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Micromachines, Volume 6, Issue 10 (October 2015)

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Open AccessArticle Analysis of Dynamic Properties of Piezoelectric Structure under Impact Load
Micromachines 2015, 6(10), 1577-1587; https://doi.org/10.3390/mi6101441
Received: 10 April 2015 / Revised: 8 October 2015 / Accepted: 12 October 2015 / Published: 21 October 2015
Cited by 5 | Viewed by 1641 | PDF Full-text (2839 KB) | HTML Full-text | XML Full-text
Abstract
An analytical model of the dynamic properties is established for a piezoelectric structure under impact load, without considering noise and perturbations in this paper. Based on the general theory of piezo-elasticity and impact mechanics, the theoretical solutions of the mechanical and electrical fields [...] Read more.
An analytical model of the dynamic properties is established for a piezoelectric structure under impact load, without considering noise and perturbations in this paper. Based on the general theory of piezo-elasticity and impact mechanics, the theoretical solutions of the mechanical and electrical fields of the smart structure are obtained with the standing and traveling wave methods, respectively. The comparisons between the two methods have shown that the standing wave method is better for studying long-time response after an impact load. In addition, good agreements are found between the theoretical and the numerical results. To simulate the impact load, both triangle and step pulse loads are used and comparisons are given. Furthermore, the influence of several parameters is discussed so as to provide some advices for practical use. It can be seen that the proposed analytical model would benefit, to some extent, the design and application (especially the airport runway) of the related smart devices by taking into account their impact load performance. Full article
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Open AccessArticle A Surface Micromachined CMOS MEMS Humidity Sensor
Micromachines 2015, 6(10), 1569-1576; https://doi.org/10.3390/mi6101440
Received: 31 August 2015 / Revised: 24 September 2015 / Accepted: 12 October 2015 / Published: 16 October 2015
Cited by 5 | Viewed by 2284 | PDF Full-text (5281 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports a CMOS MEMS (complementary metal oxide semiconductor micro electromechanical system) piezoresistive humidity sensor fabricated by a surface micromachining process. Both pre-CMOS and post-CMOS technologies were used to fabricate the piezoresistive humidity sensor. Compared with a bulk micromachined humidity sensor, the [...] Read more.
This paper reports a CMOS MEMS (complementary metal oxide semiconductor micro electromechanical system) piezoresistive humidity sensor fabricated by a surface micromachining process. Both pre-CMOS and post-CMOS technologies were used to fabricate the piezoresistive humidity sensor. Compared with a bulk micromachined humidity sensor, the machining precision and the sizes of the surface micromachined humidity sensor were both improved. The package and test systems of the sensor were designed. According to the test results, the sensitivity of the sensor was 7 mV/%RH (relative humidity) and the linearity of the sensor was 1.9% at 20 °C. Both the sensitivity and linearity were not sensitive to the temperature but the curve of the output voltage shifted with the temperature. The hysteresis of the humidity sensor decreased from 3.2% RH to 1.9% RH as the temperature increased from 10 to 40 °C. The recovery time of the sensor was 85 s at room temperature (25 °C). Full article
(This article belongs to the Special Issue CMOS-MEMS Sensors and Devices)
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Open AccessArticle Manufacturing and Characterization of a Thermoelectric Energy Harvester Using the CMOS-MEMS Technology
Micromachines 2015, 6(10), 1560-1568; https://doi.org/10.3390/mi6101439
Received: 15 September 2015 / Revised: 9 October 2015 / Accepted: 12 October 2015 / Published: 16 October 2015
Cited by 6 | Viewed by 1949 | PDF Full-text (13449 KB) | HTML Full-text | XML Full-text
Abstract
The fabrication and characterization of a thermoelectric energy harvester using the complementary metal oxide semiconductor (CMOS)-microelectromechanical system (MEMS) technology were presented. The thermoelectric energy harvester is composed of eight circular energy harvesting cells, and each cell consists of 25 thermocouples in series. The [...] Read more.
