Micromachines

6627 KiB

Open AccessArticle

Electroosmotic Flows of Power-Law Fluids with Asymmetric Electrochemical Boundary Conditions in a Rectangular Microchannel

by WooSeok Choi, Sungchan Yun and Du-Soon Choi

Micromachines 2017, 8(5), 165; https://doi.org/10.3390/mi8050165 - 20 May 2017

Cited by 6 | Viewed by 3871

Abstract

In this paper, a systematic study of a fully developed electroosmotic flow of power-law fluids in a rectangular microchannel bounded by walls with different zeta potentials is described. Because the upper and lower layers of most microchannels are made of different materials, it [...] Read more.

In this paper, a systematic study of a fully developed electroosmotic flow of power-law fluids in a rectangular microchannel bounded by walls with different zeta potentials is described. Because the upper and lower layers of most microchannels are made of different materials, it is necessary to study the flow characteristics for cases in which the microchannels have different zeta potentials at each wall. The electrical potential and momentum equations were solved numerically using a finite element analysis. The velocity profiles and flow rates were studied parametrically by varying the fluid behavior index, channel aspect ratio, and electrochemical properties of the liquid and the bounding walls. The calculated volumetric flow rates in a rectangular microchannel were compared with those between two infinite parallel plates. Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)

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2076 KiB

Open AccessArticle

Rapid and Effective Electrical Conductivity Improvement of the Ag NW-Based Conductor by Using the Laser-Induced Nano-Welding Process

by Phillip Lee, Jinhyeong Kwon, Jinhwan Lee, Habeom Lee, Young D. Suh, Sukjoon Hong and Junyeob Yeo

Micromachines 2017, 8(5), 164; https://doi.org/10.3390/mi8050164 - 19 May 2017

Cited by 17 | Viewed by 5931

Abstract

To date, the silver nanowire-based conductor has been widely used for flexible/stretchable electronics due to its several advantages. The optical nanowire annealing process has also received interest as an alternative annealing process to the Ag nanowire (NW)-based conductor. In this study, we present [...] Read more.

To date, the silver nanowire-based conductor has been widely used for flexible/stretchable electronics due to its several advantages. The optical nanowire annealing process has also received interest as an alternative annealing process to the Ag nanowire (NW)-based conductor. In this study, we present an analytical investigation on the phenomena of the Ag NWs’ junction and welding properties under laser exposure. The two different laser-induced welding processes (nanosecond (ns) pulse laser-induced nano-welding (LINW) and continuous wave (cw) scanning LINW) are applied to the Ag NW percolation networks. The Ag NWs are selectively melted and merged at the junction of Ag NWs under very short laser exposure; these results are confirmed by scanning electron microscope (SEM), focused-ion beam (FIB), electrical measurement, and finite difference time domain (FDTD) simulation. Full article

(This article belongs to the Special Issue Flexible and Stretchable Electronics)

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Graphical abstract

1519 KiB

Open AccessReview

A Review on Lattice Defects in Graphene: Types, Generation, Effects and Regulation

by Wenchao Tian, Wenhua Li, Wenbo Yu and Xiaohan Liu

Micromachines 2017, 8(5), 163; https://doi.org/10.3390/mi8050163 - 18 May 2017

Cited by 183 | Viewed by 12418

Abstract

Graphene, having a perfect two-dimensional crystal structure, has many excellent features such as a high specific surface area, and extraordinary electrical, thermal and mechanical properties. However, during the production process, lattice defects will inevitably be produced. Therefore, the performance of graphene with various [...] Read more.

Graphene, having a perfect two-dimensional crystal structure, has many excellent features such as a high specific surface area, and extraordinary electrical, thermal and mechanical properties. However, during the production process, lattice defects will inevitably be produced. Therefore, the performance of graphene with various defects is much lower than its theoretical value. We summarize the major advances of research into graphene defects in engineering in this paper. Firstly, the main types and causes of defects in graphene are introduced. Secondly, the influence of different defects in graphene on the chemical, electronic, magnetic and mechanical properties is discussed. Also, the control methods of graphene defects are reviewed. Finally, we propose the future challenges and prospects for the study of the defects of graphene and other nano-carbon materials. Full article

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5961 KiB

Open AccessArticle

Design, Fabrication and Characterization of Molybdenum Field Emitter Arrays (Mo-FEAs)

by Ningli Zhu and Jing Chen

Micromachines 2017, 8(5), 162; https://doi.org/10.3390/mi8050162 - 18 May 2017

Cited by 5 | Viewed by 4298

Abstract

We report on the fabrication of highly uniform field emitter arrays (FEAs) with an integrated self-aligned extraction gate from bulk molybdenum. All critical dimensions of the emitter tip were determined by a single process step of Inductively Coupled Plasma (ICP) etching. In addition, [...] Read more.

We report on the fabrication of highly uniform field emitter arrays (FEAs) with an integrated self-aligned extraction gate from bulk molybdenum. All critical dimensions of the emitter tip were determined by a single process step of Inductively Coupled Plasma (ICP) etching. In addition, the height difference between the emitter tip and the gate plane was controlled by the thickness of the SiO₂ dielectric layer. A 10 µm gate aperture molybdenum-FEAs (Mo-FEAs) at a typical 20 µm pitch with 6 µm height was achieved with 8.4 mA/cm² current density at gate voltages of 110 V and the turn-on field of 1.4 V/µm. These self-aligned Mo-FEAs could be expanded to active larger areas to increase the emission current. Full article

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1685 KiB

Open AccessArticle

Fabrication of Cell-Laden Hydrogel Fibers with Controllable Diameters

by Zhuoqun Cheng, Maosheng Cui, Yu Shi, Yanding Qin and Xin Zhao

Micromachines 2017, 8(5), 161; https://doi.org/10.3390/mi8050161 - 18 May 2017

Cited by 6 | Viewed by 4501

Abstract

Cell-laden hydrogel fibers are widely used as the fundamental building blocks to fabricate more complex functional three-dimensional (3D) structures that could mimic biological tissues. The control on the diameter of the hydrogel fibers is important so as to precisely construct structures in the [...] Read more.

