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Micromachines, Volume 10, Issue 1 (January 2019)

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Cover Story (view full-size image) Moore’s Law for silicon transistors is coming to an end. The use of liquid-metal electrodes on [...] Read more.
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Open AccessArticle High Performance Drain Engineered InGaN Heterostructure Tunnel Field Effect Transistor
Micromachines 2019, 10(1), 75; https://doi.org/10.3390/mi10010075
Received: 27 December 2018 / Revised: 18 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
A drain engineered InGaN heterostructure tunnel field effect transistor (TFET) is proposed and investigated by Silvaco Atlas simulation. This structure uses an additional metal on the drain region to modulate the energy band near the drain/channel interface in the drain regions, and increase [...] Read more.
A drain engineered InGaN heterostructure tunnel field effect transistor (TFET) is proposed and investigated by Silvaco Atlas simulation. This structure uses an additional metal on the drain region to modulate the energy band near the drain/channel interface in the drain regions, and increase the tunneling barrier for the flow of holes from the conduction band of the drain to the valence band of the channel region under negative gate bias for n-TFET, which induces the ambipolar current being reduced from 1.93 × 10−8 to 1.46 × 10−11 A/μm. In addition, polar InGaN heterostructure TFET having a polarization effect can adjust the energy band structure and achieve steep interband tunneling. The average subthreshold swing of the polar drain engineered heterostructure TFET (DE-HTFET) is reduced by 53.3% compared to that of the nonpolar DE-HTFET. Furthermore, ION increases 100% from 137 mA/mm of nonpolar DE-HTFET to 274 mA/mm of polar DE-HTFET. Full article
(This article belongs to the Special Issue Miniaturized Transistors)
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Open AccessArticle Magneto-Elastic μ-Vibrator for Smashing Thrombus
Micromachines 2019, 10(1), 74; https://doi.org/10.3390/mi10010074
Received: 17 December 2018 / Revised: 13 January 2019 / Accepted: 18 January 2019 / Published: 21 January 2019
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Abstract
A miniaturized thrombus dredger is proposed and developed in this study. The flexural resonance of the µ-resonator dredger is driven by a bulk-extensional magneto-elastic vibrator that is externally excited by alternating magnetic-field. With the fabricated prototype of the resonant dredger, a mice thrombus [...] Read more.
A miniaturized thrombus dredger is proposed and developed in this study. The flexural resonance of the µ-resonator dredger is driven by a bulk-extensional magneto-elastic vibrator that is externally excited by alternating magnetic-field. With the fabricated prototype of the resonant dredger, a mice thrombus blocked in a simulated vessel is broken into micro-pieces, and the previously blocked vessel can recover to an unobstructed state within 1 h. A flow-rate ratio detection method is used to evaluate the thrombus-cleaning effectiveness. The comparison between the finite-element simulation and the experimental results validates the flow-rate ratio detection method. By optimally exciting the resonant dredger in its third resonant mode, the flow-rate ratio in the cleaned vessel increases by about 2.7 times compared with that in the partly blocked vessel, and the thrombus is smashed into micro-pieces. Full article
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Open AccessArticle Optical Properties of Au-Based and Pt-Based Alloys for Infrared Device Applications: A Combined First Principle and Electromagnetic Simulation Study
Micromachines 2019, 10(1), 73; https://doi.org/10.3390/mi10010073
Received: 28 December 2018 / Revised: 14 January 2019 / Accepted: 15 January 2019 / Published: 20 January 2019
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Abstract
Due to the rapid progress in MEMS-based infrared emitters and sensors, strong demand exists for suitable plasmonic materials for such microdevices. We examine the possibility of achieving this goal by alloying other metals with the noble metals Au and Pt, which have some [...] Read more.
Due to the rapid progress in MEMS-based infrared emitters and sensors, strong demand exists for suitable plasmonic materials for such microdevices. We examine the possibility of achieving this goal by alloying other metals with the noble metals Au and Pt, which have some drawbacks, such as low melting point, structural instability, and high costs. The six different metals (Ir, Mo, Ni, Pb, Ta, and W) which possess good properties for heat resistance, stability, and magnetism are mixed with noble metals to improve the properties. The optical properties are calculated by density functional theory and they are used for further investigations of the optical responses of alloy nanorods. The results show that the studied alloy nanorods have wavelength selective properties and can be useful for infrared devices and systems. Full article
(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)
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Open AccessArticle Multi-Response Optimization of Electrical Discharge Machining Using the Desirability Function
Micromachines 2019, 10(1), 72; https://doi.org/10.3390/mi10010072
Received: 16 November 2018 / Revised: 9 January 2019 / Accepted: 14 January 2019 / Published: 20 January 2019
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Abstract
Electrical discharge machining (EDM) is a modern technology that is widely used in the production of difficult to cut conductive materials. The basic problem of EDM is the stochastic nature of electrical discharges. The optimal selection of machining parameters to achieve micron surface [...] Read more.
Electrical discharge machining (EDM) is a modern technology that is widely used in the production of difficult to cut conductive materials. The basic problem of EDM is the stochastic nature of electrical discharges. The optimal selection of machining parameters to achieve micron surface roughness and the recast layer with the maximal possible value of the material removal rate (MRR) is quite challenging. In this paper, we performed an analytical and experimental investigation of the influence of the EDM parameters: Surface integrity and MRR. Response surface methodology (RSM) was used to build empirical models on the influence of the discharge current I, pulse time ton, and the time interval toff, on the surface roughness (Sa), the thickness of the white layer (WL), and the MRR, during the machining of tool steel 55NiCrMoV7. The surface and subsurface integrity were evaluated using an optical microscope and a scanning profilometer. Analysis of variance (ANOVA) was used to establish the statistical significance parameters. The calculated contribution indicated that the discharge current had the most influence (over the 50%) on the Sa, WL, and MRR, followed by the discharge time. The multi-response optimization was carried out using the desirability function for the three cases of EDM: Finishing, semi-finishing, and roughing. The confirmation test showed that maximal errors between the predicted and the obtained values did not exceed 6%. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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Open AccessArticle A Novel Fabricating Process of Catalytic Gas Sensor Based on Droplet Generating Technology
Micromachines 2019, 10(1), 71; https://doi.org/10.3390/mi10010071
Received: 25 November 2018 / Revised: 25 December 2018 / Accepted: 15 January 2019 / Published: 20 January 2019
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Abstract
Catalytic gas sensors are widely used for measuring concentrations of combustible gases to prevent explosive accidents in industrial and domestic environments. The typical structure of the sensitive element of the sensor consists of carrier and catalyst materials, which are in and around a [...] Read more.
