Resonance characteristics of lead zirconate titanate/epoxy 1-3 composite rings

Lead zirconate titanate (PZT)/epoxy 1-3 composite rings with PZT volume fractions φ ranging from 0.82 to 0.94 are fabricated, and their resonance characteristics are studied. These composite rings have sufficiently small epoxy width (∼ 77 μm) and can be treated as effective homogeneous media in which stopband resonances are not observed in the frequency band of interest (< 4 MHz). A mode coupling theory is applied to predict the longitudinal-thickness fH and lateral fL mode resonances of PZT elements inside the rings. By thinning the rings and by measuring the resonance peaks using an impedance analyzer, fH is observed to increase linearly with the decrease in element height while fL remains constant. When the height and width of the elements become comparable, mode coupling occurs. To avoid spurious modes being coupled to fH, the rings cannot be too thin in order to keep fH smaller than fL. In the lower frequency regime, they cannot be too thick to avoid coupling of fH with the wall-thickness fW and radial fR mode resonances. fW and fR are found to be independent of ring thickness but increase as φ increases.