Multiple-frequency SAW devices for chemical sensing and materials characterization

The authors have demonstrated the use of multiple-frequency SAW (surface acoustic wave) devices for chemical detection and characterization of thin-film properties. A seven-frequency SAW device was designed and fabricated with nominal Rayleigh wave center frequencies ranging from 25 to 200 MHz in square root 2 multiples. For this device, transducer periodicity, finger length, and center-to-center transducer separation all scale with the reciprocal of the center frequency. Coating this device with a thin polymer film allows the study of frequency-dependent changes in the viscoelastic properties of the polymer as a function of temperature and of the concentration of various organic solvents, which in turn provides a means for selectivity detecting these compounds. Multifrequency devices provide a means of distinguishing among the many perturbations affecting SAW propagation.<
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