The development of electromagnetic systems to detect and monitor an in-situ underground coal gasification process requires a knowledge of the electrical properties of coal. Using a two-path interferometer at microwave frequencies, the samples were tested as a function of temperature, electric field polarization and direction of the coal samples. There were not any significant changes in the electrical properties of coal as a function of temperature from ambient up to 700 degree F. However, there were significant variations in the conductivity as a function of polarization, with the vertical polarization possessing lower conductivity. Measurements of electrical properties of coal were also made in the 0. 5-100 MHz region using capacitance techniques. In general, there was a decrease in the values of dielectric constant and an increase in conductivity as the frequency increased.
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