Accurate permittivity estimation method for double-layered dielectric object for UWB radars

A microwave ultra-wideband (UWB) radar system is one of the most promising technologies for the internal imaging of dielectric objects in applications such as non-invasive inspection and non-destructive measurement. For such applications, we have already proposed an efficient method of estimating permittivity employing a geometrical optics (GO) approximation and exploiting dielectric outer boundary points and their normal vector accurately obtained with the range points migration (RPM) method. However, this method assumes that there is a highly lossy object buried in a single-layered homogeneous dielectric medium. This paper proposes an accurate permittivity estimation method for a double layered dielectric medium that employs the RPM or Envelope method extended to boundary extraction for each dielectric layer, and an estimation of time delay based on a geometrical optics approximation. The results from finite-difference time-domain (FDTD) based simulations demonstrate that our method accurately estimates permittivity and the boundary of the two layers simultaneously.