Showing papers in "Sensors and Actuators A-physical in 2003"
TL;DR: In this article, the authors presented an analytical model for support loss in clamped-free (C-F) and clampedclamped (C -C) micromachined beam resonators with in-plane flexural vibrations.
Abstract: This paper presents an analytical model for support loss in clamped–free (C–F) and clamped–clamped (C–C) micromachined beam resonators with in-plane flexural vibrations. In this model, the flexural vibration of a beam resonator is described using the beam theory. An elastic wave excited by the shear stress of the beam resonator and propagating in the support structure is described through the 2D elastic wave theory, with the assumption that the beam thickness (h) is much smaller than the transverse elastic wavelength (λT). Through the combination of these two theories and the Fourier transform, closed-form expressions for support loss in C–F and C–C beam resonators are obtained. Specifically, closed-form expression for the support loss in a C–C beam resonator is derived for the first time. The model suggests lower support quality factor (Qsupport) for higher order resonant modes compared to the fundamental mode of a beam resonator. Through comparison with experimental data, the validity of the presented analytical model is demonstrated. © 2003 Elsevier B.V. All rights reserved.
374 citations
TL;DR: In this paper, the effective transverse piezoelectric coefficient e(31,f) of sol-gel processed films was investigated as a function of composition, film texture and film thickness.
Abstract: Pb(Zr-x, Ti1-x)O-3 (PZT) piezoelectric thin films are of major interest in MEMS technology for their ability to provide electro-mechanical coupling. In this work, the effective transverse piezoelectric coefficient e(31,f) of sol-gel processed films was investigated as a function of composition, film texture and film thickness. Dense, textured and crack-free PZT films have been obtained on silicon substrates up to a thickness of 4 mum. Crystallization anneals have been performed for every 0.25 mum. Nucleation on the previous perovskite layer combined with directional growth leads to a gradient of the compositional parameter x of +/-20% (at x = 0.53 average composition). Best properties have been achieved with {100}-textured film of x = 0.53 composition. Large remanent e(31,f) values of -11 to -12 C/m(2) have been obtained in the whole thickness range of 1-4 mum. These values are superior to values of undoped bulk ceramics, but smaller than in current, optimized (doped) bulk PZT. (C) 2003 Elsevier Science B.V. All rights reserved.
370 citations
TL;DR: In this paper, the Bead ARray Counter (BARC) was developed for the capture and detection of micron-sized, paramagnetic beads on a chip containing an array of giant magnetoresistive sensors.
Abstract: We are developing a biosensor system, the Bead ARray Counter (BARC), based on the capture and detection of micron-sized, paramagnetic beads on a chip containing an array of giant magnetoresistive (GMR) sensors. Here we describe the design and performance of our current chip with 64 sensor zones, compare its performance with the previous chip design, and discuss a simple analytical model of the sensor micromagnetics. With assay-ready Dynal M-280 microbeads (2.8 μm diameter), our threshold for detection is approximately 10 beads per 200 μm-diameter sensor. Single beads made of solid Ni 30 Fe 70 can easily be detected, but they must be made biocompatible. The relatively large size of our sensors helps to improve their practical sensitivity compared with other microsensor-based magnetic particle detectors.
364 citations
TL;DR: In this paper, the authors present fluxgate sensors with a resolution comparable with high-temperature superconducting quantum interference devices (SQUIDs), while their precision is the best of vectorial field sensors.
Abstract: This paper reviews recent achievements in the technology and design of fluxgate sensors and magnetometers. The major recent trends were decreasing of the sensor size, power consumption and price, and, on the other hand, increasing of the precision in the large range of the measured fields. The potential frequency range was increased up to units of kHz. Present fluxgate sensors have a resolution comparable with high-temperature superconducting quantum interference devices (SQUIDs), while their precision is the best of vectorial field sensors.
302 citations
TL;DR: In this paper, various principles of piezoelectric motors are introduced in addition to suitable fabrication processes for their miniaturization, proper fabrication processes including thick deposition methods are important.
