Showing papers on "Computational electromagnetics published in 1991"

Electromagnetic Processes in Dispersive Media

Abstract: Part I. Electromagnetic Fields in Vacuo: 1. Electromagnetic fields 2. Cartesian tensors 3. The stress tensor and multipole moments 4. Fourier transforms 5. Greens functions Part II. The Electromagnetic Responses of Media: 6. The response of a medium 7. General properties of response tensors 8. Analytic properties of response functions 9. Response tensors for some idealized media 10. Response tensors for plasmas Part III. Wave Properties: 11. Dispersion relations and polarization vectors 12. Waves in dielectrics and anisotropic crystals 13. Waves in plasmas 14. The polarization of transverse waves 15. Energetics and damping of waves Part IV. Theory of Emission Processes: 16. The emission formula 17. Emission by multipoles 18. The Larmor formula 19. Alternative treatment of emission processes Part V. Specific Emission Processes: 20. Cerenkov emission 21. Bremsstrahlung 22. Formal theory of gyromagnetic emission 23. Gyroemission by mildly relativistic electrons 24. Synchrotron emission 25. Scattering of waves by particles 26. Nonlinear emission processes Bibliographic notes Glossary of symbols Index.

Electromagnetic Compatibility: Principles and Applications

Abstract: Introduction to EMI and the electromagnetic environment introduction to E and H, near and far fields, radiators, receptors, and antennas typical sources and characteristics of radiated and conducted emissions crosstalk and electromagnetic coupling between PCB tracks, wires and cables components, emission reduction techniques, and noise immunity electromagnetic shielding cable shielding, coupling from E and H fields, and cable emissions grounding and bonding EMI measurements, control requirements, and test methods systems EMC and antenna coupling printed circuit boards EMI and EMC control, case studies, EMC prediction techniques, and computational electromagnetic modeling. Appendices: characteristic impedance of conductors, wires and cables units and conversion factors electric field strength to magnetic field to power density conversions commonly-used related formulae data on bare solid copper wire (dimensions, weight and resistance).

A scalar finite-difference time-domain approach to guided-wave optics

Abstract: A finite-difference time-domain approach that solves the scalar wave equations is proposed and validated. The propagation, reflection, scattering, and radiation of electromagnetic waves in weakly guiding optical devices are described explicitly in the time domain. The method is applied to the simulation of guided-wave devices such as directional couplers and distributed feedback reflectors. A comparison to known analytical solutions shows good agreement. >

Evaluation of corona and line models in electromagnetic transients simulations

Abstract: The main purpose of this study is to make a comparative evaluation of the large number of available corona models in terms of their accuracy and suitability for interface with the EMTP (electromagnetic transients program). The recommended models have been interfaces with the standard frequency dependent transmission line model in the EMTP. This line model has been modified to avoid error accumulation over the large number of line segments needed in corona representations. Field test comparisons have been performed and good agreement was found with a classical field test. >

Electromagnetics of superconductors

Abstract: It is shown that a superconductor cannot be simply treated as a low-loss conductor; rather, it should be treated as a negative dielectric material (with a negative dielectric constant). This approach is good only for vanishingly small field application with frequency significantly smaller than gap frequency and temperature not too close to the critical temperature of the superconductor. The electromagnetics of negative dielectric materials are discussed in terms of causality, perturbation technique, surface impedance, time-domain interpretation of current components, and computational electrodynamics. >

Automated swept-angle bistatic scattering measurements using continuous wave radar

