New Piezoelectric Materials for Ultrasonic Transducers

Abstract
Two types of piezoelectric ceramics with large electromechanical anisotropies (planar coupling factor k p is much less than thickness dilatational coupling factor k t) have been developed for use as high-frequency ultrasonic transducer materials: modified lead titanate ceramics (Pb, Sm)(Ti, Mn)O3 and ferroelectric PbZrO3 ceramics modified by adding small amounts of Pb(Mn1/3Nb2/3)O3 and PbTiO3. These new ceramics have a large k t and k t/k p. PZT/polymer piezoelectric composite sheets have also been developed for use in medical transducers. These composite sheets were fabricated using a “dicing and filling” technique. The resulting composites are highly flexible and show both a large k t and a low acoustic impedance.