Abstract: There is great demand for micro- or miniaturized actuators for practical application. However, magnetic coils of electromagnetic motors are an obstacle to such miniaturization because of their complicated construction. Furthermore, electrostatic micro-motors fabricated by IC-processing cannot generate sufficient output power. Piezoelectric motors are promising because of their simple construction and high power density. In fact, some piezoelectric actuators have been or are close to being launched in the market. For their miniaturization, proper fabrication processes including thick deposition methods are important. In this review, various principles of piezoelectric motors are introduced in addition to suitable fabrication processes.
296 citations
TL;DR: In this paper, an optoelectrowetting (OEW) surface is realized by integrating a photoconductive material underneath a two-dimensional array of electrowetting electrodes, and a micro-liter droplet of deionized water has been successfully transported by a 4 mW laser beam across a 1 cm � 1 cm OEW surface.
Abstract: Optical actuation of liquid droplets has been experimentally demonstrated for the first time using a novel optoelectrowetting (OEW) principle. The optoelectrowetting surface is realized by integrating a photoconductive material underneath a two-dimensional array of electrowetting electrodes. Contact angle change as large as 308 has been achieved when illuminated by a light beam with an intensity of 65 mW/cm 2 . A micro-liter droplet of deionized water has been successfully transported by a 4 mW laser beam across a 1 cm � 1 cm OEW surface. The droplet speed is measured to be 7 mm/s. Light actuation enables complex microfluidic functions to be performed on a single chip without encountering the wiring bottleneck of two-dimensional array of electrowetting electrodes. Published by Elsevier Science B.V.
260 citations
TL;DR: In this article, the authors extend the electromechanical characterisation of dielectric elastomer actuators by measuring the isotonic transverse strain, the isometric transverse stress and the driving current due to a 2 s high voltage impulse.
Abstract: This work intends to extend the electromechanical characterisation of dielectric elastomer actuators. Planar actuators were realised with a 50m-thick film of an acrylic elastomer coated with compliant electrodes. The isotonic transverse strain, the isometric transverse stress and the driving current, due to a 2 s high voltage impulse, were measured for four electrode materials (thickened electrolyte solution, graphite spray, carbon grease and graphite powder), four transverse prestress values (19.6, 29.4, 39.2 and 49.0 kPa) and different driving voltages (up to the dielectric breakdown voltage). Results showed that the electrode material and prestress strongly influence the electromechanical performances of the devices. Actuators with graphite spray electrodes and transverse prestress of 39.2 kPa exhibited an isotonic transverse strain of 6% at 49 V/m, with a driving current per unit electrode area of 3.5 A/cm 2 , and an isometric transverse stress of 49 kPa at 42 V/m. An electromechanical coupling efficiency of 10% at 21 V/m was calculated for actuators with thickened electrolyte solution electrodes and a transverse prestress of 29.4 kPa. The presented data permits to choose the best electrode material and the best prestress value (among those tested), to obtain the maximum isotonic transverse strain, the maximum isometric transverse stress or the maximum efficiency for different ranges of applied electric field. © 2003 Elsevier B.V. All rights reserved.
253 citations
TL;DR: In this paper, the extrinsic Fabry-Perot interferometer (EFPI) and fiber Bragg grating (FBG) sensors are real-time employed to simultaneously monitor the cure process of CFRP composite laminates with and without damage.
Abstract: Structural health monitoring (SHM) including the real-time cure monitoring and non-destructive evaluation (NDE) in-service is very important and definitely demanded for safely working of high performance composite structures in situ. It is very difficult to carry out by using conventional methods. A unique opportunity was provided to real-time monitor the health status of composite structures by using embedded fiber optic sensors (FOSs). In this paper, the extrinsic Fabry–Perot interferometer (EFPI) and fiber Bragg grating (FBG) sensors are real-time employed to simultaneously monitoring the cure process of CFRP composite laminates with and without damage. The results show that both embedded EFPI and FBG sensors could be used to monitor the cure progress of composite materials and detect the occurred damage on-line during the fabrication of composite structures. Furthermore, the NDE of smart composite laminates embedded both EFPI and FBG sensors are performed by using the three-point bending test. The experimental results present that the flexural strain of CFRP composite laminates with damage is more than that of CFRP laminates without damage under same load as we expected. Both EFPI and FBG sensors also show the excellent correlation during the cure monitoring and bending test.
