Improved technique for measuring permittivity of thin dielectrics with a cylindrical resonant cavity

A technique for measuring the relative permittivity of thin, low-loss dielectric materials in a cylindrical resonant cavity has been developed. A thin dielectric sample, of unknown characteristics, is placed upon a thicker dielectric sample whose permittivity is well characterized. Both samples are then placed on the end plate in the cylindrical resonant cavity. In this way, the thin sample is placed in a region of the cavity where interaction with the electromagnetic fields is greater. From knowledge of the cavity's resonant frequency, dimensions of the cavity and both dielectric samples, and from the permittivity of the thicker sample, the authors are able to use iterative techniques to accurately determine the permittivity of the thin dielectric sample. A derivation and discussion of the theory used in this layered-dielectric permittivity measurement technique are provided. Measurement results at frequencies between 9 and 10 GHz confirm the accuracy of the technique. Preliminary error estimates are also given to show the worst-case uncertainties associated with this new method.<
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