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Micromachines, Volume 8, Issue 2 (February 2017)

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Cover Story (view full-size image) We present a novel approach to the rapid and green fabrication of highly conductive patterns on [...] Read more.
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Open AccessArticle Droplet Microfluidics Approach for Single-DNA Molecule Amplification and Condensation into DNA-Magnesium-Pyrophosphate Particles
Micromachines 2017, 8(2), 62; https://doi.org/10.3390/mi8020062
Received: 7 December 2016 / Revised: 3 February 2017 / Accepted: 14 February 2017 / Published: 20 February 2017
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Abstract
Protein expression in vitro has broad applications in directed evolution, synthetic biology, proteomics and drug screening. However, most of the in vitro expression systems rely on relatively high DNA template concentrations to obtain sufficient amounts of proteins, making it harder to perform in
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Protein expression in vitro has broad applications in directed evolution, synthetic biology, proteomics and drug screening. However, most of the in vitro expression systems rely on relatively high DNA template concentrations to obtain sufficient amounts of proteins, making it harder to perform in vitro screens on gene libraries. Here, we report a technique for the generation of condensed DNA particles that can serve as efficient templates for in vitro gene expression. We apply droplet microfluidics to encapsulate single-DNA molecules in 3-picoliter (pL) volume droplets and convert them into 1 μm-sized DNA particles by the multiple displacement amplification reaction driven by phi29 DNA polymerase. In the presence of magnesium ions and inorganic pyrophosphate, the amplified DNA condensed into the crystalline-like particles, making it possible to purify them from the reaction mix by simple centrifugation. Using purified DNA particles, we performed an in vitro transcription-translation reaction and successfully expressed complex enzyme β-galactosidase in droplets and in the 384-well format. The yield of protein obtained from DNA particles was significantly higher than from the corresponding amount of free DNA templates, thus opening new possibilities for high throughput screening applications. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies, Volume II)
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Open AccessErratum Erratum: Hayakawa, M., et al. Influence of Asymmetry and Driving Forces on the Propulsion of Bubble-Propelled Catalytic Micromotors. Micromachines 2016, 7, 229
Micromachines 2017, 8(2), 61; https://doi.org/10.3390/mi8020061
Received: 14 February 2017 / Revised: 14 February 2017 / Accepted: 17 February 2017 / Published: 20 February 2017
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Open AccessArticle Visible to Infrared Diamond Photonics Enabled by Focused Femtosecond Laser Pulses
Micromachines 2017, 8(2), 60; https://doi.org/10.3390/mi8020060
Received: 18 January 2017 / Revised: 10 February 2017 / Accepted: 13 February 2017 / Published: 17 February 2017
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Abstract
Diamond’s nitrogen-vacancy (NV) centers show great promise in sensing applications and quantum computing due to their long electron spin coherence time and because they can be found, manipulated, and read out optically. An important step forward for diamond photonics would be connecting multiple
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Diamond’s nitrogen-vacancy (NV) centers show great promise in sensing applications and quantum computing due to their long electron spin coherence time and because they can be found, manipulated, and read out optically. An important step forward for diamond photonics would be connecting multiple diamond NVs together using optical waveguides. However, the inertness of diamond is a significant hurdle for the fabrication of integrated optics similar to those that revolutionized silicon photonics. In this work, we show the fabrication of optical waveguides in diamond, enabled by focused femtosecond high repetition rate laser pulses. By optimizing the geometry of the waveguide, we obtain single mode waveguides from the visible to the infrared. Additionally, we show the laser writing of individual NV centers within the bulk of diamond. We use µ-Raman spectroscopy to gain better insight on the stress and the refractive index profile of the optical waveguides. Using optically detected magnetic resonance and confocal photoluminescence characterization, high quality NV properties are observed in waveguides formed in various grades of diamond, making them promising for applications such as magnetometry, quantum information systems, and evanescent field sensors. Full article
(This article belongs to the collection Laser Micromachining and Microfabrication)
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Open AccessReview Internal Laser Writing of High-Aspect-Ratio Microfluidic Structures in Silicate Glasses for Lab-on-a-Chip Applications
Micromachines 2017, 8(2), 59; https://doi.org/10.3390/mi8020059
Received: 21 December 2016 / Revised: 8 February 2017 / Accepted: 9 February 2017 / Published: 16 February 2017
Cited by 3 | PDF Full-text (6173 KB) | HTML Full-text | XML Full-text
Abstract
Femtosecond laser direct writing is unique in allowing for fabrication of 3D micro- and nanofluidic structures, thereby enabling rapid and efficient manipulation of fluidic dynamics in 3D space to realize innovative functionalities. Here, I discuss the challenges in producing fully functional and highly
[...] Read more.
