Piezoelectricity of vinylidene cyanide copolymers and their applications

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Abstract
P(VDCN/VAc) film which received a poling treatment near Tg exhibited large piezoelectricity. The electromechanical coupling constant kt of the P(VDCN/VAc) film at high frequencies is larger than that of PVDF, and is similar to P(VDF/TrFE). The acoustic impedance of P(VDCN/VAc) is smaller than that of PVDF, and is one tenth that of inorganic materials. This makes a good matching of P(VDCN/VAc) to water or living bodies. An ultrasonic transducer using a P(VDCN/VAc) piezoelectric film exhibits broad frequency performance with superior damping characteristics at higher frequencies. It is possible to focus ultrasonic beams at a focal point without an acoustic lens because a concave transducer can be easily fabricated taking advantage of the flexibility of P(VDCN/VAc). As a result of fabricating a 20–50 MHz concave polymer probe, it has become possible to detect defects or small cracks near the surfaces of samples, which was difficult using conventional crack detectors.