Cell-laden hydrogel fibers are widely used as the fundamental building blocks to fabricate more complex functional three-dimensional (3D) structures that could mimic biological tissues. The control on the diameter of the hydrogel fibers is important so as to precisely construct structures in the above 3D bio-fabrication. In this paper, a pneumatic-actuated micro-extrusion system is developed to produce hydrogel fibers based on the crosslinking behavior of sodium alginate with calcium ions. Excellent uniformity has been obtained in the diameters of the fabricated hydrogel fibers as a proportional-integral-derivative (PID) control algorithm is applied on the driving pressure control. More importantly, a linear relationship has been obtained between the diameter of hydrogel fiber and the driving pressure. With the help of the identified linear model, we can precisely control the diameter of the hydrogel fiber via the control of the driving pressure. The differences between the measured and designed diameters are within ±2.5%. Finally, the influence of the calcium ions on the viability of the encapsulated cells is also investigated by immersing the cell-laden hydrogel fibers into the CaCl₂ bath for different periods of time. LIVE/DEAD assays show that there is little difference among the cell viabilities in each sample. Therefore, the calcium ions utilized in the fabrication process have no impact on the cells encapsulated in the hydrogel fiber. Experimental results also show that the cell viability is 83 ± 2% for each sample after 24 h of culturing. Full article

(This article belongs to the Special Issue Additive Manufacturing for Medical Applications)

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2196 KiB

Open AccessArticle

A Miniature On-Chip Methane Sensor Based on an Ultra-Low Loss Waveguide and a Micro-Ring Resonator Filter

by Yingying Qiao, Jifang Tao, Chia-Hung Chen, Jifang Qiu, Ye Tian, Xiaobin Hong and Jian Wu

Micromachines 2017, 8(5), 160; https://doi.org/10.3390/mi8050160 - 17 May 2017

Cited by 15 | Viewed by 4913

Abstract

A miniature methane sensor composed of a long ultra-low loss waveguide and a micro-ring resonator filter is proposed with high sensitivity and good selectivity. This sensor takes advantage of the evanescent field to implement methane concentration detection at a near infrared band (1650 [...] Read more.

A miniature methane sensor composed of a long ultra-low loss waveguide and a micro-ring resonator filter is proposed with high sensitivity and good selectivity. This sensor takes advantage of the evanescent field to implement methane concentration detection at a near infrared band (1650 nm). In the sensor, two waveguides, a strip waveguide and a slot waveguide, are specially designed and discussed based on three common semiconductor materials, including silica, silicon nitride, and silicon. Through simulations and numerical calculations, we determine that for the strip waveguide, the optimal evanescent field ratio (EFR) is approximately 39.8%, while the resolution is 32.1 ppb using a 15-cm waveguide length. For the slot waveguide, the optimal EFR is approximately 61.6%, and the resolution is 20.8 ppb with a 15-cm waveguide length. Full article

(This article belongs to the Special Issue Optofluidics 2016)

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5794 KiB

Open AccessFeature PaperArticle

An Electrostatic MEMS Translational Scanner with Large Out-of-Plane Stroke for Remote Axial-Scanning in Multi-Photon Microscopy

by Haijun Li, Xiyu Duan, Gaoming Li, Kenn R. Oldham and Thomas D. Wang

Micromachines 2017, 8(5), 159; https://doi.org/10.3390/mi8050159 - 15 May 2017

Cited by 18 | Viewed by 6046

Abstract

We present an electrostatic microelectromechanical systems (MEMS) resonant scanner with large out-of-plane translational stroke for fast axial-scanning in a multi-photon microscope system for real-time vertical cross-sectional imaging. The scanner has a compact footprint with dimensions of 2.1 mm × 2.1 mm × 0.44 [...] Read more.

We present an electrostatic microelectromechanical systems (MEMS) resonant scanner with large out-of-plane translational stroke for fast axial-scanning in a multi-photon microscope system for real-time vertical cross-sectional imaging. The scanner has a compact footprint with dimensions of 2.1 mm × 2.1 mm × 0.44 mm, and employs a novel lever-based compliant mechanism to enable large vertical displacements of a reflective mirror with slight tilt angles. Test results show that by using parametrical resonance, the scanner can provide a fast out-of-plane translational motion with ≥400 μm displacement and ≤0.14° tilt angle over a wide frequency range of ~390 Hz at ambient pressure. By employing this MEMS translational scanner and a biaxial MEMS mirror for lateral scanning, vertical cross-sectional imaging with a beam axial-scanning range of 200 μm and a frame rate of ~5–10 Hz is enabled in a remote scan multi-photon fluorescence imaging system. Full article

(This article belongs to the Special Issue MEMS Mirrors)

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3581 KiB

Open AccessArticle

Investigation of Au/Si Eutectic Wafer Bonding for MEMS Accelerometers

by Dongling Li, Zhengguo Shang, Yin She and Zhiyu Wen

Micromachines 2017, 8(5), 158; https://doi.org/10.3390/mi8050158 - 15 May 2017

Cited by 21 | Viewed by 9273

Abstract

Au/Si eutectic bonding is considered to BE a promising technology for creating 3D structures and hermetic packaging in micro-electro-mechanical system (MEMS) devices. However, it suffers from the problems of a non-uniform bonding interface and complex processes for the interconnection of metal wires. This [...] Read more.

Au/Si eutectic bonding is considered to BE a promising technology for creating 3D structures and hermetic packaging in micro-electro-mechanical system (MEMS) devices. However, it suffers from the problems of a non-uniform bonding interface and complex processes for the interconnection of metal wires. This paper presents a novel Au/Si eutectic wafer bonding structure and an implementation method for MEMS accelerometer packaging. The related processing parameters influencing the Au/Si eutectic bonding quality were widely investigated. It was found that a high temperature of 400 °C with a low heating/cooling rate of 5 °C/min is crucial for successful Au/Si eutectic bonding. High contact force is beneficial for bonding uniformity, but the bonding strength and bonding yield decrease when the contact force increases from 3000 to 5000 N due to the metal squeezing out of the interface. The application of TiW as an adhesion layer on a glass substrate, compared with a commonly used Cr or Ti layer, significantly improves the bonding quality. The bonding strength is higher than 50 MPa, and the bonding yield is above 90% for the presented Au/Si eutectic bonding. Furthermore, the wafer-level vacuum packaging of the MEMS accelerometer was achieved based on Au/Si eutectic bonding and anodic bonding with one process. Testing results show a nonlinearity of 0.91% and a sensitivity of 1.06 V/g for the MEMS accelerometer. This Au/Si eutectic bonding process can be applied to the development of reliable, low-temperature, low-cost fabrication and hermetic packaging for MEMS devices. Full article