251 citations
TL;DR: In this article, the transverse piezoelectric properties of Pb(Zr, Ti)O 3 (PZT) films were estimated using a simple measuring method.
Abstract: Transverse piezoelectric properties of Pb(Zr, Ti)O 3 (PZT) films were estimated using a simple measuring method we developed. The c -axis oriented PZT films were epitaxially grown on Pt/MgO substrates, while the polycrystalline PZT films with the preferential orientation of 〈1 1 1〉 were deposited on Pt/Ti/Si substrates using rf sputtering technique. The piezoelectric characteristics of the PZT films with different crystalline structures were evaluated by the tip deflection of the unimorph cantilevers of the strip specimen just cleaved out from the substrates. The PZT films on MgO substrates showed excellent linear piezoelectric deflection to the applied voltage with the stable piezoelectric coefficient e 31 of −4.7 to −4.9 C/m 2 which is caused by the ideal lattice motion of the single domain structure. On the other hand, the PZT films on Si substrates showed large hysteresis of the deflection and the value of e 31 ranged from −4.3 to −7.5 C/m 2 according to the applied voltage. The non-linear as well as large piezoelectric response of the PZT films on Si is similar to conventional bulk PZT ceramics, indicating that the reorientation of domains whose polar axes are not parallel to the electric field is superimposed on the lattice motion.
208 citations
TL;DR: Magnetic micro-electro-mechanical systems (Magnetic MEMS) as mentioned in this paper are based on electromagnetic interactions between magnetic materials and active (coils) or passive magnetic field sources (permanent magnets).
Abstract: Magnetic micro-electro-mechanical-systems (Magnetic MEMS) present a new class of conventional MEMS devices with great potential for science and applications. Using the same technology as for MEMS and incorporating magnetic materials as the sensing or active element offer new capabilities and open new markets within the information technology, automotive, biomedical, space and instrumentation. Magnetic MEMS are based on electromagnetic interactions between magnetic materials and active (coils) or passive magnetic field sources (permanent magnets). At the micrometer scale Magnetic MEMS offer distinct advantages as compared with electrostatic and piezoelectric actuators in strength, polarity and distance of actuation to name a few. The compatibility of magnetic materials with MEMS technology is a key issue, which is addressed by a number of groups worldwide. In this article, we will present an overview of the Magnetic MEMS technology and we will present some of the existing and future applications.
185 citations
TL;DR: In this article, a 3 mm ×3 mm ×0.003 ǫmm piezoelectric membrane acoustic device, which works as a microphone and a microspeaker, is presented.
Abstract: This paper reports on a 3 mm ×3 mm ×0.003 mm piezoelectric membrane acoustic device, which works as a microphone and a microspeaker. It has a 0.5 μm thick zinc oxide (ZnO) piezoelectric thin film on a 1.5 μm thick low-stress silicon nitride membrane, made of LPCVD. The maximum deflection in the center of membrane, using laser Doppler vibrometer (LDV), is 1 μm at 7.3 kHz with input drive 15 V0-P (zero-peak). The output sound pressure level (SPL) of microspeaker is 76.3 dB SPL at 7.3 kHz, and 83.1 dB SPL at 13.3 kHz with input drive 15 V0-P. The distance between the reference microphone and piezoelectric microspeaker is 1 cm. The sensitivity of the microphone is 0.51 mV/Pa at 7.3 kHz with noise level of 18 dB SPL.
TL;DR: In this article, the dynamic response of a Bimorph® cantilever (10 mm × 1 mm × 0.5 ǫ) is investigated in air and in Fluorinert™ (3M) liquids with varying viscosity but nearly the same density.