The fabrication and characterization of a thermoelectric energy harvester using the complementary metal oxide semiconductor (CMOS)-microelectromechanical system (MEMS) technology were presented. The thermoelectric energy harvester is composed of eight circular energy harvesting cells, and each cell consists of 25 thermocouples in series. The thermocouples are made of p-type and n-type polysilicons. The output power of the energy harvester relies on the number of the thermocouples. In order to enhance the output power, the energy harvester increases the thermocouple number per area. The energy harvester requires a post-CMOS process to etch the sacrificial silicon dioxide layer and the silicon substrate to release the suspended structures of hot part. The experimental results show that the energy harvester has an output voltage per area of 0.178 mV·mm−2·K−1 and a power factor of 1.47 × 10−3 pW·mm−2·K−2. Full article
(This article belongs to the Special Issue CMOS-MEMS Sensors and Devices)
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Open AccessArticle Paper-Based Electrodeposition Chip for 3D Alginate Hydrogel Formation
Micromachines 2015, 6(10), 1546-1559; https://doi.org/10.3390/mi6101438
Received: 6 September 2015 / Accepted: 13 October 2015 / Published: 15 October 2015
Cited by 6 | Viewed by 2760 | PDF Full-text (4224 KB) | HTML Full-text | XML Full-text
Abstract
Hydrogel has been regarded as one significant biomaterial in biomedical and tissue engineering due to its high biocompatibility. This paper proposes a novel method to pattern calcium alginate hydrogel in a 3D way via electrodeposition process based on a piece of paper. Firstly, [...] Read more.
Hydrogel has been regarded as one significant biomaterial in biomedical and tissue engineering due to its high biocompatibility. This paper proposes a novel method to pattern calcium alginate hydrogel in a 3D way via electrodeposition process based on a piece of paper. Firstly, one insulating paper with patterned holes is placed on one indium tin oxide (ITO) glass surface, which is put below another ITO glass. Then, 1% sodium alginate solution with 0.25% CaCO3 nano particles is filled between these two glasses. In the bottom glass, patterns of electrodes followed patterns of holes on the insulating layer. Hydrogel forms on patterned electrodes when electrochemical potential is applied due to electrodeposition. The experiments demonstrate that the pattern of alginate hydrogels follows the pattern of electrodes exactly. In addition, the hydrogel’s height is controllable by applied potential and reaction time. An equivalent circuit model and a hydrogel growth model have been built to predict the electrodeposition current and hydrogel’s growth. This method for gel formation is easy and cheap since the main material is one piece of insulated paper, which provides an easy and controllable method for 3D hydrogel patterning. Full article
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Open AccessArticle Dynamic Wet Etching of Silicon through Isopropanol Alcohol Evaporation
Micromachines 2015, 6(10), 1534-1545; https://doi.org/10.3390/mi6101437
Received: 1 August 2015 / Revised: 6 October 2015 / Accepted: 9 October 2015 / Published: 15 October 2015
Cited by 13 | Viewed by 2367 | PDF Full-text (12221 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, Isopropanol (IPA) availability during the anisotropic etching of silicon in Potassium Hydroxide (KOH) solutions was investigated. Squares of 8 to 40 µm were patterned to (100) oriented silicon wafers through DWL (Direct Writing Laser) photolithography. The wet etching process was [...] Read more.
In this paper, Isopropanol (IPA) availability during the anisotropic etching of silicon in Potassium Hydroxide (KOH) solutions was investigated. Squares of 8 to 40 µm were patterned to (100) oriented silicon wafers through DWL (Direct Writing Laser) photolithography. The wet etching process was performed inside an open HDPE (High Density Polyethylene) flask with ultrasonic agitation. IPA volume and evaporation was studied in a dynamic etching process, and subsequent influence on the silicon etching was inspected. For the tested conditions, evaporation rates for water vapor and IPA were determined as approximately 0.0417 mL/min and 0.175 mL/min, respectively. Results demonstrate that IPA availability, and not concentration, plays an important role in the definition of the final structure. Transversal SEM (Scanning Electron Microscopy) analysis demonstrates a correlation between microloading effects (as a consequence of structure spacing) and the angle formed towards the (100) plane. Full article
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Open AccessArticle Observation and Manipulation of a Capillary Jet in a Centrifuge-Based Droplet Shooting Device
Micromachines 2015, 6(10), 1526-1533; https://doi.org/10.3390/mi6101436
Received: 1 September 2015 / Accepted: 3 October 2015 / Published: 10 October 2015
Cited by 4 | Viewed by 2751 | PDF Full-text (4457 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report observation and manipulation of a capillary jet under ultra-high centrifugal gravity in a proposed capillary-based fluidic device for the synthesis of microparticles in a centrifugal tube called Centrifuge-Based Droplet Shooting Device (CDSD). Using a high-speed camera, we directly observed the dripping [...] Read more.
