A Novel Time Domain Model for Permittivity and Thickness Measurement.

Motivated by the necessity of acquiring wall parameters for through-the-wall radar (TWR), a novel and general time domain model is proposed to measure the thickness and permittivity of single-layered slab-shaped materials, by exploiting the delays of the two surface reflections in the bistatic radar scheme. First, the two surface delays are formulated as functions of the unknown permittivity and thickness, as well as the accessible incident angle, and a nonlinear equation set is formed. Then based on a geometric analysis, in two separate bistatic delay tests with different antenna separations and standoff distances, the condition of identical incident angle is established. As such, the intra-wall delay is the same for the two delay tests, leading to a significant simplification and a closed-form solution to the equation set. Finally, a three-antenna test setup is constructed, with which the desired parameters can be acquired conveniently and accurately by performing bistatic tests at a set of standoff distances. Simulation and experiment show that our method can achieve high accuracy and strong robustness against noise.