Development and Synthesis of High Performance 103 Piezocomposites

Composite materials comprising an active piezoelectric phase and a passive polymer phase offer significant advantages over their single phase counterparts. These include higher electromechanical performance and vastly enhanced design versatility. Several combinations of polymer/ceramic connectivity are feasible of which 0-3 and 1-3 connectivity have emerged as the most practical. The so called "dice and fill" technique of cutting two sets of grooves in a block of piezoceramic at right angles to each other and subsequently casting a polymer into the grooves is the most widely employed method for realizing 1-3 connectivity. This method is quite simple but requires time consuming repetitive dicing with a relatively expensive precision saw and is suitable for only making square posts with facing parallel surfaces that are symmetrically distributed in the composite. The situation potentially gives rise to undesirable inter-post resonant activity. This problem may be eliminated if circular posts distributed randomly, or pseudo-randomly, are used instead. An inexpensive yet versatile technique for fabricating 1-3 connectivity is proposed comprising ceramic posts whose distribution in the composite is tailored to the application. The method is versatile enough to implement performance enhancing properties such as apodization of ceramic content (both lateral and axial) to reduce sidelobes in imaging arrays, control over the distribution of posts within the structure to reduce crosstalk, and, the use of aligned compressible inclusions for improving the overall efficiency of the composite. The technique is useful for achieving greater than 40% ceramic volume fraction composites in the 100 kHz-8 MHz frequency range for underwater sonar and medical imaging applications. Preliminary data for samples fabricated at 800 kHz and 4 MHz are presented with electromechanical coupling coefficient (kt) as high as 0.75.