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Micromachines, Volume 12, Issue 11 (November 2021) – 161 articles

Cover Story (view full-size image): The over-reliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. Hence, alternate renewable resources are much desired; of these, cellulose is one of the most abundant forms of lignocellulosic biomass. For a sustainable future, the electroreforming of cellulose, or its derivatives, could offer value-added chemicals and green hydrogen fuel when driven by renewable electricity. In our review paper, recent developments in both the anodic and cathodic electroreforming of cellulose and cellulose derivatives are reported together with our perspective on the challenges and future research directions of biomass electroreforming. View this paper
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Article
Dynamic pH and Thermal Analysis of Paper-Based Microchip Electrophoresis
Micromachines 2021, 12(11), 1433; https://doi.org/10.3390/mi12111433 - 22 Nov 2021
Viewed by 287
Abstract
Paper-based microchip electrophoresis has the potential to bring laboratory electrophoresis tests to the point of need. However, high electric potential and current values induce pH and temperature shifts, which may affect biomolecule electrophoretic mobility thus decrease test reproducibility and accuracy of paper-based microfluidic [...] Read more.
Paper-based microchip electrophoresis has the potential to bring laboratory electrophoresis tests to the point of need. However, high electric potential and current values induce pH and temperature shifts, which may affect biomolecule electrophoretic mobility thus decrease test reproducibility and accuracy of paper-based microfluidic electrophoresis. We have previously developed a microchip electrophoresis system, HemeChip, which has the capability of providing low-cost, rapid, reproducible, and accurate point-of-care (POC) electrophoresis tests for hemoglobin analysis. Here, we report the methodologies we implemented for characterizing HemeChip system pH and temperature during the development process, including utilizing commercially available universal pH indicator and digital camera pH shift characterization, and infrared camera characterizing temperature shift characterization. The characterization results demonstrated that pH shifts up to 1.1 units, a pH gradient up to 0.11 units/mm, temperature shifts up to 40 °C, and a temperature gradient up to 0.5 °C/mm existed in the system. Finally, we report an acid pre-treatment of the separation media, a cellulose acetate paper, mitigated both pH and temperature shifts and provided a stable environment for reproducible HemeChip hemoglobin electrophoresis separation. Full article
(This article belongs to the Special Issue Microdevices for Disease Diagnosis and Monitoring via Electrokinetics)
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Article
Edge Cooling of a Fuel Cell during Aerial Missions by Ambient Air
Micromachines 2021, 12(11), 1432; https://doi.org/10.3390/mi12111432 - 21 Nov 2021
Viewed by 293
Abstract
During aerial missions of fuel-cell (FC) powered drones, the option of FC edge cooling may improve FC performance and durability. Here we describe an edge cooling approach for fixed-wing FC-powered drones by removing FC heat using the ambient air during flight. A set [...] Read more.
During aerial missions of fuel-cell (FC) powered drones, the option of FC edge cooling may improve FC performance and durability. Here we describe an edge cooling approach for fixed-wing FC-powered drones by removing FC heat using the ambient air during flight. A set of experiments in a wind tunnel and numerical simulations were performed to examine the efficiency of FC edge cooling at various flight altitudes and cruise speeds. The experiments were used to validate the numerical model and prove the feasibility of the proposed method. The first simulation duplicated the geometry of the experimental setup and boundary conditions. The calculated temperatures of the stack were in good agreement with those of the experiments (within ±2 °C error). After validation, numerical models of a drone’s fuselage in ambient air with different radiator locations and at different flight speeds (10–30 m/s) and altitudes (up to 5 km) were examined. It was concluded that onboard FC edge cooling by ambient air may be applicable for velocities higher than 10 m/s. Despite the low pressure, density, and Cp of air at high altitudes, heat removal is significantly increased with altitude at all power and velocity conditions due to lower air temperature. Full article
(This article belongs to the Special Issue Miniaturized Generators, Volume II)
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Article
Novel Platform for Regulation of Extracellular Vesicles and Metabolites Secretion from Cells Using a Multi-Linkable Horizontal Co-Culture Plate
Micromachines 2021, 12(11), 1431; https://doi.org/10.3390/mi12111431 - 21 Nov 2021
Viewed by 365
Abstract
Microfluidics is applied in biotechnology research via the creation of microfluidic channels and reaction vessels. Filters are considered to be able to simulate microfluidics. A typical example is the cell culture insert, which comprises two vessels connected by a filter. Cell culture inserts [...] Read more.
Microfluidics is applied in biotechnology research via the creation of microfluidic channels and reaction vessels. Filters are considered to be able to simulate microfluidics. A typical example is the cell culture insert, which comprises two vessels connected by a filter. Cell culture inserts have been used for years to study cell-to-cell communication. These systems generally have a bucket-in-bucket structure and are hereafter referred to as a vertical-type co-culture plate (VTCP). However, VTCPs have several disadvantages, such as the inability to simultaneously observe samples in both containers and the inability of cell-to-cell communication through the filters at high cell densities. In this study, we developed a novel horizontal-type co-culture plate (HTCP) to overcome these disadvantages and confirm its performance. In addition, we clarified the migration characteristics of substances secreted from cells in horizontal co-culture vessels. It is generally assumed that less material is exchanged between the horizontal vessels. However, the extracellular vesicle (EV) transfer was found to be twice as high when using HTCP. Other merits include control of the degree of co-culture via the placement of cells. We believe that this novel HTCP container will facilitate research on cell-to-cell communication in various fields. Full article
(This article belongs to the Special Issue Microfluidic Flow Cells: Modelling and Experiments)
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Article
Micromachined Tactile Sensor Array for RTSA
Micromachines 2021, 12(11), 1430; https://doi.org/10.3390/mi12111430 - 21 Nov 2021
Viewed by 199
Abstract
This work presents a polymer-based tactile capacitive sensor capable of measuring joint reaction forces of reverse total shoulder arthroplasty (RTSA). The capacitive sensor contains a polydimethylsiloxane (PDMS) dielectric layer with an array of electrodes. The sensor was designed in such a way that [...] Read more.
