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Micromachines, Volume 7, Issue 10 (October 2016)

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Editorial

Jump to: Research, Review

Open AccessEditorial Multiscale and Multimaterial Fabrication: The Challenge Ahead
Micromachines 2016, 7(10), 178; doi:10.3390/mi7100178
Received: 26 September 2016 / Revised: 27 September 2016 / Accepted: 27 September 2016 / Published: 1 October 2016
Cited by 1 | PDF Full-text (136 KB) | HTML Full-text | XML Full-text

Research

Jump to: Editorial, Review

Open AccessArticle A New Method for a Piezoelectric Energy Harvesting System Using a Backtracking Search Algorithm-Based PI Voltage Controller
Micromachines 2016, 7(10), 171; doi:10.3390/mi7100171
Received: 14 July 2016 / Revised: 28 August 2016 / Accepted: 1 September 2016 / Published: 23 September 2016
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Abstract
This paper presents a new method for a vibration-based piezoelectric energy harvesting system using a backtracking search algorithm (BSA)-based proportional-integral (PI) voltage controller. This technique eliminates the exhaustive conventional trial-and-error procedure for obtaining optimized parameter values of proportional gain (Kp), and integral gain
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This paper presents a new method for a vibration-based piezoelectric energy harvesting system using a backtracking search algorithm (BSA)-based proportional-integral (PI) voltage controller. This technique eliminates the exhaustive conventional trial-and-error procedure for obtaining optimized parameter values of proportional gain (Kp), and integral gain (Ki) for PI voltage controllers. The generated estimate values of Kp and Ki are executed in the PI voltage controller that is developed through the BSA optimization technique. In this study, mean absolute error (MAE) is used as an objective function to minimize output error for a piezoelectric energy harvesting system (PEHS). The model for the PEHS is designed and analyzed using the BSA optimization technique. The BSA-based PI voltage controller of the PEHS produces a significant improvement in minimizing the output error of the converter and a robust, regulated pulse-width modulation (PWM) signal to convert a MOSFET switch, with the best response in terms of rise time and settling time under various load conditions. Full article
(This article belongs to the Special Issue MEMS Energy Harvesters)
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Open AccessArticle Full Polymer Dielectric Elastomeric Actuators (DEA) Functionalised with Carbon Nanotubes and High-K Ceramics
Micromachines 2016, 7(10), 172; doi:10.3390/mi7100172
Received: 6 July 2016 / Revised: 11 August 2016 / Accepted: 5 September 2016 / Published: 23 September 2016
Cited by 1 | PDF Full-text (6112 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Dielectric elastomer actuators (DEA) are special devices which have a simple working and construction principle and outstanding actuation properties. The DEAs consist of a combination of different materials for the dielectric and electrode layers. The combination of these layers causes incompatibilities in their
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Dielectric elastomer actuators (DEA) are special devices which have a simple working and construction principle and outstanding actuation properties. The DEAs consist of a combination of different materials for the dielectric and electrode layers. The combination of these layers causes incompatibilities in their interconnections. Dramatic differences in the mechanical properties and bad adhesion of the layers are the principal causes for the reduction of the actuation displacement and strong reduction of lifetime. Common DEAs achieve actuation displacements of 2% and a durability of some million cycles. The following investigations represent a new approach to solving the problems of common systems. The investigated DEA consists of only one basic raw polymer, which was modified according to the required demands of each layer. The basic raw polymer was modified with single-walled carbon nanotubes or high-k ceramics, for example, lead magnesium niobate-lead titanate. The development of the full polymer DEA comprised the development of materials and technologies to realise a reproducible layer composition. It was proven that the full polymer actuator worked according to the theoretical rules. The investigated system achieved actuation displacements above 20% regarding thickness, outstanding interconnections at each layer without any failures, and durability above 3 million cycles without any indication of an impending malfunction. Full article
(This article belongs to the Special Issue Polymeric Microsystems)
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Open AccessArticle A Simple Method for Fabrication of Microstructures Using a PDMS Stamp
Micromachines 2016, 7(10), 173; doi:10.3390/mi7100173
Received: 14 June 2016 / Revised: 3 September 2016 / Accepted: 19 September 2016 / Published: 1 October 2016
Cited by 1 | PDF Full-text (2903 KB) | HTML Full-text | XML Full-text
Abstract
We report a simple method to fabricate PDMS (polydimethylsiloxane) microwell arrays on glass by using a PDMS stamp to study cell-to-cell adhesion. In the cell-to-cell study, a glass substrate is required since glass has better cell attachment. The microwell arrays are replicated from
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We report a simple method to fabricate PDMS (polydimethylsiloxane) microwell arrays on glass by using a PDMS stamp to study cell-to-cell adhesion. In the cell-to-cell study, a glass substrate is required since glass has better cell attachment. The microwell arrays are replicated from an SU-8 master mold, and then are transferred to a glass substrate by lifting the PDMS stamp, followed by oxygen plasma bonding of the PDMS stamp on the glass substrate. For the cell-to-cell adhesion, four different types of PDMS arrays (e.g., rectangle, bowtie, wide-rhombus, and rhombus) were designed to vary the cell-to-cell contact length. The transfer success rates of the microwell arrays were measured as a function of both the contact area of the PDMS and the glass substrate and the different ratios between the base polymers and the curing agent. This method of generating the microwell arrays will enable a simple and robust construction of PDMS-based devices for various biological applications. Full article
