Publications

We summarize the narrow slot algorithms, including the thick electrically small depth case, conductive gaskets, the deep general depth case, multiple fasteners along the length, and finally varying slot width.

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In this paper, we investigate the coupling from external electromagnetic (EM) fields to the interior EM fields of a high-quality factor cylindrical cavity through a small perturbing slot. We illustrate the shielding effectiveness versus frequency, highlighting bounds on the penetrant power through the slot. Because internal fields may become larger than external ones, we then introduce a small amount of microwave absorbing materials decorating the slot to improve shielding effectiveness considerably, as shown by both simulations and experiments. Although the cylindrical cavity is used for demonstration purposes in this paper, the conclusions presented here can be leveraged for use with more complex cavity structures.

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This report explores the potential for reducing the fields and the quality factor within a system cavity by introducing microwave absorbing materials. Although the concept of introducing absorbing (lossy) materials within a cavity to drive the interior field levels down is well known, increasing the loading into a complex weapon cavity specifically for improved electromagnetic performance has not, in general, been considered, and this will be the subject of this work. We compare full-wave simulations to experimental results, demonstrating the applicability of the proposed method.

This report compares ATLOG modeling results for the response of a finite-length dissipative buried conductor interacting with a conducting ground to a measurement taken November 2016 at the High-Energy Radiation Megavolt Electron Source (HERMES) facility. We use the ATLOG frequency-domain method based on transmission line theory. Estimates of the impedance per unit length and admittance per unit length for a cable laying in a PVC pipe embedded in a concrete block are reported. Current wave shapes from both a single conductor and composite differential mode and antenna mode arrangements are close to those observed in the experiments. Intentionally Left Blank

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In this paper, we report the formulation to account for dielectrics in a first principles multipole-based cable braid electromagnetic penetration model. To validate our first principles model, we consider a one-dimensional array of wires, which can be modeled analytically with a multipole-conformal mapping expansion for the wire charges; however, the first principles model can be readily applied to realistic cable geometries. We compare the elastance (i.e., the inverse of the capacitance) results from the first principles cable braid electromagnetic penetration model to those obtained using the analytical model. The results are found in good agreement up to a radius to half spacing ratio of 0.5–0.6, depending on the permittivity of the dielectric used, within the characteristics of many commercial cables. We observe that for typical relative permittivities encountered in braided cables, the transfer elastance values are essentially the same as those of free space; the self-elastance values are also approximated by the free space solution as long as the dielectric discontinuity is taken into account for the planar mode.

We report a frequency-domain method based on transmission line theory that we name ATLOG-Analytic Transmission Line Over Ground-to model finite or infinite wires interacting with a conducting ground excited by an electromagnetic pulse. This method allows for the treatment of finite or infinite lossy, coated wires above a lossy ground, as well as resting on or buried beneath the ground. Comparisons with full-wave simulations strengthen the validity of the proposed method.

We propose a cable braid electromagnetic penetration model that is based on first-principles and is derived strictly from the geometrical parameters of the cable in question. We apply this formulation to the case of a one-dimensional array of wires, which can also be modeled analytically via a multipole-conformal mapping expansion for the wire charges and is extended by means of Laplace solutions in bipolar coordinates. Both electric and magnetic penetrations are analyzed, and comparisons are performed between results from the first principles cable braid electromagnetic penetration model and those obtained using the multipole-conformal mapping expansion method. We find results in very good agreement when using up to the octopole moment (for the first principles model), covering a dynamic range of radius-to-half-spacing ratio up to 0.6. These results give us the confidence that our first principles model is applicable to the geometric characteristics of many commercial cables.

In this report we overview the fundamental concepts for a pair of techniques which together greatly hasten computational predictions of electromagnetic pulse (EMP) excitation of finite-length dissipative conductors over a ground plane. In a time- domain, transmission line (TL) model implementation, predictions are computationally bottlenecked time-wise, either for late-time predictions (about 100ns-10000ns range) or predictions concerning EMP excitation of long TLs (order of kilometers or more ). This is because the method requires a temporal convolution to account for the losses in the ground. Addressing this to facilitate practical simulation of EMP excitation of TLs, we first apply a technique to extract an (approximate) complex exponential function basis-fit to the ground/Earth's impedance function, followed by incorporating this into a recursion-based convolution acceleration technique. Because the recursion-based method only requires the evaluation of the most recent voltage history data (versus the entire history in a "brute-force" convolution evaluation), we achieve necessary time speed- ups across a variety of TL/Earth geometry/material scenarios. Intentionally Left Blank

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This report details the modeling results for the response of a finite-length dissipative conductor interacting with a conducting ground to a hypothetical nuclear device with the same output energy spectrum as the Fat Man device. We use a frequency-domain method based on transmission line theory and implemented it in a code we call ATLOG - Analytic Transmission Line Over Ground. Select results are compared to ones computed using the circuit simulator Xyce. Intentionally Left Blank

This report details the modeling results for the response of a finite-length dissipative conductor interacting with a conducting ground to a hypothetical nuclear device with the same output energy spectrum as the Fat Man device. We use a time-domain method based on transmission line theory that allows accounting for time-varying air conductivities. We implemented such method in a code we call ATLOG - Analytic Transmission Line Over Ground. Results are compared the frequency-domain version of ATLOG previously developed and to the circuit simulator Xyce in some instances. Intentionally Left Blank