We report observation and manipulation of a capillary jet under ultra-high centrifugal gravity in a proposed capillary-based fluidic device for the synthesis of microparticles in a centrifugal tube called Centrifuge-Based Droplet Shooting Device (CDSD). Using a high-speed camera, we directly observed the dripping to jetting transition of a viscous capillary jet of water and Sodium alginate solution generated from a glass capillary-orifice of a diameter of O (100) m under centrifugal gravity ranging from 190 to 450 g. A non-dimensional analysis shows that the mechanism of the dripping-jetting transition in the CDSD may follow that previously reported for a dripping faucet under standard gravity. We also fabricated calcium alginate microparticles by gelating droplets of sodium alginate solution obtained in the break-up of the capillary jet in the jetting regime and demonstrated fabrication of microbeads-on-a-string structures. We confirmed that the jetting regime of the capillary jet could be used to fabricate smaller particles than that of the dripping regime. The results show that the CDSD would be a more useful device to fabricate various polymeric structures and understand the physics of fluid jets under ultra-high gravity. Full article
(This article belongs to the Special Issue Centrifugal (Compact-Disc) Microfluidics for Extreme POC)
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Open AccessArticle Droplet Microfluidic Technique for the Study of Fermentation
Micromachines 2015, 6(10), 1514-1525; https://doi.org/10.3390/mi6101435
Received: 14 August 2015 / Revised: 25 September 2015 / Accepted: 1 October 2015 / Published: 7 October 2015
Cited by 5 | Viewed by 2287 | PDF Full-text (4875 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrate a technique that uses microdroplets for culturing and selecting bacterial cultures in a model biotechnological application. We propose an assay for determination of ethanol concentration that provides increased dynamic range and is compatible with droplet microfluidic screening technologies. The assay comprises [...] Read more.
We demonstrate a technique that uses microdroplets for culturing and selecting bacterial cultures in a model biotechnological application. We propose an assay for determination of ethanol concentration that provides increased dynamic range and is compatible with droplet microfluidic screening technologies. The assay comprises two enzymes—alcohol oxidase (AOX) and horseradish peroxidase (HRP)—and a colorimetric readout system of phenol-4-sulfonic acid (PSA) and 4-aminoantipyrine (4-AAP). The microdroplet method provides high repeatability (a relative error of measured ethanol concentration < 5%), high specificity for ethanol, low consumption of reagents and wide dynamic range (1–70 g·L-1) compared to existing assays. We report the use of this method in a screen of ethanol generation efficiency of Zymomonas mobilis (strain 3881) against the concentration of glucose in the culture media. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle Refined Method for Droplet Microfluidics-Enabled Detection of Plasmodium falciparum Encoded Topoisomerase I in Blood from Malaria Patients
Micromachines 2015, 6(10), 1505-1513; https://doi.org/10.3390/mi6101432
Received: 17 August 2015 / Revised: 23 September 2015 / Accepted: 29 September 2015 / Published: 5 October 2015
Cited by 4 | Viewed by 2305 | PDF Full-text (4055 KB) | HTML Full-text | XML Full-text
Abstract
Rapid and reliable diagnosis is essential in the fight against malaria, which remains one of the most deadly infectious diseases in the world. In the present study we take advantage of a droplet microfluidics platform combined with a novel and user-friendly biosensor for [...] Read more.
