Characterization of multilayered piezoelectric ceramics for high power transducers

In some circumstances, large vibrational displacements at ultrasonic frequency must be generated using a low voltage drive. This result cannot be obtained with monolithic PZT ceramics which require voltages larger than 1000 V to produce displacements of the micrometer order at resonance. The use of multilayered hard lead zirconate titanate ceramics as transduction material in resonant devices is experimentally investigated for Langevin-type transducers. Large amplitudes are obtained under low drive (5 microm under 10 V). Material constant (compliance, losses) variations under large dynamic stress are, at least, one order of magnitude larger than for monolithic ceramics. Depolarization is found to be a critical issue when the transducer is driven continuously. It is demonstrated that this problem can be solved by polishing the interfaces between different parts of the device and applying an electrical DC bias to the transducer.