Abstract: The dynamic response of a Bimorph® cantilever ( 10 mm ×1 mm ×0.5 mm) is investigated experimentally in air and in Fluorinert™ (3M™) liquids with varying viscosity but nearly the same density. The gap height d between the cantilever and a solid surface is varied from millimeter to micrometer range and the response of the cantilever is interpreted in terms of added mass ma and viscous damping coefficient cv. Key dimensionless parameters based on the Navier–Stokes (N–S) equations include the kinetic Reynolds number Rk=ωb2/4η (ω is the circular frequency and η the kinematic viscosity) and the dimensionless gap height d/b, where b is the cantilever width. The added mass increases (and resonance frequency decreases) with increasing fluid density and decreasing d/b, where the dimensionless gap height d/b has a stronger effect. The added mass coefficient is independent of Rk for Rk>270 and d/b>0.01. The N–S equations can be linearized when d/b>0.1. In liquids, the viscous damping coefficient increases (and the Q-factor decreases) with increasing dynamic viscosity (decreasing Rk) and decreasing d/b. In general, the viscous terms in the N–S equations affect the viscous damping coefficient at all gaps. The implications of the results on sensor design are briefly discussed.
TL;DR: In this paper, the surface area of sputtered gold and electrodeposited gold was quantitatively compared by quantitatively comparing the surface areas obtained by different current densities, and it was found that the electroplated gold layer deposited at 125nA out of a 4.5mM Au(CN) 2 − solution for 8min (deposition charge density of 4.8c/cm 2 ) gives an electrodeposed gold layer having eight times larger effective surface area compared to a sputtered Gold layer.
Abstract: For sensor and actuator devices where conducting polymers are electrochemically deposited on the surface of electrodes, the adhesion between the deposited polymer film and substrate metal electrode is crucial for maintaining the long-term performance. Electroplating gold on sputtered gold microelectrode sites was studied as a means to provide a fuzzy, roughened surface for electrodeposited conducting polymers to adhere. It was found that concentration of Au(CN) 2 − solution and current density played important roles in controlling the morphology of the deposits. Impedance spectroscopy was used to quantitatively compare the surface area of sputtered gold and electrodeposited gold obtained by different current densities. By examining the impedance response in the limit of low frequencies, we found that the electroplated gold layer deposited at 125 nA out of a 4.5 mM Au(CN) 2 − solution for 8 min (deposition charge density of 4.8 C/cm 2 ) gives an electrodeposited gold layer having eight times larger effective surface area compared to a sputtered gold layer. This increase in surface area leads to improved adhesion of the subsequently deposited electropolymerized conducting polymers. Conducting polymer PPy/PSS deposited on the electrodes that were pre-processed with a fuzzy electroplated gold layer showed electrochemical properties and morphologies similar to those deposited on smooth sputtered gold electrodes. A significant improvement on adhesion of these polymer films on the fuzzy gold substrate was demonstrated.
TL;DR: Transfection of an individual cell is shown to prove the feasibility of single-cell genetic engineering and an improved micro-electroporation chip that employs microfluidic channels to precisely handle cells in a flow-through manner is introduced to achieve high effectiveness in genetic manipulation of cells.
Abstract: Genetic manipulation of individual cells is of great interests in biology and biotechnology. Micro-electroporation technology has been demonstrated in our previous work with the capability of performing controlled electroporation to facilitate gene transfer in individual biological cells. This paper extends the work by introducing the design and fabrication of an improved micro-electroporation chip that employs microfluidic channels to precisely handle cells in a flow-through manner to achieve high effectiveness in genetic manipulation of cells. Controlled introduction of macromolecules into individual cells are also demonstrated. Transfection of an individual cell is shown to prove the feasibility of single-cell genetic engineering.
TL;DR: In this article, replica molded elastomeric micro-channels with filtered silicon detector arrays are used to miniaturize spectrometers for spectroscopy in the visible and near-UV wavelength range.