Rapid and reliable diagnosis is essential in the fight against malaria, which remains one of the most deadly infectious diseases in the world. In the present study we take advantage of a droplet microfluidics platform combined with a novel and user-friendly biosensor for revealing the main malaria-causing agent, the Plasmodium falciparum (P. falciparum) parasite. Detection of the parasite is achieved through detection of the activity of a parasite-produced DNA-modifying enzyme, topoisomerase I (pfTopoI), in the blood from malaria patients. The assay presented has three steps: (1) droplet microfluidics-enabled extraction of active pfTopoI from a patient blood sample; (2) pfTopoI-mediated modification of a specialized DNA biosensor; (3) readout. The setup is quantitative and specific for the detection of Plasmodium topoisomerase I. The procedure is a considerable improvement of the previously published Rolling Circle Enhanced Enzyme Activity Detection (REEAD) due to the advantages of involving no signal amplification steps combined with a user-friendly readout. In combination these alterations represent an important step towards exploiting enzyme activity detection in point-of-care diagnostics of malaria. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle Enhancing Throughput of Combinatorial Droplet Devices via Droplet Bifurcation, Parallelized Droplet Fusion, and Parallelized Detection
Micromachines 2015, 6(10), 1490-1504; https://doi.org/10.3390/mi6101434
Received: 3 August 2015 / Revised: 23 September 2015 / Accepted: 24 September 2015 / Published: 5 October 2015
Cited by 3 | Viewed by 2249 | PDF Full-text (8434 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Combinatorial droplet microfluidic devices with programmable microfluidic valves have recently emerged as a viable approach for performing multiplexed experiments in microfluidic droplets. However, the serial operation in these devices restricts their throughput. To address this limitation, we present a parallelized combinatorial droplet device [...] Read more.
Combinatorial droplet microfluidic devices with programmable microfluidic valves have recently emerged as a viable approach for performing multiplexed experiments in microfluidic droplets. However, the serial operation in these devices restricts their throughput. To address this limitation, we present a parallelized combinatorial droplet device that enhances device throughput via droplet bifurcation, parallelized droplet fusion, and parallelized droplet detection. In this device, sample droplets split evenly at bifurcating Y-junctions before multiple independent reagent droplets are injected directly into the split sample droplets for robust droplet fusion. Finally, the fused sample and reagent droplets can be imaged in parallel via microscopy. The combination of these approaches enabled us to improve the throughput over traditional, serially-operated combinatorial droplet devices by 16-fold—with ready potential for further enhancement. Given its current performance and prospect for future improvements, we believe the parallelized combinatorial droplet device has the potential to meet the demand as a flexible and cost-effective tool that can perform high throughput screening applications. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle Ultrafast Laser Engraving Method to Fabricate Gravure Plate for Printed Metal-Mesh Touch Panel
Micromachines 2015, 6(10), 1483-1489; https://doi.org/10.3390/mi6101433
Received: 9 July 2015 / Revised: 17 September 2015 / Accepted: 26 September 2015 / Published: 5 October 2015
Cited by 1 | Viewed by 2940 | PDF Full-text (11147 KB) | HTML Full-text | XML Full-text
Abstract
In order to engrave gravure plate with fine lines structures, conventional art used lithography with dry/wet etching. Lithography with dry/wet etching method allows to engrave lines with smooth concave shape, but its disadvantages include difficulty in controlling aspect ratio, high and uniform in [...] Read more.
In order to engrave gravure plate with fine lines structures, conventional art used lithography with dry/wet etching. Lithography with dry/wet etching method allows to engrave lines with smooth concave shape, but its disadvantages include difficulty in controlling aspect ratio, high and uniform in large size process, substrate material limitation due to etching solution availability, and process complexity. We developed ultra-fast laser technology to directly engrave a stainless plate, a gravure plate, to be used for fabricating 23 in. metal-mesh touch panel by gravure offset printing process. The technology employs high energy pulse to ablate materials from a substrate. Because the ultra-fast laser pulse duration is shorter than the energy dissipation time between material lattices, there is no heating issue during the ablation process. Therefore, no volcano-type protrusion on the engraved line edges occurs, leading to good printing quality. After laser engraving, we then reduce surface roughness of the gravure plate using electro-polishing process. Diamond like carbon (DLC) coating layer is then added onto the surface to increase scratch resistance. We show that this procedure can fabricate gravure plate for gravure offset printing process with minimum printing linewidth 10.7 μm. A 23 in. metal-mesh pattern was printed using such gravure plate and fully functional touch panel was demonstrated in this work. Full article
(This article belongs to the collection Laser Micromachining and Microfabrication)
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Open AccessArticle Floating Droplet Array: An Ultrahigh-Throughput Device for Droplet Trapping, Real-time Analysisand Recovery
Micromachines 2015, 6(10), 1469-1482; https://doi.org/10.3390/mi6101431
Received: 17 August 2015 / Revised: 22 September 2015 / Accepted: 25 September 2015 / Published: 30 September 2015
Cited by 9 | Viewed by 3755 | PDF Full-text (8525 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We describe the design, fabrication and use of a dual-layered microfluidic device for ultrahigh-throughput droplet trapping, analysis, and recovery using droplet buoyancy. To demonstrate the utility of this device for digital quantification of analytes, we quantify the number of droplets, which contain a [...] Read more.
