| Much work has been conducted on the design of ultrasound transducers using piezoelectric ceramics, but a great deal of this work does not apply when using the piezoelectric polymers because of their unique electrical and mechanical properties. For poly(vinylidene fluoride) [P(VDF)] and their copolymers poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)], good mechanical flexibility and piezoelectricity make them become the better choice for applications of wideband hydrophones and ultrasound imaging systems. Giant electrostrictive response was observed in high-energy electron irradiated P(VDF-TrFE) copolymers, which indicates great potentials in electromechanical transducers and actuators.The purpose of this work is to investigate and present new insight into these copolymers and their ultrasound transducers. Structural evolution and dielectric relaxation behavior of electron-irradiated P(VDF-TrFE) 80/20 mol% and 56/44 mol% copolymers were carried out by X-ray, differential scanning calorimetery (DSC), dielectric constant and polarization hysteresis loops measurements. Thermal stimulated depolarization current (TSDC) and pyroelectric coefficient were also measured based on the phase transition and irradiation effect of P(VDF-TrFE) copolymers. A detailed discussion about the design and performance of a bimorph-based dilatometer was given using different sensor heads and platforms both experimentally and theoretically. Important considerations for the design of active polymer ultrasound transducers were listed, including piezoelectric polymer materials selections, transducers constructions and packaging requirements, materials characterization and modeling, film thickness and active area design, electrode selection, backing materials design, and front protection /matching layer design. At last, single-element, planar transducers were fabricated and characterized using electron-irradiated P(VDF-TrFE) 80/20 mol% copolymers with different electron dosage.
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