Estimation of one-dimensional complex-permittivity profiles: a feasibility study

Abstract This paper examines the feasibility of using the frequency responses of parallel-plate and interdigital-electrode structures to determine the one-dimensional complex-permittivity distribution of heterogeneous materials. This is achieved by relating the complex capacitance of these structures to the complex-permittivity distribution in a material. For parallel-plate structures, it is shown that the temporal frequency response provides, at most, information about the dispersive nature of the complex permittivity averaged over the thickness of the material. Similarly, the temporal frequency response of interdigital-electrode structures yields a nonunique distribution for piecewise-homogeneous materials in which the spatial variation in the complex permittivity is a perturbation about a uniform value. For these same materials, the spatial frequency response of interdigital-electrode structures, obtained by means of electrode structures with multiple wavelengths, is shown to yield a unique complex-permittivity distribution.