We describe the design, fabrication and use of a dual-layered microfluidic device for ultrahigh-throughput droplet trapping, analysis, and recovery using droplet buoyancy. To demonstrate the utility of this device for digital quantification of analytes, we quantify the number of droplets, which contain a β-galactosidase-conjugated bead among more than 100,000 immobilized droplets. In addition, we demonstrate that this device can be used for droplet clustering and real-time analysis by clustering several droplets together into microwells and monitoring diffusion of fluorescein, a product of the enzymatic reaction of β-galactosidase and its fluorogenic substrate FDG, between droplets. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle Shielding Electric Fields to Prevent Coalescence of Emulsions in Microfluidic Channels Using a 3D Metallic Coil
Micromachines 2015, 6(10), 1459-1468; https://doi.org/10.3390/mi6101430
Received: 14 August 2015 / Revised: 16 September 2015 / Accepted: 23 September 2015 / Published: 30 September 2015
Viewed by 2656 | PDF Full-text (3012 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In microfluidics, electric fields are widely used to assist the generation and the manipulation of droplets or jets. However, uncontrolled electric field can disrupt the operation of an integrated microfluidic system, for instance, through undesired coalescence of droplets, undesired changes in the wettability [...] Read more.
In microfluidics, electric fields are widely used to assist the generation and the manipulation of droplets or jets. However, uncontrolled electric field can disrupt the operation of an integrated microfluidic system, for instance, through undesired coalescence of droplets, undesired changes in the wettability of the channel wall or unexpected death of cells. Therefore, an approach to control the distribution of electric fields inside microfluidic channels is needed. Inspired by the electro-magnetic shielding effect in electrical and radiation systems, we demonstrate the shielding of electric fields by incorporating 3D metallic coils in microfluidic devices. Using the degree of coalescence of emulsion drops as an indicator, we have shown that electric fields decrease dramatically in micro-channels surrounded by these conductive metallic coils both experimentally and numerically. Our work illustrates an approach to distribute electric fields in integrated microfluidic networks by selectively installing metallic coils or electrodes, and represents a significant step towards large-scale electro-microfluidic systems. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle Hydrophilic Surface Modification of PDMS Microchannel for O/W and W/O/W Emulsions
Micromachines 2015, 6(10), 1445-1458; https://doi.org/10.3390/mi6101429
Received: 21 August 2015 / Revised: 11 September 2015 / Accepted: 16 September 2015 / Published: 29 September 2015
Cited by 8 | Viewed by 2695 | PDF Full-text (4104 KB) | HTML Full-text | XML Full-text
Abstract
A surface modification method for bonded polydimethylsiloxane (PDMS) microchannels is presented herein. Polymerization of acrylic acid was performed on the surface of a microchannel using an inline atmospheric pressure dielectric barrier microplasma technique. The surface treatment changes the wettability of the microchannel from [...] Read more.
A surface modification method for bonded polydimethylsiloxane (PDMS) microchannels is presented herein. Polymerization of acrylic acid was performed on the surface of a microchannel using an inline atmospheric pressure dielectric barrier microplasma technique. The surface treatment changes the wettability of the microchannel from hydrophobic to hydrophilic. This is a challenging task due to the fast hydrophobic recovery of the PDMS surface after modification. This modification allows the formation of highly monodisperse oil-in-water (O/W) droplets. The generation of water-in-oil-in-water (W/O/W) double emulsions was successfully achieved by connecting in series a hydrophobic microchip with a modified hydrophilic microchip. An original channel blocking technique to pattern the surface wettability of a specific section of a microchip using a viscous liquid comprising a mixture of honey and glycerol, is also presented for generating W/O/W emulsions on a single chip. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle Biconvex Polymer Microlenses with Tunable Imaging Properties Designed by Janus Droplet Microfluidics
Micromachines 2015, 6(10), 1435-1444; https://doi.org/10.3390/mi6101428
Received: 26 August 2015 / Revised: 17 September 2015 / Accepted: 22 September 2015 / Published: 29 September 2015
Cited by 7 | Viewed by 2061 | PDF Full-text (6114 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This work presents a technique for fabricating biconvex polymer microlenses using microfluidics, and then evaluates their tunable optical properties. A glass microfluidic channel was employed to rapidly mass-produce nanoliter-sized biphasic Janus droplets, which consist of a biconvex segment of a photocurable monomer and [...] Read more.
