Andrew E. Bogle

A novel and simple technique for measuring low-loss materials using the two flanged waveguides measurement geometry *

In this paper, a novel technique is developed to practically and accurately measure the permittivity and permeability of low-loss materials using the two flanged waveguides measurement geometry (originally designed to characterize strongly absorbing materials only). A review of the two flanged waveguides measurement technique (tFWMT) as well as the Greens function-based flange-design criterion is provided. This review is followed by the introduction of the novel method (called tFWMT time-domain gating). It is shown that tFWMT time-domain gating extends the range of applicability of the tFWMT to low-loss materials and provides a clear flange-size design requirement which, for low-loss materials, is approximately two orders of magnitude smaller than that stipulated by the existing Greens function-based criterion. Lastly, material-characterization measurement results of low-loss acrylic and ECCOSORB? FGM-125, using flanges of two different sizes, are presented to validate the new technique.

Three-dimensional isotropic meta-materials

This paper addresses the design and construction of metallic structures, whose induced electric and/or magnetic dipole moments are equal in all three principle directions. These materials can be used to make a 3-dimensional, negative-refractive index metamaterial. Meta-materials are constructed of three-dimensional materials, but the electromagnetic response has only been realized in one or two dimensions. In this paper, when we refer to the dimensionality of a material, we mean the number of directions that have equal and non-trivial response to incident fields. We also consider whether a structure has a polarization dependent response. Although Silveririnha (2004) has shown that the periodic square or cubic grids that are used are not truly isotropic in that the response is angle dependant, the same response in all coordinate directions is a good start

Scattering of a partially-coherent wave from a material circular cylinder

The case of a partially-coherent wave scattered from a material circular cylinder is investigated. Expressions for the TMz and TEz scattered-field cross-spectral density functions are derived by utilizing the plane-wave spectrum representation of electromagnetic fields and cylindrical wave transformations. From the analytical scattered-field cross-spectral density functions, the mean scattering widths are derived and subsequently validated via comparison with those computed from Method of Moments Monte Carlo simulations. The analytical relations as well as the simulation results are discussed and physically interpreted. Key insights are noted and subsequently analyzed.

An Improved Two-Layer Method for Nondestructively Characterizing Magnetic Sheet Materials Using a Single Rectangular Waveguide Probe

Abstract An improved single waveguide probe technique is presented to nondestructively determine the permittivity and permeability of sheet materials. The impetus for the technique is to address the unreliable results yielded by the existing single-probe two-layer method while preserving its physical ease of measurement. Included in this article is the theoretical development of the method and its experimental validation. The theoretical development uses Loves equivalence theorem to derive a magnetic field integral equation that is subsequently solved for the theoretical reflection coefficient using the method of moments. Experimental permittivity and permeability results for two magnetic shielding materials are presented and compared to results obtained using established techniques to validate the proposed method. Profile plots of the electric and magnetic fields in the material under test region of the measurement geometry are provided and analyzed to yield further physical insight.

Broadband Characterization of Materials Using a Dual-Ridged Waveguide

A transmission/reflection material characterization technique that uses dual-ridged waveguides is presented. The proposed dual-ridged-waveguide system combines many of the positive aspects of traditional transverse electromagnetic-mode (e.g., coaxial, free space, and stripline) and rectangular waveguide systems, i.e., broadband measurements and accurate calibration. A brief discussion on the derivation of the theoretical scattering parameters, required for the extraction of permittivity and permeability of a material under test, is provided. Two methods for computing the cutoff wavenumber of the dual-ridged waveguide-essential to the material characterization process-are also discussed. The first, which utilizes the mode-matching technique, is applicable to dual-ridged-waveguide apertures composed of right-angled corners. The second uses the surface equivalence principle and a magnetic-field integral equation formulation to find the cutoff wavenumber. This approach is applicable to dual-ridged waveguides with rounded corners, which often result from the dual-ridged waveguide manufacturing process. Thus, for the first time, the effect of rounded dual-ridged-waveguide aperture corners on the measurement of permittivity and permeability is assessed. Experimental material characterization results of a magnetic absorbing material are presented and analyzed to validate the proposed technique. An extensive error analysis on the extracted values of permittivity and permeability is also performed by taking into account manufacturer-specified dual-ridged-waveguide design tolerances as well as uncertainties in sample position, sample thickness, sample-holder length, and measured scattering parameters.