Abstract: We describe a new approach for miniaturizing spectrometers by combining replica molded elastomeric micro-channels with filtered silicon detector arrays. Elastomers are excellent transparent materials, which provide hermetic seals to silicon dioxide and allow sensitive absorption and fluorescent spectroscopy in the visible and near-UV wavelength range. When integrated on dense detector arrays, such spectroscopy can be conducted on picoliter sample volumes. Elastomeric fluidic systems also permit easy integration of spectroscopic measurements with control functions for reaction monitoring and biological drug delivery and analysis systems. Here we present some results from our first experiments in which we explore the sensitivity of spectroscopic measurements within microfluidic channels. We show that multi-channel spectrometers defined on complementary metal oxide semiconductor (CMOS) silicon detector arrays can be used to obtain absorption signatures even for dilute dye solutions.
TL;DR: In this paper, room and elevated temperature tensile, creep and high-cycle fatigue properties of electrodeposited LIGA Ni microsamples have been measured and are being used to predict the reliability of LigA Ni MEMS structures.
Abstract: Room and elevated temperature tensile, creep and high-cycle fatigue properties of electrodeposited LIGA Ni microsamples have been measured and are being used to predict the reliability of LIGA Ni MEMS structures Tensile specimens with dimensions of hundreds of microns have been LIGA fabricated and characterized in terms of their underlying microstructure, elevated temperature tensile and creep strength and their high-cycle fatigue performance The stiffness of these LIGA Ni structures was found to be reduced by the introduction of porosity during the plating process The strength of these structures was observed to decrease dramatically at temperatures above 200 °C At stresses significantly below the yield strength, substantial creep deformation was observed at moderately elevated temperatures The fatigue life of the LIGA Ni microsamples increased with decreasing stress amplitude in a manner comparable to what has been reported for wrought Ni An apparent fatigue limit was observed for the LIGA Ni microsamples, but the importance of underlying microstructure and component geometry on the fatigue life was also highlighted
TL;DR: In this article, the development and testing of a micro heat engine is presented, which is an external combustion engine that converts thermal power to mechanical power through the use of a novel thermodynamic cycle.
Abstract: The development and testing of a micro heat engine is presented. For the first time the production of electrical power by a dynamic micro heat engine is demonstrated. The prototype micro heat engine is an external combustion engine that converts thermal power to mechanical power through the use of a novel thermodynamic cycle. Mechanical power is converted into electrical power through the use of a thin-film piezoelectric membrane generator. This design is well suited to photolithography-based batch fabrication methods, and is unlike any conventionally manufactured macro-scale engine.
TL;DR: In this article, the authors demonstrate the importance of thermoelastic damping (TED) in MEMS resonant sensors and demonstrate that both the choice of materials and variations in device design can lead to significant differences in the measured quality (Q) factors of the device.
Abstract: We present new experimental data illustrating the importance of thermoelastic damping (TED) in MEMS resonant sensors. MEMS gyroscopes have been used to demonstrate that both the choice of materials and variations in device design can lead to significant differences in the measured quality (Q) factors of the device. These differences in the Q-factor can be explained by including the contribution of thermoelastic damping, which varies strongly between the different silicon etch-stop compositions used in this study. Known damping mechanisms, such as fluid damping, anchor damping, and electronics damping are minimized and held fixed in this experiment so that materials effects can be isolated.
TL;DR: In this paper, a linear strain distribution is assumed across the thickness of the passive plate of the lead zirconate titanate (PZT) actuator given that the mechanical properties such as Young's modulus and Poisson ratio of the actuator and passive plate are close.
Abstract: Closed form analytical equations are important tools for predicting and optimizing the behavior of a piezoelectric microactuator for micropump applications. However, there is no reliable analytical solution to date to analyze the behavior of a circular piezoelectric microactuator for a valveless micropump. In this paper, a linear strain distribution is assumed across the thickness of the passive plate of the lead zirconate titanate (PZT) actuator given that the mechanical properties such as Young’s modulus and Poisson ratio of the actuator and the passive plate are close. An analytical equation for the passive plate deflection is derived upon this assumption. The analytical result shows excellent agreement with experimental data as well as the results from finite element simulation. Based on this analytical model, the effects of several important parameters and nondimensional variable groups on the actuator performance have been investigated. These parameters and variables include the dimensions and mechanical properties of the PZT disk, the passive plate, and the bonding layer material.
