Efficient Demodulation for Measuring the Amplitude of Mechanical Oscillations

The accurate detection and demodulation of mechanical oscillations is crucial for the performance of miniaturized resonant sensors and scanners. Demodulation by external instruments such as lock-in amplifiers or spectrum analyzers is not always desired due to their large size, complexity and cost. The demodulation technique proposed in this paper enables a simplified measurement of the oscillation amplitude of a mechanical oscillator with integrated deflection sensors, such as piezoresistive or capacitive elements. Configuring the sensors in an AC bridge circuit operated at the oscillator resonance frequency leads to a direct demodulation at the output of the bridge circuit. The presented method is experimentally verified on an AFM cantilever with integrated piezoresistive elements.