1-3 single crystal composites for ultrasonic transducer arrays

The development of single crystal relaxor-PT piezoelectrics is an exciting advance in ultrasound transducer technology. The high electromechanical coupling coefficients and variable dielectric constant could be used to significantly enhance bandwidth and sensitivity of array transducers. In this study 1-3 composites of single crystal material were engineered and applied to an array design. Both predicted and actual performances are reported and compared to array designs using PZT-SH based 1-3 composite material. In order to take advantage of the performance enhancement of single crystal materials a 1-3 composite connectivity was selected. Two techniques were used to tile together small pieces of crystal into a larger composite plate suitable for array applications. A coupling coefficient of .81 and an acoustic impedance of 15.6 Mrayls were obtained using a 58% volume fraction of single crystal. A comparable PZT composite displayed a coupling coefficient of .66 and an acoustic impedance of 17.0 Mrayls. A sufficiently fine spatial scale resulted in lateral resonances being well above the thickness mode resonance fbr both materials. One-dimensional modeling using the Redwood equivalant circuit in PSpice was used to investigate matching and backing. An optimization scheme resulted in a modeled bandwidth of 134% and a -6 dB pulse length of only one cycle using a single front matching layer and a castable backing. Eight element arrays of single crystal and PZT-SH composite were constructed to verify the theoretical results.