Piezoelectric and ferroelectric properties of P (VDF-TrFE) copolymers and their application to ultrasonic transducers

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Abstract
The copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) have been found to be effective ultrasonic transducer materials because of their large electromechanical coupling factor kt . On the basis of the results obtained by SEM, X-ray diffraction, and ferroelectric polarization reversal studies of copolymer films, the large kt is ascribed to their high remanent polarization, which may originate from high crystallinity and preferential orientation of well-grown crystallites. Various single element transducers for medical ultrasound imaging have been developed utilizing PVDF and P(VDF-TrFE) films. The performance of these transducers is in good agreement with a theoretical prediction in which their dielectric and mechanical losses are taken into account. The P(VDF-TrFE) transducers have a two-pathway sensitivity 10 dB higher than that of PVDF transducers. They give high resolution medical images much superior in quality to those obtained with conventional ceramic transducers. Linear transducer arrays of P(VDF-TrFE) also give ultrasound images which show their potentiality for real-time imaging.