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Three-Dimensional Electromagnetic High Frequency Concave Cavity Scars

Warne, Larry K.; Jorgenson, Roy E.; Reines, Isak C.; Coats, Rebecca S. ; Pack, Alden R.; Zinser, B.Z.

This report examines the localization of high frequency electromagnetic fields in general three-dimensional cavities along periodic paths between opposing sides of the cavity. The focus is on the case where the mirrors at the ends of the orbit are concave and have two different radii of curvature. The cases where these orbits lead to unstable localized modes are known as scars. The ellipsoidal coordinate system is utilized in the construction of the scarred modes. The field at the interior foci is examined as well as trigonometric projections along the periodic scarred ray path.

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Maximum Interior Voltage and Magnetic Field Penetration Through a Ferromagnetic Layer

Warne, Larry K.; Chen, Kenneth C.; Johnson, William Arthur.

This report examines the problem of magnetic penetration of a conductive layer, including nonlinear ferromagnetic layers, excited by an electric current filament. The electric current filament is, for example, a nearby wire excited by a lightning strike. The internal electric field and external magnetic field are determined. Numerical results are compared to various analytical approximations to help understand the physics involved in the penetration.

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Capacitive/Inductive Corrections for Numerical Implementation of Thin-Slot Transmission Line Models and Other Useful Formulas

Warne, Larry K.; Johnson, William Arthur.

Capacitance/inductance corrections for grid induced errors for a thin slot models are given for both one and four point testing on a rectangular grid for surface currents surrounding the slot. In addition a formula for translating from one equivalent radius to another is given for the thin-slot transmission line model. Additional formulas useful for this slot modeling are also given.

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Asymptotic Expansion of the Impedance Per Unit Length for Rectangular Conductors

Warne, Larry K.

An iteration method is introduced to obtain the asymptotic form of the impedance per unit length of a rectangular conductor when the half side lengths are large compared to the skin depth. The first terms of the asymptotic expansion are extracted in closed form. The manner in which the corner corrections fit into the expansion are illustrated. The asymptotic results are compared to a numerical solution in the square limit. The odd corner correction for a right angle edge is also discussed.

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Eddy Current Power Dissipation at the Edge of a Thin Conductive Layer

Warne, Larry K.; Johnson, William Arthur.

A method used to solve the problem of water waves on a sloping beach is applied to a thin conducting half plane described by a thin layer impedance boundary condition. The solution for the electric field behavior near the edge is obtained and a simple fit for this behavior is given. This field is used to determine the correction to the impedance per unit length of a conductor due to a sharp edge. The results are applied to the strip conductor. The final appendix also discusses the solution to the dual-sided (impedance surface & perfect conductor surface) half plane problem.

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Three Dimensional Electromagnetic High Frequency Convex Cavity Scars

Warne, Larry K.; Jorgenson, Roy E.; Coats, Rebecca S.

This report examines the localization of high frequency electromagnetic fields in general three-dimensional convex walled cavities along periodic paths between opposing sides of the cavity. The report examines the three-dimensional case where the mirrors at the end of the orbit have two different radii of curvature. The cases where these orbits lead to unstable localized modes are known as scars.

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Penetration Bounds For Azimuthal Slot On Infinite Cylinder With Finite Length Backing Cylindrical Cavity

Warne, Larry K.; Campione, Salvatore; Martin, Luis S.; Pack, Alden R.; Langston, William L.; Zinser, Brian &.

We examine coupling into azimuthal slots on an infinite cylinder with a infinite length interior cavity operating both at the fundamental cavity modal frequencies, with small slots and a resonant slot, as well as higher frequencies. The coupling model considers both radiation on an infinite cylindrical exterior as well as a half space approximation. Bounding calculations based on maximum slot power reception and interior power balance are also discussed in detail and compared with the prior calculations. For higher frequencies limitations on matching are imposed by restricting the loads ability to shift the slot operation to the nearest slot resonance; this is done in combination with maximizing the power reception as a function of angle of incidence. Finally, slot power mismatch based on limited cavity load quality factor is considered below the first slot resonance.

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Penetration through Slots in Overmoded Cavities

IEEE Transactions on Electromagnetic Compatibility

Campione, Salvatore; Warne, Larry K.

A resonant cavity undergoes three distinct behaviors with increasing frequency: 1) fundamental modes, localized in frequency with well defined modal distribution; 2) undermoded region, where modes are still separated, but are sufficiently perturbed by small imperfections that their spectral positions (and distributions) are statistical in nature; and 3) overmoded region, where modes overlap, field distributions follow stochastic distributions, and the slot acts as if in free space. Understanding the penetration through slots in the overmoded region is of great interest, and is the focus of this article. Since full-wave solvers may not be able to provide a timely answer for very high frequencies due to a lack of memory and/or computation resources, we develop bounding methods to estimate worst-case average and maximum fields within the cavity. After discussing the bounding formulation, we compare its results to full-wave simulations at the first, second, and third resonance supported by the slot in the case of a cylindrical cavity. Note that the bounding formulation indicates that results are nearly independent of cavity shape: only the cavity volume, frequency, and cavity quality factor affect the overmoded region, making this formulation a powerful tool to assess electromagnetic interference and electromagnetic compatibility effects within cavities.

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Developing Uncertainty Quantification Strategies in Electromagnetic Problems Involving Highly Resonant Cavities

Journal of Verification, Validation and Uncertainty Quantification

Campione, Salvatore; Stephens, John A.; Martin, Nevin; Eckert, Aubrey C.; Warne, Larry K.; Huerta, Jose G.; Pfeiffer, Robert A.; Jones, Adam J.

High-quality factor resonant cavities are challenging structures to model in electromagnetics owing to their large sensitivity to minute parameter changes. Therefore, uncertainty quantification (UQ) strategies are pivotal to understanding key parameters affecting the cavity response. We discuss here some of these strategies focusing on shielding effectiveness (SE) properties of a canonical slotted cylindrical cavity that will be used to develop credibility evidence in support of predictions made using computational simulations for this application.

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Penetration through slots in cylindrical cavities with cavity modes overlapping with the first slot resonance

Electromagnetics

Campione, Salvatore; Warne, Larry K.; Langston, William L.; Gutierrez, Roy K.; Hicks, Jeorge W.; Reines, Isak C.; Pfeiffer, Robert A.; Himbele, John J.; Williams, Jeffery T.

We analyze the coupling into a slotted cylindrical cavity operating at fundamental cavity modal frequencies overlapping with the slot’s first resonance frequency through an unmatched formulation that accounts for the slot’s absorption and radiation processes. The model is validated through full-wave simulations and experimental data. We then couple the unmatched formulation to a perturbation theory model to investigate an absorber within the cavity to reduce the interior field strength, also validated with full-wave simulations and experiments. These models are pivotal to understanding the physical processes involved in the electromagnetic penetration through slots, and may constitute design tools to mitigate electromagnetic interference effects within cavities.

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Electromagnetic Pulse – Resilient Electric Grid for National Security: Research Program Executive Summary

Guttromson, Ross G.; Lawton, Craig R.; Halligan, Matthew H.; Huber, Dale L.; Flicker, Jack D.; Hoffman, Matthew J.; Bowman, Tyler B.; Campione, Salvatore; Clem, Paul G.; Fiero, Andrew F.; Hansen, Clifford H.; Llanes, Rodrigo E.; Pfeiffer, Robert A.; Pierre, Brian J.; Martin, Luis S.; Sanabria, David E.; Schiek, Richard S.; Slobodyan, Oleksiy S.; Warne, Larry K.

Sandia National Laboratories sponsored a three-year internally funded Laboratory Directed Research and Development (LDRD) effort to investigate the vulnerabilities and mitigations of a high-altitude electromagnetic pulse (HEMP) on the electric power grid. The research was focused on understanding the vulnerabilities and potential mitigations for components and systems at the high voltage transmission level. Results from the research included a broad array of subtopics, covered in twenty-three reports and papers, and which are highlighted in this executive summary report. These subtopics include high altitude electromagnetic pulse (HEMP) characterization, HEMP coupling analysis, system-wide effects, and mitigating technologies.

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Estimation of the Attenuation Caused by Power Line Towers on an E1-HEMP Induced Excitation

Martin, Luis S.; Warne, Larry K.

In a transmission line, the coupling between a line and a tower above ground is evaluated when the excitation is an E1 high-altitude electromagnetic pulse (HEMP). The model focuses on capturing correctly the effect of the coupling on the peak of the HEMP induced current that propagates along the line. This assessment is necessary to accurately estimate the effect of the excitation on the systems and components of the power grid. This analysis is a step towards a quantitative evaluation of HEMP excitation on the power grid. The results obtained indicate that the effect can be significant, especially for lines heights of 20 meters or more.

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Penetration through Slots in Cylindrical Cavities Operating at Fundamental Cavity Modes

IEEE Transactions on Electromagnetic Compatibility

Campione, Salvatore; Warne, Larry K.; Langston, William L.; Pfeiffer, Robert A.; Martin, Nevin S.; Williams, Jeffery T.; Gutierrez, Roy K.; Reines, Isak C.; Huerta, Jose G.; Dang, Vinh Q.