Catalytic gas sensors are widely used for measuring concentrations of combustible gases to prevent explosive accidents in industrial and domestic environments. The typical structure of the sensitive element of the sensor consists of carrier and catalyst materials, which are in and around a platinum coil. However, the size of the platinum coil is micron-grade and typically has a cylindrical shape. It is extremely difficult to control the amount of carrier and catalyst materials and to fulfill the inner cavity of the coil, which adds to the irreproducibility and uncertainty of the sensor performance. To solve this problem, this paper presents a new method which uses a drop-on-demand droplet generator to add the carrier and catalytic materials into the platinum coil and fabricate the micropellistor. The materials in this article include finely dispersed Al2O3 suspension and platinum palladium (Pd-Pt) catalyst. The size of the micropellistor with carrier material can be controlled by the number of the suspension droplets, while the amount of Pd-Pt catalyst can be controlled by the number of catalyst droplets. A bridge circuit is used to obtain the output signal of the gas sensors. The original signals of the micropellistor at 140 mV and 80 mV remain after aging treatment. The sensitivity and power consumption of the pellistor are 32 mV/% CH4 and 120 mW, respectively. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application)
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Open AccessArticle A Miniaturized Circularly-Polarized Antenna for In-Body Wireless Communications
Micromachines 2019, 10(1), 70; https://doi.org/10.3390/mi10010070
Received: 5 December 2018 / Revised: 10 January 2019 / Accepted: 16 January 2019 / Published: 19 January 2019
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Abstract
A novel miniaturized single-fed circularly-polarized (CP) microstrip patch antenna operating in the Industrial, Scientific, Medical (ISM) band of 2.40–2.48 GHz, is comprehensively proposed for implantable wireless communications. By employing reactive loading in the arrow-shaped slotted patch to form slow wave effect and embedding [...] Read more.
A novel miniaturized single-fed circularly-polarized (CP) microstrip patch antenna operating in the Industrial, Scientific, Medical (ISM) band of 2.40–2.48 GHz, is comprehensively proposed for implantable wireless communications. By employing reactive loading in the arrow-shaped slotted patch to form slow wave effect and embedding V-shaped slots into patch to lengthen the current path, the proposed implantable antenna is minimized with the overall dimensions of 9.2 mm × 9.2 mm × 1.27 mm. The radiation patterns of the proposed antenna illustrate the performance of left-handed circular polarization. The simulated results show that an impedance bandwidth of 7.2% (2.39–2.57 GHz) and an axial ratio bandwidth of 3.7% (2.39–2.48 GHz) at the ISM band are achieved, respectively. Ex vivo measured results are in good agreement with the corresponding simulated ones. Full article
(This article belongs to the Special Issue Implantable Microdevices)
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Open AccessFeature PaperArticle Vibration Induced Transport of Enclosed Droplets
Micromachines 2019, 10(1), 69; https://doi.org/10.3390/mi10010069
Received: 7 December 2018 / Revised: 13 January 2019 / Accepted: 16 January 2019 / Published: 19 January 2019
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Abstract
The droplet response to vibrations has been well characterized on open substrates, but microfluidic applications for droplets on open systems are limited by rapid evaporation rates and prone to environmental contamination. However, the response of enclosed droplets to vibration is less understood. Here, [...] Read more.
The droplet response to vibrations has been well characterized on open substrates, but microfluidic applications for droplets on open systems are limited by rapid evaporation rates and prone to environmental contamination. However, the response of enclosed droplets to vibration is less understood. Here, we investigate the effects of a dual-plate enclosure on droplet transport for the anisotropic ratchet conveyor system. This system uses an asymmetric pattern of hydrophilic rungs to transport droplets with an applied vibration. Through this work, we discovered that the addition of a substrate on top of the droplet, held in place with a 3D printed fixture, extends the functional frequency range for droplet transport and normalizes the device performance for droplets of different volumes. Furthermore, we found that the edge movements are anti-phasic between top and bottom substrates, providing a velocity profile that is correlated to vibration frequency, unlike the resonance-dependent profiles observed on open systems. These results expand the capabilities of this system, providing avenues for new applications and innovation, but also new insights for droplet mechanics in response to applied vibration. Full article
(This article belongs to the Special Issue Microscale Surface Tension and Its Applications)
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Open AccessArticle Marine Polysaccharide-Collagen Coatings on Ti6Al4V Alloy Formed by Self-Assembly
Micromachines 2019, 10(1), 68; https://doi.org/10.3390/mi10010068
Received: 30 November 2018 / Revised: 16 January 2019 / Accepted: 18 January 2019 / Published: 19 January 2019
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Abstract
Polysaccharides of marine origin are gaining interest as biomaterial components. Bacteria derived from deep-sea hydrothermal vents can produce sulfated exopolysaccharides (EPS), which can influence cell behavior. The use of such polysaccharides as components of organic, collagen fibril-based coatings on biomaterial surfaces remains unexplored. [...] Read more.
