Interface circuit for multiple-harmonic analysis on quartz resonator sensors to investigate on liquid solution microdroplets

This work proposes an interface circuit which exploits a compact implementation of impedance measurement to innovatively analyze a quartz crystal resonator (QCR) sensor across multiple-harmonic overtones. The system measures the real and imaginary parts of the sensor electrical admittance, from which the series resonant frequency and the motional resistance are derived for each overtone. By probing the resonator at multiple-harmonic modes, enhanced sensing capabilities can be conveniently achieved because a larger set of parameters can be measured with a single sensor. Experimental tests run with 5-MHz QCR sensors on which microdroplets of a sugar–water solution were deposited by a piezoelectric microdispenser show that the response patterns measured across different harmonics can be put in relation with the changes in the acoustic wavelength into the loading medium.