A computer-controlled remote measurement system for resonant BAW sensors

A novel microprocessor-controlled remote measurement system for resonant piezoelectric bulk acoustic wave (BAW) sensors is presented. The system supports various sensor types for different physical quantities, such as temperature, humidity, viscosity, density and speed of sound of liquids, and film thickness. The measurement principle is based on the determination of the locus of admittance curves of the respective sensors for one or several resonances (fundamental and/or overtones). Measurement results are calculated from the measured resonance frequencies or quality factors by applying the appropriate sensor function for each type of sensor. The system covers sensors with resonance frequencies ranging from 30 kHz to 30 MHz. Special electronics have been developed to transform the sensor admittance values to voltage signals that are acquired by the computer system. Disturbing effects caused by the capacitance of the sensor connecting cable are minimized by special electronic circuitry.