Polysaccharides of marine origin are gaining interest as biomaterial components. Bacteria derived from deep-sea hydrothermal vents can produce sulfated exopolysaccharides (EPS), which can influence cell behavior. The use of such polysaccharides as components of organic, collagen fibril-based coatings on biomaterial surfaces remains unexplored. In this study, collagen fibril coatings enriched with HE800 and GY785 EPS derivatives were deposited on titanium alloy (Ti6Al4V) scaffolds produced by rapid prototyping and subjected to physicochemical and cell biological characterization. Coatings were formed by a self-assembly process whereby polysaccharides were added to acidic collagen molecule solution, followed by neutralization to induced self-assembly of collagen fibrils. Fibril formation resulted in collagen hydrogel formation. Hydrogels formed directly on Ti6Al4V surfaces, and fibrils adsorbed onto the surface. Scanning electron microscopy (SEM) analysis of collagen fibril coatings revealed association of polysaccharides with fibrils. Cell biological characterization revealed good cell adhesion and growth on bare Ti6Al4V surfaces, as well as coatings of collagen fibrils only and collagen fibrils enhanced with HE800 and GY785 EPS derivatives. Hence, the use of both EPS derivatives as coating components is feasible. Further work should focus on cell differentiation. Full article
(This article belongs to the Special Issue Self-Assembly of Polymers)
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Open AccessArticle Scanning MEMS Mirror for High Definition and High Frame Rate Lissajous Patterns
Micromachines 2019, 10(1), 67; https://doi.org/10.3390/mi10010067
Received: 4 December 2018 / Revised: 16 January 2019 / Accepted: 17 January 2019 / Published: 18 January 2019
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Abstract
Scanning MEMS (micro-electro-mechanical system) mirrors are attractive given their potential use in a diverse array of laser scanning display and imaging applications. Here we report on an electrostatic MEMS mirror for high definition and high frame rate (HDHF) Lissajous scanning. The MEMS mirror [...] Read more.
Scanning MEMS (micro-electro-mechanical system) mirrors are attractive given their potential use in a diverse array of laser scanning display and imaging applications. Here we report on an electrostatic MEMS mirror for high definition and high frame rate (HDHF) Lissajous scanning. The MEMS mirror comprised a low Q-factor inner mirror and frame mirror, which provided two-dimensional scanning at two similar resonant scanning frequencies with high mechanical stability. The low Q inner mirror enabled a broad frequency selection range. The high definition and high frame rate (HDHF) Lissajous scanning of the MEMS mirror was achieved by selecting a set of scanning frequencies near its resonance with a high greatest common divisor (GCD) and a high total lobe number. The MEMS mirror had resonant scanning frequencies at 5402 Hz and 6702 Hz in x and y directions, respectively. The selected pseudo-resonant frequencies of 5450 Hz and 6700 Hz for HDHF scanning provided 50 frames per second with 94% fill factor in 256 × 256 pixels. This Lissajous MEMS mirror could be utilized for assorted HDHF laser scanning imaging and display applications. Full article
(This article belongs to the Special Issue MEMS Technology for Biomedical Imaging Applications)
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Open AccessArticle Growth Process and CQDs-modified Bi4Ti3O12 Square Plates with Enhanced Photocatalytic Performance
Micromachines 2019, 10(1), 66; https://doi.org/10.3390/mi10010066
Received: 27 December 2018 / Revised: 9 January 2019 / Accepted: 16 January 2019 / Published: 18 January 2019
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Abstract
Bi4Ti3O12 square plates were synthesized via a hydrothermal route, and their growth process was systematically investigated. Carbon quantum dots (CQDs) were prepared using glucose as the carbon source, which were then assembled on the surface of Bi4 [...] Read more.
Bi4Ti3O12 square plates were synthesized via a hydrothermal route, and their growth process was systematically investigated. Carbon quantum dots (CQDs) were prepared using glucose as the carbon source, which were then assembled on the surface of Bi4Ti3O12 square plates via a hydrothermal route with the aim of enhancing the photocatalytic performance. XRD (X-ray powder diffraction), SEM (scanning electron microscopy), TEM (transmission electron microscopy), UV-vis DRS (diffuse reflectance spectroscopy), XPS (X-ray photoelectron spectroscopy), FTIR (Fourier transform infrared spectroscopy), PL (photoluminescence) spectroscopy, EIS (electrochemical impedance spectroscopy) and photocurrent spectroscopy were used to systematically characterize the as-prepared samples. It is demonstrated that the decoration of CQDs on Bi4Ti3O12 plates leads to an increased visible light absorption, slightly increased bandgap, increased photocurrent density, decreased charge-transfer resistance, and decreased PL intensity. Simulated sunlight and visible light were separately used as a light source to evaluate the photocatalytic activity of the samples toward the degradation of RhB in aqueous solution. Under both simulated sunlight and visible light irradiation, [email protected]4Ti3O12 composites with an appropriate amount of CQDs exhibit obviously enhanced photocatalytic performance. However, the decoration of excessive CQDs gives rise to a decrease in the photocatalytic activity. The enhanced photocatalytic activity of CQDs-modified Bi4Ti3O12 can be attributed to the following reasons: (1) The electron transfer between Bi4Ti3O12 and CQDs promotes an efficient separation of photogenerated electron/hole pairs in Bi4Ti3O12; (2) the up-conversion photoluminescence emitted from CQDs could induce the generation of additional electron/hole pairs in Bi4Ti3O12; and (3) the photoexcited electrons in CQDs could participate in the photocatalytic reactions. Full article
(This article belongs to the Special Issue Nanostructures for Photocatalysis)
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Open AccessArticle Microswimmer Propulsion by Two Steadily Rotating Helical Flagella
Micromachines 2019, 10(1), 65; https://doi.org/10.3390/mi10010065
Received: 31 December 2018 / Revised: 15 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
Many theoretical studies of bacterial locomotion adopt a simple model for the organism consisting of a spheroidal cell body and a single corkscrew-shaped flagellum that rotates to propel the body forward. Motivated by experimental observations of a group of magnetotactic bacterial strains, we [...] Read more.
