Improved Surface Voltage Uniformity on Electrets Obtained by Modified Corona Charging Method

The common corona charger consisting of wire or needle, gnrd, and one side metalized sample has been modified to obtain a more uniform surface potential over the area of interest. The better uniformity is obtained by adding an aperture between grid and sample close to the surface to be charged. This aperture is connected to the grid potential. The surface potential obtained by this method varies about ±0.5 percent over the entire charged area and exhibits a steep voltage drop at the edge of the aperture. Theoretical and experimental results are compared for the common corona geometry and the new aperture corona charger.