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This paper describes the proper calculation of the complex permittivity for general building materials from the magnitude of the reflection loss measured by the free space measurement. Most building materials are very inhomogeneous, due to (among other factors) varying thickness, rough surface condition, water content and distribution. In this paper the free space measurement is chosen to determine complex permittivities, as the sample preparation is relatively easy and precision machining of materials to be tested is not required. Iterative calculation for the complex permittivity deduces by using four measured data, which come from measurements of samples backed by a metal plate from front side (front-short), samples only from front side (front-open), samples backed by a metal plate from back side (back-short), and samples only from back side (back-open), under the condition that the frequency variation of the standard deviation of the complex permittivity is small. This paper also presents the relation of the complex permittivites to water contents for three kinds of building materials (fiber reinforced cement boards, calcium silicate boards and mortar boards) in the frequency range between 1.55 GHz to 6.5 GHz, which is agree to the other past analytical work.

An Experimental Study on the Calculation of the Complex Permittivity for Building Materials from the Reflection Loss by Free Space Measurement