(This article belongs to the Special Issue Biomedical Microfluidic Devices)
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Open AccessArticle In-Situ Testing of the Thermal Diffusivity of Polysilicon Thin Films
Micromachines 2016, 7(10), 174; doi:10.3390/mi7100174
Received: 27 July 2016 / Revised: 17 September 2016 / Accepted: 20 September 2016 / Published: 1 October 2016
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Abstract
This paper presents an intuitive yet effective in-situ thermal diffusivity testing structure and testing method. The structure consists of two doubly clamped beams with the same width and thickness but different lengths. When the electric current is applied through two terminals of one
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This paper presents an intuitive yet effective in-situ thermal diffusivity testing structure and testing method. The structure consists of two doubly clamped beams with the same width and thickness but different lengths. When the electric current is applied through two terminals of one beam, the beam serves as thermal resistor and the resistance R(t) varies as temperature rises. A delicate thermodynamic model considering thermal convection, thermal radiation, and film-to-substrate heat conduction was established for the testing structure. The presented in-situ thermal diffusivity testing structure can be fabricated by various commonly used micro electro mechanical systems (MEMS) fabrication methods, i.e., it requires no extra customized processes yet provides electrical input and output interfaces for in-situ testing. Meanwhile, the testing environment and equipment had no stringent restriction, measurements were carried out at normal temperatures and pressures, and the results are relatively accurate. Full article
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Open AccessFeature PaperArticle Baking Powder Actuated Centrifugo-Pneumatic Valving for Automation of Multi-Step Bioassays
Micromachines 2016, 7(10), 175; doi:10.3390/mi7100175
Received: 4 August 2016 / Revised: 4 September 2016 / Accepted: 19 September 2016 / Published: 1 October 2016
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Abstract
We report a new flow control method for centrifugal microfluidic systems; CO2 is released from on-board stored baking powder upon contact with an ancillary liquid. The elevated pressure generated drives the sample into a dead-end pneumatic chamber sealed by a dissolvable film
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We report a new flow control method for centrifugal microfluidic systems; CO2 is released from on-board stored baking powder upon contact with an ancillary liquid. The elevated pressure generated drives the sample into a dead-end pneumatic chamber sealed by a dissolvable film (DF). This liquid incursion wets and dissolves the DF, thus opening the valve. The activation pressure of the DF valve can be tuned by the geometry of the channel upstream of the DF membrane. Through pneumatic coupling with properly dimensioned disc architecture, we established serial cascading of valves, even at a constant spin rate. Similarly, we demonstrate sequential actuation of valves by dividing the disc into a number of distinct pneumatic chambers (separated by DF membranes). Opening these DFs, typically through arrival of a liquid to that location on a disc, permits pressurization of these chambers. This barrier-based scheme provides robust and strictly ordered valve actuation, which is demonstrated by the automation of a multi-step/multi-reagent DNA-based hybridization assay. Full article
(This article belongs to the Special Issue Biomedical Microfluidic Devices)
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Open AccessArticle An On-Chip RBC Deformability Checker Significantly Improves Velocity-Deformation Correlation
Micromachines 2016, 7(10), 176; doi:10.3390/mi7100176
Received: 19 August 2016 / Revised: 8 September 2016 / Accepted: 19 September 2016 / Published: 1 October 2016
Cited by 4 | PDF Full-text (6891 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
An on-chip deformability checker is proposed to improve the velocity–deformation correlation for red blood cell (RBC) evaluation. RBC deformability has been found related to human diseases, and can be evaluated based on RBC velocity through a microfluidic constriction as in conventional approaches. The
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An on-chip deformability checker is proposed to improve the velocity–deformation correlation for red blood cell (RBC) evaluation. RBC deformability has been found related to human diseases, and can be evaluated based on RBC velocity through a microfluidic constriction as in conventional approaches. The correlation between transit velocity and amount of deformation provides statistical information of RBC deformability. However, such correlations are usually only moderate, or even weak, in practical evaluations due to limited range of RBC deformation. To solve this issue, we implemented three constrictions of different width in the proposed checker, so that three different deformation regions can be applied to RBCs. By considering cell responses from the three regions as a whole, we practically extend the range of cell deformation in the evaluation, and could resolve the issue about the limited range of RBC deformation. RBCs from five volunteer subjects were tested using the proposed checker. The results show that the correlation between cell deformation and transit velocity is significantly improved by the proposed deformability checker. The absolute values of the correlation coefficients are increased from an average of 0.54 to 0.92. The effects of cell size, shape and orientation to the evaluation are discussed according to the experimental results. The proposed checker is expected to be useful for RBC evaluation in medical practices. Full article
(This article belongs to the Special Issue Biomedical Microfluidic Devices)
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Open AccessArticle Bifurcation Control of an Electrostatically-Actuated MEMS Actuator with Time-Delay Feedback
Micromachines 2016, 7(10), 177; doi:10.3390/mi7100177
