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Flexible components have always been an attraction in all engineering fields; ultrasound transducers are no exception to this. Capacitive micromachined ultrasound transducers (CMUTs) have started to challenge the piezoelectric dominance in ultrasound imaging industry due to their wider bandwidth and excellent integration with electronics. We present a new fabrication technique for making flexible polymer-based CMUTs that is simple, inexpensive, and robust. The proposed technique includes forming CMUT cells through four lithography steps on a polyimide substrate, and then chemically releasing it from the silicon carrier (by a sacrificial layer) to reduce residual stress. The fabricated 1D, 8-element flexible array showed similar resonant response at 5.8 MHz on flat and curved surfaces without compromising functionality. Our finite element analysis also confirmed the minimal change in resonant frequency. The proposed device could be used for conformal ultrasound imaging of anatomical features.

The authors report the fabrication of polymer MEMS transducers, without using any sacrificial layers, on flexible substrates. The elimination of sacrificial layers and the process overhead associated with them is achieved through maskless grayscale UV lithography of SU-8 photoresist, and results in a simplification of the overall fabrication process. Six batches, with a total of 60 cantilevers and 60 double- clamped beams, and three batches, with a total of 1500 circular membranes, have been fabricated on commercially available, 45 um Kapton® polyimide sheets coated with a 35um copper layer. The validation of the fabrication process has been done through functional characterization of the bi-directional electro-mechanical interface and robustness to mechanical bending. The test and measurement results of the fabricated microstructures validate a good design predictability (geometry error

In this paper, a simple fabrication process for SU-8 in-plane micro electro-mechanical systems (MEMS) structures, called &ldquo, border-bulk micromachining&rdquo, is introduced. It aims to enhance the potential of SU-8 MEMS structures for applications such as low-cost/disposable microsystems and wearable MEMS. The fabrication process is robust and uses only four processing steps to fabricate SU-8 in-plane MEMS structures, simplifying the fabrication flow in comparison with other reported attempts. The whole fabrication process has been implemented on copper-polyimide composites. A new processing method enables the direct, laser-based micromachining of polyimide in a practical way, bringing in extra processing safety and simplicity. After forming the polymeric in-plane MEMS structures through SU-8 lithography, a copper wet etching masked by the SU-8 structure layers is carried out. After the wet etching, fabricated in-plane MEMS structures are suspended within an open window on the substrate, similar to the final status of in-plane MEMS devices made from industrial silicon micromachining methods (such as SOIMUMPS). The last step of the fabrication flow is a magnetron sputtering of aluminum. The border-bulk micromachining process has been experimentally evaluated through the fabrication and the characterization of simple in-plane electrically actuated MEMS test structures. The characterization results of these simple test structures have verified the following process qualities: controllability, reproducibility, predictability and general robustness.

A recently proposed method for measuring minute changes in capacitance based on weakly coupled resonators has been examined for its sensitivity with respect to unwanted resonant frequency changes. This sensitivity has been compared with the conventional capacitance measurement method based on the capacitance to frequency conversion. It has been analytically shown that both sensitivities are nearly equal but with opposite signs. This has led to a new hybrid capacitance measurement method to reduce the error by at least an order of magnitude. The analytical results have been validated by various simulations and experimental measurements.

The ultrasonic transducer industry is dominated by piezoelectric materials. As an emerging alternative, capacitive micromachined ultrasound transducers (CMUTs) offer wider bandwidth, better integration with electronics, and ease of fabricating large arrays. CMUTs have a sealed cavity between a fixed electrode and a suspended metalized membrane. Manufacturing cost and sensitivity are limiting factors in current CMUTs that depend on the fabrication equipment and, especially, on the materials used. For widespread use of CMUTs, a much lower fabrication cost that uses inexpensive materials, which maintain or improve upon existing sensitivity, is needed. Herein, a new fabrication process is described for polymer-based CMUTs (polyCMUTs) using the photopolymer SU-8 and Omnicoat. The first ultrasound B-mode image of a wire phantom created with a 64-element linear array using synthetic aperture beamforming techniques is presented. A 12 VAC signal superimposed on a 10 VDC signal was used on the transmission side, and only a bias-tee, with no amplifiers, was used on the receiving side. The low operational voltage and high sensitivity of this device can be partially attributed to a pre-biasing condition on the membrane. By using a novel sacrificial layer combined with a top electrode embedded inside the membrane, we demonstrated that SU-8 can be used to manufacture CMUTs inexpensively. Moreover, the fabrication used relatively simple equipment, and the number of fabrication steps was reduced compared to traditional CMUT fabrication. This new fabrication process has the potential to increase the use of CMUTs in the ultrasound market, including the market for wearable transducers.