Many theoretical studies of bacterial locomotion adopt a simple model for the organism consisting of a spheroidal cell body and a single corkscrew-shaped flagellum that rotates to propel the body forward. Motivated by experimental observations of a group of magnetotactic bacterial strains, we extended the model by considering two flagella attached to the cell body and rotating about their respective axes. Using numerical simulations, we analyzed the motion of such a microswimmer in bulk fluid and close to a solid surface. We show that positioning the two flagella far apart on the cell body reduces the rate of rotation of the body and increases the swimming speed. Near surfaces, we found that swimmers with two flagella can swim in relatively straight trajectories or circular orbits in either direction. It is also possible for the swimmer to escape from surfaces, unlike a model swimmer of similar shape but with only a single flagellum. Thus, we conclude that there are important implications of swimming with two flagella or flagellar bundles rather than one. These considerations are relevant not only for understanding differences in bacterial morphology but also for designing microrobotic swimmers. Full article
(This article belongs to the Special Issue Microswimmer)
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Open AccessArticle Fabrication of Adhesive Resistance Surface with Low Wettability on Ti6Al4V Alloys by Electro-Brush Plating
Micromachines 2019, 10(1), 64; https://doi.org/10.3390/mi10010064
Received: 17 December 2018 / Revised: 10 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
Anti-adhesive Ni coatings with low wettability were successfully fabricated on Ti6Al4V substrates via an electro-brush plating method, and subsequently modified with a fluoroalkylsilane (FAS) film. The surface morphology, chemical compositions, and wettability of the as-prepared coatings were measured using scanning electron microscopy (SEM), [...] Read more.
Anti-adhesive Ni coatings with low wettability were successfully fabricated on Ti6Al4V substrates via an electro-brush plating method, and subsequently modified with a fluoroalkylsilane (FAS) film. The surface morphology, chemical compositions, and wettability of the as-prepared coatings were measured using scanning electron microscopy (SEM), X-ray diffractometer (XRD), Fourier transform infrared spectrophotometry (FTIR), and contact angle measurements. The results showed that the surface of Ti6Al4V substrate was endowed with flower-like structures. Each flower-like cluster was constituted by a large number of Ni ions. After surface modification of FAS, the as-prepared Ti6Al4V surface had a water contact angle as high as 151.5°, a sliding angle close to 2.1°, and a solid surface energy as low as 0.97 mJ/m2. Potentiodynamic polarization tests showed that the Ni coating could provide a stable corrosion protection. In addition, the effects of processing conditions, such as working voltage, relative velocity, electrolyte concentration, and processing time, were investigated. The mechanism of the adhesive resistance was proposed, and the low wettability of Ti6Al4V surfaces was explained by Cassie–Baxter model. As a result, it was necessary to reduce the fraction of the solid–liquid interface in order to achieve anti-adhesive surface. Full article
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Open AccessArticle Laser Treatments for Improving Electrical Conductivity and Piezoresistive Behavior of Polymer–Carbon Nanofiller Composites
Micromachines 2019, 10(1), 63; https://doi.org/10.3390/mi10010063
Received: 13 December 2018 / Revised: 9 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
The effect of carbon nanotubes, graphene-like platelets, and another carbonaceous fillers of natural origin on the electrical conductivity of polymeric materials was studied. With the aim of keeping the filler content and the material cost as low as possible, the effect of laser [...] Read more.
The effect of carbon nanotubes, graphene-like platelets, and another carbonaceous fillers of natural origin on the electrical conductivity of polymeric materials was studied. With the aim of keeping the filler content and the material cost as low as possible, the effect of laser surface treatments on the conductivity of polymer composites with filler load below the percolation threshold was also investigated. These treatments allowed processing in situ conductive tracks on the surface of insulating polymer-based materials. The importance of the kinds of fillers and matrices, and of the laser process parameters was studied. Carbon nanotubes were also used to obtain piezoresistive composites. The electrical response of these materials to a mechanical load was investigated in view of their exploitation for the production of pressure sensors and switches based on the piezoresistive effect. It was found that the piezoresistive behavior of composites with very low filler concentration can be improved with proper laser treatments. Full article
(This article belongs to the Special Issue Carbon Based Electronic Devices)
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Open AccessReview Progress in the Field of Micro-Electrocorticography
Micromachines 2019, 10(1), 62; https://doi.org/10.3390/mi10010062
Received: 9 December 2018 / Revised: 10 January 2019 / Accepted: 15 January 2019 / Published: 17 January 2019
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Abstract
Since the 1940s electrocorticography (ECoG) devices and, more recently, in the last decade, micro-electrocorticography (µECoG) cortical electrode arrays were used for a wide set of experimental and clinical applications, such as epilepsy localization and brain–computer interface (BCI) technologies. Miniaturized implantable µECoG devices have [...] Read more.
Since the 1940s electrocorticography (ECoG) devices and, more recently, in the last decade, micro-electrocorticography (µECoG) cortical electrode arrays were used for a wide set of experimental and clinical applications, such as epilepsy localization and brain–computer interface (BCI) technologies. Miniaturized implantable µECoG devices have the advantage of providing greater-density neural signal acquisition and stimulation capabilities in a minimally invasive fashion. An increased spatial resolution of the µECoG array will be useful for greater specificity diagnosis and treatment of neuronal diseases and the advancement of basic neuroscience and BCI research. In this review, recent achievements of ECoG and µECoG are discussed. The electrode configurations and varying material choices used to design µECoG arrays are discussed, including advantages and disadvantages of µECoG technology compared to electroencephalography (EEG), ECoG, and intracortical electrode arrays. Electrode materials that are the primary focus include platinum, iridium oxide, poly(3,4-ethylenedioxythiophene) (PEDOT), indium tin oxide (ITO), and graphene. We discuss the biological immune response to µECoG devices compared to other electrode array types, the role of µECoG in clinical pathology, and brain–computer interface technology. The information presented in this review will be helpful to understand the current status, organize available knowledge, and guide future clinical and research applications of µECoG technologies. Full article
(This article belongs to the Special Issue Neural Microelectrodes: Design and Applications)
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Open AccessArticle Dextran as a Resorbable Coating Material for Flexible Neural Probes
Micromachines 2019, 10(1), 61; https://doi.org/10.3390/mi10010061
Received: 13 November 2018 / Revised: 27 December 2018 / Accepted: 15 January 2019 / Published: 17 January 2019
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Abstract
In the quest for chronically reliable and bio-tolerable brain interfaces there has been a steady evolution towards the use of highly flexible, polymer-based electrode arrays. The reduced mechanical mismatch between implant and brain tissue has shown to reduce the evoked immune response, which [...] Read more.
