Nathan J. Champagne

On attaching a wire to a triangulated surface

There have been many papers that have focused on the attachment of wires to surfaces. The focus of this paper is on wires connected to arbitrarily shaped surfaces, a body that may be modeled with triangles as described by Rao, Wilton and Glisson (1982). The basis function for the wire-to-surface junction is constructed by building the 1/r variation of the surface current near the junction into the surface current. In the following we summarize junction bases as currently used. In the presentation we consider their numerical implementation, examine alternative formulations, and review validation studies that prove the approach is robust with respect to wire orientation and surface geometry at the junction.

Measurements of glottal structure dynamics

Low power, radarlike electromagnetic (EM) wave sensors, operating in a homodyne interferometric mode, are being used to measure tissue motions in the human vocal tract during speech. However, when these and similar sensors are used in front of the laryngeal region during voiced speech, there remains an uncertainty regarding the contributions to the sensor signal from vocal fold movements versus those from pressure induced trachea-wall movements. Several signal-source hypotheses are tested by performing experiments with a subject who had undergone tracheostomy, and who still was able to phonate when her stoma was covered (e.g., with a plastic plate). Laser-doppler motion-measurements of the subjects posterior trachea show small tissue movements, about 15 microns, that do not contribute significantly to signals from presently used EM sensors. However, signals from the anterior wall do contribute. EM sensor and air-pressure measurements, together with 3-D EM wave simulations, show that EM sensors measure movements of the vocal folds very well. The simulations show a surprisingly effective guiding of EM waves across the vocal fold membrane, which, upon glottal opening, are interrupted and reflected. These measurements are important for EM sensor applications to speech signal de-noising, vocoding, speech recognition, and diagnostics.

Modeling and simulation of circuit-electromagnetic effects in electronic design flow

The goal of this paper is to describe a methodology for modeling and simulation of circuit-electromagnetic (EM) effects that fits into a current electronic design flow Our methodology is based on using time-domain macromodels implemented in a hardware description language (HDL). Simulation of the entire coupled circuit-EM system can be carried out either entirely in the HDL simulator or in a SPICE-type circuit simulator (using a model compiler for macromodel import). We also describe in detail a circuit-EM contact interface and a neutral mesh format necessary to allow for flexibility in choice of EM simulators. At each step of our methodology, we provide an overview of current problems and solutions with reference to existing publications. As a demonstration example, we consider a simple coupled system (MEMS resonator connected to a lumped circuit) and show that simulations using a VHDL-AMS macromodel match full-wave EM results but easily fit in the design flow and take significantly less time. Our methodology is straightforward and permits the use of various EM simulators and macromodel identification algorithms.

Electromagnetic interactions GEneRalized (EIGER): algorithm abstraction and HPC implementation

Modern software development methods combined with key generalizations of standard computational algorithms enable the development of a new class of electromagnetic modeling tools. This paper describes current and anticipated capabilities of a frequency domain modeling code, EIGER, which has an extremely wide range of applicability. In addition, software implementation methods and high performance computing issues are discussed.

Evaluating the gradient of the thin wire kernel

A formulation of the gradient of the thin wire kernel is presented. This formulation is useful when the observation point is close to, but not on the wire. Results are compared with previous formulations to demonstrate the accuracy of the approach. This formulation is readily applied to integrations over the wire using approaches similar to those in (Wilton, 2006).

Integrating the gradient of the thin wire kernel

A formulation for integrating the gradient of the thin wire kernel is presented. This approach employs a new expression for the gradient of the thin wire kernel derived from a recent technique for numerically evaluating the exact thin wire kernel. This approach should provide essentially arbitrary accuracy and may be used with higher-order elements and basis functions using the procedure described in [4].

A Hybrid FEM-BEM Unified Boundary Condition with Sub-Cycling for Electromagnetic Radiation

This paper details a hybrid solver using the coupled first-order equations for the E and H fields in the finite-element region. This formulation is explicit, with a restriction on the time step for stability. When this time step is used in conjunction with the boundary elements forming either an inhomogenous Dirichlet or Neuman boundary condition on the finite-element mesh, late time instabilities occur. To combat this, a unified boundary condition (UBC), for the second-order wave equation, is used. Even when this UBC is used, the late time instabilities are merely delayed if standard testing in time is used. However, the late time instabilities can be removed by replacing centroid based time interpolation with quadrature point based time interpolation for the boundary elements or by sub-cycling the boundary element portion of the formulation. This sub-cycling, for FDTD to reduce complexity, is shown here to improve stability and overall accuracy of the technique

A Finite‐Difference Frequency‐Domain Code for Electromagnetic Induction Tomography

The effect of shrapnel on target chamber components and experiments at large lasers such as the National Ignition Facility at LLNL and the Megajoule Laser at CESTA in France is an important issue in fielding targets and exposure samples. Modeling calculations are likely to be an important component of this effort. Some work in this area has been performed by French workers, who are collaborating with the LLNL on many issues relating to target chamber, experiment-component, and diagnostics survival. Experiments have been performed at the PhCbus laser in France to measure shrapnel produced by laser-driven targets; among these shots were experiments that accelerated spheres of a size characteristic of some of the more damaging shrapnel. These spheres were stopped in polyethylene witness plates. The penetration depth is characteristic of the velocity of the shrapnel. Experimental calibration of steel sphere penetration into polyethylene was performed at the CESTA facility. The penetration depth has been reported (ref. 1) and comparisons with modeling calculations have been made (ref. 2). There was interest in a comparison study of the modeling of these experiments to provide independent checks of the calculations. This work has been approved both by DOE headquarters and by the French Atomic Energy Commission (CEA); it is task number 99-3.2 of the 1999 ICF agreement between the DOE and the CEA. Daniel Gogny of the CEA who is on a long-term assignment to LLNL catalyzed this collaboration. This report contains the initial results of our modeling effort.

EIGER™ development and application to an IR frequency-selective surface

As presented in (Crruz-Cabera et al., 2008), our experimental counterparts have recently obtained exciting results for a frequency-selective surface (FSS) operating in the mid-wave to long-wave infrared frequency range. While that paper emphasizes fabrication and experimental results, it also includes a numerical validation check based on the EIGER electromagnetics simulation tool (the comparison shows favorable agreement). EIGER is a general purpose frequency-domain integral equation code that supports a variety of Greenpsilas functions (GFs), including 2D and 3D free space GFs, symmetry-plane GFs, periodic GFs, and layered media GFs. While the choice of integral equations as a modeling tool may first appear to be the most complex choice, the strength of this method lies in the fact that code generality is realized on the development of the corresponding Greenpsilas functions. In other words, the capability of integral-equation-based code to handle a wide variety of problems is obtained by incorporating more Greenpsilas functions into the software and furthermore, to complement the generality, code speedup can be obtained by taking advantage of the amenability of GFs to analytic techniques. For example, applications of EIGER at Sandia have addressed EMC and EMI problems including thin-slot coupling, periodic diffraction gratings for a petawatt laser, photonic band-gap structures, and electro- and magnetostatic problems for pulsed power and micromachine designs.

Differential forms basis functions for better conditioned integral equations

Discretized differential-forms basis functions were formulated and implemented for surface integral equation problems. Making the degrees of freedom scale invariant with element size leads to better conditioning of the system matrix for both electrostatic and frequency-domain scattering problems on meshes with a large variation in patch size.