In this article, we examine the coupling into an electrically short azimuthal slot on a cylindrical cavity operating at fundamental cavity modal frequencies. We first develop a matched bound formulation through which we can gather information for maximum achievable levels of interior cavity fields. Actual field levels are below this matched bound; therefore, we also develop an unmatched formulation for frequencies below the slot resonance to achieve a better insight on the physics of this coupling. Good agreement is observed between the unmatched formulation, full-wave simulations, and experimental data, providing a validation of our analytical models. We then extend the unmatched formulation to treat an array of slots, found again in good agreement with full-wave simulations. These analytical models can be used to investigate ways to mitigate electromagnetic interference and electromagnetic compatibility effects within cavities.

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Diffusion Models to Construct a First Principles Multipole-Based Cable Braid Model for Conducting Wires in the Time Domain

Campione, Salvatore; Warne, Larry K.

We describe here diffusion models apt to construct a multipole-based, cable braid time domain model for conducting wires. Implementation details of both a ladder network valid for time-domain signals with all frequency content and an approximate single-stage circuit valid for low-frequency dominated time signals (such as electromagnetic pulses) are reported. This time domain model can be leveraged to treat system-generated electromagnetic pulse events, as well as used to further confirm the correctness of the multipole-based, cable braid frequency domain model.

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Penetration through slots in cylindrical cavities operating at fundamental cavity modes in the presence of electromagnetic absorbers

Progress In Electromagnetics Research M

Campione, Salvatore; Warne, Larry K.; Reines, Isak C.; Gutierrez, Roy K.; Williams, Jeffery T.

Placing microwave absorbing materials into a high-quality factor resonant cavity may in general reduce the large interior electromagnetic fields excited under external illumination. In this paper, we aim to combine two analytical models we previously developed: 1) an unmatched formulation for frequencies below the slot resonance to model shielding effectiveness versus frequency; and 2) a perturbation model approach to estimate the quality factor of cavities in the presence of absorbers. The resulting model realizes a toolkit with which design guidelines of the absorber’s properties and location can be optimized over a frequency band. Analytic predictions of shielding effectiveness for three transverse magnetic modes for various locations of the absorber placed on the inside cavity wall show good agreement with both full-wave simulations and experiments, and validate the proposed model. This analysis opens new avenues for specialized ways to mitigate harmful fields within cavities.

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Multipole-based cable braid electromagnetic penetration model: Magnetic penetration case

Progress In Electromagnetics Research C

Campione, Salvatore; Warne, Larry K.; Langston, William L.

The goal of this paper is to present, for the first time, calculations of the magnetic penetration case of a first principles multipole-based cable braid electromagnetic penetration model. As a first test case, a one-dimensional array of perfect electrically conducting wires, for which an analytical solution is known, is investigated: We compare both the self-inductance and the transfer inductance results from our first principles cable braid electromagnetic penetration model to those obtained using the analytical solution. These results are found in good agreement up to a radius to half spacing ratio of about 0.78, demonstrating a robustness needed for many commercial and non-commercial cables. We then analyze a second set of test cases of a square array of wires whose solution is the same as the one-dimensional array result and of a rhomboidal array whose solution can be estimated from Kley’s model. As a final test case, we consider two layers of one-dimensional arrays of wires to investigate porpoising effects analytically. We find good agreement with analytical and Kley’s results for these geometries, verifying our proposed multipole model. Note that only our multipole model accounts for the full dependence on the actual cable geometry which enables us to model more complicated cable geometries.

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TATB Sensitivity to Shocks from Electrical Arcs

Propellants, Explosives, Pyrotechnics

Chen, Kenneth C.; Warne, Larry K.; Jorgenson, Roy E.; Niederhaus, John H.

Use of insensitive high explosives (IHEs) has significantly improved ammunition safety because of their remarkable insensitivity to violent cook-off, shock and impact. Triamino-trinitrobenzene (TATB) is the IHE used in many modern munitions. Previously, lightning simulations in different test configurations have shown that the required detonation threshold for standard density TATB at ambient and elevated temperatures (250 C) has a sufficient margin over the shock caused by an arc from the most severe lightning. In this paper, the Braginskii model with Lee-More channel conductivity prescription is used to demonstrate how electrical arcs from lightning could cause detonation in TATB. The steep rise and slow decay in typical lightning pulse are used in demonstrating that the shock pressure from an electrical arc, after reaching the peak, falls off faster than the inverse of the arc radius. For detonation to occur, two necessary detonation conditions must be met: the Pop-Plot criterion and minimum spot size requirement. The relevant Pop-Plot for TATB at 250 C was converted into an empirical detonation criterion, which is applicable to explosives subject to shocks of variable pressure. The arc cross-section was required to meet the minimum detonation spot size reported in the literature. One caveat is that when the shock pressure exceeds the detonation pressure the Pop-Plot may not be applicable, and the minimum spot size requirement may be smaller.

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Modeling shielded cables in Xyce based on transmission-line theory

2019 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2019 - Proceedings

Campione, Salvatore; Pung, Aaron J.; Warne, Larry K.; Langston, William L.; Mei, Ting M.

Electromagnetic shields are usually employed to protect cables and other devices; however, these are generally not perfect, and may permit external magnetic and electric fields to penetrate into the interior regions of the cable, inducing unwanted current and voltages. The aim of this paper is to verify a circuit model tool with our previously proposed analytical model [1] for evaluating currents and voltages induced in the inner conductor of braided-shield cables. This circuit model will enable coupling between electromagnetic and circuit simulations.

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Modeling and experiments of high-quality factor cavity shielding effectiveness

2019 International Applied Computational Electromagnetics Society Symposium in Miami, ACES-Miami 2019

Campione, Salvatore; Warne, Larry K.; Reines, Isak C.; Williams, Jeffery T.; Gutierrez, Roy K.; Coats, Rebecca S.; Basilio, Lorena I.

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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Quality factor assessment of finite-size all-dielectric metasurfaces at the magnetic dipole resonance

Nanomaterials and Nanotechnology

Warne, Larry K.; Jorgenson, Roy E.; Campione, Salvatore

Recently there has been a large interest in achieving metasurface resonances with large quality factors. In this article, we examine metasurfaces that comprised a finite number of magnetic dipoles oriented parallel or orthogonal to the plane of the metasurface and determine analytic formulas for their resonances’ quality factors. These conditions are experimentally achievable in finite-size metasurfaces made of dielectric cubic resonators at the magnetic dipole resonance. Our results show that finite metasurfaces made of parallel (to the plane) magnetic dipoles exhibit low quality factor resonances with a quality factor that is independent of the number of resonators. More importantly, finite metasurfaces made of orthogonal (to the plane) magnetic dipoles lead to resonances with large quality factors, which ultimately depend on the number of resonators comprising the metasurface. In particular, by properly modulating the array of dipole moments by having a distribution of resonator polarizabilities, one can potentially increase the quality factor of metasurface resonances even further. These results provide design guidelines to achieve a sought quality factor applicable to any resonator geometry for the development of new devices such as photodetectors, modulators, and sensors.

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Preliminary Survey on the Effectiveness of an Electromagnetic Dampener to Improve System Shielding Effectiveness

Campione, Salvatore; Reines, Isak C.; Warne, Larry K.; Williams, Jeffery T.; Gutierrez, Roy K.; Coats, Rebecca S.; Basilio, Lorena I.

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.

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Improved quantitative circuit model of realistic patch-based nanoantenna-enabled detectors

Journal of the Optical Society of America B: Optical Physics

Campione, Salvatore; Warne, Larry K.; Goldflam, Michael G.; Peters, D.W.; Sinclair, Michael B.

Improving the sensitivity of infrared detectors is an essential step for future applications, including satellite- and terrestrial-based systems. We investigate nanoantenna-enabled detectors (NEDs) in the infrared, where the nanoantenna arrays play a fundamental role in enhancing the level of absorption within the active material of a photodetector. The design and optimization of nanoantenna-enabled detectors via full-wave simulations is a challenging task given the large parameter space to be explored. Here, we present a fast and accurate fully analytic circuit model of patch-based NEDs. This model allows for the inclusion of real metals, realistic patch thicknesses, non-absorbing spacer layers, the active detector layer, and absorption due to higher-order evanescent modes of the metallic array. We apply the circuit model to the design of NED devices based on Type II superlattice absorbers, and show that we can achieve absorption of ∼70% of the incoming energy in subwavelength (∼λ∕5) absorber layers. The accuracy of the circuit model is verified against full-wave simulations, establishing this model as an efficient design tool to quickly and accurately optimize NED structures.

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ATLOG Modeling of Buried Cables from the November 2016 HERMES Electromagnetic Pulse Experiments

Warne, Larry K.; Campione, Salvatore; Yee, Benjamin T.; Cartwright, Keith C.; Basilio, Lorena I.

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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Formulas For Plane Wave Coupling To A Transmission Line Above Ground With Terminating Loads

Warne, Larry K.; Campione, Salvatore

This report considers plane wave coupling to a transmission line consisting of a wire above a conducting ground. Comparisons are made for the two types of available source models, along with a discussion about the decomposition of the line currents. Simple circuit models are constructed for the terminating impedances at the ends of the line including radiation effects. Results from the transmission line with these loads show good agreement with full wave simulations. Intentionally Left Blank

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First principles model of electric and magnetic cable braid penetrations

2018 International Applied Computational Electromagnetics Society Symposium in Denver, ACES-Denver 2018

Campione, Salvatore; Warne, Larry K.; Langston, William L.

