Surface charging limit for a woven fabric on a ground plane

Abstract

Abstract This paper investigates the problem of depositing the maximum possible charge on a sheet of porous material, such as cloth, using a corona discharge. In the experiments, 50 to 75 μm-thick samples of nylon parachute fabric of varying porosity were charged over a ground plane using corona ions generated by a pin array energized at 6 kV – 9 kV dc and 0.5 cm gap spacing. The cloth exhibited a material-dependent maximum surface potential that was independent of the potential of the corona electrodes. This characteristic maximum surface potential was larger for low-porosity fabrics (tighter weave pattern), reaching a high of approximately 600V for 65 μm-thick, “zero porosity”, calendared ripstop nylon. Maximum surface potentials on the order of 200–500 V were observed on higher-porosity, “standard-issue” parachute fabrics of similar thicknesses. The experiments suggest a fundamental limit to surface charge that depends on the properties of the cloth, but not on the corona charging voltage. The observed results can be explained, in part, by a back ionization discharge mechanism that limits the indefinite build up of surface charge. The onset of back ionization is predicted from the Paschen breakdown curve and the weave geometry of the cloth. Breakdown field strengths inside the pores of the material were estimated using a simple dielectric layer model.