Techniques for using the air-gap method for the precise determination of the dielectric constant and loss angle of solid disk specimens

The air-gap method of making dielectric measurements is an attractive one because it is not necessary to apply electrodes to the specimen or to measure its area. The disadvantages of the air-gap method are (1) that it can be used effectively for precise measurements only with a guard-ring type of cell (or holder) and (2) that the thickness of the specimen must be measured more precisely than when contact electrodes are used. The second requires that the specimen must be very carefully prepared to a uniform thickness. This means that a three-terminal measurement must be made and such measurements can in general only be made at frequencies of 100 KHz and below.