Nonlinear piezoelectricity in PZT ceramics for generating ultrasonic phaseconjugate waves

We have succeeded in the generation of acoustic phase conjugate waves with nonlinear PZT piezoelectric ceramics and applied them to ultrasonic imaging systems. Our aim is to make a phase conjugator with 100% efficiency. For t his purpose, it is important to clarify the mechanism of acoustic phase con jugation through nonlinear piezoelectricity. The process is explained by th e parametric interaction via the third-order nonlinear piezoelectricity bet ween the incident acoustic wave at angular frequency omega and the pump ele ctric field at 2 omega. We solved the coupling equations including the thir d-ordered nonlinear piezoelectricity and theoretically derived the amplitud e efficiency of the acoustic phase conjugation. We compared the efficiencie s between the theoretical and experimental values for PZT ceramics with eig ht different compositions. Pb[(Zn1/3Nb2/3)(1-x)Ti-X]O-3 (X = 0.09, PZNT91/9 ) piezoelectric single crystals have been investigated for high-performance ultrasonic transducer application, because these have large piezoelectric constants, high electrical-mechanical coupling factors and high dielectric constants. We found that they have third-order nonlinear piezoelectric cons tants much larger than PZT and are hopeful that the material as a phase con jugator has over 100% efficiency. (C) 2000 Elsevier Science B.V. All rights reserved.