Low energy consumption and wide operating temperature range of capacitors made them common in sensor designs, e.g., MEMS accelerometers, and hence increased the popularity of capacitive readout circuits. Their main challenges, in either discrete or integrated implementations, are sensitivity, noise, energy consumption, and parasitic components at the analog front end. Compared to conventional “frequency-shift monitoring” which is one of the most accurate and common methods for capacitance measurements, weakly-coupled resonators (well-known in mechanical systems) can offer up to three orders of magnitude increase in sensitivity. Therefore, this concept has been recently applied to the design of micromechanical sensors, e.g., for sensitive mass sensing. This paper applies, for the first time in the electrical domain, the concept of monitoring the eigenstates variations in weakly-coupled resonators as a generic readout circuit technique for measuring very small capacitance changes. The outstanding sensitivity of this method is verified analytically and demonstrated using both extensive circuit simulations and experimental measurements.

This article describes a new low-cost rapid microfabrication technology for high-density interconnects and passive devices on flexible substrates for sensing applications. Silver nanoparticles with an average size of 80 nm were used to create a conductive SU-8 mixture with a concentration of wt 25%. The patterned structures after hard baking have a sheet resistance of 11.17 Ω /□. This conductive SU-8 was used to pattern planar inductors, capacitors and interconnection lines on flexible Kapton film. The conductive SU-8 structures were used as a seed layer for a subsequent electroplating process to increase the conductivity of the devices. Examples of inductors, resistor-capacitor (RC) and inductor-capacitor (LC) circuits, interconnection lines and a near-field communication (NFC) antenna are presented as a demonstration. As an example of high-resolution miniaturization, we fabricated microinductors having line widths of 5 μ m. Mechanical bending tests were successful down to a 5 mm radius. To the best of the authors’ knowledge, this is the first report of conductive SU-8 used to fabricate such planar devices and the first on flexible substrates. This is a proof of concept that this fabrication approach can be used as an alternative for microfabrication of planar passive devices on flexible substrates.

In the new age of technology, internet and ever-improving communications many trends and fields have been appearing, such as smart phones and their applications, internet of things, renewable energy sources and smart buildings. The latter utilizes a number of aspects from the former, as the size of the buildings keeps growing, the engineers and designers aim to reduce energy consumption and ecological footprint, make the building safer and more sustainable. This has stimulated the growth of the field of sensor networks. This paper discusses a smart sensor network which utilizes Power over Ethernet, P.o.E., supplied by a Cisco Catalyst 4507R+E switch and cloud computing to provide an easily scalable and adaptable system that would be able to adapt easily to a wide array of applications and fit the demands of new trends. The system was tested on Raspberry Pi and BeagleBone microcontroller boards as sensor hubs, and uses DigitalOcean as the cloud computing service of choice. The server in this implementation acts as a user interface, front end, and as the console unit, back end. The system has demonstrated to have fast communication times of below 200ms in a cross-continental setting and able to provide fast processing times of under 1s.

In this paper, we present a disposable inkjet dispenser platform technology and demonstrate the Lab-on-a-Printer concept, an extension of the ubiquitous Lab-on-a-Chip concept, whereby microfluidic modules are directly integrated into the printhead. The concept is demonstrated here through the integration of an inkjet dispenser and a microfluidic mixer enabling control over droplet composition from a single nozzle in real-time during printing. The inkjet dispenser is based on a modular design platform that enables the low-cost microfluidic component and the more expensive actuation unit to be easily separated, allowing for the optional disposal of the former and reuse of the latter. To limit satellite droplet formation, a hydrophobic-coated and tapered micronozzle was microfabricated and integrated with the fluidics to realize the dispenser. The microfabricated devices generated droplets with diameters ranging from 150-220 μm, depending mainly on the orifice diameter, with printing rates up to 8000 droplets per second. The inkjet dispenser is capable of dispensing materials with a viscosity up to ∼19 mPa s. As a demonstration of the inkjet dispenser function and application, we have printed type I collagen seeded with human liver carcinoma cells (cell line HepG2), to form patterned biological structures.

We demonstrate large-area silicon-on-insulator ring resonators with Q values of about 2×10sup6/supat critical coupling and 3.6×10sup6/supfor heavily undercoupled conditions. A model has been developed to understand the impact of waveguide backscattering and subcomponent imperfections on the spectral response of our devices. The model predicts the appearance of signals at ports that would not have them under backscattering-free, ideal-power-splitting conditions. The predictions of our model are shown to match the phenomena observed in our measurements.

This paper describes the application of a novel band-pass sliding mode control (SMC) to the driving mode of MEMS-based resonators and resonant sensors (e.g. vibrating gyroscopes). The proposed technique relies on binary electrostatic actuation of the movable mass, dependent on the dynamics of the sliding/switching surface, in such a way that the generated actuation tracks possible changes in the mechanical resonant frequency induced by external factors (humidity, temperature, pressure, etc.). The core of the proposed adaptive method is the implementation in hardware of an adaptive behavioral reference model used by the controller, able to track the sensed changes in dynamics. The architecture has a low hardware complexity and is suitable for VLSI implementation, in addition to a robust tracking behavior for large variations in the parameters of the resonator (e.g. temperature-induced changes in the stiffness coefficient). Simulation results demonstrate the effectiveness of the proposed technique by maintaining the actuation of the system at its resonance frequency even in the presence of variations of the stiffness coefficient (step, linear)or of applied external forces (external acceleration and noise). Simulations results suggest that the novel SMC-based oscillator offers an advantageous alternative to more complex phase-locked loop (PLL) architectures, traditionally used for the driving of MEMS resonator structures.