(This article belongs to the Special Issue 3D Integration Technologies for MEMS)

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4213 KiB

Open AccessArticle

Low Temperature Plasma Nitriding of Inner Surfaces in Stainless Steel Mini-/Micro-Pipes and Nozzles

by Tatsuhiko Aizawa and Kenji Wasa

Micromachines 2017, 8(5), 157; https://doi.org/10.3390/mi8050157 - 13 May 2017

Cited by 11 | Viewed by 4228

Abstract

Metallic miniature products have been highlighted as mini-/micro-structural components working as a precise mechanism, in dispensing systems, and in medical operations. In particular, the essential mechanical parts such as pipes and nozzles have strength and hardness sufficient for ejecting viscous liquids, solders, and [...] Read more.

Metallic miniature products have been highlighted as mini-/micro-structural components working as a precise mechanism, in dispensing systems, and in medical operations. In particular, the essential mechanical parts such as pipes and nozzles have strength and hardness sufficient for ejecting viscous liquids, solders, and particles. A low-temperature plasma nitriding process was proposed as a surface treatment to improve the engineering durability of stainless steel mini-/micro-pipes and nozzles. Various analyses were performed to describe the inner nitriding process only, from the inner surface of pipes and nozzles to their depth in thickness. AISI316 pipes and AISI316/AISI304 nozzle specimens were used to demonstrate by plasma nitriding for 14.4 ks at 693 K that their inner surfaces had a hardness higher than 800 HV. Full article

(This article belongs to the Special Issue Micro/Nano Manufacturing)

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14338 KiB

Open AccessArticle

Development of Novel Platform to Predict the Mechanical Damage of a Miniature Mobile Haptic Actuator

by Byungjoo Choi, Jiwoon Kwon, Yongho Jeon and Moon Gu Lee

Micromachines 2017, 8(5), 156; https://doi.org/10.3390/mi8050156 - 13 May 2017

Cited by 4 | Viewed by 4335

Abstract

Impact characterization of a linear resonant actuator (LRA) is studied experimentally by a newly-developed drop tester, which can control various experimental uncertainties, such as rotational moment, air resistance, secondary impact, and so on. The feasibility of this test apparatus was verified by a [...] Read more.

Impact characterization of a linear resonant actuator (LRA) is studied experimentally by a newly-developed drop tester, which can control various experimental uncertainties, such as rotational moment, air resistance, secondary impact, and so on. The feasibility of this test apparatus was verified by a comparison with a free fall test. By utilizing a high-speed camera and measuring the vibrational displacement of the spring material, the impact behavior was captured and the damping ratio of the system was defined. Based on the above processes, a finite element model was established and the experimental and analytical results were successfully correlated. Finally, the damage of the system from impact loading can be expected by the developed model and, as a result, this research can improve the impact reliability of the LRA. Full article

(This article belongs to the Special Issue Micro/Nano Manufacturing)

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1256 KiB

Open AccessArticle

Enhanced Sensitivity of MoTe₂ Chemical Sensor through Light Illumination

by Zhihong Feng, Yuan Xie, Enxiu Wu, Yuanyuan Yu, Shijun Zheng, Rui Zhang, Xuejiao Chen, Chonglin Sun, Hao Zhang, Wei Pang, Jing Liu and Daihua Zhang

Micromachines 2017, 8(5), 155; https://doi.org/10.3390/mi8050155 - 12 May 2017

Cited by 30 | Viewed by 5761

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) semiconducting materials have recently attracted wide attention and been regarded as promising building blocks for chemical sensors due to their high surface-to-volume ratio. However, their low response hinders the realization of high-performance 2D TMDCs chemical sensors. Here, [...] Read more.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) semiconducting materials have recently attracted wide attention and been regarded as promising building blocks for chemical sensors due to their high surface-to-volume ratio. However, their low response hinders the realization of high-performance 2D TMDCs chemical sensors. Here, we demonstrate the improvement of sensing performance of molybdenum ditelluride (MoTe₂) gas sensor through continuous light illumination. The dependence of sensing performance on the energy of photons and light intensity is systematically studied. The response to NH₃ is dramatically enhanced by more than 25 times under 254 nm ultraviolet (UV) light illumination with intensity of 2.5 mW/cm². Moreover, a remarkable low detection limit of 3 ppb is achieved, which is improved by 80 times compared with that in dark condition. The results demonstrate that light illumination is a promising method to improve the sensitivity of 2D TMDCs chemical sensors. Full article

(This article belongs to the Special Issue Nanomaterials Based Sensors)

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3489 KiB

Open AccessArticle

Wide Range Simulation Study of Taylor Bubbles in Circular Milli and Microchannels

by Luis A. M. Rocha, João M. Miranda and Joao B. L. M. Campos

Micromachines 2017, 8(5), 154; https://doi.org/10.3390/mi8050154 - 12 May 2017

Cited by 32 | Viewed by 4024

Abstract

A deep knowledge of the hydrodynamics of two-phase flow in millichannels and microchannels is relevant to the design and control of micro structured equipment. While there is plenty of work published in this area, there is a lack of studies over a wide [...] Read more.

A deep knowledge of the hydrodynamics of two-phase flow in millichannels and microchannels is relevant to the design and control of micro structured equipment. While there is plenty of work published in this area, there is a lack of studies over a wide range of dimensionless numbers and some factors have not been properly addressed, such as the role of the Reynolds number, the features of recirculation regions in the liquid slug and the liquid film development length. Therefore, a wide range parametric study of isolated gas Taylor bubbles flowing in co-current with liquid in circular milli- and microchannels is presented, in a wide range of Capillary (Ca_B) (0.01–2) and Reynolds numbers (Re_B) (0.01–700). The shape and velocity of the bubbles are, together with the flow patterns in the flowing liquid, analyzed and compared with numerical and experimental correlations available in the literature. For low values of Ca_B, the streamlines (moving reference frame (MRF)) in the liquid slug show semi-infinite recirculations occupying a large portion of the cross-section of the channel. The mean velocity of the fluid moving inside the external envelope of the semi-infinite streamlines is equal to the bubble velocity. For high values of Ca_B, there are no recirculations and the bubble is moving faster or at least at the velocity of the liquid in the center of the tube; this flow pattern is often called bypass flow. The results also indicate that the liquid film surrounding the bubbles is for low Ca_B and Re_B numbers almost stagnant, and its thickness accurately estimated with existing correlations. The stagnant film hypothesis developed provides an accurate approach to estimate the velocity of the bubble, in particular for low values of Ca_B. The asymptotic behavior of the studied parameters enables the extrapolation of data for Ca_B lower than 0.01. In addition to the simulations of isolated bubbles, simulations with two consecutive bubbles were also carried out; coalescence was only observed in very specific conditions. The results obtained in this study are directly applicable to co-current slug flow in milli- and microchannels for 0.1 < Re_B < 1000 and 0.02 < Ca_B < 2. Full article