Abstract: The establishment of the IEEE Electromagnetic Modeling Software Committee and the Department of Defense sponsored Electromagnetic Code Consortium indicates the electromagnetics community is interested in validating general electromagnetic modeling software. An important part of this validation is obtaining reliable bistatic scattering measurements on canonical scatterers. The author describes a simple system well suited for such measurements. The system is capable of measuring bistatic scattering from near backscatter through forward scatter. At X-band frequencies, scattering levels of -50 dBsm in the backscattering region and -20 dBsm near forward scatter can be measured to an accuracy of +or-1 dB. This fully automated indoor system fixes the target and direction of illumination and sweeps the receive antenna to collect data as a direct function of bistatic angle. A broad band, coherent, continuous wave radar is used to obtain both amplitude and phase of the component of the total field aligned with the receive antenna polarization. The system design, calibration procedures, and measurement accuracy are considered. >

A hybrid finite element method for near bodies of revolution (EM scattering)

Abstract: A genetic formulation for a hybrid finite element solution for three-dimensional electromagnetic scattering is given using the equivalent current approach. The major computational tasks involved in monostatic scattering calculations are analyzed and compared as a function of the method of implementing the near-field radiation condition, i.e. method of moments, model expansion, and body of revolution (BOR). A method utilizing a BOR formulation that addresses these computational issues is given. This BOR implementation utilizes Hermite cubic basis functions and a variable number of modes per basis function in order to achieve the greatest efficiency. The combined field integral equation formulation is used to eliminate nonphysical resonance of the mesh boundary. Examples are given showing the efficiency and accuracy of this BOR code by itself, and as part of this hybrid finite-element method. >

Equivalence of propagation characteristics for the transmission-line matrix and finite-difference time-domain methods in two dimensions

Abstract: The equivalence of propagation characteristics for the transmission line matrix (TLM) and finite-difference-time-domain (FD-TD) methods in two dimensions is discussed. A propagation analysis of a TLM shunt node complete with permittivity and loss stubs and a dispersion analysis of the two-dimensional FD-TD method in an arbitrary medium are performed and yield dispersion relations. The relations are identical when the FD-TD method is operated at the upper limit of its stability range. >

Introduction to electromagnetic wave propagation

Abstract: General principles electromagnetic wave propagation sky-wave propagation propagation of electromagnetic waves of the various frequency ranges noise and the signal-to-noise ratio radio link design considerations.

Electromagnetic radiation from a VLSI package and heatsink configuration

Abstract: The electromagnetic radiation from a very large scale integration (VLSI) chip package and heatsink structure is analyzed by means of the finite-difference-time-domain (FD-TD) method. The FD-TD algorithm implemented incorporates a multizone gridding scheme to accommodate fine grid cells in the vicinity of the heatsink and package cavity and sparse gridding in the remainder of the computational domain. The issues pertaining to the effects of the heatsink in influencing the overall radiating capacity of the configuration are addressed. Analyses are facilitated by using simplified heatsink models and by using dipole elements as sources of electromagnetic energy to model the VLSI chip. The potential for enhancement of spurious emissions by the heatsink structure is illustrated. For heatsinks of typical dimensions, resonance is possible within the low gigahertz frequency range. The potential exploitation of the heatsink as an emissions shield by appropriate implementation schemes is discussed and evaluated. >

Spurious modes of the TLM-condensed node formulation

Abstract: The TLM (transmission line matrix) method is based on temporal and spatial sampling of electromagnetic fields. As with he FDTD (finite-difference-time-domain) method, this results in dispersive effects and propagating spurious modes that corrupt the field solution. The general dispersion relation for the TLM condensed node is used to quantify the propagation attributes of these spurious modes. The propagating and evanescent spurious modes of the condensed TLM node formulation are derived. When the condensed node mesh is applied to problems involving scattering or source structures that have feature dimensions of several lattice spacings, high-order spatial modes are generated. These modes suffer significant dispersion effects. If the spatial frequency of the mode is sufficiently high, it will propagate as a spurious node with an incorrect propagation constant and in some cases with no loss. Spurious modes may have positive or negative group velocities. >