We propose a novel adaptive technique based on pseudo-random (PN) sequences for self-calibration and self-testing of MEMS-based inertial sensors (accelerometers and gyroscopes). The method relies on using a parameterized behavioral model implemented on FPGA, whose parameters values are adaptively tuned, based on the response to test pseudo-random actuation of the physical structure. Dedicated comb drives actuate the movable mass with binary maximum length pseudo-random sequences of small amplitude, to keep the device within the linear operating regime. The frequency of the stimulus is chosen within the mechanical spectral operating range of the micro-device, such that the induced response leads to the identification of the mechanical transfer function, and to the tuning of the associated digital behavioral model. In case of a micro-gyroscope, experimental results demonstrate the adaptive tracking of the damping coefficient from 5.57 × 10−5 Kg/s to 7.12 × 10−5 Kg/s and of the stiffness coefficient from 132 N/m to 137.7 N/m. In the case of a MEMS accelerometer, the damping and stiffness coefficients are correctly tracked from 3.4 × 10−3 Kg/s and 49.56 N/m to 4.57 × 10−3 Kg/s and 51.48 N/m, respectively—the former values are designer-specified target values, while the latter are experimentally measured parameters for fabricated devices operating in a real environment. Hardware resources estimation confirms the small area the proposed algorithm occupies on the targeted FPGA device.

Semiconductor ring resonators as the core components of instruments and devices have found applications in the areas of telecommunications and sensors. In this study, the feasibility of using ring resonators as solid-state angular rate sensors (gyroscopes) based on the Sagnac effect is assessed, and an extensive analysis of the optimal values of resonator length, coupling, and detuning is carried out, for the drop port of a double-bus ring, and for an all-pass, single-bus ring, for different values of propagation losses, consistent with different available technologies. We show that for both the all-pass and the drop-port configurations, optimally undercoupled rings show larger extinction ratios and, thus, better resolutions than critically coupled rings of the same length, contrary to our initial intuitive assumption that critically coupled rings should offer the best resolutions. Our analysis also shows that the ring resonator gyroscopes require a technology-constrained optimization, with the propagation loss as the main factor that hinders the resolution, and that determines the optimum values of all other parameters, namely length, coupling, and resonance detuning. According to our model, standard-chip-sized racetrack gyroscopes are suitable for rate- and tactical-grade applications for selected, currently feasible low propagation loss waveguides.

The pull-in time (tpi) of electrostatically actuated parallel-plate microstructures enables the realization of a high-sensitivity accelerometer that uses time measurement as the transduction mechanism. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. Parallel-plate MEMS structures have been designed and fabricated using a SOI micromachining process (SOIMUMPS) for the implementation of the accelerometer. This paper presents the experimental characterization of the microdevices, validating the concept and the analytical models used. The accelerometer has a measured sensitivity of 0.25 μs/μg and a bandwidth that is directly related to the pull-in time, BW = 1/2tpi ≈ 50 Hz. These specifications place this sensor between the state of the art accelerometers found both in the literature and commercially. More importantly, the resolution of the measurement method used is very high, making the mechanical–thermal noise the only factor limiting the resolution. The in-depth noise analysis to the system supports these conclusions. The total measured noise floor of 400 μg (100 μs) is mainly due to the contribution of the environmental noise, due to lack of isolation of the experimental setup from the building vibrations (estimated mechanical thermal noise of 2.8 μg/√Hz). The low requirements of the electronic readout circuit makes this an interesting approach for high-resolution accelerometers., ADI - Agência de Inovação, Fundação para a Ciência e a Tecnologia (FCT)

This paper reports on the simulation and characterization of a microelectromechanical system (MEMS) micromirror fabricated with PolyMUMPs. The overall diameter of the hexagonal micrimirror, including mirror plate and 3 supporting cantilevers fixed around, is 450um. A 3D model is built in finite element method (FEM) with COMSOL. Simulations of the elevated height of mirror plate, pull-in voltage and eigenfrequency of the micromirror are carried out. The static and dynamic performances of the fabricated micromirror are characterized by Veeco Optical Profiler and Polytek MEMS System Analyzer. The comparison between measurement and simulation exhibits good concordance. Surface topography measurement shows the elevated height and stress-induced concave deformation of mirror plate almost the same scale as demonstrated in FEM simulation. The Pull-In voltages are measured to be around 32V in current-voltage curve which is almost the same as in FEM simulation with one electrode biased. The fundamental resonant frequency is measured to be 4.3k Hz in torsional motion and 4.9k Hz in piston motion.

This paper investigates the concept of tiltable ultrasonic transducers, and their application in focusing and steering in a transducer array. Results of simulated imaging processes suggest that physical focusing and steering with tiltable transducers is promising in reducing grating lobe and side lobe artifacts, and preserving the beam power, especially when steering to large angles. We propose that one embodiment of the tiltable transducers can be adaptive capacitive micromachined ultrasonic transducers (CMUTs) modeled as clamped plate radiators. By applying different levels of electrical field on their split electrodes, one can adjust the shape and orientation of the adaptive CMUTs adaptively and dynamically, creating a tilted effect in the beam direction. The feasibility of using adaptive CMUTs to implement tiltable transducers is studied using finite element modeling (FEM) and analytical modeling. Experimental measurements of the tilted behavior of fabricated adaptive CMUTs are also provided. Possible applications of the tiltable transducers, including spatial compounding, high intensity focused ultrasound (HIFU), adaptive imaging, and harmonic imaging, are discussed.