In this paper, we report our recent findings about a first principles, multipole-based model of electric and magnetic cable braid penetrations. We consider for brevity a one-dimensional array of wires, but the model can be readily applied to realistic cable geometries. Comparisons between the first principles method and analytical formulas will be provided for both electric and magnetic penetration cases. These comparisons confirm that our first principles model works within the geometric characteristics of many commercial cables.

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First principles model of electric cable braid penetration with dielectrics

Progress In Electromagnetics Research C

Campione, Salvatore; Warne, Larry K.; Langston, William L.; Basilio, Lorena I.

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.

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Realistic full wave modeling of focal plane array pixels

Applied Computational Electromagnetics Society Journal

Campione, Salvatore; Warne, Larry K.; Jorgenson, Roy E.; Davids, Paul D.; Peters, D.W.

In this paper we investigate full-wave simulations of realistic implementations of multifunctional nanoantenna enabled detectors (NEDs). We focus on a 2x2 pixelated array structure that supports two wavelengths of operation. We design each resonating structure independently using full-wave simulations with periodic boundary conditions mimicking the whole infinite array. We then construct a supercell made of a 2x2 pixelated array with periodic boundary conditions mimicking the full NED; in this case, however, each pixel comprises 10-20 antennas per side. In this way, the cross-talk between contiguous pixels is accounted for in our simulations. We observe that, even though there are finite extent effects, the pixels work as designed, each responding at the respective wavelength of operation. This allows us to stress that realistic simulations of multifunctional NEDs need to be performed to verify the design functionality by taking into account finite extent and cross-talk effects.

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Finite and infinite lossy conductors over a lossy ground plane excited by an electromagnetic pulse

2017 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2017

Campione, Salvatore; Warne, Larry K.; Basilio, Lorena I.; Turner, C.D.; Cartwright, Keith C.; Chen, Kenneth C.

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.

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A first principles cable braid electromagnetic penetration model

Proceedings of the 2017 19th International Conference on Electromagnetics in Advanced Applications, ICEAA 2017

Campione, Salvatore; Warne, Larry K.; Coats, Rebecca S.; Langston, William L.; Basilio, Lorena I.; Johnson, W.A.

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.

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Integrating Resonant Structures with IR Detectors

Goldflam, Michael G.; Goldflam, Michael G.; Anderson, Evan M.; Anderson, Evan M.; Campione, Salvatore; Campione, Salvatore; Coon, Wesley T.; Coon, Wesley T.; Davids, Paul D.; Davids, Paul D.; Fortune, Torben R.; Fortune, Torben R.; Hawkins, Samuel D.; Hawkins, Samuel D.; Kadlec, Clark N.; Kadlec, Clark N.; Kadlec, Emil A.; Kadlec, Emil A.; Kim, Jin K.; Kim, Jin K.; Klem, John F.; Klem, John F.; Shaner, Eric A.; Shaner, Eric A.; Sinclair, Michael B.; Sinclair, Michael B.; Tauke-Pedretti, Anna; Tauke-Pedretti, Anna; Warne, Larry K.; Warne, Larry K.; Wendt, J.R.; Wendt, J.R.; Beechem, Thomas E.; Beechem, Thomas E.; Howell, Stephen W.; Howell, Stephen W.; McDonald, Anthony E.; McDonald, Anthony E.; Ruiz, Isaac R.; Ruiz, Isaac R.

Abstract not provided.

Accelerated Time-Domain Modeling of Electromagnetic Pulse Excitation of Finite-Length Dissipative Conductors over a Ground Plane via Function Fitting and Recursive Convolution

Campione, Salvatore; Warne, Larry K.; Sainath, Kamalesh S.; Basilio, Lorena I.

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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Improved infrared detection using nanoantennas

International Conference on Optical MEMS and Nanophotonics

Peters, D.W.; Sinclair, Michael B.; Goldflam, Michael G.; Warne, Larry K.; Campione, Salvatore; Kim, Jin K.; Davids, Paul D.; Tauke-Pedretti, Anna; Wendt, J.R.; Klem, John F.; Hawkins, Samuel D.; Parameswaran, Sivasubramanian P.; Coon, W.T.; Keeler, G.A.; Fortune, Torben R.

We examine integration of a patterned metal nanoantenna (or metasurface) directly onto long-wave infrared detectors. These structures show significantly improved external quantum efficiency compared to their traditional counterparts. We will show simulation and experimental results.

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Electromagnetic Pulse Excitation of Finite-Long Dissipative Conductors over a Conducting Ground Plane in the Frequency Domain

Campione, Salvatore; Warne, Larry K.; Schiek, Richard S.; Basilio, Lorena I.

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

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Electromagnetic Pulse Excitation of Finite-Long Dissipative Conductors over a Conducting Ground Plane in the Time Domain

Campione, Salvatore; Warne, Larry K.; Schiek, Richard S.; Basilio, Lorena I.

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

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Comparison of ATLOG and Xyce for Bell Labs Electromagnetic Pulse Excitation of Finite-Long Dissipative Conductors over a Ground Plane

Campione, Salvatore; Warne, Larry K.; Schiek, Richard S.; Basilio, Lorena I.

This report details the modeling results for the response of a finite-length dissipative conductor interacting with a conducting ground to the Bell Labs electromagnetic pulse excitation. We use both a frequency-domain and a time-domain method based on transmission line theory through a code we call ATLOG - Analytic Transmission Line Over Ground. Results are compared to the circuit simulator Xyce for selected cases. Intentionally Left Blank

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ATLOG Modeling of Aerial Cable from the November 2016 HERMES Electromagnetic Pulse Experiments

Campione, Salvatore; Warne, Larry K.; Yee, Benjamin T.; Cartwright, Keith C.; Basilio, Lorena I.

This report details the comparison of ATLOG modeling results for the response of a finite-length dissipative aerial 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 time-domain method based on transmission line theory. Good agreement is observed between simulations and experiments. Intentionally Left Blank

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Dipole Approximation to Predict the Resonances of Dimers Composed of Dielectric Resonators for Directional Emission

Radio Science

Campione, Salvatore; Warne, Larry K.; Basilio, Lorena I.

In this paper we develop a fully retarded, dipole approximation model to estimate the effective polarizabilities of a dimer made of dielectric resonators. They are computed from the polarizabilities of the two resonators composing the dimer. We analyze the situation of full cubes as well as split cubes, which have been shown to exhibit overlapping electric and magnetic resonances. We compare the effective dimer polarizabilities to ones retrieved via full-wave simulations as well as ones computed via a quasi-static, dipole approximation. We observe good agreement between the fully retarded solution and the full-wave results, whereas the quasi-static approximation is less accurate for the problem at hand. The developed model can be used to predict the electric and magnetic resonances of a dimer under parallel or orthogonal (to the dimer axis) excitation. This is particularly helpful when interested in locating frequencies at which the dimer will emit directional radiation.

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Resonantly enhanced infrared detectors based on type-II superlattice absorbers

Goldflam, Michael G.; Goldflam, Michael G.; Campione, Salvatore; Campione, Salvatore; Kadlec, Emil A.; Kadlec, Emil A.; Hawkins, Samuel D.; Hawkins, Samuel D.; Coon, Wesley T.; Coon, Wesley T.; Fortune, Torben R.; Fortune, Torben R.; Parameswaran, Sivasubramanian P.; Parameswaran, Sivasubramanian P.; Keeler, Gordon A.; Keeler, Gordon A.; Klem, John F.; Klem, John F.; Tauke-Pedretti, Anna; Tauke-Pedretti, Anna; Shaner, Eric A.; Shaner, Eric A.; Davids, Paul D.; Davids, Paul D.; Warne, Larry K.; Warne, Larry K.; Wendt, J.R.; Wendt, J.R.; Kim, Jin K.; Kim, Jin K.; Peters, D.W.; Peters, D.W.

Abstract not provided.

Multipole-Based Cable Braid Electromagnetic Penetration Model: Electric Penetration Case

IEEE Transactions on Electromagnetic Compatibility

Campione, Salvatore; Warne, Larry K.; Langston, William L.; Johnson, William A.; Coats, Rebecca S.; Basilio, Lorena I.

In this paper, we investigate the electric penetration case of the first principles multipole-based cable braid electromagnetic penetration model reported in the Progress in Electromagnetics Research B 66, 63–89 (2016). We first analyze the case of a 1-D array of wires: this is a problem which is interesting on its own, and we report its modeling based on a multipole-conformal mapping expansion and extension by means of Laplace solutions in bipolar coordinates. We then compare the elastance (inverse of capacitance) results from our first principles cable braid electromagnetic penetration model to that obtained using the multipole-conformal mapping bipolar solution. These results are found in a good agreement up to a radius to half spacing ratio of 0.6, demonstrating a robustness needed for many commercial cables. We then analyze realistic cable implementations without dielectrics and compare the results from our first principles braid electromagnetic penetration model to the semiempirical results reported by Kley in the IEEE Transactions on Electromagnetic Compatibility 35, 1–9 (1993). Finally, although we find results on the same order of magnitude of Kley's results, the full dependence on the actual cable geometry is accounted for only in our proposed multipole model which, in addition, enables us to treat perturbations from those commercial cables measured.