Received: 11 August 2016 / Revised: 8 September 2016 / Accepted: 19 September 2016 / Published: 1 October 2016
Cited by 1 | PDF Full-text (5038 KB) | HTML Full-text | XML Full-text
Abstract
The parametric excitation system consisting of a flexible beam and shuttle mass widely exists in microelectromechanical systems (MEMS), which can exhibit rich nonlinear dynamic behaviors. This article aims to theoretically investigate the nonlinear jumping phenomena and bifurcation conditions of a class of electrostatically-driven
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The parametric excitation system consisting of a flexible beam and shuttle mass widely exists in microelectromechanical systems (MEMS), which can exhibit rich nonlinear dynamic behaviors. This article aims to theoretically investigate the nonlinear jumping phenomena and bifurcation conditions of a class of electrostatically-driven MEMS actuators with a time-delay feedback controller. Considering the comb structure consisting of a flexible beam and shuttle mass, the partial differential governing equation is obtained with both the linear and cubic nonlinear parametric excitation. Then, the method of multiple scales is introduced to obtain a slow flow that is analyzed for stability and bifurcation. Results show that time-delay feedback can improve resonance frequency and stability of the system. What is more, through a detailed mathematical analysis, the discriminant of Hopf bifurcation is theoretically derived, and appropriate time-delay feedback force can make the branch from the Hopf bifurcation point stable under any driving voltage value. Meanwhile, through global bifurcation analysis and saddle node bifurcation analysis, theoretical expressions about the system parameter space and maximum amplitude of monostable vibration are deduced. It is found that the disappearance of the global bifurcation point means the emergence of monostable vibration. Finally, detailed numerical results confirm the analytical prediction. Full article
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Open AccessArticle Hybrid Microfluidic Platform for Multifactorial Analysis Based on Electrical Impedance, Refractometry, Optical Absorption and Fluorescence
Micromachines 2016, 7(10), 181; doi:10.3390/mi7100181
Received: 1 June 2016 / Revised: 12 September 2016 / Accepted: 26 September 2016 / Published: 7 October 2016
Cited by 1 | PDF Full-text (6198 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes the development of a novel microfluidic platform for multifactorial analysis integrating four label-free detection methods: electrical impedance, refractometry, optical absorption and fluorescence. We present the rationale for the design and the details of the microfabrication of this multifactorial hybrid microfluidic
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This paper describes the development of a novel microfluidic platform for multifactorial analysis integrating four label-free detection methods: electrical impedance, refractometry, optical absorption and fluorescence. We present the rationale for the design and the details of the microfabrication of this multifactorial hybrid microfluidic chip. The structure of the platform consists of a three-dimensionally patterned polydimethylsiloxane top part attached to a bottom SU-8 epoxy-based negative photoresist part, where microelectrodes and optical fibers are incorporated to enable impedance and optical analysis. As a proof of concept, the chip functions have been tested and explored, enabling a diversity of applications: (i) impedance-based identification of the size of micro beads, as well as counting and distinguishing of erythrocytes by their volume or membrane properties; (ii) simultaneous determination of the refractive index and optical absorption properties of solutions; and (iii) fluorescence-based bead counting. Full article
(This article belongs to the Special Issue Advances in Microfluidic Devices for Cell Handling and Analysis)
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Open AccessFeature PaperArticle Modeling of Microdevices for SAW-Based Acoustophoresis — A Study of Boundary Conditions
Micromachines 2016, 7(10), 182; doi:10.3390/mi7100182
Received: 2 August 2016 / Accepted: 23 September 2016 / Published: 5 October 2016
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Abstract
We present a finite-element method modeling of acoustophoretic devices consisting of a single, long, straight, water-filled microchannel surrounded by an elastic wall of either borosilicate glass (pyrex) or the elastomer polydimethylsiloxane (PDMS) and placed on top of a piezoelectric transducer that actuates the
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We present a finite-element method modeling of acoustophoretic devices consisting of a single, long, straight, water-filled microchannel surrounded by an elastic wall of either borosilicate glass (pyrex) or the elastomer polydimethylsiloxane (PDMS) and placed on top of a piezoelectric transducer that actuates the device by surface acoustic waves (SAW). We compare the resulting acoustic fields in these full solid-fluid models with those obtained in reduced fluid models comprising of only a water domain with simplified, approximate boundary conditions representing the surrounding solids. The reduced models are found to only approximate the acoustically hard pyrex systems to a limited degree for large wall thicknesses and but not very well for acoustically soft PDMS systems shorter than the PDMS damping length of 3 mm. Full article
(This article belongs to the Special Issue Surface Acoustic Wave Microfluidics)
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Open AccessArticle Continuously Operating Biosensor and Its Integration into a Hermetically Sealed Medical Implant
Micromachines 2016, 7(10), 183; doi:10.3390/mi7100183
Received: 28 June 2016 / Revised: 23 September 2016 / Accepted: 28 September 2016 / Published: 9 October 2016
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Abstract
An integration concept for an implantable biosensor for the continuous monitoring of blood sugar levels is presented. The system architecture is based on technical modules used in cardiovascular implants in order to minimize legal certification efforts for its perspective usage in medical applications.