The experimental evaluation of damping-improved parallel-plate geometries is reported in this paper. An improved damper geometry with air channels was developed to address contradictory design constraints: large sensing parallel-plate area is desirable for a significant readout capacitance as well as reduced damping coefficient. Damping coefficients were measured at different gaps in conventional parallel-plates MEMS and in parallel-plates with air channels. The inertial masses of the fabricated structures were pulled-in and released. From the return to rest position trajectory, the damping coefficients, at each point, were extracted. Results show a significant damping decrease in parallel-plates with air channels without visible reduction in the capacitance value., Fundação para a Ciência e a Tecnologia (FCT)

The present paper analyzes numerically and experimentally the dependence of the dynamic pull-in voltage amplitude on the values of externally-induced accelerations (e.g. Coriolis accelerations in the case of vibratory gyroscopes). We have investigated the nonlinear dynamic behavior on two different device types, a micro-gyroscope (A) and a micro-accelerometer (B), both fabricated in the SOI-MUMPs process (25 μm thick structural layer). Experimental measurements on the MEMS structures have been performed using Polytec MSA-500 equipment for analyzing the mechanical motion. They indicate that the dynamic pull-in voltages reduce from 100 V to 56 V for device A and from 21.77 V to 17.3 V for device B, for an equivalent acceleration of 0.319 ms-2, when the structures are actuated at their resonance frequency. If the induced acceleration is translated into an equivalent angular rate, _ equivalent, modulating the Coriolisinduced motion, the dynamic pull-in voltages vary from 57.612 V to 56.5 V for device A type and from 20.9 V to 10.75 V for device B type, for a change of 1 rad/s to 5 rad/s in _equivalent.

This paper describes the application of a novel band-pass sliding mode control (SMC) to MEMS-based resonators and resonant sensors (e.g. vibrating gyroscopes). The proposed technique relies on a binary electrostatic actuation of the movable mass, dependent on the dynamics of the sliding surface, in such a way that the generated oscillations track changes in the mechanical resonant frequency. The architecture has a low hardware complexity and is suitable for VLSI implementation, in addition to a robust tracking behavior for large variations in the parameters of the resonator (e.g. temperature-induced changes in the stiffness coefficient). The results suggests that the novel SMC- based oscillator offers an advantageous alternative to more costly phased-locked loop (PLL) architectures traditionally used for the driving of MEMS resonator structures.

This work reports the design, modelling, fabrication and preliminary functionality testing of a dual-mass MEMS vibratory gyroscope for application in medical instrumentation, among others. The two-framed gyro has drive and sense mode resonance frequencies of 2500Hz and 2830Hz, with its bandwidth tunable between 40-330Hz. Adopted design and technological features such as the use of double-folded springs, quadrature-error-compensation electrodes and 50μm thick-SOI mechanical layer enable high resolution sensing. The designed sensor characteristics have been validated using FEM simulation and equivalent circuit modelling.

The pull-in time of electrostatically actuated parallel-plate microstructures enables the realization of a high-sensitivity accelerometer that uses time measurement as the transduction mechanism. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. Parallel-plate MEMS structures have been designed and fabricated using a SOI micromachining process (SOIMUMPS) for the implementation of the accelerometer. This paper presents the experimental characterization of the microdevices that validates the concept and the analytical models used. The accelerometer has a measured resolution of 0.25 ?s/?g and an estimated mechanical-thermal noise of View the MathML source2.8?g/Hz. Since the bandwidth of the sensor is directly related to the pull-in time (BW=2/tpi?180 Hz), the total measured noise floor of 400 ?g (110 ?s) suggests that the main noise source comes from the building vibrations

In this paper, we describe the system architecture and prototype measurements of a MEMS gyroscope system with a resolution of 0.025 degrees/s/root Hz. The architecture makes extensive use of control loops, which are mostly in the digital domain. For the primary mode both the amplitude and the resonance frequency are tracked and controlled. The secondary mode readout is based on unconstrained Sigma Delta force-feedback, which does not require a compensation filter in the loop and thus allows more beneficial quantization noise shaping than prior designs of the same order. Due to the force-feedback, the gyroscope has ample dynamic range to correct the quadrature error in the digital domain. The largely digital setup also gives a lot of flexibility in characterization and testing, where system identification techniques have been used to characterize the sensors. This way, a parasitic direct electrical coupling between actuation and readout of the mass-spring systems was estimated and corrected in the digital domain. Special care is also given to the capacitive readout circuit, which operates in continuous time.

