Optimization of the piezoelectricity in ferroelectret sensor films

Inhalt:
Ferroelectrets are internally charged non-polar polymer foams and cavity-containing polymer-film systems. Through internal bi-polar charging (poling), the cavities can be turned into macroscopic dipoles, which renders the materials piezoelectric. The charging efficiency of the cavities needs to be enhanced in order to optimize the piezoelectricity of ferroelectrets. Here, we introduce two charging strategies (namely, thermal charging and charging assisted by gas exchange) through which the charging efficiency of ferroelectrets can be greatly improved. With both charging schemes, the breakdown strength of the cavities is first lowered, so that a small voltage is required for triggering the breakdown and for introducing high polarization. The breakdown strength of the cavities is then increased while the charging voltage is on. Finally, the charging voltage is switched off, and a high remanent polarization is attained.