MEASUREMENT OF THE DIELECTRIC CONSTANT OF ALUMINUM OXIDE.

The dielectric constant of aluminum oxide may be measured by finding the change in cutoff frequency of air-filled waveguide by filling the waveguide with aluminum oxide. The theoretical transmission of electric and magnetic waves in a dielectric-filled waveguide is presented. Attenuation of the waves in the waveguide is the basic part of this discussion. Conditions considered cover the range of frequencies from above to below cutoff. The experimental procedure describes the problems encountered in obtaining a good frequency response of the dielectric-filled waveguide. The signal must be coupled into the waveguide so that the attenuation which is measured is that due to the dielectric-filled waveguide only. The waveguide must conform well to the dielectric, or the dielectric constant will appear to be less than it actually is. The exact cutoff frequency of the dielectric-filled waveguide must be obtained to determine the dielectric constant of the dielectric. This is done by comparing the experimental attenuation below cutoff with the theoretical attenuation below cutoff. The cutoff frequency which is determined is checked by knowing what the theoretical attenuation should be exactly at cutoff. The dielectric constant would then be a function of this cutoff frequency and the cutoff of the same air-filled guide. The results obtained will have a rather high degree of accuracy. Author