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Next-generation infrared focal plane arrays for high-responsivity low-noise applications

IEEE Aerospace Conference Proceedings

Goldflam, Michael G.; Hawkins, Samuel D.; Parameswaran, Sivasubramanian P.; Tauke-Pedretti, Anna; Warne, Larry K.; Peters, D.W.; Campione, Salvatore; Coon, W.T.; Keeler, Gordon A.; Shaner, Eric A.; Wendt, J.R.; Kadlec, Emil A.; Fortune, Torben R.; Klem, John F.; Davids, Paul D.; Kim, Jin K.

High-quality infrared focal plane arrays (FPAs) are used in many satellite, astronomical, and terrestrial applications. These applications require highly-sensitive, low-noise FPAs, and therefore do not benefit from advances made in low-cost thermal imagers where reducing cost and enabling high-temperature operation drive device development. Infrared detectors used in FPAs have been made for decades from alloys of mercury cadmium telluride (MCT). These infrared detectors are nearing the believed limit of their performance. This limit, known in the infrared detector community as Rule 07, dictates the dark current floor for MCT detectors, in their traditional architecture, for a given temperature and cutoff wavelength. To overcome the bounds imposed by Rule 07, many groups are working on detector compounds other than MCT. We focus on detectors employing III-V-based gallium-free InAsSb superlattice active regions while also changing the basic architecture of the pixel to improve signal-to-noise. Our architecture relies on a resonant, metallic, subwavelength nanoantenna patterned on the absorber surface, in combination with a Fabry-Pérot cavity, to couple the incoming radiation into tightly confined modes near the nanoantenna. This confinement of the incident energy in a thin layer allows us to greatly reduce the volume of the absorbing layer to a fraction of the free-space wavelength, yielding a corresponding reduction in dark current from spontaneously generated electron-hole pairs in the absorber material. This architecture is detector material agnostic and could be applied to MCT detector structures as well, although we focus on using superlattice antimonide-based detector materials. This detector concept has been applied to both mid-wave (3-5 μm) and longwave (8-12 μm) infrared detectors and absorbers. Here we examine long-wave devices, as these detectors currently have a larger gap between desired device performance and that of currently existing detectors. The measured structures show an external quantum efficiency exceeding 50%. We present a comparison of the modeled and measured photoresponse of these detectors and compare these detectors to currently available commercial detectors using relevant metrics such as external quantum efficiency. We also discuss modeling of crosstalk between adjacent pixels and its influence on the potential for a dual-wavelength detector. Finally, we evaluate potential advances in these detectors that may occur in the near future.

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Simulations of realistic multifunctional nanoantenna enabled detectors

2017 International Applied Computational Electromagnetics Society Symposium - Italy, ACES 2017

Campione, Salvatore; Warne, Larry K.; Jorgenson, Roy E.; Davids, Paul D.; Peters, D.W.

The goal of this paper is to investigate full-wave simulations of realistic implementations of multifunctional nanoantenna enabled detectors (NEDs). We realize a 2×2 pixelated array structure that supports two wavelengths of operation. After designing each resonating structure independently using full-wave simulations with periodic boundary conditions mimicking the whole infinite array, we construct a supercell made of a 2×2 pixelated array with periodic boundary conditions mimicking the full NED. In the NED, each pixel comprises 10-20 nanoantennas. Our simulations account for the cross-talk between contiguous pixels. We observe that, even though there are finite extent effects, the pixels work as designed, each responding at the respective wavelength of operation. We want to stress that realistic simulations of multifunctional NEDs need to be performed to verify the design functionality by taking into account finite extent and cross-talk effects.

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Radiation-MHD simulations for the development of a spark discharge channel

Niederhaus, John H.; Jorgenson, Roy E.; Warne, Larry K.; Chen, Kenneth C.

The growth of a cylindrical s park discharge channel in water and Lexan is studied using a series of one - dimensional simulations with the finite - element radiation - magnetohydrodynamics code ALEGRA. Computed solutions are analyzed in order to characterize the rate of growth and dynamics of the spark c hannels during the rising - current phase of the drive pulse. The current ramp rate is varied between 0.2 and 3.0 kA/ns, and values of the mechanical coupling coefficient K p are extracted for each case. The simulations predict spark channel expansion veloc ities primarily in the range of 2000 to 3500 m/s, channel pressures primarily in the range 10 - 40 GPa, and K p values primarily between 1.1 and 1.4. When Lexan is preheated, slightly larger expansion velocities and smaller K p values are predicted , but the o verall behavior is unchanged.

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Electromagnetic pulse excitation of finite- and infinitely-long lossy conductors over a lossy ground plane

Journal of Electromagnetic Waves and Applications

Campione, Salvatore; Warne, Larry K.; Basilio, Lorena I.; Turner, C.D.; Cartwright, Keith C.; Chen, Kenneth C.

This paper details a model for the response of a finite- or an infinite-length wire interacting with a conducting ground to an electromagnetic pulse excitation. We develop a frequency–domain method based on transmission line theory that we name ATLOG–Analytic Transmission Line Over Ground. This method is developed as an alternative to full-wave methods, as it delivers a fast and reliable solution. It allows for the treatment of finite or infinite lossy, coated wires, and lossy grounds. The cases of wire above ground, as well as resting on the ground and buried beneath the ground are treated. The reported method is general and the time response of the induced current is obtained using an inverse Fourier transform of the current in the frequency domain. The focus is on the characteristics and propagation of the transmission line mode. Comparisons with full-wave simulations strengthen the validity of the proposed method.

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Broken Symmetry Dielectric Resonators for High Quality Factor Fano Metasurfaces

ACS Photonics

Campione, Salvatore; Liu, Sheng L.; Basilio, Lorena I.; Warne, Larry K.; Langston, William L.; Luk, Ting S.; Wendt, J.R.; Reno, J.L.; Keeler, Gordon A.; Brener, Igal; Sinclair, Michael B.

We present a new approach to dielectric metasurface design that relies on a single resonator per unit cell and produces robust, high quality factor Fano resonances. Our approach utilizes symmetry breaking of highly symmetric resonator geometries, such as cubes, to induce couplings between the otherwise orthogonal resonator modes. In particular, we design perturbations that couple "bright" dipole modes to "dark" dipole modes whose radiative decay is suppressed by local field effects in the array. Our approach is widely scalable from the near-infrared to radio frequencies. We first unravel the Fano resonance behavior through numerical simulations of a germanium resonator-based metasurface that achieves a quality factor of ∼1300 at ∼10.8 μm. Then, we present two experimental demonstrations operating in the near-infrared (∼1 μm): a silicon-based implementation that achieves a quality factor of ∼350; and a gallium arsenide-based structure that achieves a quality factor of ∼600, the highest near-infrared quality factor experimentally demonstrated to date with this kind of metasurface. Importantly, large electromagnetic field enhancements appear within the resonators at the Fano resonant frequencies. We envision that combining high quality factor, high field enhancement resonances with nonlinear and active/gain materials such as gallium arsenide will lead to new classes of active optical devices.

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Transmission-line modeling of shielding effectiveness of multiple shielded cables with arbitrary terminations

2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016

Campione, Salvatore; Basilio, Lorena I.; Warne, Larry K.; Langston, William L.

Cable shielding to protect against coupling of electromagnetic radiation into a component or circuit, particularly over large frequency bands, is at times a challenging task. It is general understanding that increasing the number of shields of a cable will improve the shielding performance. However, there are situations in which a cable with multiple shields may perform similar to or in some cases worse than a cable with a single shield, and this analysis has seldom been discussed in the literature. We intend to shed more light onto this topic in this paper.

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Tailoring dielectric resonator geometries for directional scattering, Huygens' metasurfaces, and high quality-factor Fano resonances

2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016

Campione, Salvatore; Basilio, Lorena I.; Warne, Larry K.; Langston, William L.; Luk, Ting S.; Wendt, J.R.; Liu, Sheng L.; Brener, Igal B.; Sinclair, Michael B.

Metamaterial dielectric resonators represent a promising path toward low-loss metamaterials at optical frequencies. In this paper we utilize perturbations of high symmetry resonator geometries, such as cubes, either to overlap the electric and magnetic dipole resonances, thereby enabling directional scattering and Huygens' metasurfaces, or to induce couplings between the otherwise orthogonal resonator modes to achieve high-quality factor Fano resonances. Our results are fully scalable across any frequency bands where high-permittivity dielectric materials are available, including microwave, THz, and infrared frequencies.

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A bound on electromagnetic penetration through a slot aperture with backing cavity

Warne, Larry K.; Jorgenson, Roy E.; Williams, Jeffery T.; Basilio, Lorena I.; Coats, Rebecca S.; Campione, Salvatore; Chen, Kenneth C.; Langston, William L.

