Separation of conduction and displacement currents by direct electric field measurement by using an acoustic transducer

A newly developed technique using an electro-acoustic transducer embedded in an electrode is used to measure the normal electric field as a function of time at the electrode surface of a plane-parallel capacitor enclosing thin film polymeric dielectrics. The displacement current Idisp is then obtained from the product of the dielectric Eonstant ε, electrode area A, and the time derivative of measured electric field E. With the total terminal current Iter measured by a pico-ammeter in series with the test capacitor and voltage source, the conduction current Icond, is obtained by taking the difference Iter-Icond This paper reports that the measured values of Idisp for a step applied voltage varied strongly with the type of polymer film insulation, PE(polyethylene) and PET(polyethylene-terephthalate), and exhibits a dependence on the magnitude and duration of the applied dc voltage, indicating space charge effects.