Air gap effect and the importance of the electrodes on the sample of the lumped-capacitance method for dielectric measurements

A theoretical analysis of the effect of an air gap in the lumped-capacitance method for dielectric-constant measurements is given. It is shown that when a measured sample has a large dielectric constant, a very small air gap or equivalent air gap, arising from poor contact between the surface of the sample and the short circuit or the end of the inner conductor, can cause a large measurement error if neglected. The importance of using electrodes on the surfaces of the sample to eliminate the small equivalent air gap and reduce the measuring error is emphasized. Experimental results are given and confirm the analysis.<>