Surface acoustic wave pressure sensor

A sensitive sensor for measurement of pressure and strain is created by fabricating a surface acoustic wave (SAW) delay line on a quartz substrate. The SAW device which acts as a band pass filter has a central frequency of 98MHz. When an external force, strain, pressure is applied to the acoustic gap, then the gap length and IDT finger spacing will change and thus cause a shift of the central frequency and of the phase. Our approach was first to generate a 98MHz signal at the input transducer and to evaluate the relative phase shift due to the pressure or the strain. The second approach was to introduce the SAW device in an oscillator loop to measure the relative variations of the central frequency. A simulation based on finite elements was carried out to compare the length variations and an experimental study of the IDTs position, substrate thickness and orientation on the sensor response.