The paper presents a combined noise and damping analysis for MEMS structures, based on frequency-dependent behavioral models extracted from finite element simulations. The design of high sensitivity MEMS-based microsystems needs to consider the frequency noise shaping induced by damping phenomena on micro scale motion, for its contribution can be significant in the system level noise analysis. Frequency-dependent behavioral models for squeeze-film damping are generated from finite element analysis simulations. Unlike existing noise analysis reported in literature, based on frequency-independent damping assumption, the paper integrates the damping and noise aspects using the same frequency-dependent models. The results can be used for a noise-based optimization procedure applied to the design of resonating microsensors, as illustrated for the case of a MEMS-based gyroscope.

A generic sensor network architecture is developed, combining Power-over-Ethernet (PoE) and Internet-of-Things (IoT) concepts. Distributed sensor nodes consist of a local controller (Raspberry-Pi board), to pre-process and format data collected from several sensors, and an Ethernet and power management circuit, to interface with PoE-enabled Ethernet ports. The system design follows a client-server architecture: by combining PoE with the IoT, the endpoint clients and servers (PoE controller modules) can communicate in local area network using the Constrained Application Protocol (CoAP). Clients can send commands to observe sensor data, change data acquisition sampling rate, and post new sensor resources. As data gets observed by clients, it can be further stored in a custom-designed HDF5 (Hierarchical Data Format 5) file format, for post-processing, visualization and data management. The convergence of data and power flow control enables a smart power management at the network level - most of the sensor nodes will be powered-up (awoken) only after custom triggering events detected by a main subset of always-on sensing nodes. These PoE controller modules are intended for structural and environment monitoring in one of the tallest wooden tower in the world, to be built in UBC campus. The generic architecture may be further adopted in the future for other types of applications, like environmental monitoring or human health.

An equivalent circuit model is developed for a special kind of CMUTs called asymmetric CMUTs, containing a membrane and two split bottom electrodes. The macromodel contains subcircuits representing different vibration modes from modal participation theory. By using a lumped parameter model, the system is not restricted around an equilibrium point, and remains valid under any kind of excitation voltage. The model predicts the frequency response of the CMUT for different media and accounts for the spring softening effect. We compare our results against FEM simulations and experimental measurements.

The nonlinear dynamics of the parallel-plate electrostatically driven microstructure have been investigated with the objective of finding a dynamic voltage drive suitable for full-gap operation. Nonlinear dynamic modeling with phase-portrait presentation of both position and velocity of a realistic microstructure demonstrate that instability is avoided by a timely and sufficient reduction of the drive voltage. The simulation results are confirmed by experiments on devices fabricated in an epi-poly process. A 5.5-V peak harmonic drive voltage with frequency higher than 300 Hz allows repetitive microstructure motion up to 70% of gap without position feedback. The results of the analysis have been applied to the design of a new concept for positioning beyond the static pull-in limitation that does include position feedback. The measured instantaneous actuator displacement is compared with the desired displacement setting and, unlike traditional feedback, the voltage applied to the actuator is changed according to the comparison result between two values. The "low" level is below the static pull-in voltage and opposes the motion, thus bringing the structure back into a stable regime, while the "high" level is larger than the static pull-in voltage and will push the structure beyond the static pull-in displacement. Operation is limited only by the position jitter due to the time delay introduced by the readout circuits. Measurements confirm flexible operation up to a mechanical stopper positioned at 2 /spl mu/m of the 2.25 /spl mu/m wide gap with a 30 nm ripple.

Harmonic displacement of a parallel-plate electrostatic actuator up to 50% of the static pull-in displacement has been achieved despite the non-linear voltage-to-displacement function using a driving voltage with a pre-distorted waveform. The microstructure is fabricated in an epi-poly process and the circuit is implemented in a CMOS process and designed for operation of the MEMS in a frequency range up to 1 kHz. The pre-distorted waveform is synthesized using 16 samples per period with 16 non-uniformly spaced quantization levels, using a ladder with accurately scaled resistors. Harmonic actuation has been demonstrated with 34 dB reduction of second-order distortion compared to systems with sinusoidal actuation. The residual second harmonic content in the harmonic displacement is typically −42 dB.

The meta-stability of the pull-in displacement of an electrostatically operated parallel plate micromechanical structure is used for the capacitive measurement of the mechanical–thermal noise spectrum in a MEMS. Pull-in time depends on force and is not affected by the input-referred noise of the readout circuit. Repeatedly bringing the microstructure to pull-in while measuring the pull-in time followed by FFT enables the measurement of the mechanical noise spectrum with a non-mechanical noise level set primarily by the resolution of the time measurement. The white noise level is found to be in agreement with the theory on damping. The 1/f noise spectrum is found to be independent of ambient gas pressure with a 1/f noise–white noise cross-over frequency at 0.007 Hz for a 1 bar gas pressure and is reproducible for devices fabricated in the same process and the same run.