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An integration concept for an implantable biosensor for the continuous monitoring of blood sugar levels is presented. The system architecture is based on technical modules used in cardiovascular implants in order to minimize legal certification efforts for its perspective usage in medical applications. The sensor chip operates via the principle of affinity viscometry, which is realized by a fully embedded biomedical microelectromechanical systems (BioMEMS) prepared in 0.25-µm complementary metal–oxide–semiconductor (CMOS)/BiCMOS technology. Communication with a base station is established in the 402–405 MHz band used for medical implant communication services (MICS). The implant shall operate within the interstitial tissue, and the hermetical sealing of the electronic system against interaction with the body fluid is established using titanium housing. Only the sensor chip and the antenna are encapsulated in an epoxy header closely connected to the metallic housing. The study demonstrates that biosensor implants for the sensing of low-molecular-weight metabolites in the interstitial may successfully rely on components already established in cardiovascular implantology. Full article
(This article belongs to the Special Issue Implantable Microsystems)
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Open AccessArticle Oxide-Oxide Thermocompression Direct Bonding Technologies with Capillary Self-Assembly for Multichip-to-Wafer Heterogeneous 3D System Integration
Micromachines 2016, 7(10), 184; doi:10.3390/mi7100184
Received: 1 July 2016 / Revised: 9 September 2016 / Accepted: 27 September 2016 / Published: 10 October 2016
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Abstract
Plasma- and water-assisted oxide-oxide thermocompression direct bonding for a self-assembly based multichip-to-wafer (MCtW) 3D integration approach was demonstrated. The bonding yields and bonding strengths of the self-assembled chips obtained by the MCtW direct bonding technology were evaluated. In this study, chemical mechanical polish
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Plasma- and water-assisted oxide-oxide thermocompression direct bonding for a self-assembly based multichip-to-wafer (MCtW) 3D integration approach was demonstrated. The bonding yields and bonding strengths of the self-assembled chips obtained by the MCtW direct bonding technology were evaluated. In this study, chemical mechanical polish (CMP)-treated oxide formed by plasma-enhanced chemical vapor deposition (PE-CVD) as a MCtW bonding interface was mainly employed, and in addition, wafer-to-wafer thermocompression direct bonding was also used for comparison. N2 or Ar plasmas were utilized for the surface activation. After plasma activation and the subsequent supplying of water as a self-assembly mediate, the chips with the PE-CVD oxide layer were driven by the liquid surface tension and precisely aligned on the host wafers, and subsequently, they were tightly bonded to the wafers through the MCtW oxide-oxide direct bonding technology. Finally, a mechanism of oxide-oxide direct bonding to support the previous models was discussed using an atmospheric pressure ionization mass spectrometer (APIMS). Full article
(This article belongs to the Special Issue 3D Integration Technologies for MEMS)
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Open AccessArticle Cell Migration According to Shape of Graphene Oxide Micropatterns
Micromachines 2016, 7(10), 186; doi:10.3390/mi7100186
Received: 26 August 2016 / Revised: 5 October 2016 / Accepted: 7 October 2016 / Published: 14 October 2016
Cited by 1 | PDF Full-text (3551 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Photolithography is a unique process that can effectively manufacture micro/nano-sized patterns on various substrates. On the other hand, the meniscus-dragging deposition (MDD) process can produce a uniform surface of the substrate. Graphene oxide (GO) is the oxidized form of graphene that has high
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Photolithography is a unique process that can effectively manufacture micro/nano-sized patterns on various substrates. On the other hand, the meniscus-dragging deposition (MDD) process can produce a uniform surface of the substrate. Graphene oxide (GO) is the oxidized form of graphene that has high hydrophilicity and protein absorption. It is widely used in biomedical fields such as drug delivery, regenerative medicine, and tissue engineering. Herein, we fabricated uniform GO micropatterns via MDD and photolithography. The physicochemical properties of the GO micropatterns were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy. Furthermore, cell migration on the GO micropatterns was investigated, and the difference in cell migration on triangle and square GO micropatterns was examined for their effects on cell migration. Our results demonstrated that the GO micropatterns with a desired shape can be finely fabricated via MDD and photolithography. Moreover, it was revealed that the shape of GO micropatterns plays a crucial role in cell migration distance, speed, and directionality. Therefore, our findings suggest that the GO micropatterns can serve as a promising biofunctional platform and cell-guiding substrate for applications to bioelectric devices, cell-on-a-chip, and tissue engineering scaffolds. Full article