In the quest for chronically reliable and bio-tolerable brain interfaces there has been a steady evolution towards the use of highly flexible, polymer-based electrode arrays. The reduced mechanical mismatch between implant and brain tissue has shown to reduce the evoked immune response, which in turn has a positive effect on signal stability and noise. Unfortunately, the low stiffness of the implants also has practical repercussions, making surgical insertion extremely difficult. In this work we explore the use of dextran as a coating material that temporarily stiffens the implant, preventing buckling during insertion. The mechanical properties of dextran coated neural probes are characterized, as well as the different parameters which influence the dissolution rate. Tuning parameters, such as coating thickness and molecular weight of the used dextran, allows customization of the stiffness and dissolution time to precisely match the user’s needs. Finally, the immunological response to the coated electrodes was analyzed by performing a histological examination after four months of in vivo testing. The results indicated that a very limited amount of glial scar tissue was formed. Neurons have also infiltrated the area that was initially occupied by the dissolving dextran coating. There was no noticeable drop in neuron density around the site of implantation, confirming the suitability of the coating as a temporary aid during implantation of highly flexible polymer-based neural probes. Full article
(This article belongs to the Special Issue Neural Microelectrodes: Design and Applications)
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Open AccessArticle Empirical Modeling of Zn/ZnO Nanoparticles Decorated/Conjugated with Fotolon (Chlorine e6) Based Photodynamic Therapy towards Liver Cancer Treatment
Micromachines 2019, 10(1), 60; https://doi.org/10.3390/mi10010060
Received: 28 November 2018 / Revised: 8 January 2019 / Accepted: 8 January 2019 / Published: 17 January 2019
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Abstract
The current study is based on Zn/ZnO nanoparticles photodynamic therapy (PDT) mediated effects on healthy liver cells and cancerous cells. The synthesis of Zn/ZnO nanoparticles was accomplished using chemical and hydrothermal methods. The characterization of the synthesized nanoparticles was carried out using manifold [...] Read more.
The current study is based on Zn/ZnO nanoparticles photodynamic therapy (PDT) mediated effects on healthy liver cells and cancerous cells. The synthesis of Zn/ZnO nanoparticles was accomplished using chemical and hydrothermal methods. The characterization of the synthesized nanoparticles was carried out using manifold techniques (e.g., transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS)). In order to study the biotoxicity of the grown nanoparticles, they were applied individually and in conjunction with the third generation photosensitiser Fotolon (Chlorine e6) in the in vivo model of the normal liver of the Wister rat, and in the in vitro cancerous liver (HepG2) model both in the dark and under a variety of laser exposures (630 nm, Ultraviolet (UV) light). The localization of ZnO nanoparticles was observed by applying fluorescence spectroscopy on a 1 cm2 selected area of normal liver, whereas the in vitro cytotoxicity and reactive oxygen species (ROS) detection were carried out by calculating the loss in the cell viability of the hepatocellular model by applying a neutral red assay (NRA). Furthermore, a statistical analysis is carried out and it is ensured that the p value is less than 0.05. Thus, the current study has highlighted the potential for applying Zn/ZnO nanoparticles in photodynamic therapy that would lead to wider medical applications to improve the efficiency of cancer treatment and its biological aspect study. Full article
(This article belongs to the Special Issue Micro/Nano-system for Drug Delivery)
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Open AccessArticle A Compact Broadband Antenna with Dual-Resonance for Implantable Devices
Micromachines 2019, 10(1), 59; https://doi.org/10.3390/mi10010059
Received: 12 November 2018 / Revised: 13 January 2019 / Accepted: 14 January 2019 / Published: 16 January 2019
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Abstract
A compact broadband implantable patch antenna is designed for the field of biotelemetry and experimentally demonstrated using the Medical Device Radiocommunications Service (MedRadio) band (401–406 MHz). The proposed antenna can obtain a broad impedance bandwidth by exciting dual-resonant frequencies, and has a compact [...] Read more.
A compact broadband implantable patch antenna is designed for the field of biotelemetry and experimentally demonstrated using the Medical Device Radiocommunications Service (MedRadio) band (401–406 MHz). The proposed antenna can obtain a broad impedance bandwidth by exciting dual-resonant frequencies, and has a compact structure using bent metal radiating strips and a short strategy. The total volume of the proposed antenna, including substrate and superstrate, is about 479 mm3 (23 × 16.4 × 1.27 mm3). The measured bandwidth is 52 MHz (382–434 MHz) at a return loss of −10 dB. The resonance, radiation and specific absorption rate (SAR) performance of the antenna are examined and characterized. Full article
(This article belongs to the Special Issue Implantable Microdevices)
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Open AccessArticle Pressure Sensitivity Enhancement of Porous Carbon Electrode and Its Application in Self-Powered Mechanical Sensors
Micromachines 2019, 10(1), 58; https://doi.org/10.3390/mi10010058
Received: 26 December 2018 / Revised: 9 January 2019 / Accepted: 10 January 2019 / Published: 16 January 2019
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Abstract
Microsystems with limited power supplies, such as electronic skin and smart fuzes, have a strong demand for self-powered pressure and impact sensors. In recent years, new self-powered mechanical sensors based on the piezoresistive characteristics of porous electrodes have been rapidly developed, and have [...] Read more.
