Mode coupling in modified lead titanate/polymer 1–3 composites

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Abstract
Modified lead titanate/polymer 1–3 composites are fabricated and their resonance characteristics determined. The mode coupling theory is applied to the pillar‐shaped ceramic elements inside the 1–3 composite. Coupling of lateral and thickness mode vibrations occurs as the width to thickness ratio increases. The experimental results agree well with the mode coupling theory predictions. It is found that the piezoelectric properties of PbTiO3/epoxy composites are similar to that of lead zirconate titanate (PZT)/epoxy composites, except that the coupling constants of lead titanate are very small due to ceramic anisotropy. The thickness mode resonant frequency times the thickness value, fH, stays steady and close to the uncoupled value as the configurational (width/thickness) L/H ratio is increased from 0.1 to 1.0. In the range L/H=1.0–1.5, the thickness and lateral mode vibrations couple. Above L/H=1.5, these modes decouple and are easily resolved. The thickness mode becomes again close to the uncoupled value. Lead titanate/epoxy composites geometries can therefore be selected with L/H>1.5. This produces better medical ultrasonic transducers than PZT/epoxy types.

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