This work presents a polymer-based tactile capacitive sensor capable of measuring joint reaction forces of reverse total shoulder arthroplasty (RTSA). The capacitive sensor contains a polydimethylsiloxane (PDMS) dielectric layer with an array of electrodes. The sensor was designed in such a way that four components of glenohumeral contact forces can be quantified to help ensure proper soft tissue tensioning during the procedure. Fabricated using soft lithography, the sensor has a loading time of approximately 400 ms when a 14.13 kPa load is applied and has a sensitivity of 1.24 × 10−3 pF/kPa at a load of 1649 kPa. A replica RTSA prothesis was 3D printed, and the sensor was mounted inside the humeral cap. Four static right shoulder positions were tested, and the results provided an intuitive graphical description of the pressure distribution across four quadrants of the glenohumeral joint contact surface. It may help clinicians choose a right implant size and offset that best fit a patient’s anatomy and reduce postoperative biomechanical complications such as dislocation and stress fracture of the scapula. Full article
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Review
Recent Advances and Challenges of Nanomaterials-Based Hydrogen Sensors
Micromachines 2021, 12(11), 1429; https://doi.org/10.3390/mi12111429 - 21 Nov 2021
Viewed by 220
Abstract
Safety is a crucial issue in hydrogen energy applications due to the unique properties of hydrogen. Accordingly, a suitable hydrogen sensor for leakage detection must have at least high sensitivity and selectivity, rapid response/recovery, low power consumption and stable functionality, which requires further [...] Read more.
Safety is a crucial issue in hydrogen energy applications due to the unique properties of hydrogen. Accordingly, a suitable hydrogen sensor for leakage detection must have at least high sensitivity and selectivity, rapid response/recovery, low power consumption and stable functionality, which requires further improvements on the available hydrogen sensors. In recent years, the mature development of nanomaterials engineering technologies, which facilitate the synthesis and modification of various materials, has opened up many possibilities for improving hydrogen sensing performance. Current research of hydrogen detection sensors based on both conservational and innovative materials are introduced in this review. This work mainly focuses on three material categories, i.e., transition metals, metal oxide semiconductors, and graphene and its derivatives. Different hydrogen sensing mechanisms, such as resistive, capacitive, optical and surface acoustic wave-based sensors, are also presented, and their sensing performances and influence based on different nanostructures and material combinations are compared and discussed, respectively. This review is concluded with a brief outlook and future development trends. Full article
(This article belongs to the Special Issue Micro-Nano Science and Engineering)
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Article
Calculation and AFM Experimental Research on Slip Friction for Unlubricated Spherical Contact with Roughness Effect
Micromachines 2021, 12(11), 1428; https://doi.org/10.3390/mi12111428 - 21 Nov 2021
Viewed by 281
Abstract
Previous research on friction calculation models has mainly focused on static friction, whereas sliding friction calculation models are rarely reported. In this paper, a novel sliding friction model for realizing a dry spherical flat contact with a roughness effect at the micro/nano scale [...] Read more.
Previous research on friction calculation models has mainly focused on static friction, whereas sliding friction calculation models are rarely reported. In this paper, a novel sliding friction model for realizing a dry spherical flat contact with a roughness effect at the micro/nano scale is proposed. This model yields the sliding friction by the change in the periodic substrate potential, adopts the basic assumptions of the Greenwood–Williamson random contact model about asperities, and assumes that the contact area between a rigid sphere and a nominal rough flat satisfies the condition of interfacial friction. It subsequently employs a statistical method to determine the total sliding friction force, and finally, the feasibility of this model presented is verified by atomic force microscopy friction experiments. The comparison results show that the deviations of the sliding friction force and coefficient between the theoretical calculated values and the experimental values are in a relatively acceptable range for the samples with a small plasticity index (Ψ1). Full article
(This article belongs to the Special Issue Functional Probes for Scanning Probe Microscopy)
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Article
Research on Task-Service Network Node Matching Method Based on Multi-Objective Optimization Model in Dynamic Hyper-Network Environment
Micromachines 2021, 12(11), 1427; https://doi.org/10.3390/mi12111427 - 21 Nov 2021
Viewed by 174
Abstract
In order to reduce the cost of manufacturing and service for the Cloud 3D printing (C3DP) manufacturing grid, to solve the problem of resources optimization deployment for no-need preference under circumstance of cloud manufacturing, consider the interests of enterprises which need Cloud 3D [...] Read more.
In order to reduce the cost of manufacturing and service for the Cloud 3D printing (C3DP) manufacturing grid, to solve the problem of resources optimization deployment for no-need preference under circumstance of cloud manufacturing, consider the interests of enterprises which need Cloud 3D printing resources and cloud platform operators, together with QoS and flexibility of both sides in the process of Cloud 3D printing resources configuration service, a task-service network node matching method based on Multi-Objective optimization model in dynamic hyper-network environment is built for resource allocation. This model represents interests of the above-mentioned two parties. In addition, the model examples are solved by modifying Mathematical algorithm of Node Matching and Evolutionary Solutions. Results prove that the model and the algorithm are feasible, effective and stable. Full article
(This article belongs to the Special Issue 3D Printed Implants for Biomedical Applications)
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Review
A Review of the High-Power All-Solid-State Single-Frequency Continuous-Wave Laser
Micromachines 2021, 12(11), 1426; https://doi.org/10.3390/mi12111426 - 20 Nov 2021
Viewed by 418
Abstract
High-power all-solid-state single-frequency continuous-wave (CW) lasers have been applied in basic research such as atomic physics, precision measurement, radar and laser guidance, as well as defense and military fields owing to their intrinsic advantages of high beam quality, low noise, narrow linewidth, and [...] Read more.
