Publications

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This report presents analytic transmission line models for calculating the shielding effectiveness of two common calibration standard cables. The two cables have different canonical aperture types, which produce the same low frequency coupling but different responses at resonance. The dominant damping mechanism is produced by the current probe loads at the ends of the cables, which are characterized through adaptor measurements. The model predictions for the cables are compared with experimental measurements and good agreement between the results is demonstrated. This setup constitutes a nice repeatable geometry that nevertheless exhibits some of the challenges involved in modeling non-radio frequency geometries.

This report estimates inductively-coupled energy to a low-impedance load in a loop-to-loop arrangement. Both analytical models and full-wave numerical simulations are used and the resulting fields, coupled powers and energies are compared. The energies are simply estimated from the coupled powers through approximations to the energy theorem. The transmitter loop is taken to be either a circular geometry or a rectangular-loop (stripline-type) geometry that was used in an experimental setup. Simple magnetic field models are constructed and used to estimate the mutual inductance to the receiving loop, which is taken to be circular with one or several turns. Circuit elements are estimated and used to determine the coupled current and power (an equivalent antenna picture is also given). These results are compared to an electromagnetic simulation of the transmitter geometry. Simple approximate relations are also given to estimate coupled energy from the power. The effect of additional loads in the form of attached leads, forming transmission lines, are considered. The results are summarized in a set of susceptibility-type curves. Finally, we also consider drives to the cables themselves and the resulting common-to-differential mode currents in the load.

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A first principles calculation for the transfer capacitance of a Beldon cable is carried out by the use of filamentary constant, dipole, quadrupole, and octopole unknown charges placed at the center of each braid wire. Results are compared with full electrostatic simulations and a phenomenological model. © 2011 IEEE.

Simplified wire-type models for split-ring resonators (SRRs), both in free-space and above a dielectric half-space, are developed. The gap of the SRR in the wire model is accurately represented by including a lumped load which is the difference between the actual gap fringe capacitance and the capacitance inherent in the code wire kernel for a delta gap voltage source. The SRR arms are represented by generalized thin wires that have both an electric equivalent radius (for the rectangular conductor resting on a dielectric substrate) and a magnetic equivalent radius (for a rectangular conductor in free space, since the substrate is assumed to be nonmagnetic). In addition, an impedance per unit length (due to finite penetration of the fields into the metal) enters a local transmission line part of the generalized thin-wire algorithm. The results from the thin-wire subcell model are compared to full wave simulations of the arrays of SRR's. The full wave simulations require tens of thousands of unknowns to resolve the field penetration into the finite conductors for a single SRR, whereas the thin-wire model has good accuracy with only tens of unknowns. © 2011 IEEE.

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This paper presents a mixed-potential integral-equation formulation for analyzing 1-D periodic leaky-wave antennas in layered media. The structures are periodic in one dimension and finite in the other two dimensions. The unit cell consists of an arbitrary-shaped metallic/dielectric structure. The formulation has been implemented in the EIGER™ code in order to obtain the real and complex propagation wavenumbers of the bound and leaky modes of such structures. Validation results presented here include a 1-D periodic planar leaky-wave antenna and a fully 3-D waveguide test case. ©2010 IEEE.

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This paper presents a mixed-potential integral-equation formulation for analyzing 1-D periodic leaky-wave antennas in layered media. The structures are periodic in one dimension and finite in the other two dimensions. The unit cell consists of an arbitrary-shaped metallic/dielectric structure. The formulation has been implemented in the EIGER{trademark} code in order to obtain the real and complex propagation wavenumbers of the bound and leaky modes of such structures. Validation results presented here include a 1-D periodic planar leaky-wave antenna and a fully 3-D waveguide test case.

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The authors experimentally demonstrate a resonant hybridization between the magnetic dipole structural resonance in the permeability of a fishnet metamaterial and an electric dipole material resonance in the permittivity of the dielectric spacer layer. The hybrid resonances in the permeability and the negative index response exhibit an anticrossing behavior. A simple analytic model and numerical simulations using a rigorous coupled-wave analysis are in excellent qualitative agreement with the experiment. © 2010 American Vacuum Society.

Plasmonic structures open up new opportunities in photonic devices, sometimes offering an alternate method to perform a function and sometimes offering capabilities not possible with standard optics. In this LDRD we successfully demonstrated metal coatings on optical surfaces that do not adversely affect the transmission of those surfaces at the design frequency. This technology could be applied as an RF noise blocking layer across an optical aperture or as a method to apply an electric field to an active electro-optic device without affecting optical performance. We also demonstrated thin optical absorbers using similar patterned surfaces. These infrared optical antennas show promise as a method to improve performance in mercury cadmium telluride detectors. Furthermore, these structures could be coupled with other components to lead to direct rectification of infrared radiation. This possibility leads to a new method for infrared detection and energy harvesting of infrared radiation.

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In this LDRD we examine techniques to analyze the electromagnetic scattering from structures that are nearly periodic. Nearly periodic could mean that one of the structure's unit cells is different from all the others--a defect. It could also mean that the structure is truncated, or butted up against another periodic structure to form a seam. Straightforward electromagnetic analysis of these nearly periodic structures requires us to grid the entire structure, which would overwhelm today's computers and the computers in the foreseeable future. In this report we will examine various approximations that allow us to continue to exploit some aspects of the structure's periodicity and thereby reduce the number of unknowns required for analysis. We will use the Green's Function Interpolation with a Fast Fourier Transform (GIFFT) to examine isolated defects both in the form of a source dipole over a meta-material slab and as a rotated dipole in a finite array of dipoles. We will look at the numerically exact solution of a one-dimensional seam. In order to solve a two-dimensional seam, we formulate an efficient way to calculate the Green's function of a 1d array of point sources. We next formulate ways of calculating the far-field due to a seam and due to array truncation based on both array theory and high-frequency asymptotic methods. We compare the high-frequency and GIFFT results. Finally, we use GIFFT to solve a simple, two-dimensional seam problem.

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Approximate formulas are constructed and numerical simulations are carried out for electric field derivative probes that have the form of flush mounted monopoles. Effects such as rounded edges are included. A method is introduced to make results from two-dimensional conformal mapping analyses accurately apply to the three-dimensional axisymmetric probe geometry

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