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3679 KiB

Open AccessArticle

Large-Area Compatible Laser Sintering Schemes with a Spatially Extended Focused Beam

by Habeom Lee, Jinhyeong Kwon, Woo Seop Shin, Hyeon Rack Kim, Jaeho Shin, Hyunmin Cho, Seungyong Han, Junyeob Yeo and Sukjoon Hong

Micromachines 2017, 8(5), 153; https://doi.org/10.3390/mi8050153 - 11 May 2017

Cited by 12 | Viewed by 5943

Abstract

Selective laser sintering enables the facile production of metal nanoparticle-based conductive layers on flexible substrates, but its application towards large-area electronics has remained questionable due to the limited throughput of the laser process that originates from the direct writing nature. In this study, [...] Read more.

Selective laser sintering enables the facile production of metal nanoparticle-based conductive layers on flexible substrates, but its application towards large-area electronics has remained questionable due to the limited throughput of the laser process that originates from the direct writing nature. In this study, modified optical schemes are introduced for the fabrication of (1) a densely patterned conductive layer and (2) a thin-film conductive layer without any patterns. In detail, a focusing lens is substituted by a micro lens array or a cylindrical lens to generate multiple beamlets or an extended focal line. The modified optical settings are found to be advantageous for the creation of repetitive conducting patterns or areal sintering of the silver nanoparticle ink layer. It is further confirmed that these optical schemes are equally compatible with plastic substrates for its application towards large-area flexible electronics. Full article

(This article belongs to the Special Issue Flexible and Stretchable Electronics)

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1759 KiB

Open AccessReview

A Perspective on the Rise of Optofluidics and the Future

by Chaolong Song and Say Hwa Tan

Micromachines 2017, 8(5), 152; https://doi.org/10.3390/mi8050152 - 08 May 2017

Cited by 32 | Viewed by 7362

Abstract

In the recent past, the field of optofluidics has thrived from the immense efforts of researchers from diverse communities. The concept of optofluidics combines optics and microfluidics to exploit novel properties and functionalities. In the very beginning, the unique properties of liquid, such [...] Read more.

In the recent past, the field of optofluidics has thrived from the immense efforts of researchers from diverse communities. The concept of optofluidics combines optics and microfluidics to exploit novel properties and functionalities. In the very beginning, the unique properties of liquid, such as mobility, fungibility and deformability, initiated the motivation to develop optical elements or functions using fluid interfaces. Later on, the advancements of microelectromechanical system (MEMS) and microfluidic technologies enabled the realization of optofluidic components through the precise manipulation of fluids at microscale thus making it possible to streamline complex fabrication processes. The optofluidic system aims to fully integrate optical functions on a single chip instead of using external bulky optics, which can consequently lower the cost of system, downsize the system and make it promising for point-of-care diagnosis. This perspective gives an overview of the recent developments in the field of optofluidics. Firstly, the fundamental optofluidic components will be discussed and are categorized according to their basic working mechanisms, followed by the discussions on the functional instrumentations of the optofluidic components, as well as the current commercialization aspects of optofluidics. The paper concludes with the critical challenges that might hamper the transformation of optofluidic technologies from lab-based procedures to practical usages and commercialization. Full article

(This article belongs to the Special Issue Insights and Advancements in Microfluidics)

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7687 KiB

Open AccessArticle

Characteristics of Double Planar Micro-Inductor with Patterned NiFe Thin-Films for DC/DC Integration

by Mingming Chen, Guifu Ding, Ping Cheng, Congchun Zhang, Xiaomin Zhu and Zhe Liu

Micromachines 2017, 8(5), 151; https://doi.org/10.3390/mi8050151 - 08 May 2017

Cited by 4 | Viewed by 6832

Abstract

This paper proposes a double-planar-coil microinductor with patterned permalloy magnetic film for high frequency DC–DC integration. The effects of magnetic film’s patterning and thickness on the inductance and quality factor of the micro-inductor are investigated by using COMSOL Multiphysics software. Simulation results indicate [...] Read more.

This paper proposes a double-planar-coil microinductor with patterned permalloy magnetic film for high frequency DC–DC integration. The effects of magnetic film’s patterning and thickness on the inductance and quality factor of the micro-inductor are investigated by using COMSOL Multiphysics software. Simulation results indicate that the magnetic film improves the inductance of microinductor effectively and patterning of the magnetic film reduces eddy current loss in high frequency range. The micro-inductor is fabricated by using micro-electro-mechanical systems (MEMS) technique. The inductance of approximately 2.17 μH at 1.5 MHz and the quality factor of 2.8 are achieved for the microinductor with patterned magnetic film. The performances of the micro-inductor applied in a low-power DC/DC converter are tested. The results indicate that the micro-inductor with the patterned magnetic film effectively has improved inductance and quality factor compared to that with non-patterned magnetic film. The maximum efficiency of measured converter is 67% at 1.5 MHz and the output current is 100 mA. Full article

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6442 KiB

Open AccessArticle

Design and Experimental Research of a Novel Stick-Slip Type Piezoelectric Actuator

by Mingxing Zhou, Zunqiang Fan, Zhichao Ma, Hongwei Zhao, Yue Guo, Kun Hong, Yuanshang Li, Hang Liu and Di Wu

Micromachines 2017, 8(5), 150; https://doi.org/10.3390/mi8050150 - 08 May 2017

Cited by 51 | Viewed by 6613

Abstract

A linear piezoelectric actuator based on the stick-slip principle is presented and tested in this paper. With the help of changeable vertical preload force flexure hinge, the designed linear actuator can achieve both large travel stick-slip motion and high-resolution stepping displacement. The developed [...] Read more.