Microsystems with limited power supplies, such as electronic skin and smart fuzes, have a strong demand for self-powered pressure and impact sensors. In recent years, new self-powered mechanical sensors based on the piezoresistive characteristics of porous electrodes have been rapidly developed, and have unique advantages compared to conventional piezoelectric sensors. In this paper, in order to optimize the mechanical sensitivity of porous electrodes, a material preparation process that can enhance the piezoresistive characteristics is proposed. A flexible porous electrode with superior piezoresistive characteristics and elasticity was prepared by modifying the microstructure of the porous electrode material and adding an elastic rubber component. Furthermore, based on the porous electrode, a self-powered pressure sensor and an impact sensor were fabricated. Through experimental results, the response signals of the sensors present a voltage peak under such mechanical effects and the sensitive signal has less clutter, making it easy to identify the features of the mechanical effects. Full article
(This article belongs to the Special Issue Carbon Based Electronic Devices)
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Open AccessArticle Multiple Laser Stripe Scanning Profilometry Based on Microelectromechanical Systems Scanning Mirror Projection
Micromachines 2019, 10(1), 57; https://doi.org/10.3390/mi10010057
Received: 10 December 2018 / Revised: 1 January 2019 / Accepted: 10 January 2019 / Published: 16 January 2019
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Abstract
In traditional laser-based 3D measurement technology, the width of the laser stripe is uncontrollable and uneven. In addition, speckle noise in the image and the noise caused by mechanical movement may reduce the accuracy of the scanning results. This work proposes a new [...] Read more.
In traditional laser-based 3D measurement technology, the width of the laser stripe is uncontrollable and uneven. In addition, speckle noise in the image and the noise caused by mechanical movement may reduce the accuracy of the scanning results. This work proposes a new multiple laser stripe scanning profilometry (MLSSP) based on microelectromechanical systems (MEMS) scanning mirror which can project high quality movable laser stripe. It can implement full-field scanning in a short time and does not need to move the measured object or camera. Compared with the traditional laser stripe, the brightness, width and position of the new multiple laser stripes projected by MEMS scanning mirror can be controlled by programming. In addition, the new laser strip can generate high-quality images and the noise caused by mechanical movement is completely eliminated. The experimental results show that the speckle noise is less and the light intensity distribution is more even. Furthermore, the number of pictures needed to be captured is significantly reduced to 1 / N ( N is the number of multiple laser stripes projected by MEMS scanning mirror) and the measurement efficiency is increased by N times, improving the efficiency and accuracy of 3D measurement. Full article
(This article belongs to the Special Issue Optical MEMS)
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Open AccessArticle Magnetically Induced Flow Focusing of Non-Magnetic Microparticles in Ferrofluids under Inclined Magnetic Fields
Micromachines 2019, 10(1), 56; https://doi.org/10.3390/mi10010056
Received: 30 December 2018 / Revised: 11 January 2019 / Accepted: 14 January 2019 / Published: 15 January 2019
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Abstract
The ability to focus biological particles into a designated position of a microchannel is vital for various biological applications. This paper reports particle focusing under vertical and inclined magnetic fields. We analyzed the effect of the angle of rotation (θ) of [...] Read more.
The ability to focus biological particles into a designated position of a microchannel is vital for various biological applications. This paper reports particle focusing under vertical and inclined magnetic fields. We analyzed the effect of the angle of rotation (θ) of the permanent magnets and the critical Reynolds number (Rec) on the particle focusing in depth. We found that a rotation angle of 10° is preferred; a particle loop has formed when Re < Rec and Rec of the inclined magnetic field is larger than that of the vertical magnetic field. We also conducted experiments with polystyrene particles (10.4 μm in diameter) to prove the calculations. Experimental results show that the focusing effectiveness improved with increasing applied magnetic field strength or decreasing inlet flow rate. Full article
(This article belongs to the Special Issue Micro- and Nanofluidics for Bionanoparticle Analysis)
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Open AccessCommunication Bacterial Concentration Detection using a PCB-based Contactless Conductivity Sensor
Micromachines 2019, 10(1), 55; https://doi.org/10.3390/mi10010055
Received: 3 December 2018 / Revised: 10 January 2019 / Accepted: 10 January 2019 / Published: 14 January 2019
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Abstract
Capacitively coupled contactless conductivity detection (C4D) is an improved approach to avoid the problems of labor-intensive, time-consuming and insufficient accuracy of plate count as well as the high-cost apparatus of flow cytometry (FCM) in bacterial counting. This article describes a novel [...] Read more.
Capacitively coupled contactless conductivity detection (C4D) is an improved approach to avoid the problems of labor-intensive, time-consuming and insufficient accuracy of plate count as well as the high-cost apparatus of flow cytometry (FCM) in bacterial counting. This article describes a novel electrode-integrated printed-circuit-board (PCB)-based C4D device, which supports the simple and safe exchange of capillaries and improves the sensitivity and repeatability of the contactless detection. Furthermore, no syringe pump is needed in the detection, it reduces the system size, and, more importantly, avoids the effect on the bacteria due to high pressure. The recovered bacteria after C4D detection at excitation of 25 Vpp and 60–120 kHz were analyzed by flow cytometry, and a survival rate higher than 96% was given. It was verified that C4D detection did not influence the bacterial viability. Moreover, bacteria concentrations from 106 cells/mL to 108 cells/mL were measured in a linear range, and relative standard deviation (RSD) is below 0.2%. In addition, the effects on bacteria and C4D from background solutions were discussed. In contrast to common methods used in most laboratories, this method may provide a simple solution to in situ detection of bacterial cultures. Full article
(This article belongs to the Special Issue Microfluidics for Cell and Other Organisms)
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Open AccessArticle Spray-On Liquid-Metal Electrodes for Graphene Field-Effect Transistors
Micromachines 2019, 10(1), 54; https://doi.org/10.3390/mi10010054
Received: 1 December 2018 / Revised: 23 December 2018 / Accepted: 8 January 2019 / Published: 14 January 2019
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Abstract
Advancements in flexible circuit interconnects are critical for widespread adoption of flexible electronics. Non-toxic liquid-metals offer a viable solution for flexible electrodes due to deformability and low bulk resistivity. However, fabrication processes utilizing liquid-metals suffer from high complexity, low throughput, and significant production [...] Read more.
