DSP measurement of dielectric property of polymeric materials using interdigital electrodes

Generally, dielectric property of insulating material is evaluated as loss tangent and capacitance by using thin samples. These bulk properties are measured by the application of electric field from one side to another side of the sample film surface. Three terminal parallel plane electrodes are usually used for this measurement. In this paper, a pair of inter-digital electrodes is set only on one side of sample surface, such as silicone and EPDM rubber insulators. Then, we evaluate the dielectric property by using the leakage of the electric field lines from the edge of interdigital finger electrode to the bulk of the sample. Digital signal processor (DSP) is used for data processing. We can successfully measure the degradation and recovery process of the surface of polymer insulating materials. Our DSP measuring system of dielectric materials can detect the change in dielectric properties of polymer surface during absorption and evaporation of the moisture for every one cycle of 50 Hz electric field applications. Both capacitive and loss currents of the polymer increase during aging of the sample by the adhesion of water droplets. They decrease during recovery by the evaporation of moisture. These changes of dielectric properties can measure not only from bulk direction but also from surface direction of electric field application by using a pair of interdigital electrodes on the sample surface