TL;DR: In this review paper, the performance (in particular the magnetic field resolution), micro-fabrication technologies and applications of micrometer sized Hall effect devices are summarized.
Abstract: In this review paper, we summarize the performance (in particular the magnetic field resolution), micro-fabrication technologies and applications of micrometer sized Hall effect devices. Additionally, our activities in this domain are briefly described.
TL;DR: In this article, the authors describe the fabrication approach of coating released microelectromechanical systems (MEMS) devices with nanometer-thin films using atomic layer deposition (ALD), which is capable of depositing a variety of thin-film materials to protect MEMS devices from electrical breakdown, mechanical wear and stiction failure.
Abstract: This paper describes the novel fabrication approach of coating released micro-electromechanical systems (MEMS) devices with nanometer-thin films using atomic layer deposition (ALD). The ALD process is capable of depositing a variety of thin-film materials to protect MEMS devices from electrical breakdown, mechanical wear and stiction failure. ALD ensures conformal film coverage on all sides of a released MEMS device and can be performed at relatively low temperature of 177 °C. The ALD film thickness can be precisely controlled at the atomic level as each reaction cycle deposits approximately one atomic monolayer. To demonstrate the concept of conformal layer deposition, ALD alumina (Al2O3) films were deposited onto released MEMS cantilever beams and the coated devices were subsequently analyzed using cross-sectional scanning electron microscopy. Electrostatic testing of the coated MEMS cantilever beams revealed that the ALD Al2O3 films prevented electrical shorting and failure when the devices were activated beyond the pull-in voltage. The curvature and increase in beam stiffness of MEMS devices resulting from the ALD Al2O3 coating were also investigated.
TL;DR: In this paper, a method to fabricate multi-layer, embedded micro fluidic structures by simply employing dosage-controlled UV exposure on thick SU-8 resist and anti-reflection coating on the bottom surface to prevent the reflection UV-light from inducing exposure was proposed.
Abstract: This paper proposes a novel method to fabricate multi-layers, embedded micro fluidic structures by simply employing dosage-controlled UV exposure on thick SU-8 resist and anti-reflection coating on the bottom surface to prevent the reflection UV-light from inducing exposure. Experimental results show the top wall thickness of the embedded micro-channels can be well controlled in a resolution of 2 μm for the UV dosage from 120 to 190 mJ/cm2. Stacked micro-channels have also been successfully realized and showed no interference on the bottom structures when the top structures are being exposed. Numerical simulation of the top wall thickness by UV exposure dosage control has also been conducted, and the comparison between the calculated and experimental results showed similarity in trend. This simple and inexpensive method can be applied to fabricate multi-layers of complex fluidic systems for the applications of μTAS (MicroTotal Analysis System), inkjet printhead, capillary electrophoresis, and micro PCR (Polymerase Chain Reaction).
TL;DR: In this paper, the temperature profile becomes asymmetric when an acceleration is applied, and two temperature detectors are placed on both sides to measure the differential temperature, and the sensitivity is proportional to the heating power and decreases when the room temperature increases.
Abstract: The techniques of micromachining silicon are used for the manufacturing of a thermal accelerometer. This sensor requires no solid proof mass and has a low cost production. A heating resistor creates a symmetrical temperature profile and two temperature detectors are placed on both sides. When an acceleration is applied, the temperature profile becomes asymmetric and the two detectors measure the differential temperature. Platinum resistors deposited by electron beam evaporation on a SiN x membrane are used as heater and temperature sensors. This paper presents measurements of temperature profile and sensitivity according to the distance heater–detector, power supplied and room temperature. It shows that the sensitivity is proportional to the heating power and decreases when the room temperature increases. Experimental results in tiltmeter utilization and in a centrifuge are also presented. A 3 dB bandwidth of 20 Hz is measured applying a sinusoidal acceleration and the equivalent acceleration noise is found to be 0.3 mg RMS.
TL;DR: In this article, the authors proposed a three-dimensional hybrid microfluidic and nanofluidic system using poly(dimethylsiloxane) (PDMS) monoliths in planes above and below a 6-10-μm thick nanoporous polycarbonate nuclear track-etched (PCTE) membrane.
