Recent Trend on Application of Piezoactve Polymers to Acoustics

Abstract : Noble sound shielding system is developed by the combination of a curved piezoelectric polymer film and a negative capacitance circuit. Incident sound produces the in-plane strain and polarization in the piezoelectric film. The charge induced on the electrode by polarization is amplified and fed-back to the electrode. The resulting electric field produces the inverse piezoelectric strain. The strain of the film is thus the sum of the sound-induced strain and the field-induced strain and can be arbitrarily increased or decreased by changing the feed back voltage. Subsequently the reflection and transmission of sound can be controlled. The complete isolation of sound is attained at a single frequency. The agreement of the value of the capacitance and its frequency dependence between the film and the capacitor in the circuit is required to achieve the sound shielding over a broad frequency range. Combining two PVDF films, about 50 dB transmission loss is observed from 200 Hz to 1000 Hz. The efficiency of shielding is more effective at the lower frequencies in contrast to the ordinary sound absorbing materials.