Advancements in flexible circuit interconnects are critical for widespread adoption of flexible electronics. Non-toxic liquid-metals offer a viable solution for flexible electrodes due to deformability and low bulk resistivity. However, fabrication processes utilizing liquid-metals suffer from high complexity, low throughput, and significant production cost. Our team utilized an inexpensive spray-on stencil technique to deposit liquid-metal Galinstan electrodes in top-gated graphene field-effect transistors (GFETs). The electrode stencils were patterned using an automated vinyl cutter and positioned directly onto chemical vapor deposition (CVD) graphene transferred to polyethylene terephthalate (PET) substrates. Our spray-on method exhibited a throughput of 28 transistors in under five minutes on the same graphene sample, with a 96% yield for all devices down to a channel length of 50 μm. The fabricated transistors possess hole and electron mobilities of 663.5 cm2/(V·s) and 689.9 cm2/(V·s), respectively, and support a simple and effective method of developing high-yield flexible electronics. Full article
(This article belongs to the Special Issue Carbon Based Electronic Devices)
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Open AccessFeature PaperArticle Slot-Die Coating of Double Polymer Layers for the Fabrication of Organic Light Emitting Diodes
Micromachines 2019, 10(1), 53; https://doi.org/10.3390/mi10010053
Received: 13 December 2018 / Accepted: 9 January 2019 / Published: 14 January 2019
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This study presents the slot-die coating process of two layers of organic materials for the fabrication of organic light emitting diodes (OLEDs). Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which is commonly used in OLEDs and in organic photovoltaic devices as the hole injection layer (HIL), [...] Read more.
This study presents the slot-die coating process of two layers of organic materials for the fabrication of organic light emitting diodes (OLEDs). Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), which is commonly used in OLEDs and in organic photovoltaic devices as the hole injection layer (HIL), has been deposited via slot-die coating. Uniform films of PEDOT:PSS were obtained after optimizing the slot-die processing parameters: substrate temperature, coating speed, and ink flow rate. The film quality was examined using optical microscopy, profilometry, and atomic force microscopy. Further, poly(9,9-dioctylfluorene) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), a well know polymer blend F8:F8BT, which is used as an emissive layer in OLEDs, has been slot-die coated. The optoelectronic properties of the slot-die coated F8:F8BT films were examined by means of photoluminescence (PL) and electroluminescence (EL) studies. The fabricated OLEDs, consisting of slot-die coated PEDOT:PSS and F8:F8BT films, were characterized to record the brightness and current efficiency. Full article
(This article belongs to the Special Issue Printed Flexible and Stretchable Electronics)
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Open AccessArticle Acoustophoretic Control of Microparticle Transport Using Dual-Wavelength Surface Acoustic Wave Devices
Micromachines 2019, 10(1), 52; https://doi.org/10.3390/mi10010052
Received: 5 December 2018 / Revised: 6 January 2019 / Accepted: 9 January 2019 / Published: 13 January 2019
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Abstract
We present a numerical and experimental study of acoustophoretic manipulation in a microfluidic channel using dual-wavelength standing surface acoustic waves (SSAWs) to transport microparticles into different outlets. The SSAW fields were excited by interdigital transducers (IDTs) composed of two different pitches connected in [...] Read more.
We present a numerical and experimental study of acoustophoretic manipulation in a microfluidic channel using dual-wavelength standing surface acoustic waves (SSAWs) to transport microparticles into different outlets. The SSAW fields were excited by interdigital transducers (IDTs) composed of two different pitches connected in parallel and series on a lithium niobate substrate such that it yielded spatially superimposed and separated dual-wavelength SSAWs, respectively. SSAWs of a singltablee target wavelength can be efficiently excited by giving an RF voltage of frequency determined by the ratio of the velocity of the SAW to the target IDT pitch (i.e., f = cSAW/p). However, the two-pitch IDTs with similar pitches excite, less efficiently, non-target SSAWs with the wavelength associated with the non-target pitch in addition to target SSAWs by giving the target single-frequency RF voltage. As a result, dual-wavelength SSAWs can be formed. Simulated results revealed variations of acoustic pressure fields induced by the dual-wavelength SSAWs and corresponding influences on the particle motion. The acoustic radiation force in the acoustic pressure field was calculated to pinpoint zero-force positions and simulate particle motion trajectories. Then, dual-wavelength SSAW acoustofluidic devices were fabricated in accordance with the simulation results to experimentally demonstrate switching of SSAW fields as a means of transporting particles. The effects of non-target SSAWs on pre-actuating particles were predicted and observed. The study provides the design considerations needed for the fabrication of acoustofluidic devices with IDT-excited multi-wavelength SSAWs for acoustophoresis of microparticles. Full article
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Open AccessFeature PaperReview State of the Art and Perspectives on Silicon Photonic Switches
Micromachines 2019, 10(1), 51; https://doi.org/10.3390/mi10010051
Received: 20 December 2018 / Revised: 8 January 2019 / Accepted: 9 January 2019 / Published: 13 January 2019
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Abstract
In the last decade, silicon photonic switches are increasingly believed to be potential candidates for replacing the electrical switches in the applications of telecommunication networks, data center and high-throughput computing, due to their low power consumption (Picojoules per bit), large bandwidth (Terabits per [...] Read more.
In the last decade, silicon photonic switches are increasingly believed to be potential candidates for replacing the electrical switches in the applications of telecommunication networks, data center and high-throughput computing, due to their low power consumption (Picojoules per bit), large bandwidth (Terabits per second) and high-level integration (Square millimeters per port). This review paper focuses on the state of the art and our perspectives on silicon photonic switching technologies. It starts with a review of three types of fundamental switch engines, i.e., Mach-Zehnder interferometer, micro-ring resonator and micro-electro-mechanical-system actuated waveguide coupler. The working mechanisms are introduced and the key specifications such as insertion loss, crosstalk, switching time, footprint and power consumption are evaluated. Then it is followed by the discussion on the prototype of large-scale silicon photonic fabrics, which are based on the configuration of above-mentioned switch engines. In addition, the key technologies, such as topological architecture, passive components and optoelectronic packaging, to improve the overall performance are summarized. Finally, the critical challenges that might hamper the silicon photonic switching technologies transferring from proof-of-concept in lab to commercialization are also discussed. Full article
(This article belongs to the Section D:Materials and Processing)
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Open AccessArticle Implementation of a CMOS/MEMS Accelerometer with ASIC Processes
Micromachines 2019, 10(1), 50; https://doi.org/10.3390/mi10010050
Received: 17 December 2018 / Revised: 7 January 2019 / Accepted: 8 January 2019 / Published: 12 January 2019
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This paper presents the design, simulation and mechanical characterization of a newly proposed complementary metal-oxide semiconductor (CMOS)/micro-electromechanical system (MEMS) accelerometer. The monolithic CMOS/MEMS accelerometer was fabricated using the 0.18 μm application-specific integrated circuit (ASIC)-compatible CMOS/MEMS process. An approximate analytical model for the spring [...] Read more.