Abstract: Crossed microfluidic channels are fabricated in poly(dimethylsiloxane) (PDMS) monoliths in planes above and below a 6–10 μm thick nanoporous polycarbonate nuclear track-etched (PCTE) membrane to form a three-dimensional hybrid microfluidic and nanofluidic system. The use of commercially available nanoporous membranes allows quick and economical fabrication of nanochannel architectures to provide fluidic communication between microfluidic layers. More importantly, these nanoporous membranes add functionality to the system as gateable interconnects. These nanofluidic interconnects enable control of net fluid flow based on a number of different physical characteristics of the sample stream, the microfluidic channels and the nanochannels, leading to hybrid fluidic architectures of considerable versatility. Because the nanofluidic membrane can have surfaces with excess charge of either polarity, the net flow direction inside the microdevices is principally controlled by two factors: the magnitude of the electrical and physical flow impedance of the nanoporous membrane relative to that of the microchannels and the surface chemical functionalities which determine the polarity of the excess charge in the nanochannels. The nanochannel impedance may be manipulated by varying membrane pore size. Flow control is investigated by monitoring electrokinetic transport of both neutral and negatively charged fluorescent probes, by means of laser-induced fluorescence and fluorescence microscopy, while varying solution and nanochannel properties. When the pore size of the PCTE membrane is small, the impedance is large and the polarity of the nanochannel surface charge determines the overall direction of the net electroosmotic flow. When the combined impedance of the upper and lower microchannels exceeds 30 times the impedance of the nanochannel membrane, the direction of the flow is based on the negative surface charge of the PDMS microchannels.
TL;DR: In this paper, an innovative micromachine-based flow cytometer integrated with buried optical waveguides on soda-lime glass substrates is reported, which increases light guiding efficiency due to smoother channel surface and larger difference of refractive index between SU-8 and organic-based SOG.
Abstract: This paper reports an innovative micromachine-based flow cytometer integrated with buried optical waveguides on soda-lime glass substrates. A novel optical waveguide using SU-8/spin-on-glass (SOG) double-layer structure is demonstrated, which increases light guiding efficiency due to smoother channel surface and larger difference of refractive index between SU-8 and organic-based SOG. Instead of using complex optical alignment system, detection light source is coupled with the waveguide with direct insertion of an etched optical fiber. A very high coupling efficiency can be achieved using this approach. In this study, the performance of the waveguides and insertion losses are measured. Experimental results show that the optical loss is less than 15 dB for a 40 mm long waveguide. With the integrated optical waveguides, a micro flow cytometer capable of particle counting has been realized. Data show that microparticles can be hydrodynamically focused and counted successfully without fluorescent labeling using the miniaturized flow cytometer with the integrated optical detection system.
TL;DR: A review of theoretical models of giant magnetoimpedance (GMI) is presented in this article, starting from simple quasistatic models and ending with the complex dynamic models based on the simultaneous solution of linearized Maxwell and Landau-Lifshitz equations.
Abstract: A review of theoretical models of giant magnetoimpedance (GMI) is presented. The whole frequency range from kHz to GHz is covered starting from the simple quasistatic models and ending with the complex dynamic models based on the simultaneous solution of linearized Maxwell and Landau–Lifshitz equations. The similarity between GMI and FMR is emphasized. The asymmetric GMI (AGMI) behavior is discussed in more detail. Three different mechanisms of asymmetry are outlined. Based on the theoretical results the rules for obtaining high performance GMI materials are put forward.
TL;DR: In this article, two kinds of hydrophobic valves in microfluidic applications were presented, one is based on special geometrical designs and chemical modification for silicon dioxide and glass microchannels.
Abstract: Fluid–surface interactions can become dominant in microfluidics, which is a central technology in a number of miniaturized systems for chemical, biological and medical applications. In this paper, two kinds of hydrophobic valves in microfluidic applications were presented. One is based on special geometrical designs and chemical modification for silicon dioxide and glass microchannels. Silicon dioxide and Pyrex glass surfaces, which are hydrophilic originally, are modified with octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) to be hydrophobic, with the contact angles up to ∼102 and 103°, respectively, for water. The formation of OTS SAMs takes
TL;DR: In this paper, an adhesive wafer-level bonding technique is described in which the adhesive material is structured prior to bonding, which can be used to create encapsulated cavities of different heights and sizes for surface micromachined devices directly in the bonding layer.
