Piezoelectricity in polymers

In the last few years it has been shown that polyvinylidene fluoride, a polymer which can.readily be formed into very thin, flexible, and transparent films, is a ferroelectric material. The availability of a ferroelectric material in this unusual form has led to a large number of possible new applications, and the Japanese company, Pioneer Electronic Corporation, has already developed a commercial product.¹ They are producing headphones in which the active element is an 8-pm-thick film of polyvinylidene fluoride. Indicative of the kind of creativity this new material permits, the headphones do not use the change in thickness of the film at all. The polymer film is stretched over a flexible polyurethane foam and application of a voltage causes a change in the area of the film so that the foam, functioning like a spring, is either compressed or allowed to expand, depending on the polarity of the applied voltage.