A method for the precise measurement of permittivity of sheet specimens

A specimen, not itself carrying electrodes, is inserted loosely in a prefabricated electrode assembly and the capacitance is measured. The specimen is then removed and the electrode separation reduced until the system has the same capacitance as before. The permittivity can then be calculated without knowledge of the electrode area or of the calibration of any capacitors. The precision of the method is limited only by the difficulty of measuring the thickness of the specimen, and errors may be as low as 1 in 1000. For measurement of power factor this method is less sensitive than others, but it is free from uncertainty about effects introduced by electrodes. It can be used at frequencies up to about 1 Mc/s, and being quick in use is suitable for routine measurements of a batch of nearly similar specimens.