Quartz pressure sensor based on SAW reflective delay line

We have developed a wireless SAW (Surface Acoustic Wave) pressure sensor operating in the pressure range from 0 Pa to 250 kPa. In order to minimize the temperature sensitivity the pressure sensor is based on an all quartz package, which has been designed with the Finite Element Method. The package of the pressure sensor consists of a diaphragm and a cover, both made of conventional Y-cut quartz. A blind-hole was structured into the sensor cover. By attaching the cover and the diaphragm with an epoxy-adhesive, this blind-hole forms a closed cavity. The SAW element is a reflective delay line, working at approximately 434 MHz. The delay line consists of ten reflectors and extends over the whole diaphragm. The pressure is determined by evaluating the change of the carrier phase shifts of the reflected impulses at the reflectors. We show that it is possible to minimize the temperature sensitivity and to achieve good linearity by correct positioning of the SAW reflectors. The measurements of the SAW pressure sensor show a deviation from linearity of less than +/-0.7%. The temperature dependence is almost negligible in the range from -20/spl deg/C to 100/spl deg/C.