High-power all-solid-state single-frequency continuous-wave (CW) lasers have been applied in basic research such as atomic physics, precision measurement, radar and laser guidance, as well as defense and military fields owing to their intrinsic advantages of high beam quality, low noise, narrow linewidth, and high coherence. With the rapid developments of sciences and technologies, the traditional single-frequency lasers cannot meet the development needs of emerging science and technology such as quantum technology, quantum measurement and quantum optics. After long-term efforts and technical research, a novel theory and technology was proposed and developed for improving the whole performance of high-power all-solid-state single-frequency CW lasers, which was implemented by actively introducing a nonlinear optical loss and controlling the stimulated emission rate (SER) in the laser resonator. As a result, the output power, power and frequency stabilities, tuning range and intensity noise of the single-frequency lasers were effectively enhanced. Full article
(This article belongs to the Special Issue Miniature Optoelectronic Resonators and Oscillators)
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Article
Anti-Methanogenic Effect of Phytochemicals on Methyl-Coenzyme M Reductase—Potential: In Silico and Molecular Docking Studies for Environmental Protection
Micromachines 2021, 12(11), 1425; https://doi.org/10.3390/mi12111425 - 19 Nov 2021
Viewed by 417
Abstract
Methane is a greenhouse gas which poses a great threat to life on earth as its emissions directly contribute to global warming and methane has a 28-fold higher warming potential over that of carbon dioxide. Ruminants have been identified as a major source [...] Read more.
Methane is a greenhouse gas which poses a great threat to life on earth as its emissions directly contribute to global warming and methane has a 28-fold higher warming potential over that of carbon dioxide. Ruminants have been identified as a major source of methane emission as a result of methanogenesis by their respective gut microbiomes. Various plants produce highly bioactive compounds which can be investigated to find a potential inhibitor of methyl-coenzyme M reductase (the target protein for methanogenesis). To speed up the process and to limit the use of laboratory resources, the present study uses an in-silico molecular docking approach to explore the anti-methanogenic properties of phytochemicals from Cymbopogon citratus, Origanum vulgare, Lavandula officinalis, Cinnamomum zeylanicum, Piper betle, Cuminum cyminum, Ocimum gratissimum, Salvia sclarea, Allium sativum, Rosmarinus officinalis and Thymus vulgaris. A total of 168 compounds from 11 plants were virtually screened. Finally, 25 scrutinized compounds were evaluated against methyl-coenzyme M reductase (MCR) protein using the AutoDock 4.0 program. In conclusion, the study identified 21 out of 25 compounds against inhibition of the MCR protein. Particularly, five compounds: rosmarinic acid (−10.71 kcal/mol), biotin (−9.38 kcal/mol), α-cadinol (−8.16 kcal/mol), (3R,3aS,6R,6aR)-3-(2H-1,3-benzodioxol-4-yl)-6-(2H-1,3-benzodioxol-5-yl)-hexahydrofuro[3,4-c]furan-1-one (−12.21 kcal/mol), and 2,4,7,9-tetramethyl-5decyn4,7diol (−9.02 kcal/mol) showed higher binding energy towards the MCR protein. In turn, these compounds have potential utility as rumen methanogenic inhibitors in the proposed methane inhibitor program. Ultimately, molecular dynamics simulations of rosmarinic acid and (3R,3aS,6R,6aR)-3-(2H-1,3-benzodioxol-4-yl)-6-(2H-1,3-benzodioxol-5-yl)-hexahydrofuro[3,4-c]furan-1-one yielded the best possible interaction and stability with the active site of 5A8K protein for 20 ns. Full article
(This article belongs to the Section D:Materials and Processing)
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Article
Synthesis and Characteristics of Double-Shell Mesoporous Hollow Silica Nanomaterials to Improve CO2 Adsorption Performance
Micromachines 2021, 12(11), 1424; https://doi.org/10.3390/mi12111424 - 19 Nov 2021
Viewed by 214
Abstract
To improve the adsorption performance of carbon dioxide, which is considered the main culprit of greenhouse gases, the specific surface area and high pore volume of the adsorbing material should be considered. For a porous material, the performance of carbon dioxide adsorption is [...] Read more.
To improve the adsorption performance of carbon dioxide, which is considered the main culprit of greenhouse gases, the specific surface area and high pore volume of the adsorbing material should be considered. For a porous material, the performance of carbon dioxide adsorption is determined by the amine groups supporting capacity; the larger the pore volume, the greater the capacity to support the amine groups. In this study, a double-shell mesoporous hollow silica nanomaterial with excellent pore volume and therefore increased amine support capacity was synthesized. A core–shell structure capable of having a hollow shape was synthesized using polystyrene as a core material, and a double-shell mesoporous shape was synthesized by sequentially using two types of surfactants. The synthesized material was subjected to a sintering process of 600 degrees, and the N2 sorption analysis confirmed a specific surface area of 690 m2/g and a pore volume of 1.012 cm3/g. Thereafter, the amine compound was impregnated into the silica nanomaterial, and then, a carbon dioxide adsorption experiment was conducted, which confirmed that compared to the mesoporous hollow silica nanomaterial synthesized as a single shell, the adsorption performance was improved by about 1.36 times. Full article
(This article belongs to the Special Issue Nano Korea 2021)
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Communication
Colorimetric Sensing with Gold Nanoparticles on Electrowetting-Based Digital Microfluidics
Micromachines 2021, 12(11), 1423; https://doi.org/10.3390/mi12111423 - 19 Nov 2021
Viewed by 262
Abstract
Digital microfluidic (DMF) has been a unique tool for manipulating micro-droplets with high flexibility and accuracy. To extend the application of DMF for automatic and in-site detection, it is promising to introduce colorimetric sensing based on gold nanoparticles (AuNPs), which have advantages including [...] Read more.
