Acoustic Filter Design Using Temperature Tuning

The material properties selection for designing acoustic filters with optimal performance over a range of frequencies requires considerable effort to fabricate and test laboratory samples. To simplify this procedure, one may test a single sample at various temperatures to design an acoustic filter for a desired band-width. The essential idea is to fabricate a single layered periodic elastic composite with constituent materials that have temperature-dependent properties. As temperature is changed, such a composite exhibits a band structure that changes with the change in temperature. Once a desired band structure is attained and the corresponding constituent properties are identified, then new constituents that have those properties at the required temperature can be selected and new sample fabricated. We fabricated a 2-phase composite with periodic layers of polyurea and steel. The temperature is changed from -20{\deg}C to 60{\deg}C and ultrasonic measurements are performed on the sample over 0.15 to 2.2MHz at each temperature. The first three pass bands are captured experimentally and significant change in the band structure is observed over the test temperature range. Experimental transmission spectrum at each temperature is compared with the theoretical band structure and it is shown that good agreement exists for the observed variation in the band structure.