Femtosecond laser direct writing is unique in allowing for fabrication of 3D micro- and nanofluidic structures, thereby enabling rapid and efficient manipulation of fluidic dynamics in 3D space to realize innovative functionalities. Here, I discuss the challenges in producing fully functional and highly integrated 3D micro- and nanofluidic systems with potential applications ranging from chemical and biological analyses to investigations of nanofluidic behaviors. In particular, I review the achievements we have made in the past decade, which have led to 3D microchannels with controllable cross-sectional profiles and large aspect ratios, 3D nanofluidic channels with widths of several tens of nanometers, and smooth inner walls with roughness on the order of ~1 nm. Integration of the microfluidics with other functional microcomponents including microoptics and microelectrodes will also be discussed, followed by conclusions and the future perspective. Full article
(This article belongs to the Special Issue Ultrafast Laser Fabrication for Lab-on-a-Chip)
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Open AccessArticle Optical Flow Cell for Measuring Size, Velocity and Composition of Flowing Droplets
Micromachines 2017, 8(2), 58; https://doi.org/10.3390/mi8020058
Received: 23 November 2016 / Revised: 21 January 2017 / Accepted: 9 February 2017 / Published: 16 February 2017
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Abstract
Here an optical flow cell with two light paths is reported that can accurately quantify the size and velocity of droplets flowing through a microchannel. The flow cell can measure the time taken for droplets to pass between and through two conjoined light
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Here an optical flow cell with two light paths is reported that can accurately quantify the size and velocity of droplets flowing through a microchannel. The flow cell can measure the time taken for droplets to pass between and through two conjoined light paths, and thereby is capable of measuring the velocities (0.2–5.45 mm/s) and sizes of droplets (length > 0.8 mm). The composition of the droplet can also be accurately quantified via optical absorption measurements. The device has a small footprint and uses low-powered, low-cost components, which make it ideally suited for use in field-deployable and portable analytical devices. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies, Volume II)
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Open AccessArticle Droplet Dynamics of Newtonian and Inelastic Non-Newtonian Fluids in Confinement
Micromachines 2017, 8(2), 57; https://doi.org/10.3390/mi8020057
Received: 30 November 2016 / Accepted: 8 February 2017 / Published: 15 February 2017
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Abstract
Microfluidic droplet technology has been developing rapidly. However, precise control of dynamical behaviour of droplets remains a major hurdle for new designs. This study is to understand droplet deformation and breakup under simple shear flow in confined environment as typically found in microfluidic
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Microfluidic droplet technology has been developing rapidly. However, precise control of dynamical behaviour of droplets remains a major hurdle for new designs. This study is to understand droplet deformation and breakup under simple shear flow in confined environment as typically found in microfluidic applications. In addition to the Newtonian–Newtonian system, we consider also both a Newtonian droplet in a non-Newtonian matrix fluid and a non-Newtonian droplet in a Newtonian matrix. The lattice Boltzmann method is adopted to systematically investigate droplet deformation and breakup under a broad range of capillary numbers, viscosity ratios of the fluids, and confinement ratios considering shear-thinning and shear-thickening fluids. Confinement is found to enhance deformation, and the maximum deformation occurs at the