Piezoelectret sensors detect geometry-related modifications of the acoustical signatures from partial discharges in an electrical equipment chamber

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.