Digital microfluidic (DMF) has been a unique tool for manipulating micro-droplets with high flexibility and accuracy. To extend the application of DMF for automatic and in-site detection, it is promising to introduce colorimetric sensing based on gold nanoparticles (AuNPs), which have advantages including high sensitivity, label-free, biocompatibility, and easy surface modification. However, there is still a lack of studies for investigating the movement and stability of AuNPs for in-site detection on the electrowetting-based digital microfluidics. Herein, to demonstrate the ability of DMF for colorimetric sensing with AuNPs, we investigated the electrowetting property of the AuNPs droplets on the hydrophobic interface of the DMF chip and examined the stability of the AuNPs on DMF as well as the influence of evaporation to the colorimetric sensing. As a result, we found that the electrowetting of AuNPs fits to a modified Young–Lippmann equation, which suggests that a higher voltage is required to actuate AuNPs droplets compared with actuating water droplets. Moreover, the stability of AuNPs was maintained during the processing of electrowetting. We also proved that the evaporation of droplets has a limited influence on the detections that last several minutes. Finally, a model experiment for the detection of Hg2+ was carried out with similar results to the detections in bulk solution. The proposed method can be further extended to a wide range of AuNPs-based detection for label-free, automatic, and low-cost detection of small molecules, biomarkers, and metal ions. Full article
(This article belongs to the Special Issue MEMS and Microfluidic Devices for Analytical Chemistry and Biosensing)
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Article
Improvement in Turn-Off Loss of the Super Junction IGBT with Separated n-Buffer Layers
Micromachines 2021, 12(11), 1422; https://doi.org/10.3390/mi12111422 - 19 Nov 2021
Viewed by 258
Abstract
In this study, we propose a super junction insulated-gate bipolar transistor (SJBT) with separated n-buffer layers to solve a relatively long time for carrier annihilation during turn-off. This proposition improves the turn-off characteristic while maintaining similar on-state characteristics and breakdown voltage. The electrical [...] Read more.
In this study, we propose a super junction insulated-gate bipolar transistor (SJBT) with separated n-buffer layers to solve a relatively long time for carrier annihilation during turn-off. This proposition improves the turn-off characteristic while maintaining similar on-state characteristics and breakdown voltage. The electrical characteristics of the devices were simulated by using the Synopsys Sentaurus technology computer-aided design (TCAD) simulation tool, and we compared the conventional SJBT with SJBT with separated n-buffer layers. The simulation tool result shows that turn-off loss (Eoff) drops by about 7% when on-state voltage (Von) and breakdown voltage (BV) are similar. Von increases by about 0.5% and BV decreases by only about 0.8%. Full article
(This article belongs to the Special Issue Nano Korea 2021)
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Article
Evanescent Field Controllable MZ Sensor via Femtosecond Laser Processing and Mechanic Polishing
Micromachines 2021, 12(11), 1421; https://doi.org/10.3390/mi12111421 - 19 Nov 2021
Viewed by 215
Abstract
Recently, optical sensors interacting with evanescent fields and the external environment around waveguides have attracted extensive attention. In the process of light propagation in the waveguide, the depth of the evanescent field is closely related to the accuracy of the optical sensor, and [...] Read more.
Recently, optical sensors interacting with evanescent fields and the external environment around waveguides have attracted extensive attention. In the process of light propagation in the waveguide, the depth of the evanescent field is closely related to the accuracy of the optical sensor, and adjusting the depth of the evanescent field to obtain higher accuracy has become the primary challenge in fabricating on-chip optical sensors. In this study, the waveguide structure of a Mach–Zehnder interferometer was written directly in Corning Eagle 2000 borosilicate glass by a femtosecond laser, and the sensing window was exposed out of the bulk material by mechanical polishing. The refractive index detection device based on the proposed on-chip Mach–Zehnder interferometer has the advantages of small volume, light weight, and good stability. Its sensitivity can reach 206 nm/RIU or 337 dB/RIU, and the theoretical maximum measurement range is 1–1.508. Therefore, it can measure the refractive index quickly and accurately in extreme or complex environments, and has excellent application prospects. Full article
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Article
Design, Analysis and Experiment of the Fiber Push-Out Device Based on Piezoelectric Actuator
Micromachines 2021, 12(11), 1420; https://doi.org/10.3390/mi12111420 - 19 Nov 2021
Viewed by 295
Abstract
In this study, a fiber push-out device based on a piezoelectric actuator was designed, analyzed and tested, and its experimental environment was designed. The piezoelectric actuator includes a flexible beam. By using response surface analysis (RSM), taking the large displacement as the objective [...] Read more.
In this study, a fiber push-out device based on a piezoelectric actuator was designed, analyzed and tested, and its experimental environment was designed. The piezoelectric actuator includes a flexible beam. By using response surface analysis (RSM), taking the large displacement as the objective function and on the premise of meeting the strength requirements, the structural parameters of the flexible beam were analyzed. In the process of fiber push-out, the interfacial shear stress was estimated by establishing the system integrating the fiber-matrix-composite three-phase model and the piezoelectric actuator model using the analytic method, and the theoretical analysis results of the fiber interface mechanical properties were given. A prototype of the system was made, and the performance tests of the piezoelectric actuator and the fiber push-out device were carried out. The test results showed that the designed piezoelectric actuator can achieve a stepping resolution of 6.67 μm and a maximum displacement of about 100 μm at the input voltage of 150 V, which is consistent with the design results. The extrusion test of a single fiber was carried out using a piezoelectric actuator. The mechanical properties of the interfacial layer during the push-out process were measured and the interfacial shear strength was calculated, which is consistent with the theoretical analysis results. Finally, based on the mechanical properties obtained from the test, the loading failure process of the fiber was simulated by finite element analysis, which well explained the failure process of the fiber, thus verifying the feasibility of the designed fiber push-out device. Full article
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Communication
Optically Transparent Flexible Broadband Metamaterial Absorber Based on Topology Optimization Design
Micromachines 2021, 12(11), 1419; https://doi.org/10.3390/mi12111419 - 18 Nov 2021
Viewed by 254
Abstract
A conformal metamaterial absorber with simultaneous optical transparency and broadband absorption is proposed in this paper. The absorptance above 90% over a wide frequency range of 5.3–15 GHz can be achieved through topology optimization combined with a genetic algorithm (GA). The broadband absorption [...] Read more.