(This article belongs to the Special Issue Microdevices and Microsystems for Cell Manipulation)
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Open AccessArticle Design Optimization and Fabrication of High-Sensitivity SOI Pressure Sensors with High Signal-to-Noise Ratios Based on Silicon Nanowire Piezoresistors
Micromachines 2016, 7(10), 187; doi:10.3390/mi7100187
Received: 15 August 2016 / Revised: 28 September 2016 / Accepted: 6 October 2016 / Published: 14 October 2016
Cited by 2 | PDF Full-text (8203 KB) | HTML Full-text | XML Full-text
Abstract
In order to meet the requirement of high sensitivity and signal-to-noise ratios (SNR), this study develops and optimizes a piezoresistive pressure sensor by using double silicon nanowire (SiNW) as the piezoresistive sensing element. First of all, ANSYS finite element method and voltage noise
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In order to meet the requirement of high sensitivity and signal-to-noise ratios (SNR), this study develops and optimizes a piezoresistive pressure sensor by using double silicon nanowire (SiNW) as the piezoresistive sensing element. First of all, ANSYS finite element method and voltage noise models are adopted to optimize the sensor size and the sensor output (such as sensitivity, voltage noise and SNR). As a result, the sensor of the released double SiNW has 1.2 times more sensitivity than that of single SiNW sensor, which is consistent with the experimental result. Our result also displays that both the sensitivity and SNR are closely related to the geometry parameters of SiNW and its doping concentration. To achieve high performance, a p-type implantation of 5 × 1018 cm−3 and geometry of 10 µm long SiNW piezoresistor of 1400 nm × 100 nm cross area and 6 µm thick diaphragm of 200 µm × 200 µm are required. Then, the proposed SiNW pressure sensor is fabricated by using the standard complementary metal-oxide-semiconductor (CMOS) lithography process as well as wet-etch release process. This SiNW pressure sensor produces a change in the voltage output when the external pressure is applied. The involved experimental results show that the pressure sensor has a high sensitivity of 495 mV/V·MPa in the range of 0–100 kPa. Nevertheless, the performance of the pressure sensor is influenced by the temperature drift. Finally, for the sake of obtaining accurate and complete information over wide temperature and pressure ranges, the data fusion technique is proposed based on the back-propagation (BP) neural network, which is improved by the particle swarm optimization (PSO) algorithm. The particle swarm optimization–back-propagation (PSO–BP) model is implemented in hardware using a 32-bit STMicroelectronics (STM32) microcontroller. The results of calibration and test experiments clearly prove that the PSO–BP neural network can be effectively applied to minimize sensor errors derived from temperature drift. Full article
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Open AccessArticle Electrostatic Comb-Drive Actuator with High In-Plane Translational Velocity
Micromachines 2016, 7(10), 188; doi:10.3390/mi7100188
Received: 6 August 2016 / Revised: 6 September 2016 / Accepted: 29 September 2016 / Published: 17 October 2016
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Abstract
This work reports the design and opto-mechanical characterization of high velocity comb-drive actuators producing in-plane motion and fabricated using the technology of deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) substrate. The actuators drive vertical mirrors acting on optical beams propagating in-plane with
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This work reports the design and opto-mechanical characterization of high velocity comb-drive actuators producing in-plane motion and fabricated using the technology of deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) substrate. The actuators drive vertical mirrors acting on optical beams propagating in-plane with respect to the substrate. The actuator-mirror device is a fabrication on an SOI wafer with 80 μm etching depth, surface roughness of about 15 nm peak to valley and etching verticality that is better than 0.1 degree. The travel range of the actuators is extracted using an optical method based on optical cavity response and accounting for the diffraction effect. One design achieves a travel range of approximately 9.1 µm at a resonance frequency of approximately 26.1 kHz, while the second design achieves about 2 µm at 93.5 kHz. The two specific designs reported achieve peak velocities of about 1.48 and 1.18 m/s, respectively, which is the highest product of the travel range and frequency for an in-plane microelectromechanical system (MEMS) motion under atmospheric pressure, to the best of the authors’ knowledge. The first design possesses high spring linearity over its travel range with about 350 ppm change in the resonance frequency, while the second design achieves higher resonance frequency on the expense of linearity. The theoretical predications and the experimental results show good agreement. Full article