This paper presents the design, simulation and mechanical characterization of a newly proposed complementary metal-oxide semiconductor (CMOS)/micro-electromechanical system (MEMS) accelerometer. The monolithic CMOS/MEMS accelerometer was fabricated using the 0.18 μm application-specific integrated circuit (ASIC)-compatible CMOS/MEMS process. An approximate analytical model for the spring design is presented. The experiments showed that the resonant frequency of the proposed tri-axis accelerometer was around 5.35 kHz for out-plane vibration. The tri-axis accelerometer had an area of 1096 μm × 1256 μm. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application)
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Open AccessEditorial Editorial for the Special Issue on Polymer Based MEMS and Microfabrication
Micromachines 2019, 10(1), 49; https://doi.org/10.3390/mi10010049
Received: 7 January 2019 / Accepted: 10 January 2019 / Published: 11 January 2019
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Abstract
Polymers are becoming increasingly important in MEMS and microfabricated products [...] Full article
(This article belongs to the Special Issue Polymer Based MEMS and Microfabrication)
Open AccessReview Recent Developments of Acoustic Energy Harvesting: A Review
Micromachines 2019, 10(1), 48; https://doi.org/10.3390/mi10010048
Received: 14 December 2018 / Revised: 3 January 2019 / Accepted: 7 January 2019 / Published: 11 January 2019
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Abstract
Acoustic energy is a type of environmental energy source that can be scavenged and converted into electrical energy for small-scale power applications. In general, incident sound power density is low and structural design for acoustic energy harvesting (AEH) is crucial. This review article [...] Read more.
Acoustic energy is a type of environmental energy source that can be scavenged and converted into electrical energy for small-scale power applications. In general, incident sound power density is low and structural design for acoustic energy harvesting (AEH) is crucial. This review article summarizes the mechanisms of AEH, which include the Helmholtz resonator approach, the quarter-wavelength resonator approach, and the acoustic metamaterial approach. The details of recently proposed AEH devices and mechanisms are carefully reviewed and compared. Because acoustic metamaterials have the advantages of compactness, effectiveness, and flexibility, it is suggested that the emerging metamaterial-based AEH technique is highly suitable for further development. It is demonstrated that the AEH technique will become an essential part of the environmental energy-harvesting research field. As a multidisciplinary research topic, the major challenge is to integrate AEH devices into engineering structures and make composite structures smarter to achieve large-scale AEH. Full article
(This article belongs to the Special Issue Smart Miniaturised Energy Harvesting)
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Open AccessArticle Hybrid 3D Shape Measurement Using the MEMS Scanning Micromirror
Micromachines 2019, 10(1), 47; https://doi.org/10.3390/mi10010047
Received: 10 December 2018 / Revised: 2 January 2019 / Accepted: 7 January 2019 / Published: 11 January 2019
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A surface with large reflection variations represents one of the biggest challenges for optical 3D shape measurement. In this work, we propose an alternative hybrid 3D shape measurement approach, which combines the high accuracy of fringe projection profilometry (FPP) with the robustness of [...] Read more.
A surface with large reflection variations represents one of the biggest challenges for optical 3D shape measurement. In this work, we propose an alternative hybrid 3D shape measurement approach, which combines the high accuracy of fringe projection profilometry (FPP) with the robustness of laser stripe scanning (LSS). To integrate these two technologies into one system, first, we developed a biaxial Microelectromechanical Systems (MEMS) scanning micromirror projection system. In this system, a shaped laser beam serves as a light source. The MEMS micromirror projects the laser beam onto the object surface. Different patterns are produced by controlling the laser source and micromirror jointly. Second, a quality wised algorithm is delivered to develop a hybrid measurement scheme. FPP is applied to obtain the main 3D information. Then, LSS helps to reconstruct the missing depth guided by the quality map. After this, the data fusion algorithm is used to merge and output complete measurement results. Finally, our experiments show significant improvement in the accuracy and robustness of measuring a surface with large reflection variations. In the experimental instance, the accuracy of the proposed method is improved by 0.0278 mm and the integrity is improved by 83.55%. Full article
(This article belongs to the Special Issue Optical MEMS)
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Open AccessCommunication Investigating the Potential of Commercial-Grade Carbon Black-Filled TPU for the 3D Printing of Compressive Sensors
Micromachines 2019, 10(1), 46; https://doi.org/10.3390/mi10010046
Received: 15 November 2018 / Revised: 30 December 2018 / Accepted: 1 January 2019 / Published: 10 January 2019
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The present research aims to exploit commercially available materials and machines to fabricate multilayer, topologically designed transducers, which can be embedded into mechanical devices, such as soft or rigid grippers. Preliminary tests on the possibility of fabricating 3D-printed transducers using a commercial conductive [...] Read more.
The present research aims to exploit commercially available materials and machines to fabricate multilayer, topologically designed transducers, which can be embedded into mechanical devices, such as soft or rigid grippers. Preliminary tests on the possibility of fabricating 3D-printed transducers using a commercial conductive elastomeric filament, carbon black-filled thermoplastic polyurethane, are presented. The commercial carbon-filled thermoplastic polyurethane (TPU), analyzed in the present paper, has proven to be a candidate material for the production of 3D printed displacement sensors. Some limitations in fabricating the transducers from a 2.85 mm filament were found, and comparisons with 1.75 mm filaments should be conducted. Moreover, further research on the low repeatability at low displacements and the higher performance of the hollow structure, in terms of repeatability, must be carried out. To propose an approach that can very easily be reproduced, only commercial filaments are used. Full article
(This article belongs to the Special Issue 2D Materials based Flexible Sensors and Electronics)
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