Nitrogen and air Paschen curves for dielectric barrier discharges in ?m-sized voids

The piezoelectric activity of ferro- or piezoelectrets (i e., charged polymer foams) is due to space charge deposited on dielectric surfaces of interior micrometer-sized voids. Typically, the space charge is created by applying large electric fields to the voids which induces dielectric barrier discharges (DBDs) resulting in charge separation within the gas. This charging process, which is a strong function of the gas pressure and void height, can be studied by monitoring light emission whose occurrence corresponds to the onset of DBDs. To investigate the breakdown behavior, single cell voids with defined heights were constructed by placing polypropylene (PP) spacers with varying thickness between 25 μm PP dielectric barriers. These were placed between glass slides with semi-transparent indium tin oxide electrodes. A high voltage charging profile was then applied while emission of light was monitored either with an electron-multiplying CCD camera (imaging mode) or a photomultiplier (non-imaging mode). Two separate methods of monitoring light emissions resulted in similar breakdown fields Ec for nitrogen and air in small voids. The breakdown fields are in good agreement with the standard Paschen curves, with small deviations for void heights less than 25 μm.