viscosity ratio of unity. The droplet orients more towards the flow direction with increasing viscosity ratio or confinement ratio. In addition, it is noticed that the wall effect becomes more significant for confinement ratios larger than 0.4. Finally, for the whole range of Newtonian carrier fluids tested, the critical capillary number above which droplet breakup occurs is only slightly affected by the confinement ratio for a viscosity ratio of unity. Upon increasing the confinement ratio, the critical capillary number increases for the viscosity ratios less than unity, but decreases for the viscosity ratios more than unity. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies, Volume II)
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Open AccessFeature PaperReview Faraday Waves-Based Integrated Ultrasonic Micro-Droplet Generator and Applications
Micromachines 2017, 8(2), 56; https://doi.org/10.3390/mi8020056
Received: 6 November 2016 / Revised: 30 January 2017 / Accepted: 3 February 2017 / Published: 14 February 2017
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Abstract
An in-depth review on a new ultrasonic micro-droplet generator which utilizes megahertz (MHz) Faraday waves excited by silicon-based multiple Fourier horn ultrasonic nozzles (MFHUNs) and its potential applications is presented. The new droplet generator has demonstrated capability for producing micro droplets of controllable
[...] Read more.
An in-depth review on a new ultrasonic micro-droplet generator which utilizes megahertz (MHz) Faraday waves excited by silicon-based multiple Fourier horn ultrasonic nozzles (MFHUNs) and its potential applications is presented. The new droplet generator has demonstrated capability for producing micro droplets of controllable size and size distribution and desirable throughput at very low electrical drive power. For comparison, the serious deficiencies of current commercial droplet generators (nebulizers) and the other ultrasonic droplet generators explored in recent years are first discussed. The architecture, working principle, simulation, and design of the multiple Fourier horns (MFH) in resonance aimed at the amplified longitudinal vibration amplitude on the end face of nozzle tip, and the fabrication and characterization of the nozzles are then described in detail. Subsequently, a linear theory on the temporal instability of Faraday waves on a liquid layer resting on the planar end face of the MFHUN and the detailed experimental verifications are presented. The linear theory serves to elucidate the dynamics of droplet ejection from the free liquid surface and predict the vibration amplitude onset threshold for droplet ejection and the droplet diameters. A battery-run pocket-size clogging-free integrated micro droplet generator realized using the MFHUN is then described. The subsequent report on the successful nebulization of a variety of commercial pulmonary medicines against common diseases and on the experimental antidote solutions to cyanide poisoning using the new droplet generator serves to support its imminent application to inhalation drug delivery. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies, Volume II)
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Open AccessArticle Ultrasonic Spray-Coating of Large-Scale TiO2 Compact Layer for Efficient Flexible Perovskite Solar Cells
Micromachines 2017, 8(2), 55; https://doi.org/10.3390/mi8020055
Received: 31 December 2016 / Revised: 23 January 2017 / Accepted: 26 January 2017 / Published: 14 February 2017
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Abstract
Flexible electronics have attracted great interest in applications for the wearable devices. Flexible solar cells can be integrated into the flexible electronics as the power source for the wearable devices. In this work, an ultrasonic spray-coating method was employed to deposit TiO2