This work presents a technique for fabricating biconvex polymer microlenses using microfluidics, and then evaluates their tunable optical properties. A glass microfluidic channel was employed to rapidly mass-produce nanoliter-sized biphasic Janus droplets, which consist of a biconvex segment of a photocurable monomer and a concave-convex segment of a non-curable silicone oil that contained a surfactant. Subsequent photopolymerization produces polymeric biconvex spherical microlenses with templated dual curvatures. By changing the flow-rate ratios of the photocurable and non-curable droplet phases in the microfluidic channel, the radii of curvature of the two lens surfaces and the thicknesses of the resultant microlenses can be varied. The resulting biconvex microlenses with different shapes were used in image projection experiments. Different magnification properties were observed, and were consistent with the properties estimated quantitatively from the geometrical parameters of the lenses. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies)
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Open AccessArticle Investigation of Micro Square Structure Fabrication by Applying Textured Cutting Tool in WEDM
Micromachines 2015, 6(10), 1427-1434; https://doi.org/10.3390/mi6101427
Received: 7 August 2015 / Revised: 29 August 2015 / Accepted: 17 September 2015 / Published: 25 September 2015
Cited by 5 | Viewed by 1718 | PDF Full-text (2851 KB) | HTML Full-text | XML Full-text
Abstract
This paper studies micro structure fabrication by means of a textured tool cutting edge, which is manufactured by applying the wire cut electrical discharge machining (WEDM). Machining performance of the square structure fabrication on the tool cutting edge is investigated in the WEDM [...] Read more.
This paper studies micro structure fabrication by means of a textured tool cutting edge, which is manufactured by applying the wire cut electrical discharge machining (WEDM). Machining performance of the square structure fabrication on the tool cutting edge is investigated in the WEDM process, and the machining accuracy is explored in experimental analyses. In this proposed method, undesired overcut comes from the discharge between the processing debris and the side wall of the target structure. Furthermore, by applying the textured cutting tool, the target square structure is directly fabricated on the alumina workpiece with just a simple turning process, which verifies the feasibility of the proposed tool cutting edge textured method by applying the WEDM. This technology is expected to become a potential method for the mass production of micro structure surfaces in the future. Full article
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Open AccessCommunication Frequency Selective Surfaces with Nanoparticles Unit Cell
Micromachines 2015, 6(10), 1421-1426; https://doi.org/10.3390/mi6101421
Received: 20 July 2015 / Revised: 3 September 2015 / Accepted: 14 September 2015 / Published: 25 September 2015
Viewed by 2129
Abstract
The frequency selective surface (FSS) is a periodic structure with filtering performance for optical and microwave signals. The general periodic arrays made with patterned metallic elements can act as an aperture or patch on a substrate. In this work, two kinds of materials [...] Read more.
The frequency selective surface (FSS) is a periodic structure with filtering performance for optical and microwave signals. The general periodic arrays made with patterned metallic elements can act as an aperture or patch on a substrate. In this work, two kinds of materials were used to produce unit cells with various patterns. Gold nanoparticles of 25 nm diameter were used to form periodic monolayer arrays by a confined photocatalytic oxidation-based surface modification method. As the other material, silver gel was used to create multiple layers of silver. Due to the ultra-thin nature of the self-assembled gold nanoparticle monolayer, it is very easy to penetrate the FSS with terahertz radiation. However, the isolated silver islands made from silver gel form thicker multiple layers and contribute to much higher reflectance. This work demonstrated that multiple silver layers are more suitable than gold nanoparticles for use in the fabrication of FSS structures. Full article
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