Piezoelectric Polymer Transducers

¹ Institute for Materials Science and Engineering, National Bureau of Standards, Gaithersburg, Maryland 20899

Poly(vinylidene fluoride) (CH₂-CF₂)_n is a tough, flexible polymer readily available in the form of thin film which can be made piezoelectric by the temporary application of a high electric field. The areas of the film which become piezoelectric can be controlled to be the areas where metal electrodes are evaporated onto the film. The same electrodes and associated leads are subsequently used to detect the electric charge generated by the application of pressure to the active area. Such films may have applications in the measurement of occlusal forces.

Many of the problems that might be encountered in an occlusal gauge have been addressed separately in other applications. For example, polymer transducers less than 100 µm thick have been developed and tested for measuring the nip pressure on an intaglio printing press. Piezoelectric polymer gauges have been successfully encased in a protective layer of another polymer to prevent the sharp edges of sand particles from breaking through the piezoelectric film. Transducer films with an array of active areas have been produced with electrical leads from each area so that the source of the signal can be traced. Electrode patterns have usually been established by evaporation of metal through a mask, but silk-screening a conductive ink has also been shown to be an effective means of defining which areas of the film are to be made piezoelectric. Finally, poly(vinylidene fluoride) has been shown to retain 80% of its initial activity after 1000 hours at 100 ° C, and it is unaffected by moisture. Therefore, if necessary, gauges to be used in dentistry could be subjected to steam sterilization for repeated use.

The physical properties of such polymer films and examples of their use in pressure transducers are reviewed with the intent of stimulating interest in development of a system useful for measuring occlusal forces.