Spherically shaped active transducer based on proton-irradiated vinylidene fluoride-trifluoroethylene 70/30 mol% copolymer

Abstract

Spherically shaped active transducers using proton-irradiated vinylidene fluoride-trifluoroethylene 70/30 mol % copolymer films as the active elements are described. The copolymer films prepared by hot compression molding were irradiated with a high energy proton over a broad dose range (20-250 Mrad). The electrostrictive and piezoelectric responses of the copolymer have been characterized before subsequent transducer fabrication. The performances of the focused transducers constructed with a 4 mm aperture size and epoxy backing were evaluated under dc bias voltages. The transducers with focal lengths of 17.4-19.0 mm and a center frequency of 19 MHz display a broad bandwidth up to 94%. Besides, the transmitting output of the transducers increases with the dc bias voltage. For the copolymer active element irradiated at a proton dose of 107 Mrad, the transducer shows the highest transmitting voltage response of 1.34 kPa/V.