Determination of complex permittivity by non-destructive method using neural networks modeling

A simple non-destructive method for determination of dielectric properties of arbitrary wall in building is presented. The free space method is based on the measurements of reflection coefficients for different angles of incidence. The walls constructed of unknown materials are modeled as homogenous dielectric plate with smooth surface. The measurements are made for the frequency of 2.4 GHz so the results can be applied to wireless local area networks (WLAN) planning and design. Complex permittivity is reconstructed using a neural network model trained by the calculated reflection coefficients for assumed permittivity. The inputs to the network are reflection coefficients and incident angles, while outputs are real and imaginary parts of the complex dielectric constant. The obtained results are compared with results obtained by a nonlinear-least-squares method.