A linear piezoelectric actuator based on the stick-slip principle is presented and tested in this paper. With the help of changeable vertical preload force flexure hinge, the designed linear actuator can achieve both large travel stick-slip motion and high-resolution stepping displacement. The developed actuator mainly consists of a bridge-type flexure hinge mechanism, a compound parallelogram flexure hinge mechanism, and two piezoelectric stacks. The mechanical structure and motion principle of the linear actuator were illustrated, and the finite element method (FEM) is adopted. An optimal parametric study of the flexure hinge is performed by a finite element analysis-based response surface methodology. In order to investigate the actuator’s working performance, a prototype was manufactured and a series of experiments were carried out. The results indicate that the maximum motion speed is about 3.27 mm/s and the minimum stepping displacement is 0.29 μm. Finally, a vibration test was carried out to obtain the first natural frequency of the actuator, and an in situ observation was conducted to investigate actuator’s stick-slip working condition. The experimental results confirm the feasibility of the proposed actuator, and the motion speed and displacement are both improved compared with the traditional stick-slip motion actuator. Full article

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2950 KiB

Open AccessArticle

Preparation of an Acridinium Ester-Labeled Antibody and Its Application in GoldMag Nanoparticle-Based, Ultrasensitive Chemiluminescence Immunoassay for the Detection of Human Epididymis Protein 4

by Ting Ma, Mengdan Zhang, Yinsheng Wan, Yali Cui and Le Ma

Micromachines 2017, 8(5), 149; https://doi.org/10.3390/mi8050149 - 07 May 2017

Cited by 10 | Viewed by 8503

Abstract

An ultrasensitive and rapid sandwich-type chemiluminescence immunoassay (CLIA) was developed for the clinical determination of human epididymis protein 4 (HE4) in human serum, using GoldMag nanoparticles as solid phase and acridinium ester (AE) as chemiluminescence system (GMP-CLIA). The process of AE labeling antibodies [...] Read more.

An ultrasensitive and rapid sandwich-type chemiluminescence immunoassay (CLIA) was developed for the clinical determination of human epididymis protein 4 (HE4) in human serum, using GoldMag nanoparticles as solid phase and acridinium ester (AE) as chemiluminescence system (GMP-CLIA). The process of AE labeling antibodies was systematically studied and evaluated. The effect of varies factors such as molar ratio of AE to antibodies, labeling time, and the components of elution buffer and trigger solution were optimized. Under the selected conditions, AE labeling experiments were successfully performed with the average labeling efficiency of 1.92 ± 0.08, and antibody utilization rate of 69.77 ± 1.19%. Antibody activity remained unchanged after labeling. The established GMP-CLIA method can detect HE4 in the range of 0.25–50 ng·mL⁻¹ (10–2000 pM) with a detection limit of 0.084 ng·mL⁻¹ (3.36 pM). The sensitivity has reached a high level, comparable with the current commercial detection kits. This proposed method has been successfully applied to the clinical determination of HE4 in 65 human sera. The results showed a good correlation with a clinical method, microplate-based chemiluminescence enzyme immunoassay (CLEIA), with the correlation coefficient of 0.9594. Full article

(This article belongs to the Special Issue Medical Microdevices and Micromachines)

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2592 KiB

Open AccessArticle

RF Sputtering, Post-Annealing Treatment and Characterizations of ZnO (002) Thin Films on 3C-SiC (111)/Si (111) Substrates

by Visakh Valliyil Sasi, Abid Iqbal, Kien Chaik, Alan Iacopi and Faisal Mohd-Yasin

Micromachines 2017, 8(5), 148; https://doi.org/10.3390/mi8050148 - 07 May 2017

Cited by 6 | Viewed by 5429

Abstract

We report on the radio frequency (RF) sputtering of c-axis oriented ZnO thin films on top of epitaxial 3C-SiC-on-Si (111) substrates, which were then subjected to post-annealing treatment at 400, 600 and 800 °C. Grazing incident X-ray Diffraction (XRD) data show that the [...] Read more.

We report on the radio frequency (RF) sputtering of c-axis oriented ZnO thin films on top of epitaxial 3C-SiC-on-Si (111) substrates, which were then subjected to post-annealing treatment at 400, 600 and 800 °C. Grazing incident X-ray Diffraction (XRD) data show that the Full Width Half Maximum (FWHM) values for O₂/Ar ratios between 30% and 60% are consistent, with a mean of 0.325° and a standard deviation of 0.03°. This is largely attributed to the smaller lattice mismatch of 5% between the ZnO (002) and SiC (111) films. The quality of the ZnO films deteriorated at the post-annealing treatment of 800 °C, as demonstrated by the increasing value of FWHM diffraction peaks, the reducing value of the peak intensity, the reducing percentage of (002) oriented area under the curve, and the increasing value of biaxial stress. We propose a simple growth model to explain the result. Full article

(This article belongs to the Special Issue SiC-Based Microsystems)

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13001 KiB

Open AccessArticle

3D Cardiac Cell Culture on Nanofiber Bundle Substrates for the Investigation of Cell Morphology and Contraction

by Xia Liu, Sixing Xu, Xuanlin Kuang and Xiaohong Wang

Micromachines 2017, 8(5), 147; https://doi.org/10.3390/mi8050147 - 05 May 2017

Cited by 5 | Viewed by 5228

Abstract

Cardiac failure is a quite severe condition that can result in life-threatening consequences. Cardiac tissue engineering is thought to be one of the most promising technologies to reconstruct damaged cardiac muscles and facilitate myocardial tissue regeneration. We report a new nanofiber bundle substrate [...] Read more.