Time-domain finite methods for electromagnetic wave propagation and scattering

Abstract: Time-domain finite methods are considered by many as good candidates for the powerful, versatile, and accurate numerical simulation of complex electromagnetic phenomena. However, some concerns still remain about the accuracy of these methods, and questions keep being raised about their modeling versatility. By reviewing the key characteristics of several of these finite methods, and considering the various sources of the associated discretization and numerical error, it is argued that their proper use permits the accurate modeling of electromagnetic scattering and propagation phenomena associated with structures of electrical size and complexity beyond the capabilities of present frequency-domain finite and integral equation methods. >

Low-frequency computational electromagnetics for antenna analysis

Abstract: An overview of computational methods for modeling the low-frequency electromagnetic characteristics of antennas is given. Presented first is a brief analytical background that forms the basis for numerically solving low-frequency antenna problems using the method of moments. Next discussed are extensions to modeling perfectly conducting objects in free space, followed by a consideration of some computational issues that affect model accuracy, efficiency, and utility. A variety of representative applications is given to illustrate various aspects of modeling and capabilities that are currently available. A fairly extensive bibliography is included. >

Analysis of electromagnetic scattering from linear periodic arrays of perfectly conducting bodies using a cylindrical-current model

Abstract: A novel solution is presented for the problem of three-dimensional scattering of a time-harmonic plane wave from a infinite periodic linear array of finite-size perfectly conducting bodies. A set of fictitious sources comprising periodic and properly modulated cylindrical electric current sheets of cross polarization is used to simulate the scattered field. The complex amplitudes of these fictitious sources are adjusted to render the tangential component of the electric field zero at a selected set of points on the surface of one of the scatterers. The suggested solution procedure is simple to implement and is applicable to linear periodic arrays composed of disjoint bodies of smooth, but otherwise arbitrary, shape. The accuracy of the method is demonstrated. It is shown that in the limiting case of widely spaced spherical scatterers the numerical solution agrees well with an approximate analytic solution. >

Integral Equation Formulation of Electromagnetic Scattering by Nonlinear Dielectric Objects

Abstract: This paper deals with electromagnetic scattering In the presence of nonlinear dielectric objects. The Introduction of equivalent source terms makes it possible to describe the electromagnetic field by an integral formalism which takes into account nonlinear effects by solving inhomogeneous wave equations through specific dyadic Green functions. Examples of application to nonlinear scattering objects, In free space and In a rectangular waveguide, are considered. The related integral problems are reduced to nonlinear systems of algebraic equations. Results of some computer simulations Involving simple scattering objects are also reported.

Picosecond time-domain electromagnetic scattering from conducting cylinders

Abstract: The microwave scattering properties of conducting cylinders are characterized by measuring their response to picosecond-duration electromagnetic pulses. The ultrafast electromagnetic transients are generated and detected with optoelectronically pulsed antennas. The time-domain response gives physical insight into the scattering process. In addition, Fourier analysis is used to obtain the frequency dependence of the scattered amplitude and phase from 15 to 140 GHz. >

A finite element analysis of an electromagnetic flow control valve

Abstract: The behavior of an electromagnetic control valve under a perturbative magnetic field is evaluated. The electromagnetic valve is numerically modeled by means of a nonlinear 2D field-element code. The electromagnetic force produced on the valve's plug is obtained using the Maxwell stress tensor approach, under both normal and perturbed conditions. The numerical results are compared with those of experimental tests, which have been carried out under the same conditions as the numerical analysis. >

Model-Based Parameter-Estimation Applications in Electromagnetics

Abstract: Numerical modeling in electromagnetics, whether based on integral, differential, or other formulations, inevitably involves a discretized, sampled-field description of the physical reality which is being modeled These descriptions exhibit a commonality with signal processing and model-based parameter estimation in terms both of sampling requirements, information content and system rank, and the role of difference-equation linear predictors This discussion surveys some aspects of computational electromagnetics from a parameter-estimation viewpoint, emphasizing the variety of ways in which an exponential-series model can arise