A conformal metamaterial absorber with simultaneous optical transparency and broadband absorption is proposed in this paper. The absorptance above 90% over a wide frequency range of 5.3–15 GHz can be achieved through topology optimization combined with a genetic algorithm (GA). The broadband absorption can be kept at incident angles within 45° and 70° for TE mode and TM mode, respectively. In the meantime, by employing transparent substrates, including polyvinyl chloride (PVC) and polyethylene terephthalate (PET), good optical transmittance and flexibility can be obtained simultaneously. The experimental results agree well with the numerical simulations, which further validates the reliability of our design and theoretical analysis. With its visible-wavelength transparency, flexibility, broadband absorption, low profile, excellent angle stability and polarization insensitivity, the proposed absorber is highly favored for practical applications in microwave engineering, such as electromagnetic interference and stealth technology. Moreover, the proposed design method of topology optimization can be extended to design the absorber quickly and efficiently, according to specific engineering requirements. Full article
(This article belongs to the Special Issue Advanced Photonics and Metamaterials)
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Article
Wavelet Frequency Separation Attention Network for Chest X-ray Image Super-Resolution
Micromachines 2021, 12(11), 1418; https://doi.org/10.3390/mi12111418 - 18 Nov 2021
Viewed by 307
Abstract
Medical imaging is widely used in medical diagnosis. The low-resolution image caused by high hardware cost and poor imaging technology leads to the loss of relevant features and even fine texture. Obtaining high-quality medical images plays an important role in disease diagnosis. A [...] Read more.
Medical imaging is widely used in medical diagnosis. The low-resolution image caused by high hardware cost and poor imaging technology leads to the loss of relevant features and even fine texture. Obtaining high-quality medical images plays an important role in disease diagnosis. A surge of deep learning approaches has recently demonstrated high-quality reconstruction for medical image super-resolution. In this work, we propose a light-weight wavelet frequency separation attention network for medical image super-resolution (WFSAN). WFSAN is designed with separated-path for wavelet sub-bands to predict the wavelet coefficients, considering that image data characteristics are different in the wavelet domain and spatial domain. In addition, different activation functions are selected to fit the coefficients. Inputs comprise approximate sub-bands and detail sub-bands of low-resolution wavelet coefficients. In the separated-path network, detail sub-bands, which have more sparsity, are trained to enhance high frequency information. An attention extension ghost block is designed to generate the features more efficiently. All results obtained from fusing layers are contracted to reconstruct the approximate and detail wavelet coefficients of the high-resolution image. In the end, the super-resolution results are generated by inverse wavelet transform. Experimental results show that WFSAN has competitive performance against state-of-the-art lightweight medical imaging methods in terms of quality and quantitative metrics. Full article
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Article
Design of Planar Array Transducers Based on Connected 1–3 Piezoelectric Composites
Micromachines 2021, 12(11), 1417; https://doi.org/10.3390/mi12111417 - 18 Nov 2021
Viewed by 320
Abstract
To improve the transmission performance and preparation of a transducer array, two planar array transducers based on connected 1–3 piezoelectric composites as a matrix were designed. Each transducer contained 25 array elements with a gap of 1 mm between them. The length, width [...] Read more.
To improve the transmission performance and preparation of a transducer array, two planar array transducers based on connected 1–3 piezoelectric composites as a matrix were designed. Each transducer contained 25 array elements with a gap of 1 mm between them. The length, width and height of each array element were 1 mm, 26 mm and 5 mm, respectively. Two kinds of array transducers were tested through finite element simulation and experiments. The array transducer prototype was fabricated based on two kinds of composite materials, and the fabrication cycle was short. Our results show that the maximum transmission voltage response of the two-phase 1–3 full array driver is up to 179 dB at 200–400 kHz and the acoustic radiation intensity can be increased by up to 22% compared with the traditional splicing transducer array. It is suitable for short-range target positioning and measurement. Moreover, in the single element mode, the beam of the three-phase 1–3 transducer has no sidelobe and a single element −3 dB beam width of up to 91°. Furthermore, the beam width of the two-phase 1–3 type is 54°, and the acoustic radiation breadth is improved by 40.6%. The three-phase 1–3 type array transducer has the characteristics of concentrated acoustic transmission energy of the whole array, and its −3 dB beam width is 3.5°. The beam width decreased by 12.5%, indicating that the three-phase 1–3 type transducer is suitable for short-range target detection and perception. The two array transducers have their own advantages in transmitting the voltage response and beam width, which must be selected on the basis of the requirements of practical applications. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Materials and Processing 2021)
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Article
Characterization of Giant Magnetostrictive Materials Using Three Complex Material Parameters by Particle Swarm Optimization
Micromachines 2021, 12(11), 1416; https://doi.org/10.3390/mi12111416 - 18 Nov 2021
Viewed by 227
Abstract
Complex material parameters that can represent the losses of giant magnetostrictive materials (GMMs) are the key parameters for high-power transducer design and performance analysis. Since the GMMs work under pre-stress conditions and their performance is highly sensitive to pre-stress, the complex parameters of [...] Read more.
Complex material parameters that can represent the losses of giant magnetostrictive materials (GMMs) are the key parameters for high-power transducer design and performance analysis. Since the GMMs work under pre-stress conditions and their performance is highly sensitive to pre-stress, the complex parameters of a GMM are preferably characterized in a specific pre-stress condition. In this study, an optimized characterization method for GMMs is proposed using three complex material parameters. Firstly, a lumped parameter model is improved for a longitudinal transducer by incorporating three material losses. Then, the structural damping and contact damping are experimentally measured and applied to confine the parametric variance ranges. Using the improved lumped parameter model, the real parts of the three key material parameters are characterized by fitting the experimental impedance data while the imaginary parts are separately extracted by the phase data. The global sensitivity analysis that accounts for the interaction effects of the multiple parameter variances shows that the proposed method outperforms the classical method as the sensitivities of all the six key parameters to both impedance and phase fitness functions are all high, which implies that the extracted material complex parameters are credible. In addition, the stability and credibility of the proposed parameter characterization is further corroborated by the results of ten random characterizations. Full article
(This article belongs to the Section E:Engineering and Technology)
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Article
Towards High Throughput Structuring of Liquid Foams in Microchannels: Effect of Geometry, Flowrate and Formulation
Micromachines 2021, 12(11), 1415; https://doi.org/10.3390/mi12111415 - 18 Nov 2021
Viewed by 209
Abstract
This work is part of a study aiming to design a high-throughput foaming microsystem. The main focused field of application is the food industry. With the objective of improving the design of the microdevice, the effects of the geometry and the nature of [...] Read more.