(This article belongs to the Special Issue Optofluidics 2016)
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Open AccessArticle Microfluidic 3D Helix Mixers
Micromachines 2016, 7(10), 189; doi:10.3390/mi7100189
Received: 12 July 2016 / Revised: 30 August 2016 / Accepted: 6 October 2016 / Published: 17 October 2016
Cited by 4 | PDF Full-text (6960 KB) | HTML Full-text | XML Full-text
Abstract
Polymeric microfluidic systems are well suited for miniaturized devices with complex functionality, and rapid prototyping methods for 3D microfluidic structures are increasingly used. Mixing at the microscale and performing chemical reactions at the microscale are important applications of such systems and we therefore
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Polymeric microfluidic systems are well suited for miniaturized devices with complex functionality, and rapid prototyping methods for 3D microfluidic structures are increasingly used. Mixing at the microscale and performing chemical reactions at the microscale are important applications of such systems and we therefore explored feasibility, mixing characteristics and the ability to control a chemical reaction in helical 3D channels produced by the emerging thread template method. Mixing at the microscale is challenging because channel size reduction for improving solute diffusion comes at the price of a reduced Reynolds number that induces a strictly laminar flow regime and abolishes turbulence that would be desired for improved mixing. Microfluidic 3D helix mixers were rapidly prototyped in polydimethylsiloxane (PDMS) using low-surface energy polymeric threads, twisted to form 2-channel and 3-channel helices. Structure and flow characteristics were assessed experimentally by microscopy, hydraulic measurements and chromogenic reaction, and were modeled by computational fluid dynamics. We found that helical 3D microfluidic systems produced by thread templating allow rapid prototyping, can be used for mixing and for controlled chemical reaction with two or three reaction partners at the microscale. Compared to the conventional T-shaped microfluidic system used as a control device, enhanced mixing and faster chemical reaction was found to occur due to the combination of diffusive mixing in small channels and flow folding due to the 3D helix shape. Thus, microfluidic 3D helix mixers can be rapidly prototyped using the thread template method and are an attractive and competitive method for fluid mixing and chemical reactions at the microscale. Full article
(This article belongs to the Special Issue Polymeric Microsystems)
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Open AccessArticle Variable-Focus Liquid Lens Integrated with a Planar Electromagnetic Actuator
Micromachines 2016, 7(10), 190; doi:10.3390/mi7100190
Received: 22 July 2016 / Revised: 30 September 2016 / Accepted: 7 October 2016 / Published: 17 October 2016
PDF Full-text (4775 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this paper, we design, fabricate and characterize a new electromagnetically actuated variable-focus liquid lens which consists of two polymethyl methacrylate (PMMA) substrates, a SU-8 substrate, a polydimethylsiloxane (PDMS) membrane, a permanent magnet and a planar electromagnetic actuator. The performance of this liquid
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In this paper, we design, fabricate and characterize a new electromagnetically actuated variable-focus liquid lens which consists of two polymethyl methacrylate (PMMA) substrates, a SU-8 substrate, a polydimethylsiloxane (PDMS) membrane, a permanent magnet and a planar electromagnetic actuator. The performance of this liquid lens is tested from four aspects including surface profiling, optical observation, variation of focal length and dynamic response speed. The results shows that with increasing current, the optical chamber PDMS membrane bulges up into a shape with a smaller radius of curvature, and the picture recorded by a charge-coupled device (CCD) camera through the liquid lens also gradually becomes blurred. As the current changes from −1 to 1.2 A, the whole measured focal length of the proposed liquid lens ranges from −133 to −390 mm and from 389 to 61 mm. Then a 0.8 A square-wave current is applied to the electrode, and the actuation time and relaxation time are 340 and 460 ms, respectively. The liquid lens proposed in the paper is easily integrated with microfluidic chips and medical detecting instruments due to its planar structure. Full article
