Noncontact Measurement of Surface Resistivity Using a Phi-Type Electrode

In this paper, a noncontact surface-resistivity measurement has been developed for the evaluation of electrostatic properties in plastic materials coated with an antistatic spray. The system includes a corona-charging electrode and an electrostatic field meter. The corona-charging electrode consists of a grounded planar electrode with a circular hole and a needle electrode that penetrates the planar electrode at the center of the hole and is thus referred to as a phi-type electrode. The test sample is placed underneath the phi-type electrode and charged by corona charging. An electrostatic field meter located on the grounded planar electrode measures the surface potential outside of the charging area. Because the surface potential is determined by the surface resistivity of the test sample, the electrostatic properties, i.e., dissipative or insulative, can be detected from the surface potential without contacting the test sample. The system for charging the test samples and measuring the surface potential is presented. The measured surface potentials are in approximate agreement with the calculated potentials. Measurement of the surface-potential distribution can also identify where a plastic sample is coated with an antistatic spray.