Air-Gap Correction for High Power Microwave Measurements of Conductive Materials

Abstract

Measurements of the complex permittivity and permeability of solids at high electromagnetic field greater than 10 kV/m pose a significant challenge to RF connectors and input amplifiers of the measurement equipment. Specifically, difficulties arise in measuring materials with high imaginary permittivity or low impedance, which act as short circuits, either exceeding the measurement equipment damage threshold or that of the material under test, and/or inducing an unacceptable signalto-noise in the collected data. In this work, we report the development of a new measurement technique where we introduce an outer air-gap between the material under test and the conductor of a coax airline. The introduced air-gap reduces the effective conductivity of the sample, mitigating damage to the materials under test and allowing for high power measurement. This study compares the ability of air-gap correction methods to recover the complex permittivity and permeability to within 10% of the value measured without an air-gap introduced.