Tunable Resonant Accelerometer via Loop Gain Control and Nonlinear Effect

This paper presents a tunable resonant accelerometer in which Duffing nonlinearity is induced to tune the senor oscillation frequency and sensitivity. The proposed sensor showed increase in both resonance frequency/bandwidth and sensitivity, and overcome the sensitivity-bandwidth trade-off in the classic second-order-system theory. The accelerometer is a MEMS oscillator based on a clamped-clamped (CC) beam resonator with electrostatic actuation and piezoresistive readout. The center oscillation frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_0$</tex> is tuned by controlling the loop gain of the sustaining feedback loop. Increased gain results in large structural displacement and shifts the oscillation to higher frequency due to the Duffing hardening effect, and thus increases the sensing bandwidth. Measurements in the current setup showed an oscillation frequency tuning range from 8.9 kHz to 24.3 kHz. The output oscillation frequency is affected when external vibration is applied. For the specific bias at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{B}=1.6\mathrm{V}$</tex>, the oscillation frequency and sensing sensitivity increased, respectively, from 21 to 24.3 kHz, and 182 to 415 Hz/g (0.99 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.87 \Delta f/f_{0}/\mathrm{g}$</tex>) with increased loop gain.