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Flexible electronics have attracted great interest in applications for the wearable devices. Flexible solar cells can be integrated into the flexible electronics as the power source for the wearable devices. In this work, an ultrasonic spray-coating method was employed to deposit TiO2 nanoparticles on polymer substrates for the fabrication of flexible perovskite solar cells (PSCs). Pre-synthesized TiO2 nanoparticles were first dispersed in ethanol to prepare the precursor solutions with different concentrations (0.5 mg/mL, 1.0 mg/mL, 2.0 mg/mL) and then sprayed onto the conductive substrates to produce compact TiO2 films with different thicknesses (from 30 nm to 150 nm). The effect of the different drying processes on the quality of the compact TiO2 film was studied. In order to further improve the film quality, titanium diisopropoxide bis(acetylacetonate) (TAA) was added into the TiO2-ethanol solution at a mole ratio of 1.0 mol % with respect to the TiO2 content. The final prepared PSC devices showed a power conversion efficiency (PCE) of 14.32% based on the indium doped tin oxide coated glass (ITO-glass) substrate and 10.87% on the indium doped tin oxide coated polyethylene naphthalate (ITO-PEN) flexible substrate. Full article
(This article belongs to the Special Issue Flexible and Stretchable Electronics) Printed Edition available
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Open AccessArticle Performance Analysis of Double-Layer Microchannel Heat Sinks under Non-Uniform Heating Conditions with Random Hotspots
Micromachines 2017, 8(2), 54; https://doi.org/10.3390/mi8020054
Received: 24 December 2016 / Revised: 20 January 2017 / Accepted: 7 February 2017 / Published: 14 February 2017
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Abstract
Performance analysis of double-layer microchannel heat sinks was performed under non-uniform heating conditions having randomly distributed hotspots. Two parallel-channel (parallel-flow and counter-flow) and one cross-channel (transverse-flow) designs of double-layer heat sink were evaluated with three sets of heating schemes. Each set of heating
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Performance analysis of double-layer microchannel heat sinks was performed under non-uniform heating conditions having randomly distributed hotspots. Two parallel-channel (parallel-flow and counter-flow) and one cross-channel (transverse-flow) designs of double-layer heat sink were evaluated with three sets of heating schemes. Each set of heating scheme consisted of eleven randomly distributed hotspots generated by Latin hypercube sampling. The heat flux, area, and location of the hotspots were selected as the design parameters. Conjugate heat transfer analysis of the heat sinks was performed by solving three-dimensional Navier–Stokes and energy equations. Water with temperature-dependent properties was selected as the coolant. The thermal resistance, pressure drop, maximum temperature rise, and temperature variation among hotspots were evaluated for all the heat sinks. The transverse-flow microchannel heat sink exhibited the lowest thermal resistance, temperature rise and temperature variation among the hotspots throughout the specified range of flow rate. The lowest pressure drop was exhibited by the counter-flow heat sink. Full article
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Open AccessReview Micro-Hole Drilling on Glass Substrates—A Review
Micromachines 2017, 8(2), 53; https://doi.org/10.3390/mi8020053
Received: 14 November 2016 / Revised: 18 January 2017 / Accepted: 3 February 2017 / Published: 13 February 2017
Cited by 7 | PDF Full-text (1207 KB) | HTML Full-text | XML Full-text
Abstract
Glass micromachining is currently becoming essential for the fabrication of micro-devices, including micro- optical-electro-mechanical-systems (MOEMS), miniaturized total analysis systems (μTAS) and microfluidic devices for biosensing. Moreover, glass is radio frequency (RF) transparent, making it an excellent material for sensor and energy transmission devices.
[...] Read more.
