In recent years, the transmission/reflection (TR) method has been successfully emplolyed to determine the complex permittivity of dielectric material. Based on the principle that different coals have different abilities to absorb microwave energy at different frequencies, it is essential to analyze the electromagnetic property of coal to realize microwave desulfurization. Samples composed of a known dielectric and coal are manufactured in order to obtain the accurate permittivity of coal. In the article, we propose an improved TR method which is insensitive to the position of the sample in its cell. Additionally, we get the suitable mass ratio of the known dielectric and sample under test in the composite sample, and the suitable thickness of the composite sample in the permittivity measurements.
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