On the connection of T matrices and integral equations

Abstract: The authors describe the connection between the major numerical techniques of computational electromagnetics. These are the T-matrix methods and the surface- or volume-integral-equation methods. Both homogeneous (e.g., guidance, resonance) and inhomogeneous (e.g.. scattering) equations can be solved with these two methods. The recursive T-matrix algorithms have been applied to the electromagnetic problem of scattering from ten strips of width w and spacing d=2w. >

On the analytical equivalence of electromagnetic fields solutions from a known source distribution

Abstract: An analytical proof of the equivalence of solutions from monopole and dipole techniques is presented for electric and magnetic fields by a simple lightning model. The proof is in the context of the lightning problem as stated by M. Rubinstein and M.A. Uman (1989). The expressions for the electric and magnetic fields are simplified considerably. >

Near field interaction of microwave signals with a bounded plasma plume

Abstract: The objective was to study the effect of the arcjet thruster plume on the performance of an onboard satellite reflector antenna. A project summary is presented along with sections on plasma and electromagnetic modeling. The plasma modeling section includes the following topics: wave propagation; plasma analysis; plume electron density model; and the proposed experimental program. The section on electromagnetic modeling includes new developments in ray modeling and the validation of three dimensional ray results.

New finite element formulation for 3-D scattering problems

Abstract: A mode-based finite-element formulation for the solution of 3D electromagnetic scattering problems is presented. The main idea of this formulation is to use different state variables for regions occupied with different materials. This allows one to circumvent the difficulties of satisfying interface boundary conditions by using conventional node-based finite elements. This also facilitates far-field computations. >

Electromagnetic interaction with a magnetic coated elliptic cylinder

Abstract: A solution for scattering of plane electromagnetic waves from a permeable elliptic cylinder with a confocal coating material is considered. The solution is formulated in terms of infinite series of Mathieu and modified Mathieu functions with unknown expansion coefficients. These coefficients are determined by enforcing exact boundary conditions on the total fields at the core and the coating surfaces. Numerical calculations are carried out for different cases including, as limiting cases, perfectly conducting objects and homogeneous objects as well as objects with circular cross sections and thin objects. >

Electromagnetic Borehole Fields In a Layered, Dipping Bed Environment With Invasion

Abstract: Electromagnetic modeling of an induction sonde (1–100 kHz) in a dipping‐bed environment is a 3-D problem. The capability for such an analysis is necessary for interpretation of oil‐well logs in offshore environments where most holes are deviated. 3-D geometrical effects require vector field analysis. The method accounts for transverse magnetic mode (TM) coupling arising from surface charges deposited by eddy currents passing through bed boundaries. If borehole and invasion effects are included, the only available rigorous analytical methods are finite elements or finite‐difference techniques. These approaches require large‐scale computing. In contrast, our method is approximate and is an extension of the geometrical‐factor theory and Born approximation. The variational method does not require matrices and is numerically simpler than the more rigorous finite element method. The method uses a new electric field vector integral equation developed by Chew. The formulation accounts for low‐frequency behavior a...

A high level compiler for the electromagnetic modeling of complex circuits by geometrical partitioning

Abstract: An electromagnetic geometrical compiler is introduced. The compiler takes the structure being investigated and breaks it down into blocks via many levels of structural decomposition. The structure is then analyzed from the bottom up using the method of moments. Using this procedure, large and complex structures can be analyzed quickly using little computer memory. >

Transient diffusive electromagnetic fields in layered anisotropic media

Abstract: The structural problem of the diffusion of transient electromagnetic fields in a stratified arbitrarily anisotropic conducting earth is investigated. In order to solve the equations governing the behavior of diffusive electromagnetic fields, an analytical method is developed based on the modified Cagniard method. Numerical results are presented. It is noted that one of the main advantages of using the modified Cagniard method is that it yields exact expressions in which arbitrary anisotropy is accounted for in the same way as isotropy, the only difference being that in the latter case simple and well known results can be obtained explicitly. >