Techniques for suppressing spurious resonant modes in 1:3 composite transducers

Conventional 1:3 composite transducers are composed of periodic arrays of fine piezoelectric ceramic pillars embedded in a polymer matrix. It is necessary to ensure that spurious interpillar (band-edge) resonant modes occur at high frequencies well separated from the practically useful thickness mode resonant mode. It is shown theoretically, and confirmed experimentally, that by using a distribution of ceramic pillar dimensions, or pillar spacings, a significant reduction in spurious resonant activity is achievable. The effects of using a small number of different dimensions, as opposed to a complete distribution, are considered. An alternative strategy, employing a polymer matrix with spatially varying material properties, is also considered