Improvement of frequency responses of an in-plane electro-thermal cantilever sensor for real-time measurement

Abstract

Resonance-based sensors ordinarily show a symmetrical amplitude shape, which is accompanied by a monotonic transition as its phase response. At its resonance state, there is a 90° phase difference between the excitation force and the system response. Nevertheless, due to some parasitic factors, resonance-based sensors might show non-ideal frequency response as seen in in-plane electro-thermal piezoresistive cantilever sensors (EtPCSs). Because of a direct thermal parasitic coupling from the excitation part to the sensing part, the sensor output shows an asymmetric amplitude shape and a reversing phase response. In some EtPCS that have relatively lower thermal exposure on their sensing part, a symmetrical amplitude shape could be demonstrated but was still accompanied with a low magnitude of monotonical phase response. In this work, a method of reference subtraction was introduced to enhance the frequency response of the EtPCS at changing ambient conditions (e.g. humidity, temperature, smoke exposure). As a result, we obtained optimized frequency responses suitable for a phase-locked loop-based system to carry out resonant-frequency tracking in real-time.