(This article belongs to the Special Issue MEMS/NEMS for Biomedical Imaging and Sensing)
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Open AccessArticle In-Plane MEMS Shallow Arch Beam for Mechanical Memory
Micromachines 2016, 7(10), 191; doi:10.3390/mi7100191
Received: 15 August 2016 / Revised: 29 September 2016 / Accepted: 11 October 2016 / Published: 18 October 2016
Cited by 2 | PDF Full-text (2332 KB) | HTML Full-text | XML Full-text
Abstract
We demonstrate a memory device based on the nonlinear dynamics of an in-plane microelectromechanical systems (MEMS) clamped–clamped beam resonator, which is deliberately fabricated as a shallow arch. The arch beam is made of silicon, and is electrostatically actuated. The concept relies on the
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We demonstrate a memory device based on the nonlinear dynamics of an in-plane microelectromechanical systems (MEMS) clamped–clamped beam resonator, which is deliberately fabricated as a shallow arch. The arch beam is made of silicon, and is electrostatically actuated. The concept relies on the inherent quadratic nonlinearity originating from the arch curvature, which results in a softening behavior that creates hysteresis and co-existing states of motion. Since it is independent of the electrostatic force, this nonlinearity gives more flexibility in the operating conditions and allows for lower actuation voltages. Experimental results are generated through electrical characterization setup. Results are shown demonstrating the switching between the two vibrational states with the change of the direct current (DC) bias voltage, thereby proving the memory concept. Full article
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Open AccessArticle Cost-Efficient Wafer-Level Capping for MEMS and Imaging Sensors by Adhesive Wafer Bonding
Micromachines 2016, 7(10), 192; doi:10.3390/mi7100192
Received: 23 August 2016 / Revised: 3 October 2016 / Accepted: 11 October 2016 / Published: 18 October 2016
Cited by 1 | PDF Full-text (4088 KB) | HTML Full-text | XML Full-text
Abstract
Device encapsulation and packaging often constitutes a substantial part of the fabrication cost of micro electro-mechanical systems (MEMS) transducers and imaging sensor devices. In this paper, we propose a simple and cost-effective wafer-level capping method that utilizes a limited number of highly standardized
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Device encapsulation and packaging often constitutes a substantial part of the fabrication cost of micro electro-mechanical systems (MEMS) transducers and imaging sensor devices. In this paper, we propose a simple and cost-effective wafer-level capping method that utilizes a limited number of highly standardized process steps as well as low-cost materials. The proposed capping process is based on low-temperature adhesive wafer bonding, which ensures full complementary metal-oxide-semiconductor (CMOS) compatibility. All necessary fabrication steps for the wafer bonding, such as cavity formation and deposition of the adhesive, are performed on the capping substrate. The polymer adhesive is deposited by spray-coating on the capping wafer containing the cavities. Thus, no lithographic patterning of the polymer adhesive is needed, and material waste is minimized. Furthermore, this process does not require any additional fabrication steps on the device wafer, which lowers the process complexity and fabrication costs. We demonstrate the proposed capping method by packaging two different MEMS devices. The two MEMS devices include a vibration sensor and an acceleration switch, which employ two different electrical interconnection schemes. The experimental results show wafer-level capping with excellent bond quality due to the re-flow behavior of the polymer adhesive. No impediment to the functionality of the MEMS devices was observed, which indicates that the encapsulation does not introduce significant tensile nor compressive stresses. Thus, we present a highly versatile, robust, and cost-efficient capping method for components such as MEMS and imaging sensors. Full article
(This article belongs to the Special Issue 3D Integration Technologies for MEMS)
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Open AccessFeature PaperArticle A WSi–WSiN–Pt Metallization Scheme for Silicon Carbide-Based High Temperature Microsystems
Micromachines 2016, 7(10), 193; doi:10.3390/mi7100193
Received: 29 July 2016 / Revised: 26 September 2016 / Accepted: 6 October 2016 / Published: 20 October 2016
Cited by 1 | PDF Full-text (1987 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we present and discuss our new WSi–WSiN–Pt metallization scheme for SiC-based microsystems for applications in harsh environments. Stoichiometric material WSi was selected as contact material for SiC. The diffusion barrier material WSiN was deposited from the same target as the
[...] Read more.
