Drude empirical models are frequently used for description of dispersion characteristics of many media

such as plasmas

and metals.Reconstructed electrical properties by directly using wide-band measured data in time domain

are better than those by application of any single-frequency technique

in amount of information

and resolution of generated images.One of difficulties in time-domain reconstruction of dispersive characteristics is their frequency correlation.In order to overcome this difficulty

an electromagnetic (EM) inverse scattering technique in time domain is proposed

in which four kinds of frequency-independence parameters from a Drude model are estimated simultaneously.Main segments for the technology are:(1) formulating the inverse scattering problem as a constrained minimization problem with a term of regularization;(2) transforming resulting problem into an unconstrained minimization one;(3) deriving a set of closed gradients of its cost functional;(4) solving iteratively resulting forward and backward sub-problems by a finite-difference time-domain (FDTD) method and any conjugate gradient (CG) algorithm

respectively.In one-dimensional (1-D) and two-dimensional (2-D) numerical examples

necessary measurements are replaced by simulated fields based on the FDTD method

and it is assumed that they are corrupted by an additive white Gaussian noise (AWGN).Numerical results preliminarily confirm performance of the inversion methodology.