This work is part of a study aiming to design a high-throughput foaming microsystem. The main focused field of application is the food industry. With the objective of improving the design of the microdevice, the effects of the geometry and the nature of the liquid base are presently investigated through visualizations of the flow typology of bubbles trains, aiming to expand the knowledge on key parameters that lead to an improved gas breakup. The tested set of conditions is not encountered in traditional microfluidics systems: i.e., throughputs up to 19 L·h−1 for the liquid phase, process velocities around 20 m·s−1 and flow of complex fluids. The behavior of solutions based on xanthan gum (XG) and whey proteins (WPI) is compared to that of solutions containing one of these ingredients or other ones (caseinates, glycerol). The structural and end-used properties of the final foams, namely the bubble diameter and rheological behavior, are evaluated. The incorporation of XG induces bubble shape stabilization even at the highest shear rates (~105 s−1) encountered in the mixing channel. “Controlled” interfacial breakup by tip-streaming or binary breakup are only observed with the WPI/XG biopolymers. This study indubitably highlights the essential role of the process/formulation interaction in the development of structural and functional properties of food foams when using microfluidics at high throughput. Full article
(This article belongs to the Special Issue Microfluidics for Food and Nutrient Applications)
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Article
Studying Corrosion Using Miniaturized Particle Attached Working Electrodes and the Nafion Membrane
Micromachines 2021, 12(11), 1414; https://doi.org/10.3390/mi12111414 - 18 Nov 2021
Viewed by 265
Abstract
We developed a new approach to attach particles onto a conductive layer as a working electrode (WE) in a microfluidic electrochemical cell with three electrodes. Nafion, an efficient proton transfer molecule, is used to form a thin protection layer to secure particle electrodes. [...] Read more.
We developed a new approach to attach particles onto a conductive layer as a working electrode (WE) in a microfluidic electrochemical cell with three electrodes. Nafion, an efficient proton transfer molecule, is used to form a thin protection layer to secure particle electrodes. Spin coating is used to develop a thin and even layer of Nafion membrane. The effects of Nafion (5 wt% 20 wt%) and spinning rates were evaluated using multiple sets of replicates. The electrochemical performance of various devices was demonstrated. Additionally, the electrochemical performance of the devices is used to select and optimize fabrication conditions. The results show that a higher spinning rate and a lower Nafion concentration (5 wt%) induce a better performance, using cerium oxide (CeO2) particles as a testing model. The WE surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy-focused ion beam (SEM-FIB), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and X-ray photoelectron spectroscopy (XPS). The comparison between the pristine and corroded WE surfaces shows that Nafion is redistributed after potential is applied. Our results verify that Nafion membrane offers a reliable means to secure particles onto electrodes. Furthermore, the electrochemical performance is reliable and reproducible. Thus, this approach provides a new way to study more complex and challenging particles, such as uranium oxide, in the future. Full article
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Article
Research on the Force-Sensitive Characteristic of InAs QD Embedded in HEMT
Micromachines 2021, 12(11), 1413; https://doi.org/10.3390/mi12111413 - 18 Nov 2021
Viewed by 225
Abstract
A force-sensitive structure of an InAs Quantum Dot (QD) embedded in a high electron mobility transistor (HEMT) is presented in this paper. The size of an InAs QD is about 30 nm prepared by the S-K growth mode, and the force-sensitive structure is [...] Read more.
A force-sensitive structure of an InAs Quantum Dot (QD) embedded in a high electron mobility transistor (HEMT) is presented in this paper. The size of an InAs QD is about 30 nm prepared by the S-K growth mode, and the force-sensitive structure is fabricated by molecular beam epitaxy (MBE). The force-sensitivity characteristic of the QD HEMT is studied by the electrical and mechanical properties. The electrical characteristics show that the InAs QD-HEMT has linear, cut-off, and saturation operating states, and produces different output currents under different gate voltages, which shows that the structure is reasonable. Furthermore, the results of the output characteristics under different pressure show that the output voltage of the QD-HEMT decreases with the increase in pressure, which indicates that the InAs QD-HEMT has a vital mechanical–electrical coupling characteristic. The output voltage of the InAs QD-HEMT in the range of 0–100 kPa shows that the sensitivity was 1.09 mV/kPa. Full article
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Article
RuO2 Nanorods as an Electrocatalyst for Proton Exchange Membrane Water Electrolysis
Micromachines 2021, 12(11), 1412; https://doi.org/10.3390/mi12111412 - 17 Nov 2021
Viewed by 243
Abstract
A custom-built PEM electrolyzer cell was assembled using 6” stainless-steel ConFlat flanges which were fitted with a RuO2 nanorod-decorated, mixed metal oxide (MMO) ribbon mesh anode catalyst. The current density–voltage characteristics were measured for the RuO2 nanorod electrocatalyst while under constant [...] Read more.
A custom-built PEM electrolyzer cell was assembled using 6” stainless-steel ConFlat flanges which were fitted with a RuO2 nanorod-decorated, mixed metal oxide (MMO) ribbon mesh anode catalyst. The current density–voltage characteristics were measured for the RuO2 nanorod electrocatalyst while under constant water feed operation. The electrocatalytic behavior was investigated by making a series of physical modifications to the anode catalyst material. These experiments showed an improved activity due to the RuO2 nanorod electrocatalyst, resulting in a corresponding decrease in the electrochemical overpotential. These overpotentials were identified by collecting experimental data from various electrolyzer cell configurations, resulting in an improved understanding of the enhanced catalytic behavior. The micro-to-nano surface structure of the anode electrocatalyst layer is a critical factor determining the overall operation of the PEM electrolyzer. The improvement was determined to be due to the lowering of the potential barrier to electron escape in an electric field generated in the vicinity of a nanorod. Full article
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Article
A Cylindrical Molding Method for the Biofabrication of Plane-Shaped Skeletal Muscle Tissue
Micromachines 2021, 12(11), 1411; https://doi.org/10.3390/mi12111411 - 17 Nov 2021
Viewed by 314
Abstract
Muscle tissues can be fabricated in vitro by culturing myoblast-populated hydrogels. To counter the shrinkage of the myoblast-populated hydrogels during culture, a pair of anchors are generally utilized to fix the two ends of the hydrogel. Here, we propose an alternative method to [...] Read more.
