A novel electrostatic MEMS gas sensor is demonstrated. It employs a dynamic-bifurcation detection technique. The sensor detects ethanol vapor in a binary mode, reporting ON-state (1) for concentrations above a preset threshold and OFF-state (0) for concentrations below the threshold. The sensing mechanism exploits the qualitative difference between the sensor state before and after the dynamic pull-in bifurcation. Experimental demonstration was carried out using a laser Doppler vibrometer to measure the sensor response before and after detection. The sensor was able to detect ethanol vapor concentrations as 100 ppb in dry nitrogen. A closed-form expression for the sensitivity of dynamic bifurcation sensors was derived. It captures the dependence of sensitivity on the sensor dimensions, material properties, and electrostatic field.

This paper investigates the responses of initially curved micro-beams subjected to an electrostatic excitation. A Euler–Bernoulli beam theory is utilized to derive the governing equation of motion. A reduced-order model was developed by discretizing the equation of motion using straight beam mode shapes as basis functions in a Galerkin expansion. The results show evidence of the superharmonic resonances of order-three and two in addition to primary resonance. The co-existence of multiple stable orbits observed around only one stable equilibrium and under excitation waveforms with RMS voltage less than the snap-back voltage. These branches are a branch of small orbits within a narrow potential well and two branches of medium-sized and large orbits within a wider potential well. The transition between them results in the characteristic of the double peaks appearing in the frequency-response curve. We also report a bubble structure along the medium-sized branch consists of a cascade of period-doubling bifurcations and a cascade of reverse period-doubling bifurcations. A chaotic attractor develops within that structure at larger excitation levels. It demonstrates evidence of chaos with a wide-based spectrum and an elevated noise-floor. Odd-periodic windows appear also within the attractor including period-three (P-3), period-five (P-5) and period-six (P-6) windows. The chaotic attractor terminates in a cascade of reverse period-doubling bifurcations of period-four (P-4) orbits and period-two (P-2) orbits.

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.

We present electrostatic Micro-Electromechanical System actuators equipped with dimples and contact pads. The introduction of dimples and contact pads is shown to prevent stiction between the actuator and bottom electrodes and minimize dielectric charging and to eliminate multi-valuedness in the response. It also increases the stable travel range by eliminating the pull-in instability and introducing new “tapping mode” oscillations, where the dimples come into regular contact with the contact pads. An experimentally validated lumped-mass model was developed and used to generate the bifurcation diagram of the actuator in the vicinity of tapping mode oscillations. The diagram showed the presence of a chaotic attractor bracketed by a type-I intermittency and a cascade of period-doubling bifurcations. However, these chaotic motions were only present for a limited range of the excitation amplitude and frequency. Provided these ranges are excluded, dimples and contact pads can be deployed to obtain efficient and well regulated electrostatic actuators. We found that these results and conclusions are valid for classes of low-frequency as well as high-frequency actuators.