Cardiac failure is a quite severe condition that can result in life-threatening consequences. Cardiac tissue engineering is thought to be one of the most promising technologies to reconstruct damaged cardiac muscles and facilitate myocardial tissue regeneration. We report a new nanofiber bundle substrate for three-dimensional (3D) cardiac cell culture as a platform to investigate cell morphology and contraction. Polymeric nanofiber bundles with various patterns act as physical cues to align the cardiac cell sheets. Comparing the uniaxial alignment with the randomly distributed pattern, we found that the bundles with the former pattern have more “grooves” for the settlement of cardiomyocytes in a 3D structure than the latter. The cardiomyocytes loaded on the aligned nanofiber bundles tend to grow along the fiber axis. The interfacial structure between a single cardiomyocyte in the cardiac cell sheet and the attached nanofibers was observed using environmental scanning electron microscope. Immunofluorescence imaging showed that the uniaxially aligned nanofibers greatly promoted cell attachment and alignment of the cardiomyocytes because of the matching morphology between the nanofiber pattern and the biological components. Moreover, we concluded that the aligned polymeric nanofibers could be a promising substrate suitable for the anisotropic contraction of cardiac cell sheets. Full article

(This article belongs to the Special Issue Bioprinting and 3D Printing in MEMS Technology)

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9305 KiB

Open AccessFeature PaperArticle

Design and Fabrication of a 2-Axis Electrothermal MEMS Micro-Scanner for Optical Coherence Tomography

by Quentin A. A. Tanguy, Sylwester Bargiel, Huikai Xie, Nicolas Passilly, Magali Barthès, Olivier Gaiffe, Jaroslaw Rutkowski, Philippe Lutz and Christophe Gorecki

Micromachines 2017, 8(5), 146; https://doi.org/10.3390/mi8050146 - 05 May 2017

Cited by 23 | Viewed by 8030

Abstract

This paper introduces an optical 2-axis Micro Electro-Mechanical System (MEMS) micromirror actuated by a pair of electrothermal actuators and a set of passive torsion bars. The actuated element is a dual-reflective circular mirror plate of 1

m m

in diameter. This inner mirror [...] Read more.

This paper introduces an optical 2-axis Micro Electro-Mechanical System (MEMS) micromirror actuated by a pair of electrothermal actuators and a set of passive torsion bars. The actuated element is a dual-reflective circular mirror plate of 1

m m

in diameter. This inner mirror plate is connected to a rigid frame via a pair of torsion bars in two diametrically opposite ends located on the rotation axis. A pair of electrothermal bimorphs generates a force onto the perpendicular free ends of the mirror plate in the same angular direction. An array of electrothermal bimorph cantilevers deflects the rigid frame around a working angle of 45

^{\circ}

for side-view scan. The performed scans reach large mechanical angles of 32

^{\circ}

for the frame and 22

^{\circ}

for the in-frame mirror. We denote three resonant main modes, pure flexion of the frame at 205

Hz

, a pure torsion of the mirror plate at 1.286

kHz

and coupled mode of combined flexion and torsion at 1.588

kHz

. The micro device was fabricated through successive stacks of materials onto a silicon-on-insulator wafer and the patterned deposition on the back-side of the dual-reflective mirror is achieved through a dry film photoresist photolithography process. Full article

(This article belongs to the Special Issue MEMS Mirrors)

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141 KiB

Open AccessEditorial

Editorial for the Special Issue on Micro/Nano-Chip Electrokinetics

by Xiangchun Xuan and Shizhi Qian

Micromachines 2017, 8(5), 145; https://doi.org/10.3390/mi8050145 - 04 May 2017

Cited by 2 | Viewed by 3453

Abstract

Micro/nanofluidics-based lab-on-a-chip devices have found extensive applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics is the method of choice in these micro/nano-chips for transporting, manipulating and sensing various analyte species (e.g., ions, molecules, fluids and particles, [...] Read more.

Micro/nanofluidics-based lab-on-a-chip devices have found extensive applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics is the method of choice in these micro/nano-chips for transporting, manipulating and sensing various analyte species (e.g., ions, molecules, fluids and particles, etc.) [1,2].[...] Full article

(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)

1858 KiB

Open AccessArticle

Rapid Fabrication of Disposable Micromixing Arrays Using Xurography and Laser Ablation

by J. Israel Martínez-López, H.A. Betancourt, Erika García-López, Ciro A. Rodriguez and Hector R. Siller

Micromachines 2017, 8(5), 144; https://doi.org/10.3390/mi8050144 - 04 May 2017

Cited by 14 | Viewed by 4956

Abstract

We assessed xurography and laser ablation for the manufacture of passive micromixers arrays to explore the scalability of unconventional manufacture technologies that could be implemented under the restrictions of the Point of Care for developing countries. In this work, we present a novel [...] Read more.

We assessed xurography and laser ablation for the manufacture of passive micromixers arrays to explore the scalability of unconventional manufacture technologies that could be implemented under the restrictions of the Point of Care for developing countries. In this work, we present a novel split-and-recombine (SAR) array design adapted for interfacing standardized dispensing (handheld micropipette) and sampling (microplate reader) equipment. The design was patterned and sealed from A4 sized vinyl sheets (polyvinyl chloride), employing low-cost disposable materials. Manufacture was evaluated measuring the dimensional error with stereoscopic and confocal microscopy. The micromixing efficiency was estimated using a machine vision system for passive driven infusion provided by micropippetting samples of dye and water. It was possible to employ rapid fabrication based on xurography to develop a four channel asymmetric split-and-recombine (ASAR) micromixer with mixing efficiencies ranging from 43% to 65%. Full article

(This article belongs to the Special Issue Micro/Nano Manufacturing)

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20731 KiB

Open AccessArticle

Fabrication of Mesoscale Channel by Scanning Micro Electrochemical Flow Cell (SMEFC)

by Cheng Guo, Jun Qian and Dominiek Reynaerts

Micromachines 2017, 8(5), 143; https://doi.org/10.3390/mi8050143 - 04 May 2017

Cited by 18 | Viewed by 5685

Abstract

A unique micro electrochemical machining (ECM) method based on a scanning micro electrochemical flow cell (SMEFC), in which the electrolyte is confined beneath the tool electrode instead of spreading on the workpiece surface, has been developed and its feasibility for fabricating mesoscale channels [...] Read more.