Muscle tissues can be fabricated in vitro by culturing myoblast-populated hydrogels. To counter the shrinkage of the myoblast-populated hydrogels during culture, a pair of anchors are generally utilized to fix the two ends of the hydrogel. Here, we propose an alternative method to counter the shrinkage of the hydrogel and fabricate plane-shaped skeletal muscle tissues. The method forms myoblast-populated hydrogel in a cylindrical cavity with a central pillar, which can prevent tissue shrinkage along the circumferential direction. By eliminating the usages of the anchor pairs, our proposed method can produce plane-shaped skeletal muscle tissues with uniform width and thickness. In experiments, we demonstrate the fabrication of plane-shaped (length: ca. 10 mm, width: 5~15 mm) skeletal muscle tissue with submillimeter thickness. The tissues have uniform shapes and are populated with differentiated muscle cells stained positive for myogenic differentiation markers (i.e., myosin heavy chains). In addition, we show the assembly of subcentimeter-order tissue blocks by stacking the plane-shaped skeletal muscle tissues. The proposed method can be further optimized and scaled up to produce cultured animal products such as cultured meat. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2021)
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Article
Exploring the Effect of a MnO2 Coating on the Electrochemical Performance of a Li1.2Mn0.54Ni0.13Co0.13O2 Cathode Material
Micromachines 2021, 12(11), 1410; https://doi.org/10.3390/mi12111410 - 17 Nov 2021
Viewed by 260
Abstract
The effect of electrochemically active MnO2 as a coating material on the electrochemical properties of a Li1.2Mn0.54Ni0.13Co0.13O2 (LTMO) cathode material is explored in this article. The structural analysis indicated that the layered structure [...] Read more.
The effect of electrochemically active MnO2 as a coating material on the electrochemical properties of a Li1.2Mn0.54Ni0.13Co0.13O2 (LTMO) cathode material is explored in this article. The structural analysis indicated that the layered structure of the LTMO was unchanged after the modification with MnO2. The morphology inspection demonstrated that the rod-like LTMO particles were encapsulated by a compact coating layer. The MnO2 layer was able to hinder the electrolyte solution from corroding the LTMO particles and optimized the formation of a solid electrolyte interface (SEI). Meanwhile, lithium ions were reversibly inserted into and extracted from MnO2, which afforded an additional capacity. Compared with the bare LTMO, the MnO2-coated sample exhibited enhanced electrochemical performance. After the MnO2 coating, the first discharge capacity rose from 224.2 to 239.1 mAh/g, and the initial irreversible capacity loss declined from 78.2 to 46.0 mAh/g. Meanwhile, the cyclic retention climbed up to 88.2% after 100 cycles at 0.5 C, which was more competitive than that of the bare LTMO with a value of 71.1%. When discharging at a high current density of 2 C, the capacity increased from 100.5 to 136.9 mAh/g after the modification. These investigations may be conducive to the practical application of LTMO in prospective automotive Li-ion batteries. Full article
(This article belongs to the Section E:Engineering and Technology)
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Review
Recent Progress in Nanomaterials Modified Electrochemical Biosensors for the Detection of MicroRNA
Micromachines 2021, 12(11), 1409; https://doi.org/10.3390/mi12111409 - 17 Nov 2021
Viewed by 409
Abstract
MicroRNAs (miRNAs) are important non-coding, single-stranded RNAs possessing crucial regulating roles in human body. Therefore, miRNAs have received extensive attention from various disciplines as the aberrant expression of miRNAs are tightly related to different types of diseases. Furthermore, the exceptional stability of miRNAs [...] Read more.
MicroRNAs (miRNAs) are important non-coding, single-stranded RNAs possessing crucial regulating roles in human body. Therefore, miRNAs have received extensive attention from various disciplines as the aberrant expression of miRNAs are tightly related to different types of diseases. Furthermore, the exceptional stability of miRNAs has presented them as biomarker with high specificity and sensitivity. However, small size, high sequence similarity, low abundance of miRNAs impose difficulty in their detection. Hence, it is of utmost importance to develop accurate and sensitive method for miRNA biosensing. Electrochemical biosensors have been demonstrated as promising solution for miRNA detection as they are highly sensitive, facile, and low-cost with ease of miniaturization. The incorporation of nanomaterials to electrochemical biosensor offers excellent prospects for converting biological recognition events to electronic signal for the development of biosensing platform with desired sensing properties due to their unique properties. This review introduces the signal amplification strategies employed in miRNA electrochemical biosensor and presents the feasibility of different strategies. The recent advances in nanomaterial-based electrochemical biosensor for the detection of miRNA were also discussed and summarized based on different types of miRNAs, opening new approaches in biological analysis and early disease diagnosis. Lastly, the challenges and future prospects are discussed. Full article
(This article belongs to the Special Issue Nanomaterials Modified Electrochemical Sensors)
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Article
An Impedance Sensor for Distinguishing Multi-Contaminants in Hydraulic Oil of Offshore Machinery
Micromachines 2021, 12(11), 1407; https://doi.org/10.3390/mi12111407 - 17 Nov 2021
Viewed by 223
Abstract
The cleanliness of hydraulic oil can reflect the service life of the oil and the wear state of hydraulic machinery. An impedance sensor is proposed to distinguish multi-contaminants in hydraulic oil. The impedance sensor has two detection modes: the inductance-resistance mode is used [...] Read more.
