Lead zirconate titanate (PZT)/epoxy 1-3 piezocomposite rings were fabricated with PZT volume fractions Φ ranging from 0.82 to 0.94 and with a small epoxy width of 77 µm in order to investigate their resonance characteristics and to reveal the mode coupling. Four major resonance modes were observed, namely the coupled longitudinal-thickness f[sub H] and lateral f[sub L1] and f[sub L2] mode resonances of individual PZT elements inside the rings as well as the radial f[sub R] and wall-thickness f[sub W] mode resonances of the whole rings. No stopband resonances were observed in the frequency range of 1 to 10 MHz. f[sub H] was found to increase linearly with the decrease in element height while f[sub L1] and f[sub L2] remained constant. When the height and width of the elements became comparable, coupling of f[sub H] with f[sub L1] and f[sub L2] occurred. The observed f[sub H], f[sub L1], and f[sub L2] for all samples agreed with those calculated by the mode-coupling theory. f[sub R] and f[sub W] were almost independent of the ring thickness but increased as Φ increased. A guide of operating f[sub H] in the rings without causing mode coupling was presented to optimize the composite structure for transducer design.
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