An ac-operated capacitive accelerometer with electrostatic force feedback is employed for direct mechanical spectrum analysis. Force feedback acts as a means for electronic modulation of the spring constant of the suspension and thus for enhancing the sensitivity. Therefore, a suitable electrostatic time-varying actuation can be used to make the accelerometer selectively sensitive to a coherent frequency component of a mechanical vibration. By sweeping the frequency of the drive voltage over a selected range, the mechanical (vibration) spectrum is analyzed in the mechanical domain. An inverted pendulum type of accelerometer structure has been fabricated in silicon using micromachining techniques and operated using electrostatic momentum feedback. The spectral performance is comparable to fast Fourier transform based systems for spectral analysis on a time series supplied by a conventional accelerometer, while the overall system features a reduced complexity and reduced power consumption.

The pull-in voltage of a suspended microstructure has been investigated for use as on-chip voltage reference in a compatible MEMS-IC process. Pull-in is detected using capacitive displacement measurement. The stability is affected by an initial parasitic charge build-up and a temperature sensitivity of −149 μV/K. A burn-in procedure is required to minimize the first effect. The temperature coefficient is compensated for by applying additional temperature dependent electrostatic energy to the microstructure. Devices fabricated in an epi-poly process and designed for a nominal pull-in voltage at 5 V have a measured value at 4.7424 V. Drift becomes negligible after 120 h of operation. The temperature reproducibility is within the resolution of the readout at 100 μV over a temperature range between 20 and 60 °C.

The pull-in voltage of one- and two-degrees-of-freedom (DOF) structures has been symbolically and numerically analyzed with respect to drive mode dependence and hysteresis. Moreover, the time and temperature stability has been investigated and tested. Modeling results have been applied in the design of both folded-spring-suspended 1-DOF structures and single-side-clamped 2-DOF beams with a nominal pull-in voltage in the 5-10 V range and fabricated in an epi-poly process. Asymmetrically driven structures reveal pull-in close to the value predicted by the model (V/sub pi/ 1-DOF is 4.65 V analytically simulated and 4.56 V measured; V/sub pi/ 2-DOF is 9.24 V analytically simulated, 9.30 V in FEM and 9.34 V measured). Also the hysteresis is in close agreement (release voltage, V/sub r/, 1-DOF is 1.41 V analytically simulated and 1.45 V measured; V/sub r/ 2-DOF is 9.17 V analytically simulated, 9.15 V in FEM and 9.27 V measured). In symmetrically operated devices the differences between the computed and measured V/sub pi/ and V/sub r/ are much larger and are due to process dependencies, which make these devices very suitable for process monitoring. The 2-DOF asymmetrically operated device is the most suitable for MEMS-based voltage reference. The stability in time is limited by charge build-up and calls for a 100-hour initial burn-in. Temperature dependence is -100 /spl mu/V/K at V/sub pi//spl ap/5 V, however, is calculable and thus can be corrected or compensated.

The most striking characteristic of the voltage-to-deflection curve of an electrostatically actuated beam is pull-in. The actual value of the pull-in voltage depends on: drive mode, temperature dependence and dielectric charging related drift. These aspects have been analysed using structures designed for a 9 V nominal pull-in voltage and fabricated in a commercially available epipoly process. Single-sided clamped beams have been used to avoid any influence of residual stress in the beam on pull-in. Typical results are: less than 5% variation of the pull-in voltage over a wafer, 0.17–1.9 V hysteresis depending on drive mode, a −1 mV/K TC and −12 mV drift during the first 2 weeks of operation.

The reproducibility over temperature and time of the pull-in voltage of micromechanical structures has been analyzed and verified using fabricated devices in silicon. The pull-in structures are intended for use as an on-chip voltage reference. Microbeams of 100-/spl mu/m length, 3-/spl mu/m width, and 11-/spl mu/m thickness are electrostatically actuated with a very reproducible pull-in voltage at 9.1 V. Devices demonstrated an initial drift of -12 mV over 10 days and stabilized within the 500-/spl mu/V measurement uncertainty. The measured temperature coefficient of -1 mV/K is in good agreement with the analysis and is due to the combined effect of thermal expansion and the temperature dependence of the Young's modulus in silicon.

During the last decades, smart tactile sensing systems based on different sensing techniques have been developed due to their high potential in industry and biomedical engineering. However, smart tactile sensing technologies and systems are still in their infancy, as many technological and system issues remain unresolved and require strong interdisciplinary efforts to address them. This paper provides an overview of smart tactile sensing systems, with a focus on signal processing technologies used to interpret the measured information from tactile sensors and/or sensors for other sensory modalities. The tactile sensing transduction and principles, fabrication and structures are also discussed with their merits and demerits. Finally, the challenges that tactile sensing technology needs to overcome are highlighted.

Large-area silicon-on-insulator (SOI) ring resonators, to be used as optical gyroscopes, have been designed and fabricated using an e-beam process. To characterize the devices, an automated turntable stage with an embedded high resolution gyroscope has been built. Its large payload capacity allows for safe rotation of a temperature-controlled opto-mechanical setup. A field programmable gate array interface has been implemented for mechanical actuation and signal acquisition. Various rotation schemes have been implemented to characterize the apparatus and devices. The turntable exhibits a bandwidth of 0.54 Hz, and minimum and maximum repeatable angular rates of 27 and 74.3 degrees per second (dps), with a maximum associated angular rate noise level of 2 dps.