Abstract: In this work we describe an adhesive wafer-level bonding technique in which the adhesive material is structured prior to bonding. This technique can be used to create encapsulated cavities of different heights and sizes for surface micromachined devices directly in the bonding layer. Benzocyclobutene (BCB) was used as the adhesive bonding material. The structuring of the BCB was done either by dry etching or by using photosensitive BCB. The process parameters needed to achieve a high bond quality while retaining the shapes of the structures in the intermediate bonding layer have been investigated extensively. Both dry-etch and photosensitive BCB were found to be suitable for selective adhesive bonding. The dry-etch BCB must be soft-baked to a polymerisation degree of 50–60% to both withstand the patterning procedure and to be sticky enough for the following bonding. Soft-baking is not necessary for the photosensitive BCB. For both types of BCB, good bond results have been achieved with a bonding pressure of 2–3 bar and full curing of the BCB at 250 °C for 1 h. Furthermore, helium leak tests have been performed to investigate the suitability of selective adhesive bonding for applications with demands on quasi-hermetic seals. Cavities created with this bonding techniques showed a leak rate between 1.4×10−8 and 4.8×10−8 kg m2 s−3 (1.4×10−7 and 4.8×10−7 mbar l s−1), which is 3–10 times higher than the limit of MIL-STD 883E. Therefore, this encapsulation technique does not provide sufficient gas-tightness to fulfill the requirements of hermetic electronic encapsulations.
TL;DR: In this paper, the authors investigated the electromechanical response characteristics of the ion exchange polymer metal composite (IPMC) actuator according to the driving method and concluded that large consumption of current during actuation is caused by the high frequency components of the driving waveforms because the IPMC actuator has the characteristics of damped high pass filter.
Abstract: Electromechanical response characteristics of ion-exchange polymer metal composite (IPMC), known as a material for artificial muscle actuators, varies extremely depending on the driving method. With respect to the power management the driving method is one of the important considerations though it has not been investigated sufficiently up to now. Its efficiency is critical to enhance the performance of an IPMC system, especially self-contained one. The primary objective of this paper is to investigate electromechanical response characteristics of the IPMC actuator according to driving methods. We begin with developing an equivalent electrical circuit model for the IPMC actuator using experimental data. Based on this model, discuss how the waveforms and frequencies of driving inputs have effect on the characteristic features of the IPMC actuator. Typically square, triangular and harmonic waves are applied as the driving waveform of the IPMC actuator. By employing Fourier techniques, the responses of the IPMC actuator on each input waveform are mathematically analyzed. From this study, we conclude that large consumption of current during actuation is caused by the high frequency components of the driving waveforms because the IPMC actuator has the characteristics of damped high pass filter. A desirable method of driving the IPMC actuator is proposed and its validity is experimentally confirmed.
TL;DR: In this paper, a piezoelectric synthetic jet actuator was used for boundary layer flow control and the results obtained showed a significant enhancement of the jet effectiveness by forcing the boundary layer flows at the natural instability frequency.
Abstract: The synthetic jet actuator (SJA) is a low power, highly compact microfluidic device which has potential application in boundary layer flow control. In recent work we have shown how synthetic jets work without cross flow and how effectively they modify the flow structure in the boundary layer under an adverse pressure gradient. This paper describes the piezoelectric synthetic jet actuator used in our experiments. The experimental set-up for flow control using this type of actuator is detailed. The results obtained show a significant enhancement of the jet effectiveness by forcing the boundary layer flow at the natural instability frequency. The actuators must have sufficient velocity output to produce strong enough vortices if they are to be effective for flow control. The forcing effect can occur at a frequency lower than the driving frequency of the actuator when used without cross flow. The forcing frequency appears to be an important parameter in synthetic jet boundary layer flow control.