The development of new cellular and porous polymers has introduced new advances on the study of the piezoelectricity characteristics of etectric charged polymers. Recently, a multi-layer space-charge electret was also fabricated using at least one "soft" porous and one "hard nonporous Teflon F' TFE film assembled in various multi-layer stacks. Now, in this paper we propose a new multi-layer spacecharge electret fabricated using at least one Teflon-FEP film with small voids homogeneously distributed on its surface. The device has the same concept of the electret microphone mechanism. When these multi-layer setups are charged by impulse voltage process, it is possible to obtain samples with high piezoelectric coefficients. Controlling the size of the voids on the film interface, we can obtain a better control of the charging processes and, can determine a better value of the charging impulse voltage.
Piezoelectrets from thin electrically charged cellular polypropylene-foam films have been suggested for numerous transducer applications, such as force sensors for keyboards, flat microphones for conference environments, or devices for ultrasound generation and detection. In addition to polypropylene piezoelectrets, other materials systems -such as thermo-fused polymer-film stacks -were developed in order to generate piezoelectrets that are thermally more stable and contain geometrically well-controlled air cavities. Here, we demonstrate the viability of the recently developed piezoelectret systems that had been prepared by thermo-lamination with templates for the acoustical detection of electric discharges in air. Furthermore, we show that the resonance behavior of the air cavity in which the electric discharge occurs can also be assessed from the acoustic signal. For the experiments, a transducer prototype with a preamplifier directly connected to the laminated piezoelectret sensor inside an electrically shielded package was developed. Reproducible sound measurements according to the ASTM E976-10 standard were performed with the transducer prototype. The prototype was later employed in acoustical measurements of electric discharges in an air gap inside an acoustical chamber -in order to reduce external noise -and in a metallic chamber for reducing electrical interference. The recorded signals were compared by means of Fast-Fourier-Transform (FFT) analysis.
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