A unique micro electrochemical machining (ECM) method based on a scanning micro electrochemical flow cell (SMEFC), in which the electrolyte is confined beneath the tool electrode instead of spreading on the workpiece surface, has been developed and its feasibility for fabricating mesoscale channels has been investigated. The effects of the surface conditions, the applied current, the feed rate, the concentration of the electrolyte and several geometrical parameters on the machining performance have been investigated through a series of experiments. The cross-sectional profile of the channels, the roughness of the channel bottom, the width and depth of the channel, the microstructures on the machined surface and the morphologies of the moving droplet have been analyzed and compared under different machining conditions. Furthermore, experiments with different overlaps of the electrolyte droplet traces have also been conducted, in which the SMEFC acts as a “milling tool”. The influences of the electrode offset distance (EOD), the current and the feed rate on the machining performance have also been examined through the comparison of the corresponding cross-sectional profiles and microstructures. The results indicate that, in addition to machining individual channels, the SMEFC system is also capable of generating shallow cavities with a suitable superimposed motion of the tool electrode. Full article

(This article belongs to the Special Issue Micro/Nano Manufacturing)

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9374 KiB

Open AccessArticle

Ultrasonic-Assisted Incremental Microforming of Thin Shell Pyramids of Metallic Foil

by Toshiyuki Obikawa and Mamoru Hayashi

Micromachines 2017, 8(5), 142; https://doi.org/10.3390/mi8050142 - 03 May 2017

Cited by 17 | Viewed by 5159

Abstract

Single point incremental forming is used for rapid prototyping of sheet metal parts. This forming technology was applied to the fabrication of thin shell micropyramids of aluminum, stainless steel, and titanium foils. A single point tool used had a tip radius of 0.1 [...] Read more.

Single point incremental forming is used for rapid prototyping of sheet metal parts. This forming technology was applied to the fabrication of thin shell micropyramids of aluminum, stainless steel, and titanium foils. A single point tool used had a tip radius of 0.1 mm or 0.01 mm. An ultrasonic spindle with axial vibration was implemented for improving the shape accuracy of micropyramids formed on 5–12 micrometers-thick aluminum, stainless steel, and titanium foils. The formability was also investigated by comparing the forming limits of micropyramids of aluminum foil formed with and without ultrasonic vibration. The shapes of pyramids incrementally formed were truncated pyramids, twisted pyramids, stepwise pyramids, and star pyramids about 1 mm in size. A much smaller truncated pyramid was formed only for titanium foil for qualitative investigation of the size reduction on forming accuracy. It was found that the ultrasonic vibration improved the shape accuracy of the formed pyramids. In addition, laser heating increased the forming limit of aluminum foil and it is more effective when both the ultrasonic vibration and laser heating are applied. Full article

(This article belongs to the Special Issue Micro/Nano Manufacturing)

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8292 KiB

Open AccessArticle

Geometric Optimization of Microfabricated Silicon Electrodes for Corona Discharge-Based Electrohydrodynamic Thrusters

by Daniel S. Drew and Kristofer S. J. Pister

Micromachines 2017, 8(5), 141; https://doi.org/10.3390/mi8050141 - 03 May 2017

Cited by 20 | Viewed by 7252

Abstract

Electrohydrodynamic thrust is an emerging propulsion mechanism for flying insect-scale robots. There is a need to both minimize the operating voltage and maximize the output force when designing microfabricated electrodes for use in these robots. In this work, an array of hybrid wire-needle [...] Read more.

Electrohydrodynamic thrust is an emerging propulsion mechanism for flying insect-scale robots. There is a need to both minimize the operating voltage and maximize the output force when designing microfabricated electrodes for use in these robots. In this work, an array of hybrid wire-needle and grid electrode geometries were fabricated and characterized to attempt to minimize both corona discharge onset voltage and thrust loss factor. Statistical analysis of this dataset was performed to screen for factors with significant effects. An optimized emitter electrode decreased onset voltage by 22%. Loss factor was found to vary significantly (as much as 30%) based on collector grid geometric parameters without affecting discharge characteristics. The results from this study can be used to drive further optimization of thrusters, with the final goal of providing a path towards autonomous flying microrobots powered by atmospheric ion engines. Full article

(This article belongs to the Special Issue Microplasma Devices)

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3093 KiB

Open AccessArticle

A Large-Size MEMS Scanning Mirror for Speckle Reduction Application

by Fanya Li, Peng Zhou, Tingting Wang, Jiahui He, Huijun Yu and Wenjiang Shen

Micromachines 2017, 8(5), 140; https://doi.org/10.3390/mi8050140 - 03 May 2017

Cited by 23 | Viewed by 6403

Abstract

Based on microelectronic mechanical system (MEMS) processing, a large-size 2-D scanning mirror (6.5 mm in diameter) driven by electromagnetic force was designed and implemented in this paper. We fabricated the micromirror with a silicon wafer and selectively electroplated Ni film on the back [...] Read more.

Based on microelectronic mechanical system (MEMS) processing, a large-size 2-D scanning mirror (6.5 mm in diameter) driven by electromagnetic force was designed and implemented in this paper. We fabricated the micromirror with a silicon wafer and selectively electroplated Ni film on the back of the mirror. The nickel film was magnetized in the magnetic field produced by external current coils, and created the force to drive the mirror’s angular deflection. This electromagnetically actuated micromirror effectively eliminates the ohmic heat and power loss on the mirror plate, which always occurs in the other types of electromagnetic micromirrors with the coil on the mirror plate. The resonant frequency for the scanning mirror is 674 Hz along the slow axis, and 1870 Hz along the fast axis. Furthermore, the scanning angles could achieve ±4.5° for the slow axis with 13.2 mW power consumption, and ±7.6° for the fast axis with 43.3 mW power consumption. The application of the MEMS mirror to a laser display system effectively reduces the laser speckle. With 2-D scanning of the MEMS mirror, the speckle contrast can be reduced from 18.19% to 4.58%. We demonstrated that the image quality of a laser display system could be greatly improved by the MEMS mirror. Full article

(This article belongs to the Special Issue MEMS Mirrors)

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1075 KiB

Open AccessArticle

Monitoring Acid–Base Titrations on Wax Printed Paper Microzones Using a Smartphone

by Sandro A. Nogueira, Lucas R. Sousa, Nathália K. L. Silva, Pedro H. F. Rodrigues and Wendell K. T. Coltro

Micromachines 2017, 8(5), 139; https://doi.org/10.3390/mi8050139 - 02 May 2017

Cited by 38 | Viewed by 8510

Abstract

This study describes the use of a smartphone for monitoring acid–base titrations on wax printed paper microzones. An array of twelve microzones of 5 mm diameter each was wax printed on filter paper. The analytical performance of the proposed devices was explored with [...] Read more.