In this paper, we present and discuss our new WSi–WSiN–Pt metallization scheme for SiC-based microsystems for applications in harsh environments. Stoichiometric material WSi was selected as contact material for SiC. The diffusion barrier material WSiN was deposited from the same target as the contact material in order to limit the number of different chemical elements in the scheme. Our scheme was kept as simple as possible regarding the number of layers and chemical elements. Our scheme shows very good long-term stability and suitability for SiC-based microsystems. The experimental evaluation concept used here includes a combination of physical, electrical, and mechanical analysis techniques. This combined advance is necessary since modern physical analysis techniques still offer only limited sensitivity for detecting minimal changes in the metallization scheme. Full article
(This article belongs to the Special Issue SiC-Based Microsystems)
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Review

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Open AccessReview Neural Probes for Chronic Applications
Micromachines 2016, 7(10), 179; doi:10.3390/mi7100179
Received: 9 July 2016 / Revised: 12 September 2016 / Accepted: 26 September 2016 / Published: 2 October 2016
Cited by 2 | PDF Full-text (8068 KB) | HTML Full-text | XML Full-text
Abstract
Developed over approximately half a century, neural probe technology is now a mature technology in terms of its fabrication technology and serves as a practical alternative to the traditional microwires for extracellular recording. Through extensive exploration of fabrication methods, structural shapes, materials, and
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Developed over approximately half a century, neural probe technology is now a mature technology in terms of its fabrication technology and serves as a practical alternative to the traditional microwires for extracellular recording. Through extensive exploration of fabrication methods, structural shapes, materials, and stimulation functionalities, neural probes are now denser, more functional and reliable. Thus, applications of neural probes are not limited to extracellular recording, brain-machine interface, and deep brain stimulation, but also include a wide range of new applications such as brain mapping, restoration of neuronal functions, and investigation of brain disorders. However, the biggest limitation of the current neural probe technology is chronic reliability; neural probes that record with high fidelity in acute settings often fail to function reliably in chronic settings. While chronic viability is imperative for both clinical uses and animal experiments, achieving one is a major technological challenge due to the chronic foreign body response to the implant. Thus, this review aims to outline the factors that potentially affect chronic recording in chronological order of implantation, summarize the methods proposed to minimize each factor, and provide a performance comparison of the neural probes developed for chronic applications. Full article
(This article belongs to the Special Issue Implantable Microsystems)
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Open AccessReview Flexible, Penetrating Brain Probes Enabled by Advances in Polymer Microfabrication
Micromachines 2016, 7(10), 180; doi:10.3390/mi7100180
Received: 23 July 2016 / Accepted: 19 September 2016 / Published: 4 October 2016
Cited by 2 | PDF Full-text (2816 KB) | HTML Full-text | XML Full-text
Abstract
The acquisition of high-fidelity, long-term neural recordings in vivo is critically important to advance neuroscience and brain–machine interfaces. For decades, rigid materials such as metal microwires and micromachined silicon shanks were used as invasive electrophysiological interfaces to neurons, providing either single or multiple
[...] Read more.
The acquisition of high-fidelity, long-term neural recordings in vivo is critically important to advance neuroscience and brain–machine interfaces. For decades, rigid materials such as metal microwires and micromachined silicon shanks were used as invasive electrophysiological interfaces to neurons, providing either single or multiple electrode recording sites. Extensive research has revealed that such rigid interfaces suffer from gradual recording quality degradation, in part stemming from tissue damage and the ensuing immune response arising from mechanical mismatch between the probe and brain. The development of “soft” neural probes constructed from polymer shanks has been enabled by advancements in microfabrication; this alternative has the potential to mitigate mismatch-related side effects and thus improve the quality of recordings. This review examines soft neural probe materials and their associated microfabrication techniques, the resulting soft neural probes, and their implementation including custom implantation and electrical packaging strategies. The use of soft materials necessitates careful consideration of surgical placement, often requiring the use of additional surgical shuttles or biodegradable coatings that impart temporary stiffness. Investigation of surgical implantation mechanics and histological evidence to support the use of soft probes will be presented. The review concludes with a critical discussion of the remaining technical challenges and future outlook. Full article
(This article belongs to the Special Issue Implantable Microsystems)
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Open AccessReview Review of Microfluidic Photobioreactor Technology for Metabolic Engineering and Synthetic Biology of Cyanobacteria and Microalgae
Micromachines 2016, 7(10), 185; doi:10.3390/mi7100185
Received: 27 April 2016 / Revised: 16 August 2016 / Accepted: 16 August 2016 / Published: 11 October 2016
PDF Full-text (2121 KB) | HTML Full-text | XML Full-text
Abstract
One goal of metabolic engineering and synthetic biology for cyanobacteria and microalgae is to engineer strains that can optimally produce biofuels and commodity chemicals. However, the current workflow is slow and labor intensive with respect to assembly of genetic parts and characterization of
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One goal of metabolic engineering and synthetic biology for cyanobacteria and microalgae is to engineer strains that can optimally produce biofuels and commodity chemicals. However, the current workflow is slow and labor intensive with respect to assembly of genetic parts and characterization of production yields because of the slow growth rates of these organisms. Here, we review recent progress in the microfluidic photobioreactors and identify opportunities and unmet needs in metabolic engineering and synthetic biology. Because of the unprecedented experimental resolution down to the single cell level, long-term real-time monitoring capability, and high throughput with low cost, microfluidic photobioreactor technology will be an indispensible tool to speed up the development process, advance fundamental knowledge, and realize the full potential of metabolic engineering and synthetic biology for cyanobacteria and microalgae. Full article
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