Werner Jenninger

Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

We describe the concept, the fabrication, and the most relevant properties of a piezoelectric-polymer system: Two fluoroethylenepropylene (FEP) films with good electret properties are laminated around a specifically designed and prepared polytetrafluoroethylene (PTFE) template at 300 °C. After removing the PTFE template, a two-layer FEP film with open tubular channels is obtained. For electric charging, the two-layer FEP system is subjected to a high electric field. The resulting dielectric barrier discharges inside the tubular channels yield a ferroelectret with high piezoelectricity. d33 coefficients of up to 160 pC/N have already been achieved on the ferroelectret films. After charging at suitable elevated temperatures, the piezoelectricity is stable at temperatures of at least 130 °C. Advantages of the transducer films include ease of fabrication at laboratory or industrial scales, a wide range of possible geometrical and processing parameters, straightforward control of the uniformity of the polymer ...

Template-based fluoropolymer ferroelectrets with multiple layers of tubular channels

Significant efforts are devoted to developing new ferroelectrets with well-controlled void distributions or uniform voids and with good long-term and thermal stability of the piezoelectricity. Here, we describe the concept, the fabrication, and the most relevant properties of fluoropolymer ferroelectret systems with three separate films of fluoroethylenepropylene (FEP), alternating with two polytetrafluoroethylene (PTFE) templates. The FEP films are selectively fused by means of a lamination process. Two practically identical PTFE templates are used, which have parallel rectangular openings (1.5×30 mm2) separated by PTFE ridges of 1.5 mm width. After removing the PTFE templates, a three-layer FEP-film sandwich with tubular channels is obtained. We demonstrate that such FEP-film systems exhibit significant and stable piezoelectricity after charging under a high DC voltage. The resulting piezoelectric effect may be further improved by carefully assembling and arranging the PTFE templates during preparation.

Dielectric resonance spectroscopy of piezoelectrets with tubular channels: Channel dimensions control resonances

Recently, a new type of polymeric piezoelectret has been proposed and demonstrated with two fluoroethylenepropy-lene (FEP) films that are laminated around a polytetrafluoroethy-lene (PTFE) template at 300 °C. After removing the PTFE template, a two-layer FEP film with open tubular channels is obtained. After internal bipolar charging, the channels form large and easily deformable electric dipoles that lead to the desired piezoelectricity. By using different templates, the channel dimensions and consequently also the resonances of the piezo-electret system can be easily tuned. Here, we describe and discuss the resonance peaks that are found in the dielectric spectra of tubular-channel piezoelectrets with different channel geometries.