Sangtak Park

Low Voltage Electrostatic Actuation and Displacement Measurement Through Resonant Drive Circuit

Most electrostatic actuators fabricated by MEMS technology require high actuation voltage and suffer from the pull-in phenomenon that limits the operation range. We present an amplitude-modulated resonant drive circuit to drive electrostatic actuators at much lower supply voltage than that of conventional actuators to extend their operation range. Analytical and numerical models facilitate stability analysis of electrostatic actuators coupled with the resonant drive circuit. We study the impact of parasitic capacitance and the quality factor of the resonant drive circuit on the operation range of electrostatic actuators. Furthermore, we present a new method to measure the displacement of electrostatic actuators by sensing the phase delay of the actuation voltage with respect to the input voltage. This measurement method allows us to easily incorporate feedback control into existing electrostatic actuators without any modification to the actuator itself.© 2012 ASME

Binary MEMS gas sensors

A novel sensing mechanism for electrostatic MEMS that employs static bifurcation-based sensing and binary detection is demonstrated. It is implemented as an ethanol vapour sensor that exploits the static pull-in bifurcation. Sensor detection of 5 ppm of ethanol vapour in dry nitrogen, equivalent to a detectable mass of 165 pg, is experimentally demonstrated. Sensor robustness to external disturbances is also demonstrated. A closed-form expression for the sensitivity of statically detected electrostatic MEMS sensors is derived. It is shown that the sensitivity of static bifurcation-based binary electrostatic MEMS sensors represents an upper bound on the sensitivity of static detection for given sensor dimensions and material properties.

A Tunable MEMS Magnetic Sensor

This paper introduces a tunable MEMS magnetic field sensor. It uses torsional vibrations excited by Lorentz force to measure the strength of external magnetic fields. The sensor sensitivity and dynamic range can be tuned on-the-fly by varying its dc bias. Experimental demonstration shows that the sensor sensitivity can be tuned in the range of 0.139–0.283V/mT as the bias voltage varies from 0 to 6V in air and in the range of 0.038–0.955V/mT as the bias voltage varies from 0 to 5V in vacuum. While the sensor can operate in either a forced or a resonant mode, it achieves higher sensitivity and bandwidth when operating near its first torsional resonance. [2015-0285]

Design and analysis of resonant drive circuit for electrostatic actuators

Most electrostatic actuators fabricated by MEMS technologies require high actuation voltage and suffer from the pull-in phenomenon in the presence of high parasitic capacitance, either driven by conventional voltage control or charge control. The resonant drive circuit presented in this paper uses much lo wer supply voltage to drive electrostatic actuators, which usually require a high actuation voltage from a high voltage am plifier, through passive amplification at its electrical resonance. Furthermore, it is shown that the resonant drive circuit is able to extend operation range of electrostatic actuators beyond the pull-in point even in the presence of high parasitic capacitance due to its inherent negative feedback. Analytical and numerical models of the resonant drive circuit are derived and built to demonstrate the advantages of the resonant drive circuit implemented with two logic gates arranged in the BTL configuration.

Nonlinear Parameter Identification of a Resonant Electrostatic MEMS Actuator

We experimentally investigate the primary superharmonic of order two and subharmonic of order one-half resonances of an electrostatic MEMS actuator under direct excitation. We identify the parameters of a one degree of freedom (1-DOF) generalized Duffing oscillator model representing it. The experiments were conducted in soft vacuum to reduce squeeze-film damping, and the actuator response was measured optically using a laser vibrometer. The predictions of the identified model were found to be in close agreement with the experimental results. We also identified the noise spectral density of process (actuation voltage) and measurement noise.

High-efficiency passive full wave rectification for electromagnetic harvesters

We compare the performance of four types of full-wave bridge rectifiers designed for electromagnetic energy harvesters based on silicon diodes, Schottky diodes, passive MOSFETs, and active MOSFETs. Simulation and experimental results show that MOSFET-type rectifiers are more efficient than diode-type rectifiers, reaching voltage and power efficiency of 99% for ideal voltage source with input amplitudes larger than 800 mV. Since active MOSFETs require extra components and an external DC power supply, we conclude that passive MOSFETs are superior for micro-power energy harvesting systems. We demonstrate passive MOSFET rectifiers implemented using discrete, off-shelf components and show that they outperform all electromagnetic harvester rectifiers hitherto reported obtaining a power efficiency of 95%. Furthermore, we show that passive MOSFET rectifiers do not affect the center frequency, harvesting bandwidth, or optimal resistance of electromagnetic harvesters. We demonstrate a complete power management modu...

Contact damping in microelectromechanical actuators

We examine the significance of the energy loss mechanisms active in electrostatic MEMS actuators. We find that the dominant loss mechanism changes depending on the actuator mode of operation. We find that the active mechanisms in the order of their significance are: fluid-structure interactions dominant for actuators operating in air, actuator-substrate interactions dominant for actuators in contact with a substrate under vacuum, and intrinsic loss mechanisms dominant for actuators in-flight under vacuum. Further, experimental results show that the quality factor of an electrostatic MEMS actuator drops drastically as the actuator first comes into line contact with a substrate. As the contact area expands along the actuator length, the quality factor increases. Measurements under 1 Torr vacuum show a three-fold increase in the quality factor as the contact area expands from a line to 30% of the actuator area. This increase in the quality factor is attributed to the drop in the contribution of friction forces into energy losses as contact expands and adhesion forces increase.

Low Voltage Electrostatic Actuation for MEMS Actuator Using Frequency Modulation

In this paper, we derive and present an analytical model of the parallel-plate electrostatic actuator coupled with the resonant drive circuit when it is driven by a frequency-modulated input signal. Using this analytical model, we determine the stability of the fixed points of the actuator without linearization process. Furthermore, we study the effect of parasitic capacitance and the quality factor of the resonant drive circuit on the operation range and stability of the electrostatic actuator.© 2013 ASME

Stabilization of Electrostatic Actuators Through Variable Gain Amplifier

In the presence of high parasitic capacitance, conventional electrostatic actuation methods fail to drive an electrostatic actuator beyond its pull-in point. Although the resonant drive circuit is able to extend the operation range of an electrostatic actuator further at a much lower input voltage, an electrostatic actuator coupled with the resonant drive circuit also undergoes pull-in in the presence of high parasitic capacitance compared to the circuit’s quality factor. To improve its robustness to high parasitic capacitance, we design a variable gain amplifier that reduces voltage gain as an electrostatic actuator moves towards its bottom electrode: the increase in the impedance of the resonant drive circuit reduces voltage gain of a variable gain amplifier through its positive feedback loop, while its negative feedback stabilizes its operation.Copyright

Techniques for dynamic analysis of bonding wire

Abstract This study describes new experimental techniques for dynamic analysis of bonding wire. The techniques employ a laser Doppler vibrometer (LDV) for non-contact measurement of wire response to transient, impact, and steady-state (harmonic) excitations. The first technique determines the transients and response time of the wire to current pulse excitations. The second technique, employs impacts delivered by a solenoid actuator to perform modal analysis on bonding wire and obtain their natural frequencies. Steady-state experimental techniques are also developed to obtain the mode shapes, nodal points, and frequency-response curves of bonding wire under thermal (current) excitation. These techniques are deployed to study the response of 300 μ m diameter Aluminum and Aluminum coated Copper bonding wires to DC and AC currents. The experimental results are interpreted and verified by comparing them to numerical results obtained from finite element analysis. This study experimentally measures and reports, for the first time, the second and fourth in-plane and the second out-of-plane bending mode shapes of bonding wire.