Glass micromachining is currently becoming essential for the fabrication of micro-devices, including micro- optical-electro-mechanical-systems (MOEMS), miniaturized total analysis systems (μTAS) and microfluidic devices for biosensing. Moreover, glass is radio frequency (RF) transparent, making it an excellent material for sensor and energy transmission devices. Advancements are constantly being made in this field, yet machining smooth through-glass vias (TGVs) with high aspect ratio remains challenging due to poor glass machinability. As TGVs are required for several micro-devices, intensive research is being carried out on numerous glass micromachining technologies. This paper reviews established and emerging technologies for glass micro-hole drilling, describing their principles of operation and characteristics, and their advantages and disadvantages. These technologies are sorted into four machining categories: mechanical, thermal, chemical, and hybrid machining (which combines several machining methods). Achieved features by these methods are summarized in a table and presented in two graphs. We believe that this paper will be a valuable resource for researchers working in the field of glass micromachining as it provides a comprehensive review of the different glass micromachining technologies. It will be a useful guide for advancing these techniques and establishing new hybrid ones, especially since this is the first broad review in this field. Full article
(This article belongs to the Special Issue Glass Micromachining)
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Open AccessArticle Direct Silver Micro Circuit Patterning on Transparent Polyethylene Terephthalate Film Using Laser-Induced Photothermochemical Synthesis
Micromachines 2017, 8(2), 52; https://doi.org/10.3390/mi8020052
Received: 16 January 2017 / Revised: 2 February 2017 / Accepted: 6 February 2017 / Published: 13 February 2017
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Abstract
This study presents a new and improved approach to the rapid and green fabrication of highly conductive microscale silver structures on low-cost transparent polyethylene terephthalate (PET) flexible substrate. In this new laser direct synthesis and pattering (LDSP) process, silver microstructures are simultaneously synthesized
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This study presents a new and improved approach to the rapid and green fabrication of highly conductive microscale silver structures on low-cost transparent polyethylene terephthalate (PET) flexible substrate. In this new laser direct synthesis and pattering (LDSP) process, silver microstructures are simultaneously synthesized and laid down in a predetermined pattern using a low power continuous wave (CW) laser. The silver ion processing solution, which is transparent and reactive, contains a red azo dye as the absorbing material. The silver pattern is formed by photothermochemical reduction of the silver ions induced by the focused CW laser beam. In this improved LDSP process, the non-toxic additive in the transparent ionic solution absorbs energy from a low cost CW visible laser without the need for the introduction of any hazardous chemical process. Tests were carried out to determine the durability of the conductive patterns, and numerical analyses of the thermal and fluid transport were performed to investigate the morphology of the deposited patterns. This technology is an advanced method for preparing micro-scale circuitry on an inexpensive, flexible, and transparent polymer substrate that is fast, environmentally benign, and shows potential for Roll-to-Roll manufacture. Full article
(This article belongs to the Special Issue Flexible and Stretchable Electronics) Printed Edition available
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Open AccessArticle Development of MEMS Multi-Mode Electrostatic Energy Harvester Based on the SOI Process
Micromachines 2017, 8(2), 51; https://doi.org/10.3390/mi8020051
Received: 6 December 2016 / Revised: 23 January 2017 / Accepted: 8 February 2017 / Published: 13 February 2017
Cited by 2 | PDF Full-text (11797 KB) | HTML Full-text | XML Full-text
Abstract
Multi-vibrational-mode electrostatic energy harvesters are designed and micro-machined utilizing a simple silicon-on-insulator (SOI) wafer-based process. Enhanced adaptability to various vibrational environments is achieved in the proposed design by using serpentine springs attached to the fishbone-shaped inertial mass. The experimental results show that the
[...] Read more.
