New Piezoelectric Materials for Ultrasonic Transducers

Two types of piezoelectric ceramics with large electromechanical anisotropies (planar coupling factor kp is much less than thickness dilatational coupling factor kt) 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 kt and kt/kp. 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 kt and a low acoustic impedance.