Nondestructive Characterization of PEC-Backed Materials Using the Combined Measurements of a Rectangular Waveguide and Coaxial Probe

A novel one-port probe technique, which combines the measurements of a rectangular waveguide and coaxial probe to nondestructively yield the permittivity and permeability of a PEC-backed material, is presented. A brief description of the derivation of the theoretical probe reflection coefficients, necessary for permittivity and permeability extraction via numerical inversion, is provided. Experimental characterization results of a PEC-backed magnetic material are presented to validate the proposed approach. Error analysis is also undertaken to quantify the new techniques sensitivity to common experimental errors.

Nondestructive Material Characterization of a Free-Space-Backed Magnetic Material Using a Dual-Waveguide Probe

A free-space-backed dual-waveguide probe measurement technique is introduced to determine nondestructively the complex permittivity and permeability of an unknown material. The purpose of this new measurement technique is to complement the existing PEC-backed dual-waveguide probe material-characterization method. Provided in this paper is the theoretical development of the new technique and its experimental validation. It is shown, by applying Loves equivalence theorem, that a system of coupled magnetic field integral equations can be formulated and subsequently solved for the dominant mode reflection and transmission coefficients using the method of moments. Also included in the theoretical development of the new technique is a derivation of the dyadic Greens function for a magnetic-current-excited two-medium grounded-slab environment. Last, experimental complex permittivity and permeability parameters extracted for two magnetic-shielding materials are presented and analyzed to validate the new technique.

On the Uncertainty of Extracted Permittivity From Inhomogeneously Filled Rectangular Waveguides

Error uncertainty is an important metric to assess the reliability of an inversion algorithm that extracts the electromagnetic constitutive parameters from a material sample. In a previous paper, the inversion algorithm for a partially filled waveguide cross section relied on the assumption that the material sample had to be perfectly centered. In this present letter, the effect of having the material sample displaced from the center is evaluated by comparing its extracted constitutive parameters (epsiv, mu) with the values corresponding to the perfectly centered case. Two low-loss cases are studied: (1) low-contrast and (2) high-contrast material. A finite-element model (FEM) is used to generate the forward data.

Nondestructive Determination of the Permittivity Tensor of a Uniaxial Material Using a Two-Port Clamped Coaxial Probe

A two-port coaxial probe is introduced to nondestructively determine the permittivity tensor of a uniaxial material. The proposed approach possesses several advantages over existing techniques, e.g., only a single sample is required, the sample does not need to be rotated, and only a single measurement system is needed. The derivation of the theoretical scattering parameters is shown. This is accomplished by applying Loves equivalence theorem and the continuity of transverse magnetic fields to formulate a system of coupled integral equations. A necessary step in this approach is the derivation of the magnetic-current-excited uniaxial parallel-plate Greens function. The development of this Greens function is presented here using a new scalar potential formulation, which significantly reduces the difficulty of the probes theoretical development. The system of coupled integral equations is solved using the method of moments to yield the theoretical scattering parameters. The permittivity tensor is found by minimizing the two-norm of the vector difference between the theoretical and measured scattering parameters via nonlinear least squares. To validate the probe, measurement results of a uniaxial absorber are presented and compared to those obtained using a focused-beam (free-space) measurement system. The probes sensitivity to uncertainties in measured scattering parameters, sample thickness, and coaxial line properties is also investigated.

Two-layer parallel-plate green’s function due to a magnetic source for electromagnetic material characterization of conductor backed lossy media

In this paper the two-layer parallel-plate Greens function due to a magnetic source is described. Confidence in the Greens function was instilled by checking the boundary conditions, having the eigenvalues of the structure match those found by Harrington, and the reduction to the single-layer Greens function when the media coincide. The authors now plan to incorporate the two-layer Greens function into various EM material characterization techniques involving conductor backed lossy media.