Three-layer ferroelectrets from perforated Teflon®-PTFE films fused between two homogeneous Teflon®-FEP films

In this contribution, we propose a new route towards polymer ferroelectrets with uniform voids: Two homogeneous Teflon®-FEP films are separated by, but also thermally fused to a Teflon®-PTFE film with several homogeneous holes. Closed voids with FEP top and bottom lids and PTFE walls are thus formed. After internally charging the top and bottom FEP layers with positive and negative polarity, respectively, the voids constitute large dipoles that can be deformed by mechanical or electrical stresses. Consequently, the three-layer sandwich exhibits direct and inverse piezoelectricity. The continuous layerfusing process involves a press with hot cylindrical rolls that operate at temperatures up to 310 °C, which may allow production of inexpensive transducer materials on a large scale. We report about the concept, the processing, the charging and the electromechanical performance of the three-layer ferroelectrets.