The pull-in voltage of a single-side anchored freestanding beam, under lateral deflection, has been investigated for application as a DC voltage reference. Two sets of electrodes, along side the tip, are used for parallel-plate type of electrostatic actuation of the 200 /spl mu/m long beam in the plane of the wafer. Another set of buried electrodes is aligned with the plate electrode at the free-standing tip and is used as a differential capacitor for the simultaneous detection of the displacement, with the purpose to determine the stability border and thus the pull-in voltage. The single-end clamping ensures that the pull-in voltage is insensitive to technology-induced stresses. A 2D energy-based analytical model for the static pull-in is compared with measurements. Bifurcation diagrams are computed numerically, based on a local continuation method. Devices have been designed and fabricated in an epi-poly process. Measurements are in agreement with modeling and confirm a pull-in voltage in the 9.1-9.5 V range. Reproducibility is limited by hysteresis and charging of the dielectric layer in between the electrodes. The device can be operated in feedback or as a seesaw, by using the two sets of electrodes.

A general dynamic model for a momentum-actuated accelerometer is constructed, where both differential and common-mode actuation voltages are considered. The equivalent quasi-static model is applied to design a measurement scheme for low-frequency accelerations. A more general method for real-time spectral analysis of mechanical vibrations is presented, which relies on a feedback loop based on capacitive sensing, on-chip signal conditioning and electrostatic actuation. Both common- and differential-mode voltages are used to tune the accelerometer spectral characteristic, in order to extract the spectral component set by the electrostatic actuation.

A local smart sensor bus is described which is designed for use in a multi-chip-composed microinstramentation system. The bus is capable of handling information in digital code, bitstream, analog voltage, and frequency or duty cycle modulation and also provides calibration facilities, service-request and interrupt-request modes. The resulting sensor bus interface has been implemented in a 1.6 μm CMOS process and successfully tested in a local sensor network.

We propose a novel sliding mode control (SMC), implemented on FPGA, for robust stabilization and high sensitivity operation of a capacitive micro-accelerometer on the pull-in border of stability. SMC feedback enforces a maximum sensitivity position of the proof mass in a normally unstable equilibrium, while the value of the external acceleration is extracted from the “chattering” noise bitstream produced by the controller action. Experimental results show a stabilization of the proof mass at the pull-in position and a measurement of small accelerations. The proposed technique, implemented in LabView and FPGA hardware, represents a promising alternative for the digital control of capacitive MEMS devices, with a lighter implementation footprint than common sigma-delta approaches used for inertial sensors.

In this paper slope-shaped comb are designed, modeled and experimentally verified for electrostatic parametric amplification of micro-displacements. Parametric resonance techniques applied to inertial sensors requires a periodic stiffness modulation, as expressed by the Mathieu equation, and is generally implemented using gap-varying and non-overlapping combs. MEMS vibratory gyroscopes provide the opportunity for applying parametric amplification for both the sensing and driving modes. While gap-varying combs are efficiently used for small displacements (e.g. the sensing mode), larger displacements require a different approach, where slope-shaped combs are a good alternative. Analytical model of slope shaped combs is carried out and compared with experimental characterization of fabricated devices. The analytical model predicts a spring modulation of 0.1%-0.65% spring modulation for 10 V to 40V applied common mode DC bias, and it can be increased for steeper slopes. The parametric amplification operation was experimentally tested using linear differential voltage actuation on the area-varying combs and a phase-synchronised common mode voltage (using a PXIe 1062Q DAQ controller) applied to the left and right shaped combs.

This paper introduces a novel ultrasensitive resonant MEMS transducer with tunable electrostatic coupling, in order to measure micro-displacements induced stiffness perturbations. Enhanced sensitivity is achieved based on the principle of energy localization in eigenvalue veering phenomena, resulting from a symmetry breaking in coupled resonator systems. Experimental results from a coupled two-resonators MEMS device are compared with both analytical calculations, and Simulink model simulations. Modal vector sensitivity is shown to be an order of magnitude higher than resonant frequency sensitivity under ambient conditions. Decreasing the coupling strength between the two resonators, using tunable electrostatic spring, is shown to enhance sensitivity, albeit in a narrowed range of perturbations.

We present a new method for removing artifacts in electroencephalography (EEG) records during Galvanic Vestibular Stimulation (GVS). The main challenge in exploiting GVS is to understand how the stimulus acts as an input to brain. We used EEG to monitor the brain and elicit the GVS reflexes. However, GVS current distribution throughout the scalp generates an artifact on EEG signals. We need to eliminate this artifact to be able to analyze the EEG signals during GVS. We propose a novel method to estimate the contribution of the GVS current in the EEG signals at each electrode by combining time-series regression methods with wavelet decomposition methods. We use wavelet transform to project the recorded EEG signal into various frequency bands and then estimate the GVS current distribution in each frequency band. The proposed method was optimized using simulated signals, and its performance was compared to well-accepted artifact removal methods such as ICA-based methods and adaptive filters. The results show that the proposed method has better performance in removing GVS artifacts, compared to the others. Using the proposed method, a higher signal to artifact ratio of −1.625 dB was achieved, which outperformed other methods such as ICA-based methods, regression methods, and adaptive filters.

