A rectangular waveguide (RWG) fixture is proposed for the high-temperature RF characterization of materials. Composed of two RWGs in a side-by-side or over-under orientation, the new apparatus permits the calibration and specimen measurements to be collected simultaneously reducing high-temperature measurement time by two full days over the traditional method. In addition, the permittivity and permeability, determined from measured S-parameters, are independent of sample position and can be found in closed form. The design and construction of the dual-chambered RWG fixture are detailed. The closed-form, position-independent, permittivity and permeability extraction method is also discussed. Finally, high-temperature material characterization experiments are performed to validate the fixture. The errors in permittivity and permeability are estimated assuming uncertainties in sample thickness and measured S-parameters.

The rapid prototyping of antennas and complex media propagation environments has been aided by recent advances in material fabrication capabilities; such as, conductive-inkjet and 3D printing. These advances have prompted the need for alternative mathematical methods of analysis, which more easily accommodate anisotropic and bianisotropic media while providing greater physical insight. For example, casting Maxwell's equations into a compact six-vector formalism aides in the mathematical manipulation, and subsequent solution, of problems involving complex media (I.V. Lindell, A.H. Sihvola, and K. Suchy, J. of Electrom. Waves and Appl., 9, 7/8, 887–903, 1955). This formulation accommodates fully-populated material tensors (i.e., material tensors where all elements are non-zero); however, the analysis does lead to a block 3×3 matrix that requires inversion.

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 Love's 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 Green's function. The development of this Green's function is presented here using a new scalar potential formulation, which significantly reduces the difficulty of the probe's 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 probe's sensitivity to uncertainties in measured scattering parameters, sample thickness, and coaxial line properties is also investigated.

A nondestructive technique to characterize Salisbury screen and Jaumann absorbers is presented. The proposed method utilizes two flanged rectangular waveguides to unambiguously determine the permittivities of two-layer dielectric absorbers. The derivation of the theoretical reflection and transmission coefficients, necessary to determine material under test permittivities, is presented. The derivation makes use of Love's equivalence principle and the continuity of transverse magnetic fields to formulate a system of coupled magnetic field integral equations. These integral equations are solved using the Method of Methods to yield theoretical scattering parameters. The unknown permittivities are then found using nonlinear least squares. To validate the proposed nondestructive technique, measurement results of three two-layer dielectric absorbers are presented and analyzed. In addition, an extensive error analysis is performed on the extracted permittivity values. The results of the proposed method are found to be in good agreement with the results returned by traditional, destructive waveguide transmission/reflection approaches. Published by Elsevier Ltd.

A non-destructive technique is presented which allows the determination of complex permittivity and permeability of uniaxial anisotropic media. The technique extends the existing isotropic material characterization two flanged waveguides measurement technique (tFWMT) (M.W. Hyde, et al., A nondestructive technique for determining complex permittivity and permeability of magnetic sheet materials using two flanged rectangular waveguides, PIER-B, vol. 79, pp. 367-386, 2008) to include uniaxial media. The desired constitutive parameters are extracted via comparison of experimentally measured and theoretically derived scattering parameters using a nonlinear least squares method.

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 applying 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.

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 technique's sensitivity to common experimental errors.

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.

The ability to determine the electromagnetic properties of materials at high temperatures has applications in the industrial, aerospace, defense and scientific communities. Currently, the industry standard method requires two levels of calibration, an initial thru-reect-line calibration of the room temperature section followed by a Tier II (short, empty) response calibration of the high temperature section, in order to extract the desired permittivity and permeability values at high temperatures. This technique requires three measurements (short, empty and sample) at the desired temperatures, thus requiring three days to perform measurements due to inherent thermal constraints.

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.

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 Love's 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.

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 Love's 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 Green's 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.

Commercial electronic devices require shielding solutions that ensure electromagnetic compatibility (EMC) while accounting for effects of specific enclosure structural features such as seams, vents, and port dimensions. In practice, suitable EMC materials combine with the device operating characteristics to determine an overall shielding response. To optimally couple plastic design practices with EMC requirements, both polymer materials science and electrical engineering concepts, must be considered. Use of extrinsically conductive polymer (ECP) formulations for electronic applications has advantages in that they can be directly molded to a desired shape and serve to provide the necessary shielding while also meeting mechanical integrity requirements. Shielding and mechanical performance can be varied via filler loading or altered through wall thickness changes to satisfy demands associated with a particular device. Injection-moldable ECP polycarbonate-based formulations can attain average shielding effectiveness (SE) levels of similar to 50-60 dB through 2 GHz at 2-mm thickness as measured using ASTM D 4935 procedures. These values vary with thickness, and SE improvements of similar to 10-20 dB are observed when increasing from I to 2 mm. Additionally, resultant mechanical properties of shielding composites are strong functions of overall fiber content. These interrelated material and shielding characteristics, which form the basis for filled conductive polymer use within practical enclosure shielding designs, are described. (c) 2007 Wiley Periodicals, Inc.

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.

In this paper the two-layer parallel-plate Green's function due to a magnetic source is described. Confidence in the Green's 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 Green's function when the media coincide. The authors now plan to incorporate the two-layer Green's function into various EM material characterization techniques involving conductor backed lossy media.