Biaxial Anisotropic Material Development and Characterization using Rectangular to Square Waveguide

The advent of 3-D printing provides a new way to develop complex electromagnetic media. Complex media poses measurement challenges and require new techniques to characterize sample constitutive parameters. A biaxial anisotropic sample is designed using crystallographic symmetry and tensor elements are predicted using equivalent capacitive and inductive lumped elements. Samples are measured using the Waveguide Rectangular to Waveguide Square (WRWS) cubic sample measurement system. The WRWS system supports the analysis of a cubic biaxial anisotropic sample by measuring the sample in different measurement orientations. The orientation S-parameter data is used to extract tensor element permittivites and permeabilities using an analytic, closed-form technique. Research performed in this document demonstrates a sample synthesis methodology, a measurement representative computational electromagnetic (CEM) prediction of WRWS sample measurements and tests results of an electrically biaxial sample. An uncertainty analysis is also conducted on the experimental data to evaluate potential error sources. The lumped element and CEM predictions agree with the test results. Supplemental discussion also provides a comparison between test data and a free-space simulated results as well as simulated example of an electrically biaxial sample loaded with alumina. These two examples demonstrate the utility of a crystallographic sample design

Non-Destructive Characterization of Rotated Uniaxial Anisotropic Materials

Electromagnetic material characterization of anisotropic media requires measurement diversity, minimal measurement uncertainty and insight into sample symmetry. Additionally, non-destructive characterization techniques are valued over legacy measurement techniques because a destructive approach requires sample preparation to execute a measurement. A Single Port Waveguide Probe (SPWP) non-destructive material characterization technique is proposed to accommodate measuring a metal backed, known thickness, rotated uniaxial anisotropic material. A rotated uniaxial sample possesses unique transverse constitutive components and a longitudinal constitutive component which is the same as one of the transverse values. The SPWP consists of a rectangular waveguide aperture cut in the center of a square angle. The angle is place upon a metal-backed material surface, which forms a parallel plate region. Two orthogonal transverse plane measurements aligned with the sample\u27s transverse constitutive parameter components offers measurement diversity. A rotated uniaxial anisotropic parallel plate Green\u27s function is developed and employed in a moment method forward model and is then used to extract the material constitutive parameters. Measured and simulated results are utilized to demonstrate the analytical approach and uncertainty is evaluated demonstrating system accuracy of the non-destructive rotated uniaxial anisotropic measurement technique

Nondestructive Electromagnetic Characterization of Uniaxial Sheet Media Using a Two-Flanged Rectangular Waveguide Probe

Excerpt: Recent advancements in fabrication capabilities have renewed interest in the electromagnetic characterization of complex media, as many metamaterials are anisotropic and/or inhomogeneous. Additionally, for composite materials, anisotropy can be introduced by load, strain, misalignment, or damage through the manufacturing process [1], [2]. Methods for obtaining the constitutive parameters for isotropic materials are well understood and widely employed [3]–[8]. Therefore, it is crucial to develop a practical method for the electromagnetic characterization of anisotropic materials

Permittivity and Permeability Tensor Extraction Technique for Arbitrary Anisotropic Materials

Computing the permittivity and permeability of complex materials has previously relied on a series of simplifying assumptions to enable analysis. The most restricting requirement is that the optical axes of the material must align with the laboratory frame of reference. This requirement cannot be met for a large group of materials, including crystalline structures and metamaterials such as tilted nanorods. Currently, designing the optical characteristics of these structures would require ellipsometric analysis, which uses an error-correction-based technique. Here, a new technique built upon the underlying physics of ellipsometry is proposed to extract arbitrary permittivity and permeability tensors using a set of off-axis measurements. This new permittivity and permeability tensor extraction technique allows all 18 elements of the permittivity and permeability tensors to be nonzero and extracts them, given a set of reflectance and transmittance measurements. Several materials are analyzed here, including a) an isotopic plane of known permittivity, b) an anisotropic aligned structure, and c) a tilted-nanorod-based sample that cannot be measured using traditional methodologies. The isotropic plane shows very low error (-4%) in the x and y tensor measurements and around 1% error in the z tensor measurement at higher (metallic) permittivities. The aligned structure\u27s characteristics are compared to measurements made with traditional techniques and show excellent agreement between the techniques. The tilted nanorod characteristics are analyzed and used to predict the reflection and transmission coefficients at other angles. The predictions compare very well with the computational electromagnetic simulations, showing at most 5% error over the range examined. © IEE