High-resolution imaging of dielectric profiles by using a time-domain ultra wideband radar sensor

This paper describes the development of an imaging instrument that capitalizes on high-resolution phenomenon in inverse scattering using a time-domain ultra wideband (UWB) sensor. The image reconstruction algorithm that accounts for the band-limited view of the UWB data is based upon the TM-mode wave equation, the Born approximation, and the adjoint method for computing the Fréchet derivatives. The computation of the sensitivity function requires the forward propagation of the UWB wavefield, as well as the reverse propagation of the residual wavefield. The electromagnetic and adjoint fields are calculated using the finite-difference time-domain (FDTD) method, implementing the first and second orders Mur’s absorbing boundaries. The overall performance of the instrumentation system is demonstrated using computer simulations and experimental measurements. Results indicate that the equipment can reconstruct fairly complicated dielectric profiles at near millimeter resolution even with the presence of large amount of noise.

Research highlights► This paper describes the development of an imaging instrument that capitalizes on high-resolution phenomenon in inverse scattering using a time-domain ultra wideband (UWB) sensor. ► The work focuses in developing a relatively simple, stable algorithm that can be applied with confidence to real data collected using fairly common scanning geometries. ► Given the nature of the approximate inversion presented here, the methods and procedures worked best when the object’s dimension was comparable to the wavelength used. ► For 1 GHz UWB sensors used in the study, targets smaller than 2 cm in diameter, corresponding to 0.3% of area of the search region, have easily been detected.