This study describes the use of a smartphone for monitoring acid–base titrations on wax printed paper microzones. An array of twelve microzones of 5 mm diameter each was wax printed on filter paper. The analytical performance of the proposed devices was explored with acid–base titrations examples, where jaboticaba peel extract was used as a natural pH indicator. The color intensity was captured using a smartphone and analyzed through a free App named Photometrix^®. Before titrations, color intensity versus pH was calibrated to be used as a reference in titrations as (i) strong acid versus strong base; (ii) strong base versus strong acid; and (iii) weak acid versus strong base. In all examples, images were obtained after the addition of each aliquot of titrant solutions. The obtained titration curves showed the same behavior as the conventional titration curves. After evaluating the feasibility of the proposed methodology, the concentration level of acetic acid was obtained in three vinegar samples. Although the obtained values ranged from 5% to 8% compared to the concentrations on the conventional method, the proposed methodology presented high analytical reliability. The calculated concentrations of acetic acid in three samples ranged from 3.87% to 3.93%, and the proposed methodology did not significantly differ from classic acid–base titration at a confidence level of 95%. The acid–base titration on paper-based devices is outstanding, since any titration can be completed within 5 min using 20 µL volumes. Besides, the use of a smartphone to capture images followed by analysis in a free app offers simplicity to all users. The proposed methodology arises as a new strand to be exploited in the diffusion of the analytical chemistry education field as well as an alternative for quantitative analysis with extremely simplified instrumentation. Full article

(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)

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3274 KiB

Open AccessArticle

Modeling of MEMS Mirrors Actuated by Phase-Change Mechanism

by David Torres, Jun Zhang, Sarah Dooley, Xiaobo Tan and Nelson Sepúlveda

Micromachines 2017, 8(5), 138; https://doi.org/10.3390/mi8050138 - 26 Apr 2017

Cited by 7 | Viewed by 5412

Abstract

Given the multiple applications for micro-electro-mechanical system (MEMS) mirror devices, most of the research efforts are focused on improving device performance in terms of tilting angles, speed, and their integration into larger arrays or systems. The modeling of these devices is crucial for [...] Read more.

Given the multiple applications for micro-electro-mechanical system (MEMS) mirror devices, most of the research efforts are focused on improving device performance in terms of tilting angles, speed, and their integration into larger arrays or systems. The modeling of these devices is crucial for enabling a platform, in particular, by allowing for the future control of such devices. In this paper, we present the modeling of a MEMS mirror structure with four actuators driven by the phase-change of a thin film. The complexity of the device structure and the nonlinear behavior of the actuation mechanism allow for a comprehensive study that encompasses simpler electrothermal designs, thus presenting a general approach that can be adapted to most MEMS mirror designs based on this operation principle. The MEMS mirrors presented in this work are actuated by Joule heating and tested using optical techniques. Mechanical and thermal models including both pitch and roll displacements are developed by combining theoretical analysis (using both numerical and analytical tools) with experimental data and subsequently verifying with quasi-static and dynamic experiments. Full article

(This article belongs to the Special Issue MEMS Mirrors)

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1672 KiB

Open AccessFeature PaperArticle

Modular, Discrete Micromixer Elements Fabricated by 3D Printing

by Krisna C. Bhargava, Roya Ermagan, Bryant Thompson, Andrew Friedman and Noah Malmstadt

Micromachines 2017, 8(5), 137; https://doi.org/10.3390/mi8050137 - 26 Apr 2017

Cited by 15 | Viewed by 5963

Abstract

3D printing facilitates the straightforward construction of microchannels with complex three-dimensional architectures. Here, we demonstrate 3D-printed modular mixing components that operate on the basis of splitting and recombining fluid streams to decrease interstream diffusion length. These are compared to helical mixers that operate [...] Read more.

3D printing facilitates the straightforward construction of microchannels with complex three-dimensional architectures. Here, we demonstrate 3D-printed modular mixing components that operate on the basis of splitting and recombining fluid streams to decrease interstream diffusion length. These are compared to helical mixers that operate on the principle of chaotic advection. Full article

(This article belongs to the Special Issue 3D Printing: Microfabrication and Emerging Concepts)

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14239 KiB

Open AccessArticle

Fabrication of Micro-Scale Gratings by Nanosecond Laser and Its Applications for Deformation Measurements

by Guanbao Yang, Wei He, Jianguo Zhu and Lei Chen

Micromachines 2017, 8(5), 136; https://doi.org/10.3390/mi8050136 - 25 Apr 2017

Cited by 5 | Viewed by 4539

Abstract

This paper experimentally investigated the fabrication and optimization of micro-scale gratings formed by nanosecond laser etching. The mechanism of nanosecond laser processing and the geometric phase analysis (GPA) are discussed, and the factors influencing the fabrication process including laser energy, laser fluence, and [...] Read more.

This paper experimentally investigated the fabrication and optimization of micro-scale gratings formed by nanosecond laser etching. The mechanism of nanosecond laser processing and the geometric phase analysis (GPA) are discussed, and the factors influencing the fabrication process including laser energy, laser fluence, and ablation threshold of material, are experimentally studied. In order to eliminate the dependence of the processing parameters on the samples, depositing Al film on a sample before laser processing is proposed for the fabrication of high-quality gratings. The energy of the laser pulse is optimized for clear line etching on Al film considering the distance between adjacent lines of parallel gratings. The optimal energy of the laser pulse is 9.8 μJ, and the optimum fluence is 9.5 J/mm² with the waist radius of the laser beam 25.7 μm. With the optimal parameters, experimental results indicate that the highest frequency of parallel gratings is about 30 lines/mm, with a line width of 29 μm, and the distance between two adjacent laser pulses being of 10 μm. By performing tensile tests, micro-scale gratings fabricated on specimens are experimentally verified. The verification tests prove that the proposed fabrication method for the micro-scale gratings in GPA measurements is reliable and applicable, and the micro-scale gratings can be fabricated in many areas of interest, such as the crack tip, for deformation measurements. Furthermore, the adhesion between the Al film and the tested sample is strong enough so that the pattern sticks well to the sample. Full article

(This article belongs to the Special Issue Laser Micromachining and Microfabrication)

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