Multiple-frequency surface acoustic wave devices as sensors

A multiple-frequency acoustic wave (MUFAW) device has been developed, fabricated, and tested on ST-cut quartz with nominal surface acoustic wave (SAW) center frequencies of 16, 40, 100, and 250 MHz. The four frequencies are obtained by patterning four sets of input and output interdigital transducers of differing periodicities on a single substrate. Such a device allows the frequency dependence of AW sensor perturbations to be examined, aiding in the elucidation of the operative interaction mechanism(s). Initial measurements of the SAW response to the vacuum deposition of a thin nickel film show the expected frequency dependence of mass sensitivity in addition to the expected frequency independence of the magnitude of the acoustoelectric effect. Measuring changes in both wave velocity and attenuation at multiple frequencies allows extrinsic perturbations such as temperature and pressure changes to be readily differentiated from one another and from changes in surface mass.<>