Pressure and Temperature Measurements with SAW Sensors

Abstract

Abstract : Two different SAW-sensors are presented: a pressure-sensor for weak pressure and a SAW-temperature sensor. The pressure sensor is built with a thin diaphragm of quartz-crystal on which two surface elastic waves are propagating in the same direction but at two different lateral positions. Pressure variations applied on the lower surface induced a strong bending which modifies both wave velocities. A differential detection enables to measure wave velocity variations (or corresponding oscillator frequency shifts) and also enables to eliminate in a large scale spurious velocity (or frequency) variations due to temperature fluctuations. Calculations of strain distribution and then of corresponding frequency shifts give both positions of SAW delay lines on the thin diaphragm to have a maximal pressure sensitivity and to minimize temperature effects at the same time. Theoretical results of Y-cut are compared with measurements performed at 105 MHz.