New opportunities in ultrasonic transducers emerging from innovations in piezoelectric materials (Invited Paper)

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Abstract
Piezoelectric materials lie at the heart of ultrasonic transducers. These materials convert electrical energy into mechanical form when generating an interrogating acoustic pulse and convert mechanical energy into an electric signal when detecting its echoes. This paper first surveys the piezoelectric materials in current use: piezoceramics, such as barium titanate, lead zirconate titanate, and modified lead titanate; piezopolymers, such as polyvinylidene difluoride and its copolymer with trifluroethylene; and piezocomposites, consisting of piezoceramic rods in a passive polymer matrix. Each material system has properties which commend them for use in the present single element transducers, annular arrays, sequenced linear arrays, and steered phased arrays. Looking to the future, new transducer possibilities are opening up due to recent piezoelectric material developments, such as, for example, synthesis techniques for fine-grained high-density piezoceramics, electrostrictive relaxor ferroelectric ceramics, novel piezoceramic forming methods, piezoceramic fiber synthesis, piezoceramic/metal multilayer structures, composite acoustoelectric materials, ferroelectric thin film growth and processing, and new piezopolymers. These innovations lead to fabrication of conventional transducers at high frequencies, fine-scale piezocomposites, 11/2-D and 2-D arrays, small intravascular transducers, as well as provide opportunities for new ultrasonic imaging techniques, using pitch-catch and non-resonant traveling wave transducers.

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