This report examines bounds on the penetrant power through ports of entry into a conductive cavity. We first replace the cavity by a load and consider the maximum power transfer properties of an antenna or an aperture. We consider how limitations on the load quality factor place limits on received power. For general frequency ranges we model the backing region by means of a uniformly distributed matched load along a slot aperture and adjust its value for maximum power transfer. This result is derived in closed form using a transmission line model for the aperture. This result illustrates the reduction in received power for low frequencies with finitely conducting wall materials. At high frequencies it approaches the receiving cross section of a linear array having the slot length dimension. Next we examine a slot aperture in a conducting rectangular enclosure and determine how the cavity wall losses and resulting quality factor limit the penetrant power. Detailed simulations and experimental measurements are compared with each other and with the bounding results to assess the accuracy of the bounds. These comparisons also indicate limitations on the accuracy of the models due to perturbing influences in construction, such as bolted joints.

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Formulation And Implementation Of A 1.75D Streamer Model

Jorgenson, Roy E.; Warne, Larry K.

Streamers are a type of ionization wave occurring during the early time phase of a gas discharge. They are typically launched when the evolving space charge of an electron avalanche reaches a certain critical level, beyond which the fi eld of the space charge itself is su ffi cient to drive further evolution of the ionization process. One of the most common ways to model streamers is known as a 1.5D model where the fi eld of a uniformly charged set of discs of chosen radius is evaluated along the cylinder axis. This fi eld drives a one-dimensional kinetic ionization process, which results in the nonlinear evolution of the streamer. This model is e ffi cient, but has the drawback of fi xing the radius and requiring it as an input parameter. Previously, we tried to extend t he 1.5D model to include evolution of its radius by developing a two-step process of axial and radial exp ansion but we encountered stability issues with the model that we thought could have been due to decoupling the two steps. In this report we introduce a new formulation of a streamer model that includes radial expansion. The goal is to take radial moments of the starting axisymmetric fl uid equations and thereby include the radial evolution of the streamer naturally and self-consistently from the beginning. We fi rst develop the fl uid model moments without electron attachment. We review the calculation of the electric fi elds required for the model and investigate approximations to improve computational e ffi ciency. We discuss the code implementation of the model and fi nally, we add attachment to allow the treatment of electronegative gases. Intentionally Left Blank

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Diffusion Through Single And Double Layer Shields And Induced Voltages From Low Frequency Electromagnetic Environments

Warne, Larry K.; Basilio, Lorena I.; Coats, Rebecca S.; Jorgenson, Roy E.; Chen, Kenneth C.

The di ff usion through shells consisting of either a single conducting or double conducting layers are examined. Exterior drives resulting from Electromagn etic Radiation (EMR), Electromagnetic Pulse (EMP), nearby (indirect) lightning, and DC (low frequency) magnetic fi eldsareused. Boththeinterior fi eld and the induced voltage from a maximally oriented and sized single turn loop are estimated. It is shown that the loop voltage with the empty cavity bounds the case where the center region is excluded by a conducting object. The cases of interior magnetic and electric fi elds from an exterior magnetic drive and the interior electric fi eld from an exterior electric drive are both solved; the magnetic interior fi eldfromanexterior magnetic drive is the only case that results in a nonzero low frequency penetration. Intentionally Left Blank

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Shielding effectiveness of multiple-shield cables with arbitrary terminations via transmission line analysis

Progress In Electromagnetics Research C

Campione, Salvatore; Basilio, Lorena I.; Warne, Larry K.; Hudson, Howard G.; Langston, William L.

In this paper we report on a transmission-line model for calculating the shielding effectiveness of multiple-shield cables with arbitrary terminations. Since the shields are not perfect conductors and apertures in the shields permit external magnetic and electric fields to penetrate into the interior regions of the cable, we use this model to estimate the effects of the outer shield current and voltage (associated with the external excitation and boundary conditions associated with the external conductor) on the inner conductor current and voltage. It is commonly believed that increasing the number of shields of a cable will improve the shielding performance. However, this is not always the case, and a cable with multiple shields may perform similar to or in some cases worse than a cable with a single shield. We want to shed more light on these situations, which represent the main focus of this paper.

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First principles cable braid electromagnetic penetration model

Progress In Electromagnetics Research B

Warne, Larry K.; Langston, William L.; Basilio, Lorena I.; Johnson, William A.

The model for penetration of a wire braid is rigorously formulated. Integral formulas are developed from energy principles for both self and transfer immittances in terms of potentials for the fields. The detailed boundary value problem for the wire braid is also set up in a very efficient manner; the braid wires act as sources for the potentials in the form of a sequence of line multipoles with unknown coefficients that are determined by means of conditions arising from the wire surface boundary conditions. Approximations are introduced to relate the local properties of the braid wires to a simplified infinite periodic planar geometry. This is used to treat nonuniform coaxial geometries including eccentric interior coaxial arrangements and an exterior ground plane.

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Cable Braid Electromagnetic Penetration Model

Warne, Larry K.; Langston, William L.; Basilio, Lorena I.; Johnson, W.A.

The model for penetration of a wire braid is rigorously formulated. Integral formulas are developed from energy principles and reciprocity for both self and transfer immittances in terms of potentials for the fields. The detailed boundary value problem for the wire braid is also setup in a very efficient manner; the braid wires act as sources for the potentials in the form of a sequence of line multipoles with unknown coefficients that are determined by means of conditions arising from the wire surface boundary conditions. Approximations are introduced to relate the local properties of the braid wires to a simplified infinite periodic planar geometry. This is used in a simplified application of reciprocity to be able to treat nonuniform coaxial geometries including eccentric interior coaxial arrangements and an exterior ground plane.

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Full-wave simulation of a three-dimensional metamaterial prism

Microwave and Optical Technology Letters

Basilio, Lorena I.; Langston, William L.; Warne, Larry K.; Langston, William L.; Sinclair, Michael B.

In this article, a negative-index metamaterial prism based on a composite unit cell containing a split-ring resonator and a z-dipole is designed and simulated. The design approach combines simulations of a single unit cell to identify the appropriate cell design (yielding the desired negative-index behavior) together with subcell modeling (which simplifies the mesh representation of the resonator geometry and allows for a larger number of resonator cells to be handled). In addition to describing the methodology used to design a n = -1 refractive index prism, results including the effective-medium parameters, the far-field scattered patterns, and the near-zone field distributions corresponding to a normally incident plane-wave excitation of the prism are presented.

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Design and simulation of a 3-dimensional metamaterial prism

2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), USNC-URSI 2014 - Proceedings

Basilio, Lorena I.; Langston, William L.; Warne, Larry K.

The goal of this paper is to define a unit cell containing an electric and magnetic complement and degenerate pair of resonators and subsequently construct a 3-dimensional (3D) n = -1 refractive index prism based upon the final unit cell design. In this effort simulating and observing the response of a negative-index metamaterial (MM) prism to a plane-wave excitation was a primary intent. However, an equally-important goal was to develop an efficient and high-fidelity process for arriving at the prism design.

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Three-Dimensional Electromagnetic High Frequency Axisymmetric Cavity Scars

Warne, Larry K.; Jorgenson, Roy E.

This report examines the localization of high frequency electromagnetic fi elds in three-dimensional axisymmetric cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This report treats both the case where the opposing sides, or mirrors, are convex, where there are no interior foci, and the case where they are concave, leading to interior foci. The scalar problem is treated fi rst but the approximations required to treat the vector fi eld components are also examined. Particular att ention is focused on the normalization through the electromagnetic energy theorem. Both projections of the fi eld along the scarred orbit as well as point statistics are examined. Statistical comparisons are m ade with a numerical calculation of the scars run with an axisymmetric simulation. This axisymmetric cas eformstheoppositeextreme(wherethetwomirror radii at each end of the ray orbit are equal) from the two -dimensional solution examined previously (where one mirror radius is vastly di ff erent from the other). The enhancement of the fi eldontheorbitaxiscanbe larger here than in the two-dimensional case. Intentionally Left Blank

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Electromagnetic field limits set by the V-Curve

Warne, Larry K.; Jorgenson, Roy E.

When emitters of electromagnetic energy are operated in the vicinity of sensitive components, the electric field at the component location must be kept below a certain level in order to prevent the component from being damaged, or in the case of electro-explosive devices, initiating. The V-Curve is a convenient way to set the electric field limit because it requires minimal information about the problem configuration. In this report we will discuss the basis for the V-Curve. We also consider deviations from the original V-Curve resulting from inductive versus capacitive antennas, increases in directivity gain for long antennas, decreases in input impedance when operating in a bounded region, and mismatches dictated by transmission line losses. In addition, we consider mitigating effects resulting from limited antenna sizes.

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Electromagnetic coupling into two standard calibration shields on the Sandia cable tester

Warne, Larry K.; Basilio, Lorena I.; Langston, William L.; Chen, Kenneth C.

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.

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Lightning responses on a finite cylindrical enclosure

Progress In Electromagnetics Research B

Chen, Kenneth C.; Warne, Larry K.; Lee, Kelvin S.H.

