mi13081340 - 18 Aug 2022
Cited by 1 | Viewed by 1445
Abstract
A ferromagnetic/insulator/ferromagnetic Rashba metal junction (FM/I/FRM) with both Rashba spin–orbit coupling (RSOC) and exchange energy splitting was studied theoretically. Two kinds of interactions in FRM generate the three metallic states in a FRM; the Rashba ring metal (RRM) state, the anomalous Rashba metal [...] Read more.
A ferromagnetic/insulator/ferromagnetic Rashba metal junction (FM/I/FRM) with both Rashba spin–orbit coupling (RSOC) and exchange energy splitting was studied theoretically. Two kinds of interactions in FRM generate the three metallic states in a FRM; the Rashba ring metal (RRM) state, the anomalous Rashba metal (ARM) state and the normal Rashba metal (NRM) state. The scattering method and the free-electron model are used to describe the transport properties of particles and to calculate the conductance spectrum and the spin polarization of current in the junction. The conductance spectrum in the applied voltage shows the prominent features at the boundaries not only for the three states of the FRM but also in the ARM state. In addition, the conductance in the RRM and ARM states is strongly influenced by both the thickness and barrier height of the insulator layer. We also found that the spin polarization obtains a high value in the ARM state and is not affected by the qualities of the insulator, unlike the RRM and NRM states. Obtaining high-spin polarization from FRM material can be useful to produce spintronic devices in future devices. Full article
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15 pages, 9503 KiB  
Article
Effect of Particle Velocity on Microcutting Process of Fe–C Alloy by Molecular Dynamics
by Chunxia Deng, Junye Li, Wenqing Meng and Weihong Zhao
Micromachines 2022, 13(8), 1339; https://doi.org/10.3390/mi13081339 - 18 Aug 2022
Viewed by 1007
Abstract
In order to study the material removal mechanism of Fe–C alloy surfaces in the particle microcutting process, the molecular dynamics method was used to study the material deformation and removal rules during the particle microcutting process. By analyzing and discussing the particle cutting [...] Read more.
In order to study the material removal mechanism of Fe–C alloy surfaces in the particle microcutting process, the molecular dynamics method was used to study the material deformation and removal rules during the particle microcutting process. By analyzing and discussing the particle cutting force, atomic energy, atomic displacement, lattice structure, and dislocation in the particle microcutting process under different cutting velocities, the material removal mechanism is revealed. The results show that the atomic binding energy of Fe–C alloy increases with an increase in particle cutting velocity. The cutting force of particles and atomic potential energy of the workpiece increase obviously. The accumulated strain energy and dislocation energy in the lattice increase, the lattice deformation becomes more severe, and the material is prone to plastic deformation. The atoms form atomic groups at the front of the particle and are then remove from the surface of Fe–C alloy in the form of chips. Full article
(This article belongs to the Section D:Materials and Processing)
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13 pages, 5344 KiB  
Article
Controlled Continuous Patterning of Spherical Stainless Steel by Multi-Axis Linkage Laser Milling
by He Li, Junjie Zhang, Wenqi Ma, Yuan Liu, Xuesen Zhao, Zhenjiang Hu, Xiaohui Wang, Min Sheng and Tao Sun
Micromachines 2022, 13(8), 1338; https://doi.org/10.3390/mi13081338 - 18 Aug 2022
Viewed by 1377
Abstract
While laser surface texturing is promising for the fabrication of planar surface microstructures, the continuously patterning with micrometer accuracy of non-planar surface on miniature parts with large curvature by laser ablation is challenging. In the present work, we demonstrate the feasibility of applying [...] Read more.
While laser surface texturing is promising for the fabrication of planar surface microstructures, the continuously patterning with micrometer accuracy of non-planar surface on miniature parts with large curvature by laser ablation is challenging. In the present work, we demonstrate the feasibility of applying the proposed multi-axis laser milling in continuous patterning of 25 mm diameter spherical stainless steel with high uniformity and precision, based on a strategy of simultaneously adjusting the position and the posture of laser-surface interaction point for enabling the constant coincidence of laser beam with ablated surface normal. Specifically, a miniaturized five-axis platform for controlling workpiece motion with high degree-of-freedom is designed and integrated with a fixed nanosecond pulsed laser beam operating at 1064 nm. The precise path of laser-surface interaction point is derived based on the projection and transformation of pre-determined planar pattern on spherical surface. Meanwhile, a virtual prototype of the multi-axis laser milling with embedded interpolation algorithm is established, which enables the generation of NC codes for subsequent laser milling experiments. Furthermore, the sampling of laser processing parameters particularly for spherical surface is carried out. Finally, complex patterns are continuously structured on the spherical surface by employing the proposed multi-axis laser milling method, and subsequent characterization demonstrates both long range uniformity and local high accuracy of the fabricated patterns. Current work provides a feasible method for the continuous laser surface texturing of non-planar surfaces for miniature parts with large curvature. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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11 pages, 2310 KiB  
Article
Bubble-Enhanced Mixing Induced by Standing Surface Acoustic Waves (SSAWs) in Microchannel
by Jingjing Zhang, Tengfei Zheng, Lin Tang, Hui Qi, Xiaoyu Wu and Linlong Zhu
Micromachines 2022, 13(8), 1337; https://doi.org/10.3390/mi13081337 - 18 Aug 2022
Cited by 6 | Viewed by 1437
Abstract
BAW-based micromixers usually achieve mixing enhancement with acoustic-induced bubbles, while SAW-based micromixers usually enhance mixing efficiency by varying the configuration of IDTs and microchannels. In this paper, bubble-enhanced acoustic mixing induced by standing surface acoustic waves (SSAWs) in a microchannel is proposed and [...] Read more.
BAW-based micromixers usually achieve mixing enhancement with acoustic-induced bubbles, while SAW-based micromixers usually enhance mixing efficiency by varying the configuration of IDTs and microchannels. In this paper, bubble-enhanced acoustic mixing induced by standing surface acoustic waves (SSAWs) in a microchannel is proposed and experimentally demonstrated. Significant enhancement in the mixing efficiency was achieved after the bubbles were stimulated in our acoustofluidic microdevice. With an applied voltage of 5 V, 50 times amplified, the proposed mixing microdevice could achieve 90.8% mixing efficiency within 60 s at a flow rate of 240 μL/h. The bubbles were generated from acoustic cavitation assisted by the temperature increase resulting from the viscous absorption of acoustic energy. Our results also suggest that a temperature increase is harmful to microfluidic devices and temperature monitoring. Regulation is essential, especially in chemical and biological applications. Full article
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