Mode coupling in lead zirconate titanate/epoxy 1–3 piezocomposite rings

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 fH and lateral fL1 and fL2 mode resonances of individual PZT elements inside the rings as well as the radial fR and wall-thickness fW mode resonances of the whole rings. No stopband resonances were observed in the frequency range of 1 to 10 MHz. fH was found to increase linearly with the decrease in element height while fL1 and fL2 remained constant. When the height and width of the elements became comparable, coupling of fH with fL1 and fL2 occurred. The observed fH, fL1, and fL2 for all samples agreed with those calculated by the mode-coupling theory. fR and fW were almost independent of the ring thickness but increased as φ increased. A guide of operating fH in the rings without causing mode coupling was presented to optimize the composite structure for transducer design.