Model-based permittivity measurement of construction materials by the standing wave method

A simplified model of a permittivity measurement system based on the standing wave method in free space has been developed to estimate the complex permittivity of construction materials accurately. It is assumed that the standing wave distribution is determined by three spherical wave components in this model that are the incident-, reflected- and scattered-waves at the edge of the material under test. The model is described by an equation in which the standing wave distribution is represented by the sum of those three wave components. By applying the least squares method to the model equation, the amplitudes and phase angles of those three wave components are estimated from the experimentally observed standing wave distribution. One can estimate the material permittivity from those estimated parameters of the model with high accuracy.