The voltage on a single-turn loop inside an enclosure characterizes the enclosure shielding effectiveness against a lightning insult. In this paper, the maximum induced voltage on a single-turn loop inside an enclosure from lightning coupling to a metal enclosure wall is expressed in terms of two multiplicative factors: (A) the normalized enclosure wall peak penetration ratio (i.e., ratio of the peak interior electric field multiplied by the sheet conductance to the exterior magnetic field) and (B) the DC voltage on an ideal optimum coupling loop assuming the ideal penetration ratio of one. As a result of the decomposition, the variation of the peak penetration ratio (A) for different coupling mechanisms is found to be small; the difference in the maximum voltage hence arises from the DC voltage on the optimum coupling loop (B). Maximum voltages on an optimum coupling loop inside a finite cylinder enclosure for direct attachment and a lightning line source at different distances from the enclosure are given in Table 3.

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Conductor fusing and gapping for bond wires

Progress in Electromagnetics Research M

Chen, Kenneth C.; Warne, Larry K.; Kinzel, Robert L.; Huff, Johnathon H.; McLean, Michael M.; Jenkins, Mark W.; Rutherford, Brian M.

In this paper, fusing of a metallic conductor is studied by judiciously using the solution of the one-dimensional heat equation, resulting in an approximate method for determining the threshold fusing current. The action is defined as an integration of the square of the wire current over time. The burst action (the action required to completely vaporize the material) for an exploding wire is then used to estimate the typical wire gapping action (involving wire fusing), from which gapping time can be estimated for a gapping current greater than a factor of two over the fusing current. The test data are used to determine the gapped length as a function of gapping current and to show, for a limited range, that the gapped length is inversely proportional to gapping time. The gapping length can be used as a signature of the fault current level in microelectronic circuits.

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Loop-to-loop coupling

Warne, Larry K.; Basilio, Lorena I.; Langston, William L.; Salazar, Robert S.; Coleman, Phillip D.; Lucero, Larry M.

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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Linear diffusion into a faraday cage

Progress In Electromagnetics Research M

Chen, Kenneth C.; Lin, Y.T.; Warne, Larry K.; Merewether, Kimball O.

In this paper, linear lightning diffusion into a Faraday cage is studied. The high-altitude Electromagnetic Pulse (HEMP) and nearby lightning are used as examples for a uniform field drive and the direct-strike lightning adjacent to the enclosure is used as a worst-case configuration of a line source excitation. The time-derivative of the magnetic field (HDOT) inside the enclosure for a uniform field drive with a decaying exponential waveform is analyzed and numerically determined. The physically relevant time-derivative of the magnetic field and voltage characterizations of an optimum coupling loop inside the enclosure for a decaying exponential waveform in a worst-case line source coupling configuration are numerically determined. First, the impulse and the unit step response peaks are shown to bound the decaying exponential peaks. Next, a simple fit function for a decaying exponential peak HDOT or a voltage bound for a single-turn loop inside the Faraday cage is constructed from peak responses of the unit step and impulse limiting cases. Excitations used are from (1) a uniform field drive of HEMP or nearby lightning and (2) a line source of direct-strike lightning. Comparisons of HDOT and voltage bounds of the fit function and actual numerical evaluations are given in Table 3.

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A Summary of the Theory and Design Team Efforts for the Sandia Metamaterials Science and Technology Grand Challenge LDRD

Basilio, Lorena I.; Brener, Igal B.; Burckel, David B.; Shaner, Eric A.; Wendt, J.R.; Luk, Ting S.; Ellis, A.R.; Bender, Daniel A.; Clem, Paul G.; Rasberry, Roger D.; Langston, William L.; Ihlefeld, Jon I.; Dirk, Shawn M.; Warne, Larry K.; Peters, D.W.; El-Kady, I.; Reinke, Charles M.; Loui, Hung L.; Williams, Jeffery T.; Sinclair, Michael B.; McCormick, Frederick B.

Abstract not provided.

Protection characteristics of a Faraday cage compromised by lightning burnthrough

Warne, Larry K.; Martinez, Leonard E.; Jorgenson, Roy E.; Merewether, Kimball O.; Jojola, John M.; Coats, Rebecca S.; Bystrom, Edward B.

A lightning flash consists of multiple, high-amplitude but short duration return strokes. Between the return strokes is a lower amplitude, continuing current which flows for longer duration. If the walls of a Faraday cage are made of thin enough metal, the continuing current can melt a hole through the metal in a process called burnthrough. A subsequent return stroke can couple energy through this newly-formed hole. This LDRD is a study of the protection provided by a Faraday cage when it has been compromised by burnthrough. We initially repeated some previous experiments and expanded on them in terms of scope and diagnostics to form a knowledge baseline of the coupling phenomena. We then used a combination of experiment, analysis and numerical modeling to study four coupling mechanisms: indirect electric field coupling, indirect magnetic field coupling, conduction through plasma and breakdown through the hole. We discovered voltages higher than those encountered in the previous set of experiments (on the order of several hundreds of volts).

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Impact of time-varying loads on the programmable pulsed power driver called genesis

Digest of Technical Papers-IEEE International Pulsed Power Conference

Glover, Steven F.; Davis, Jean-Paul D.; Schneider, Larry X.; Reed, Kim W.; Pena, Gary P.; Hall, Clint A.; Hanshaw, Heath L.; Hickman, Randy J.; Hodge, K.C.; Lemke, Raymond W.; Lehr, J.M.; Lucero, D.J.; McDaniel, Dillon H.; Puissant, J.G.; Rudys, Joseph M.; Sceiford, Matthew S.; Tullar, S.J.; Van De Valde, D.M.; White, F.E.; Warne, Larry K.; Coats, Rebecca S.; Johnson, William Arthur.

The success of dynamic materials properties research at Sandia National Laboratories has led to research into ultra-low impedance, compact pulsed power systems capable of multi-MA shaped current pulses with rise times ranging from 220-500 ns. The Genesis design consists of two hundred and forty 200 kV, 80 kA modules connected in parallel to a solid dielectric disk transmission line and is capable of producing 280 kbar of magnetic pressure (>500 kbar pressure in high Z materials) in a 1.75 nH, 20 mm wide stripline load. Stripline loads operating under these conditions expand during the experiment resulting in a time-varying load that can impact the performance and lifetime of the system. This paper provides analysis of time-varying stripline loads and the impact of these loads on system performance. Further, an approach to reduce dielectric stress levels through active damping is presented as a means to increase system reliability and lifetime. © 2011 IEEE.

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Modeling Braided Shields via multipole representations for the braid charges and currents

Proceedings - 2011 International Conference on Electromagnetics in Advanced Applications, ICEAA'11

Johnson, William Arthur.; Langston, William L.; Basilio, Lorena I.; Warne, Larry K.

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.

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A negative-index metamaterial design based on metal-core, dielectric shell resonators

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest)

Basilio, L.I.; Warne, Larry K.; Langston, William L.; Johnson, William Arthur.; Sinclair, M.B.

In this paper a simple effective-media analysis (including higher-order multipoles) is used to design a single-resonator, negative-index design based on a metal-core, dielectric-shell (MCDS) unit cell. In addition to comparing the performance of the MCDS design to other core-shell negative-index designs, performance trade-offs resulting from the relative positioning of the electric and magnetic modal resonances in the MCDS design are also discussed. © 2011 IEEE.

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Subcell models with application to split-ring resonators in the infrared

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest)

Johnson, William Arthur.; Warne, Larry K.; Basilio, Lorena I.; Langston, W.L.; Sinclair, M.B.

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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Time harmonic two-dimensional cavity scar statistics: Convex mirrors and bowtie

Electromagnetics

Warne, Larry K.; Jorgenson, Roy E.; Kotulski, J.D.; Lee, K.S.H.

This article examines the localization of time harmonic high-frequency modal fields in two-dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This article examines the enhancements for these unstable orbits when the opposing mirrors are convex, constructing the high-frequency field in the scar region using elliptic cylinder coordinates in combination with a random reflection phase from the outer chaotic region. The enhancements when the cavity is symmetric as well as asymmetric about the orbit are examined. © Taylor & Francis Group, LLC.

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An effective media toolset for use in metamaterial design

Warne, Larry K.; Johnson, William Arthur.; Langston, William L.; Sinclair, Michael B.

This paper introduces an effective-media toolset that can be used for the design of metamaterial structures based on metallic components such as split-ring resonators and dipoles, as well as dielectric spherical resonators. For demonstration purposes the toolset will be used to generate infrared metamaterial designs, and the predicted performances will be verified with full-wave numerical simulations.

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Electromagnetic coupling between transmitters and electro-explosive devices located within an enclosure

Jorgenson, Roy E.; Warne, Larry K.; Coats, Rebecca S.

This report documents calculations conducted to determine if 42 low-power transmitters located within a metallic enclosure can initiate electro-explosive devices (EED) located within the same enclosure. This analysis was performed for a generic EED no-fire power level of 250 mW. The calculations show that if the transmitters are incoherent, the power available is 32 mW - approximately one-eighth of the assumed level even with several worst-case assumptions in place.

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Surface interactions involved in flashover with high density electronegative gases

Warne, Larry K.; Jorgenson, Roy E.; Lehr, J.M.

