Composite piezoelectrics: Basic research to a practical device

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Abstract
The adaptability of 1–3 PZT-rod/polymer-matrix piezoelectric composites commends them for the requirements of medical ultrasonic imaging transducers. We describe material fabrication techniques, material design considerations, and transducer design trade-offs involved in this application. A simple dice-and-fill fabrication technique yields material suitable for transducers with frequencies approaching 10 MHz. The piezocomposites provide high electromechanical coupling and low acoustic impedance – properties superior to those of the conventional piezoceramics and piezopolymers. Composite piezoelectric plates can be formed into complex shapes for beam focusing and steering. Moreover, arrays defined by simply patterning the electrode – not cutting the plate – exhibit no spurious modes in individual elements and low cross-talk between array elements. The resulting device performance is illustrated with a concave annular array which shows high sensitivity (8 dB insertion loss), large bandwidth (57%), compact impulse response (-20 dB ringdown of 3.3 periods, -40 dB ringdown of 6.2 periods) and good beam focusing. Such composite-piezoelectric ultrasonic transducers provide a paradigm for engineering material properties to optimize the performance of a practical device.