RESONANT PRESSURE SENSOR BASED ON PIEZOELECTRIC PROPERTIES OF FERROELECTRIC THICK-FILMS

The paper describes the design, implementation and performance of a resonant sensor for gas-pressure measurement realized with screen-printed and fired PZT-based layers on an alumina diaphragm. The piezoelectric properties of these layers have been exploited to excite (with low voltage signals) and detect oscillations of the diaphragm. The layer configurations and associated vibrational modes of the diaphragm have been designed and a phase-locked loop (PLL) technique implemented in electronic circuits able to keep the resonant condition, despite the change of resonance frequency due to variation of the applied differential pressure. It is shown that for an adequate choice of operating frequency (i.e. of the vibrational mode) a good sensitivity and thermal stability of the sensor can be obtained; in this device, operating at frequency around 57.8 kHz, corresponding to the third-mode frequency f0.3, a shift DELTA-f0.3 = 650 Hz is found by changing the pressure from 0 to 900 mmHg. We found also that f0.3 changes less than 6 x 10(-3) by changing the temperature from 23 to 100-degrees-C. Moreover the sensor allows long-term measurements of static pressures without significant hysteresis effects.