This report examines the interactions involved with flashover along a surface in high density electronegative gases. The focus is on fast ionization processes rather than the later time ionic drift or thermalization of the discharge. A kinetic simulation of the gas and surface is used to examine electron multiplication and includes gas collision, excitation and ionization, and attachment processes, gas photoionization and surface photoemission processes, as well as surface attachment. These rates are then used in a 1.5D fluid ionization wave (streamer) model to study streamer propagation with and without the surface in air and in SF6. The 1.5D model therefore includes rates for all these processes. To get a better estimate for the behavior of the radius we have studied radial expansion of the streamer in air and in SF6. The focus of the modeling is on voltage and field level changes (with and without a surface) rather than secondary effects, such as, velocities or changes in discharge path. An experiment has been set up to carry out measurements of threshold voltages, streamer velocities, and other discharge characteristics. This setup includes both electrical and photographic diagnostics (streak and framing cameras). We have observed little change in critical field levels (where avalanche multiplication sets in) in the gas alone versus with the surface. Comparisons between model calculations and experimental measurements are in agreement with this. We have examined streamer sustaining fields (field which maintains ionization wave propagation) in the gas and on the surface. Agreement of the gas levels with available literature is good and agreement between experiment and calculation is good also. Model calculations do not indicate much difference between the gas alone versus the surface levels. Experiments have identified differences in velocity between streamers on the surface and in the gas alone (the surface values being larger).

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Streamer initiation in volume and surface discharges in atmospheric gases

Proceedings of the 2008 IEEE International Power Modulators and High Voltage Conference, PMHVC

Lehr, J.M.; Warne, Larry K.; Jorgenson, Roy E.; Wallace, Z.R.; Hodge, K.C.; Caldwell, Michele C.

It is generally acknowledged that once a highly conductive channel is established between two charged and conducting materials, electrical breakdown is well established and difficult to interrupt. An understanding of the initiation mechanism for electrical breakdown is crucial for devising mitigating methods to avoid catastrophic failures. Both volumetric and surface discharges are of interest. An effort is underway where experiments and theory are being simultaneously developed. The experiment consists of an impedance matched discharge chamber capable of investigating various gases and pressures to ten atmospheres. In addition to current and voltage measurements, a high dynamic range streak camera records streamer velocities. The streamer velocities are particularly valuable for comparison with theory. A streamer model is being developed which includes photo-ionization and particle interactions with an insulating surface. The combined theoretical and experimental effort is aimed at detailed comparisons of streamer development as well as a quantitative understanding of how streamers interact with dielectric surfaces and the resulting effects on breakdown voltage. © 2008 IEEE.

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Copy of An overview of pulse compression and power flow in the upgraded Z pulsed power driver

Savage, Mark E.; Maenchen, John E.; McDaniel, Dillon H.; Pasik, Michael F.; Pointon, Timothy D.; Owen, Albert C.; Seidel, David B.; Stoltzfus, Brian S.; Struve, Kenneth W.; Warne, Larry K.; Bennett, Lawrence F.; Woodworth, Joseph R.; Bliss, David E.; Clark, Waylon T.; Coats, Rebecca S.; Elizondo-Decanini, Juan M.; LeChien, Keith R.; Harjes, Henry C.; Lehr, J.M.

Abstract not provided.

Joint voltages resulting from lightning currents

Warne, Larry K.; Johnson, William Arthur.; Chen, Kenneth C.; Merewether, Kimball O.

Simple formulas are given for the interior voltages appearing across bolted joints from exterior lightning currents. External slot and bolt inductances as well as internal slot and bolt diffusion effects are included. Both linear and ferromagnetic wall materials are considered. A useful simplification of the slot current distribution into linear stripline and cylindrical parts (near the bolts) allows the nonlinear voltages to be estimated in closed form.

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Fundamental science investigations to develop a 6-MV laser triggered gas switch for ZR: first annual report

Maenchen, John E.; Savage, Mark E.; Struve, Kenneth W.; Woodworth, Joseph R.; Lehr, J.M.; Warne, Larry K.; Bliss, David E.; Jorgenson, Roy E.; LeChien, Keith R.; McKee, George R.; Pasik, Michael F.; Rosenthal, Stephen E.

In October 2005, an intensive three-year Laser Triggered Gas Switch (LTGS) development program was initiated to investigate and solve observed performance and reliability issues with the LTGS for ZR. The approach taken has been one of mission-focused research: to revisit and reassess the design, to establish a fundamental understanding of LTGS operation and failure modes, and to test evolving operational hypotheses. This effort is aimed toward deploying an initial switch for ZR in 2007, on supporting rolling upgrades to ZR as the technology can be developed, and to prepare with scientific understanding for the even higher voltage switches anticipated needed for future high-yield accelerators. The ZR LTGS was identified as a potential area of concern quite early, but since initial assessments performed on a simplified Switch Test Bed (STB) at 5 MV showed 300-shot lifetimes on multiple switch builds, this component was judged acceptable. When the Z{sub 20} engineering module was brought online in October 2003 frequent flashovers of the plastic switch envelope were observed at the increased stresses required to compensate for the programmatically increased ZR load inductance. As of October 2006, there have been 1423 Z{sub 20} shots assessing a variety of LTGS designs. Numerous incremental and fundamental switch design modifications have been investigated. As we continue to investigate the LTGS, the basic science of plastic surface tracking, laser triggering, cascade breakdown, and optics degradation remain high-priority mission-focused research topics. Significant progress has been made and, while the switch does not yet achieve design requirements, we are on the path to develop successively better switches for rolling upgrade improvements to ZR. This report summarizes the work performed in FY 2006 by the large team. A high-level summary is followed by detailed individual topical reports.

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Two dimensional unstable scar statistics

Warne, Larry K.; Jorgenson, Roy E.; Kotulski, J.D.

This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.

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Analysis of electromagnetic scattering by nearly periodic structures: an LDRD report

Jorgenson, Roy E.; Basilio, Lorena I.; Johnson, William Arthur.; Warne, Larry K.; Peters, D.W.

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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Measurement of the energy and power radiated by a pulsed blackbody x-ray source

Proposed for publication in Physical Review E.

Stygar, William A.; Leeper, Ramon J.; Mazarakis, Michael G.; McDaniel, Dillon H.; Mckenney, John M.; Mills, Jerry A.; Ruggles, Larry R.; Seamen, Johann F.; Simpson, Walter W.; Dropinski, Steven D.; Warne, Larry K.; York, Matthew W.; McGurn, John S.; Bryce, Edwin A.; Chandler, Gordon A.; Cuneo, M.E.; Johnson, William Arthur.; Jorgenson, Roy E.

We have developed a diagnostic system that measures the spectrally integrated (i.e. the total) energy and power radiated by a pulsed blackbody x-ray source. The total-energy-and-power (TEP) diagnostic system is optimized for blackbody temperatures between 50 and 350 eV. The system can view apertured sources that radiate energies and powers as high as 2 MJ and 200 TW, respectively, and has been successfully tested at 0.84 MJ and 73 TW on the Z pulsed-power accelerator. The TEP system consists of two pinhole arrays, two silicon-diode detectors, and two thin-film nickel bolometers. Each of the two pinhole arrays is paired with a single silicon diode. Each array consists of a 38 x 38 square array of 10-{micro}m-diameter pinholes in a 50-{micro}m-thick tantalum plate. The arrays achromatically attenuate the x-ray flux by a factor of {approx}1800. The use of such arrays for the attenuation of soft x rays was first proposed by Turner and co-workers [Rev. Sci. Instrum. 70, 656 (1999)RSINAK0034-674810.1063/1.1149385]. The attenuated flux from each array illuminates its associated diode; the diode's output current is recorded by a data-acquisition system with 0.6-ns time resolution. The arrays and diodes are located 19 and 24 m from the source, respectively. Because the diodes are designed to have an approximately flat spectral sensitivity, the output current from each diode is proportional to the x-ray power. The nickel bolometers are fielded at a slightly different angle from the array-diode combinations, and view (without pinhole attenuation) the same x-ray source. The bolometers measure the total x-ray energy radiated by the source and--on every shot--provide an in situ calibration of the array-diode combinations. Two array-diode pairs and two bolometers are fielded to reduce random uncertainties. An analytic model (which accounts for pinhole-diffraction effects) of the sensitivity of an array-diode combination is presented.

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Resistance of a water spark

Warne, Larry K.; Jorgenson, Roy E.; Lehr, J.M.

The later time phase of electrical breakdown in water is investigated for the purpose of improving understanding of the discharge characteristics. One dimensional simulations in addition to a zero dimensional lumped model are used to study the spark discharge. The goal is to provide better electrical models for water switches used in the pulse compression section of pulsed power systems. It is found that temperatures in the discharge channel under representative drive conditions, and assuming small initial radii from earlier phases of development, reach levels that are as much as an order of magnitude larger than those used to model discharges in atmospheric gases. This increased temperature coupled with a more rapidly rising conductivity with temperature than in air result in a decreased resistance characteristic compared to preceding models. A simple modification is proposed for the existing model to enable the approximate calculation of channel temperature and incorporate the resulting conductivity increase into the electrical circuit for the discharge channel. Comparisons are made between the theoretical predictions and recent experiments at Sandia. Although present and past experiments indicated that preceding late time channel models overestimated channel resistance, the calculations in this report seem to underestimate the resistance relative to recent experiments. Some possible reasons for this discrepancy are discussed.

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Dipole radiation from a cylindrical hole in the earth

Warne, Larry K.; Johnson, William Arthur.