The cleanliness of hydraulic oil can reflect the service life of the oil and the wear state of hydraulic machinery. An impedance sensor is proposed to distinguish multi-contaminants in hydraulic oil. The impedance sensor has two detection modes: the inductance-resistance mode is used to detect metal debris, and the capacitance mode is used to distinguish water droplets and air bubbles. By adding a built-in silicon steel strip and an external silicon steel strip with high magnetic permeability, the distribution area, strength, and uniformity of the magnetic field are enhanced to improve the detection sensitivity under inductance and resistance parameters. In addition, the silicon steel strips are used as electrode plates to introduce capacitance parameter detection. The experimental results show that the resistance detection method based on coil successfully improves the detection ability for non-ferromagnetic metal debris. The impedance sensor for distinguishing multi-contaminants in hydraulic oil can provide technical support for fault diagnosis of offshore hydraulic machinery. Full article
(This article belongs to the Special Issue Ocean MEMS)
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Article
Parametric Study of Jet/Droplet Formation Process during LIFT Printing of Living Cell-Laden Bioink
Micromachines 2021, 12(11), 1408; https://doi.org/10.3390/mi12111408 - 16 Nov 2021
Viewed by 270
Abstract
Bioprinting offers great potential for the fabrication of three-dimensional living tissues by the precise layer-by-layer printing of biological materials, including living cells and cell-laden hydrogels. The laser-induced forward transfer (LIFT) of cell-laden bioinks is one of the most promising laser-printing technologies enabling biofabrication. [...] Read more.
Bioprinting offers great potential for the fabrication of three-dimensional living tissues by the precise layer-by-layer printing of biological materials, including living cells and cell-laden hydrogels. The laser-induced forward transfer (LIFT) of cell-laden bioinks is one of the most promising laser-printing technologies enabling biofabrication. However, for it to be a viable bioprinting technology, bioink printability must be carefully examined. In this study, we used a time-resolved imaging system to study the cell-laden bioink droplet formation process in terms of the droplet size, velocity, and traveling distance. For this purpose, the bioinks were prepared using breast cancer cells with different cell concentrations to evaluate the effect of the cell concentration on the droplet formation process and the survival of the cells after printing. These bioinks were compared with cell-free bioinks under the same printing conditions to understand the effect of the particle physical properties on the droplet formation procedure. The morphology of the printed droplets indicated that it is possible to print uniform droplets for a wide range of cell concentrations. Overall, it is concluded that the laser fluence and the distance of the donor–receiver substrates play an important role in the printing impingement type; consequently, a careful adjustment of these parameters can lead to high-quality printing. Full article
(This article belongs to the Special Issue Advanced Laser Bio-Printing)
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Article
Fabrication of Antireflection Micro/Nanostructures on the Surface of Aluminum Alloy by Femtosecond Laser
Micromachines 2021, 12(11), 1406; https://doi.org/10.3390/mi12111406 - 16 Nov 2021
Viewed by 321
Abstract
Designed micro-nano structures on the surface of aluminum alloy provide excellent light trapping properties that can be used extensively in thermal photovoltaics, sensors, etc. However, the fabrication of high-performance antireflective micro-nano structures on aluminum alloy is challenging because aluminum has shallow intrinsic losses [...] Read more.
Designed micro-nano structures on the surface of aluminum alloy provide excellent light trapping properties that can be used extensively in thermal photovoltaics, sensors, etc. However, the fabrication of high-performance antireflective micro-nano structures on aluminum alloy is challenging because aluminum has shallow intrinsic losses and weak absorption. A two-step strategy is proposed for fabricating broadband antireflection structures by superimposing nanostructures onto microscale structures. By optimizing the processing parameters of femtosecond laser, the average reflectances of 2.6% within the visible spectral region (400–800 nm) and 5.14% within the Vis-NIR spectral region (400–2500 nm) are obtained. Full article
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Review
Electroreforming of Biomass for Value-Added Products
Micromachines 2021, 12(11), 1405; https://doi.org/10.3390/mi12111405 - 16 Nov 2021
Viewed by 430
Abstract
Humanity’s overreliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. To address this issue, there is a growing body of research on renewable resources such as biomass, of which [...] Read more.
Humanity’s overreliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. To address this issue, there is a growing body of research on renewable resources such as biomass, of which cellulose is the most abundant type. In particular, the electrochemical reforming of biomass is especially promising, as it allows greater control over valorization processes and requires milder conditions. Driven by renewable electricity, electroreforming of biomass can be green and sustainable. Moreover, green hydrogen generation can be coupled to anodic biomass electroforming, which has attracted ever-increasing attention. The following review is a summary of recent developments related to electroreforming cellulose and its derivatives (glucose, hydroxymethylfurfural, levulinic acid). The electroreforming of biomass can be achieved on the anode of an electrochemical cell through electrooxidation, as well as on the cathode through electroreduction. Recent advances in the anodic electroreforming of cellulose and cellulose-derived glucose and 5-hydrooxylmethoylfurural (5-HMF) are first summarized. Then, the key achievements in the cathodic electroreforming of cellulose and cellulose-derived 5-HMF and levulinic acid are discussed. Afterward, the emerging research focusing on coupling hydrogen evolution with anodic biomass reforming for the cogeneration of green hydrogen fuel and value-added chemicals is reviewed. The final chapter of this paper provides our perspective on the challenges and future research directions of biomass electroreforming. Full article
(This article belongs to the Special Issue Recent Advances in Nanotechnology and Nanomaterials)
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Article
Main Problems Using DEM Modeling to Evaluate the Loose Soil Collection by Conceptual Machine as a Background for Future Extraterrestrial Regolith Harvesting DEM Models
Micromachines 2021, 12(11), 1404; https://doi.org/10.3390/mi12111404 - 15 Nov 2021
Viewed by 223
Abstract
Nowadays, rapid product development is a key factor influencing a company’s success. In the Space 4.0. era, an integrated approach with the use of 3D printing and DEM modeling can be particularly effective in the development of technologies related to space mining. Unfortunately, [...] Read more.
Nowadays, rapid product development is a key factor influencing a company’s success. In the Space 4.0. era, an integrated approach with the use of 3D printing and DEM modeling can be particularly effective in the development of technologies related to space mining. Unfortunately, both 3D printing and DEM modeling are not without flaws. This article shows the possibilities and problems resulting from the use of DEM simulation and 3D printing simultaneously in the rapid development of a hypothetical mining machine. For the subsequent development of the regolith harvesting model, loose soil harvesting simulations were performed and the underlying problems were defined and discussed. The results show that it is possible to use both technologies simultaneously to be able to effectively and accurately model the behavior of this type of machine in various gravitational conditions in the future. Full article
(This article belongs to the Special Issue Space Robotics)
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