Multi-vibrational-mode electrostatic energy harvesters are designed and micro-machined utilizing a simple silicon-on-insulator (SOI) wafer-based process. Enhanced adaptability to various vibrational environments is achieved in the proposed design by using serpentine springs attached to the fishbone-shaped inertial mass. The experimental results show that the developed device could convert an input vibration of 6 g at 1272 Hz to 2.96, 3.28, and 2.30 μW for different vibrational directions of 0°, 30°, and 45° with respect to a reference direction, respectively, when all serpentine springs are identical. An alternative device design using serpentine springs with different stiffnesses between x- and y-axes exhibited resonance frequencies at 1059 and 1635 Hz for an input vibrational direction of 45° and acceleration amplitude of 4 g, successfully generating 0.723 and 0.927 μW of electrical power at each resonance, respectively. Full article
(This article belongs to the Special Issue MEMS Energy Harvesters)
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Open AccessFeature PaperArticle The Effects of Profile Errors of Microlens Surfaces on Laser Beam Homogenization
Micromachines 2017, 8(2), 50; https://doi.org/10.3390/mi8020050
Received: 4 January 2017 / Revised: 6 February 2017 / Accepted: 8 February 2017 / Published: 13 February 2017
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Abstract
Microlens arrays (MLAs) are key optical components in laser beam homogenization. However, due to imperfect surface profiles resulting from microfabrication, the functionalities of MLAs in beam modulation could be compromised to some extent. In order to address this issue, the effects of surface
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Microlens arrays (MLAs) are key optical components in laser beam homogenization. However, due to imperfect surface profiles resulting from microfabrication, the functionalities of MLAs in beam modulation could be compromised to some extent. In order to address this issue, the effects of surface profile mismatches between ideal and fabricated MLAs on beam homogenization were analyzed. Four types of surface profile errors of MLAs were modeled theoretically and numerical simulations were conducted to quantitatively estimate the effects of these profile errors on beam homogenization. In addition, experiments were conducted to validate the simulation results, revealing that profile errors leading to optical deviations located on the apex of microlenses affected beam homogenization less than deviations located further away from it. This study can provide references for the further applications of MLAs in beam homogenization. Full article
(This article belongs to the Special Issue Micro/Nano Manufacturing) Printed Edition available
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Open AccessArticle Analysis of Liquid–Liquid Droplets Fission and Encapsulation in Single/Two Layer Microfluidic Devices Fabricated by Xurographic Method
Micromachines 2017, 8(2), 49; https://doi.org/10.3390/mi8020049
Received: 16 December 2016 / Revised: 26 January 2017 / Accepted: 4 February 2017 / Published: 10 February 2017
Cited by 3 | PDF Full-text (5844 KB) | HTML Full-text | XML Full-text
Abstract
This paper demonstrates a low cost fabrication approach for microscale droplet fission and encapsulation. Using a modified xurography method, rapid yet reliable microfluidic devices with flexible designs (single layer and double layer) are developed to enable spatial control of droplet manipulation. In this
[...] Read more.
This paper demonstrates a low cost fabrication approach for microscale droplet fission and encapsulation. Using a modified xurography method, rapid yet reliable microfluidic devices with flexible designs (single layer and double layer) are developed to enable spatial control of droplet manipulation. In this paper, two different designs are demonstrated, i.e., droplet fission (single layer) and droplet encapsulation (double layer). In addition, the current fabrication approach reduces the overall production interval with the introduction of a custom-made polydimethylsiloxane (PDMS) aligner. Apart from that, the fabricated device is able to generate daughter droplets with the coefficient of variance (CV) below 5% and double emulsions with CV maintained within 10% without involvement of complex surface wettability modification. Full article
(This article belongs to the Special Issue Insights and Advancements in Microfluidics) Printed Edition available
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Open AccessArticle Laser Fabrication of Miniature Internal Thread in Glass Substrate
Micromachines 2017, 8(2), 48; https://doi.org/10.3390/mi8020048
Received: 21 December 2016 / Revised: 1 February 2017 / Accepted: 3 February 2017 / Published: 8 February 2017
Cited by 2 | PDF Full-text (789 KB) | HTML Full-text | XML Full-text
Abstract
Miniature internal threads (tapped holes) of S0.5 were fabricated in a glass substrate. Water-assisted laser drilling was applied for fabrication of the threads of S0.5 standard using a subnanosecond laser as a light source. The landscape of the inner surface of the threads
[...] Read more.
Miniature internal threads (tapped holes) of S0.5 were fabricated in a glass substrate. Water-assisted laser drilling was applied for fabrication of the threads of S0.5 standard using a subnanosecond laser as a light source. The landscape of the inner surface of the threads was measured by a laser microscope, and showed reasonable agreement with the desired standard. As a proof of concept, a commercial external screw was fitted to the fabricated internal thread. Full article
(This article belongs to the Special Issue Ultrafast Laser Fabrication for Lab-on-a-Chip)
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