The effective area of a guarded electrode

An accurate determination of the low frequency dielectric constant of a solid specimen is usually made with a guarded electrode. In order to calculate the dielectric constant of the specimen accurately, it is necessary to know the effective area of the guarded electrode, which is greater than the actual area. The correction for this increase in area depends upon the width of the gap, g, between the guard and guarded electrodes, the thickness of the electrodes, d, the thickness of the specimen, t, and the ratio of the dielectric constant of the specimen, ε, and the dielectric constant of the media filling the gap between the electrodes ε_g. The purpose of this paper is to discuss certain misstatements appearing in the recent literature concerning this correction and to present some new results that elucidate the dependence of this correction upon the various factors cited above.