Transduction Phenomena in Ferroelectric Polymers and Their Role in Biomedical Applications

摘要

The ferroelectric polymers such as polyvinylidene fluoride (PVF2), polyvinyl fluoride (PVF), and several copolymers and blends are used as electromechanical and electrothermal transducing materials with promising biomedical applications. The flexibility of a polymer, when in thin-sheet from, the ease with which it can be cut into special patterns, formed into special geometries such as a tube, and conformed or molded to a surface with compound curvature, are well known external features which already make possible a wide variety of transducers. These polymers, copolymers and blends when poled have pressure and temperature transduction properties which are related mainly to volume changes. Because of compressional heating effects, the pressure response includes both piezoelectric and pyroelectric terms, the latter representing nominally a -10 percent effect under diabatic conditions. For sensors in good thermal contact with thermally conducting surroundings, the time constant for internal thermal equilibration of the polymer becomes relevant also along with the polarization distribution function, unless the latter is uniform. The piezoelectric response of thin tubes, balloons and caps is discussed within the dipole density model for which the response is determined by thickness changes.