This report examines the problem of an antenna radiating from a cylindrical hole in the earth and the subsequent far-zone field produced in the upper air half space. The approach used for this analysis was to first examine propagation characteristics along the hole for surrounding geologic material properties. Three cases of sand with various levels of moisture content were considered as the surrounding material to the hole. For the hole diameters and sand cases examined, the radiation through the earth medium was found to be the dominant contribution to the radiation transmitted through to the upper half-space. In the analysis presented, the radiation from a vertical and a horizontal dipole source within the hole is used to determine a closed-form expression for the radiation in the earth medium which represents a modified element factor for the source and hole combination. As the final step, the well-known results for a dipole below a half space, in conjunction with the use of Snell's law to transform the modified element factor to the upper half space, determine closed-form expressions for the far-zone radiated fields in the air region above the earth.

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An improved statistical model for linear antenna input impedance in an electrically large cavity

Johnson, William Arthur.; Jorgenson, Roy E.; Warne, Larry K.

This report presents a modification of a previous model for the statistical distribution of linear antenna impedance. With this modification a simple formula is determined which yields accurate results for all ratios of modal spectral width to spacing. It is shown that the reactance formula approaches the known unit Lorentzian in the lossless limit.

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Capacitance and effective area of flush monopole probes

Basilio, Lorena I.; Warne, Larry K.; Johnson, William Arthur.; Higgins, Matthew B.; Lehr, J.M.

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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Approximations to wire grid inductance

Proposed for publication in the Journal of Electrostatics.

Warne, Larry K.; Merewether, Kimball O.; Johnson, William Arthur.

By using a multipole-conformal mapping expansion for the wire currents we examine the accuracy of approximations for the transfer inductance of a one dimensional array of wires (wire grid). A simple uniform fit is constructed by introduction of the decay factor from bipolar coordinates into existing formulas for this inductance.

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Long line coupling models

Warne, Larry K.; Chen, Kenneth C.

This report assembles models for the response of a wire interacting with a conducting ground to an electromagnetic pulse excitation. The cases of an infinite wire above the ground as well as resting on the ground and buried beneath the ground are treated. The focus is on the characteristics and propagation of the transmission line mode. Approximations are used to simplify the description and formulas are obtained for the current. The semi-infinite case, where the short circuit current can be nearly twice that of the infinite line, is also examined.

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Electromagnetic analysis and modeling of the coax-to-triplate transition for the pulse-compression section of the ZR accelerator

Digest of Technical Papers-IEEE International Pulsed Power Conference

Johnson, William Arthur.; Coats, Rebecca S.; Jorgenson, Roy E.; Kotulski, J.D.; Lehr, J.M.; Pasik, Michael F.; Rosenthal, Stephen E.; Turner, C.D.; Warne, Larry K.

Transverse electromagnetic (TEM) wave analysis is used to estimate the efficiencies of the coax to triplate transition in Sandia's Z-20 test module. The structure of both the TEM mode and higher order TE modes in the triplate transmission line are characterized. In addition, three dimensional time domain simulations are carried out and used in conjunction with the modal analysis to provide insight into the wave structure excited in the triplate transmission line.

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Ionization coefficient approach to modeling breakdown in nonuniform geometries

Warne, Larry K.; Warne, Larry K.; Jorgenson, Roy E.; Nicolaysen, Scott D.

This report summarizes the work on breakdown modeling in nonuniform geometries by the ionization coefficient approach. Included are: (1) fits to primary and secondary ionization coefficients used in the modeling; (2) analytical test cases for sphere-to-sphere, wire-to-wire, corner, coaxial, and rod-to-plane geometries; a compilation of experimental data with source references; comparisons between code results, test case results, and experimental data. A simple criterion is proposed to differentiate between corona and spark. The effect of a dielectric surface on avalanche growth is examined by means of Monte Carlo simulations. The presence of a clean dry surface does not appear to enhance growth.

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Effect of Dielectric Photoemission on Surface Breakdown: An LDRD Report

Jorgenson, Roy E.; Jorgenson, Roy E.; Warne, Larry K.

The research discussed in this report was conceived during our earlier attempts to simulate breakdown across a dielectric surface using a Monte Carlo approach. While cataloguing the various ways that a dielectric surface could affect the breakdown process, we found that one obvious effect--photoemission from the surface--had been ignored. Initially, we felt that inclusion of this effect could have a major impact on how an ionization front propagates across a surface because of the following argument chain: (1) The photon energy required to release electrons from a surface via photoemission is less than the photon energy required to ionize gas molecules directly. (2) The mean free path of a photon in gas is longer for low-energy photons than for high-energy photons. (3) Photoionization is a major effect in advancing the ionization front for breakdown in gas without a surface, therefore, we know that even high-energy photons can be released from the head of a streamer and propagate some distance through the gas. Our hypothesis, therefore, was that photons with energies near the threshold of photoemission could travel further in front of the streamer before being absorbed than higher-energy photons needed for photoionization, yet the lower-energy photons, with the help of the surface, could still create seed electrons for new avalanches. Thus, the streamer would advance more rapidly next to a surface than in gas alone. Additionally, the photoemission from the surface would add to the electrons in the avalanche and cause the avalanche to grow faster. After some study, however, we are forced to conclude that although photoemission does contribute to avalanche growth at fields near breakdown threshold, secondary electron emission causes electrons to stick to the surface and cancels out the growth due to photoemission. This conclusion assumes a discharge that occurs over a short period of time so that charging of the surface, which could alter its secondary electron emission characteristics, does not occur. This report documents the numerical work we did on investigating this effect and the experimental work we did on pre-breakdown phenomena in gas.

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Assembly of LIGA using Electric Fields

Feddema, John T.; Warne, Larry K.; Johnson, William Arthur.; Routson, Allison J.; Armour, David L.

The goal of this project was to develop a device that uses electric fields to grasp and possibly levitate LIGA parts. This non-contact form of grasping would solve many of the problems associated with grasping parts that are only a few microns in dimensions. Scaling laws show that for parts this size, electrostatic and electromagnetic forces are dominant over gravitational forces. This is why micro-parts often stick to mechanical tweezers. If these forces can be controlled under feedback control, the parts could be levitated, possibly even rotated in air. In this project, we designed, fabricated, and tested several grippers that use electrostatic and electromagnetic fields to grasp and release metal LIGA parts. The eventual use of this tool will be to assemble metal and non-metal LIGA parts into small electromechanical systems.

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Useful Equations for Calculating the Induced Voltage Inside a Faraday Cage that has been Struck by Lightning

Jorgenson, Roy E.; Warne, Larry K.

One of the tasks performed routinely by the Electromagnetics and Plasma Physics Analysis Department at Sandia National Laboratories is analyzing the effects of direct-strike lightning on Faraday cages that protect sensitive items. The Faraday cages analyzed thus far have many features in common. This report is an attempt to collect equations and other information that have been routinely used in the past in order to facilitate future analysis.

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Statistical Properties of Antenna Impedance in an Electrically Large Cavity

IEEE Transactions on Antennas and Propagation

Warne, Larry K.; Hudson, Howard G.; Johnson, William Arthur.; Jorgenson, Roy E.; Stronach, Stephen L.

This paper presents models and measurements of antenna input impedance in resonant cavities at high frequencies.The behavior of input impedance is useful in determining the transmission and reception characteristics of an antenna (as well as the transmission characteristics of certain apertures). Results are presented for both the case where the cavity is undermoded (modes with separate and discrete spectra) as well as the over moded case (modes with overlapping spectra). A modal series is constructed and analyzed to determine the impedance statistical distribution. Both electrically small as well as electrically longer resonant and wall mounted antennas are analyzed. Measurements in a large mode stirred chamber cavity are compared with calculations. Finally a method based on power arguments is given, yielding simple formulas for the impedance distribution.

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Lightning Induced Arcing an LDRD Report

Jorgenson, Roy E.; Warne, Larry K.

The purpose of this research was to develop a science-based understanding of the early-time behavior of electric surface arcing in air at atmospheric pressure. As a first step towards accomplishing this, we used a kinetic approach to model an electron swarm as it evolved in a neutral gas under the influence of an applied electric field. A computer code was written in which pseudo-particles, each representing some number of electrons, were accelerated by an electric field. The electric field due to the charged particles was calculated efficiently using a tree algorithm. Collision of the electrons with the background gas led to the creation of new particles through the processes of ionization and photoionization. These processes were accounted for using measured cross-section data and Monte Carlo methods. A dielectric half-space was modeled by imaging the charges in its surface. Secondary electron emission from the surface, resulting in surface charging, was also calculated. Simulation results show the characteristics of a streamer in three dimensions. A numerical instability was encountered before the streamer matured to form branching.

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Some remarks on antenna response in a reverberation chamber

IEEE Transaction Electromagnetic Capabilities

Warne, Larry K.

The simple formula, {l_angle}P{sub r}{r_angle}=(E{sub o}{sup 2}/{eta})({lambda}{sup 2}/8{pi}), for the received power of an antenna with a matched load in an over-moded cavity actually holds for an antenna of any shape and size. This can be seen from the close connection between the correlation tensor of the cavity field at two different points and the imaginary part of the free-space dyadic Green's function.

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184 Results
184 Results