Closed-loop pull-in time operated devices are a good alternative for high sensitivity accelerometers. This paper proposes the use of time measurement as the transduction mechanism for the realization of a high-precision accelerometer. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. The main design challenges for a pull-in time parallel-plate capacitive Microelectromechanical system (MEMS) accelerometer are related to the damping and the associated tradeoff between sensitivity and noise is discussed. Parallel-plate MEMS structures designed and fabricated in a 25 um-thick SOI micromachining process (SOIMUMPS) are used to demonstrate the accelerometer time-based approach and experimental results demonstrate a sensitivityof 0.25 us/ ug., Fundação para a Ciência e a Tecnologia (FCT), ADI - Agência de Inovação

A high-resolution, high-sensitivity capacitive accelerometer based on pull-in time measurement is described in this paper. The high sensitivity of pull-in time is being explored to implement high performance accelerometers, and non-linearity is the main characteristic compromising device performance. An electrostatic compensation technique that addresses the non-linearity problem, based on pull-in time duration control, is presented and tested. Capacitive parallel-plates MEMS structures were used and the measured sensitivities for different acceleration ranges confirm the potential of this technique and the overall accelerometer concept. The results show an accelerometer with 0.26 μs/μg sensitivity, over a 120 dB dynamic range., Fundação para a Ciência e a Tecnologia (FCT)

We propose a novel adaptive technique based on pseudo-random (PN) sequences for self-calibration and self-testing of capacitive-based sensing and resonator microstructures, using an FPGA-implemented algorithm. The movable mass is actuated electrically with maximum length pseudo-random sequences (PN) of small amplitude, to keep the device in the linear operating regime. The frequency of the stimulus is chosen within the spectral operating range of the microdevice, such that the induced mechanical response is used for the identification of the mechanical transfer function. The proposed technique uses the steady-state and dynamic responses and it is applied to a MEMS gyroscope, for closed-loop characterization and real-time calibration. The core of the adaptive method is the implementation in FPGA of a reference model of the device under test (DUT). Experimental results demonstrate the real-time model-based identification of the damping and stiffness coefficients for the sensing mode of the fabricated vibratory microgyroscope, using modest hardware resources.

This paper describes an electro-mechanical auto-calibration technique for use in capacitive MEMS accelerometers. Auto-calibration is achieved using the combined information derived from an initial measurement of the resonance frequency and the measurement of the pull-in voltages during device operation, with an estimation of process-induced variations in device dimensions from layout and deviations in material properties from the known nominal value. An experiment-based analytical model is used to compute the required electrostatic forces required to simulate external accelerations allowing the electro-mechanical calibration of the accelerometer. Measurements on fabricated devices confirm the validity of the proposed technique and electro-mechanical calibration is experimentally demonstrated.

Closed-loop pull-in time operated devices are a good alternative for high sensitivity accelerometers. The main design challenges for a pull-in time parallel-plate capacitive MEMS accelerometer are related to damping and therefore an improved damper geometry is introduced in this paper that enables the reduction of the damping forces without changing the capacitance value. MEMS structures designed and fabricated in a 60µm-thick SOI micromachining process are used to demonstrate the accelerometer time-based approach. The characteristics of this process are considered to simulate and discuss the benefits of the proposed damping-reduction geometry.

A novel approach to the design of a Capacitive Micromachined Ultrasound Transducer (CMUT) cells is presented, using a Genetic Algorithm (GA) based optimization that couples finite element simulations with parameter changes tuned through Matlab scripts. The optimization goal is a maximization of the CMUT efficiency in coupling the electrical, mechanical and acoustic energy domains. Global constraints are related to the pull-in actuation voltage, resonant frequency (set to 5–6MHz, suitable for biomedical applications) and limits on the achievable geometric dimensions. A CMUT is a relatively new MEMS device used to generate and sense ultrasound waves through electrical actuation. Our CMUT design aims to generate ultrasound waves in the 5–6 MHz range, suitable for breast tumor detection. The electro-mechano-acoustical nonlinear coupling makes the design and optimization process difficult, requiring several cycles of finite element analysis. Therefore, a genetic constrained optimization algorithm implemented in Matlab is coupled with finite element simulations of a parameterized structure modeled in COMSOL Multiphysics, in order to maximize the efficiency of the CMUT cell. The main goal is to achieve maximum transducer efficiency, reflected in a better operating device with lower power consumption. The Matlab-FEA optimization loop is driven by the transducer electro-mechanical efficiency, used as a main performance measure to vary the CMUT geometry parameters from one generation to another.Copyright © 2010 by ASME

Squeeze-film damping is highly inadequate in low-pressure systems or in systems where air pressure and/or gap dimensions are poorly defined. Input shaping has been used to circumvent the oscillations typically associated with under-damped mass-spring-damper systems and drastically decrease the settling time. The proposed method does not rely on feedback but solely on the system dynamics. The required input signal is derived analytically from the differential equation describing the system. The resulting device response is simulated and experimentally verified on an electrostatically actuated microstructure. Settling occurs even faster than for an equivalent critically damped system.