Rectangular waveguide resonant slot electromagnetic material characterization technique

Summary form only given. Waveguide probes have been vastly studied with applications including subsurface crack detection, medical treatments, and electromagnetic (EM) characterization of materials. While their geometry is ideal for the nondestructive evaluation (NDE) of materials, the vast majority of the work focuses on methods for obtaining the reflection coefficient via a single probe. This setup is ideal for determining the complex permittivity of an unknown material, yet it presents challenges when one also wants to find the complex permeability. Several techniques (including the two thickness, frequency varying, and sample added methods) have been developed to overcome this limitation; unfortunately, these techniques are not always applicable. A desirable alternative to this limitation are probes that simultaneously collect the reflection and transmission coefficients, as these are the ideal measurements for determining the complex constitutive parameters, since they are independent over all wavelengths. Recently, dual probe waveguide methods have been investigated (M. Hyde IV, et al., Radio Sci., 44, RS3013, 2009.), that provide the ability to obtain multiple independent interrogations of the material, without altering the experimental setup.Presented here is an alternative nondestructive technique, using a rectangular waveguide resonant slot (RWRS) probe, for determining the complex permittivity and permeability of a perfect electric conductor backed simple media (linear, homogeneous and isotropic). The RWRS probe consists of a rectangular waveguide centered on a PEC flange with a transverse slot cut through the flange wall of the rectangular waveguide, allowing for simultaneous measurement of reflection and transmission coefficients. These measurements are then compared (and the difference minimized) to theoretical values using a root search algorithm to find the desired complex constitutive parameters. The theoretical coefficients are formulated by apply- ng Loves equivalence principle at the slot boundaries to ultimately form a system of coupled magnetic field integral equations, which is then solved via the method of moments. Results are presented and compared to a traditional method for the purpose of validating the technique. The probes sensitivity to uncertainties in sample thickness, waveguide length, slot dimensions, and measured S-parameters is also investigated.