TRANSDUCTION PHENOMENA IN FERROELECTRIC POLYMERS AND THEIR ROLE IN BIOMEDICAL APPLICATIONS

Ferroelectric polymers such as polyvinylidene fluoride, polyvinyl fluoride, and several 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 adiabatic conditions. At low frequencies, where there is enough time in a cycle period for significant heat to be exchanged between the polymer and the surroundings, the time constant characterizing the thermal coupling to the surroundings becomes relevant as well as the compressional heating of the surroundings. 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.