Non Contacting Measurement of Surface Resistivity Using Phi Type Electrodes

Non contacting measurement of surface resistivity has been investigated by simultaneous applications of corona charging to a test sample and measuring surface potential around the charged spot. The corona charging electrodes are consisted of a grounded plane electrode with a circular hole and a needle electrode penetrating the plane electrode at the center of the hole, defined as phi type electrodes. The test sample to be measured is placed underneath of the phi type electrode and is charged partially around the needle electrode where the corona ions emitted from. An electrostatic field meter is located on the grounded plane electrode to measure the surface potential around the needle electrode. Because the surface potential distribution around the charged area is determined by its surface resistivity, the electrostatic properties of the sample, i.e. dissipative or insulative, can be detected without any contact electrode onto the sample. The experimental setup, measured and predicted surface potentials are presented. Distribution of surface potential at the test surface partly covered with antistatic spray is also presented for a possible application of non contacting measurement of the surface resistivity.