Showing papers on "Electromagnetics published in 1997"

Genetic algorithms in engineering electromagnetics

Abstract: This paper presents a tutorial and overview of genetic algorithms for electromagnetic optimization. Genetic-algorithm (GA) optimizers are robust, stochastic search methods modeled on the concepts of natural selection and evolution. The relationship between traditional optimization techniques and the GA is discussed. Step-by-step implementation aspects of the GA are detailed, through an example with the objective of providing useful guidelines for the potential user. Extensive use is made of sidebars and graphical presentation to facilitate understanding. The tutorial is followed by a discussion of several electromagnetic applications in which the GA has proven useful. The applications discussed include the design of lightweight, broadband microwave absorbers, the reduction of array sidelobes in thinned arrays, the design of shaped-beam antenna arrays, the extraction of natural resonance modes of radar targets from backscattered response data, and the design of broadband patch antennas. Genetic-algorithm optimization is shown to be suitable for optimizing a broad class of problems of interest to the electromagnetic community. A comprehensive list of key references, organized by application category, is also provided.

Genetic algorithm optimization applied to electromagnetics: a review

Abstract: Genetic algorithms are on the rise in electromagnetics as design tools and problem solvers because of their versatility and ability to optimize in complex multimodal search spaces. This paper describes the basic genetic algorithm and recounts its history in the electromagnetics literature. Also, the application of advanced genetic operators to the field of electromagnetics is described, and design results are presented for a number of different applications.

Fast solution methods in electromagnetics

Abstract: Various methods for efficiently solving electromagnetic problems are presented. Electromagnetic scattering problems can be roughly classified into surface and volume problems, while fast methods are either differential or integral equation based. The resultant systems of linear equations are either solved directly or iteratively. A review of various differential equation solvers, their complexities, and memory requirements is given. The issues of grid dispersion and hybridization with integral equation solvers are discussed. Several fast integral equation solvers for surface and volume scatterers are presented. These solvers have reduced computational complexities and memory requirements.

Electroseismic waves from point sources in layered media

Abstract: In a porous material saturated by a fluid electrolyte, mechanical and electromagnetic (EM) disturbances are coupled. The coupling is electrokinetic in nature. The seismic waves generate relative fluid-solid motion that induces an electrical streaming current. When a seismic pulse traverses contrasts in elastic and/or fluid-chemistry properties, the streaming-current imbalance creates dipolar and multipolar charge separations across the interface that, in turn, produce EM disturbances that are measurable at the earth's surface. This paper numerically determines a full-waveform electroseismic point-source response in a stratified porous medium. It is shown that the macroscopic governing equations controlling the coupled electromagnetics and acoustics of porous media decouple into two sets corresponding to vertical or horizontal polarization of the transverse wave fields. The frequency content of the converted EM field has the same frequency content (at the generating interface) as the incident seismic pulse. Snapshots in time and converted EM amplitudes versus source to antenna offset are calculated for contrasts in mechanical and/or electrical medium properties. The converted EM radiation pattern away from the interface is similar to having an effective vertical-electric dipole centered right beneath the source on the contrast. The transverse magnetic mode amplitudes fall off rapidly with distance, from the generating interface thus suggesting the importance of a vertical electroseismic profiling geometry to record the converted EM signal at antennas close to an interface of interest.

Magnetostatic and Electrostatic Problems in Inhomogeneous Anisotropic Media with Irregular Boundary and Mixed Boundary Conditions

Abstract: Magnetostatic and electrostatic problems with mixed boundary conditions are studied. The medium can have a nonsmooth boundary and very irregular physical properties due to inhomogeneity and anisotropy. The topological assumptions are general enough to meet the requirements of the engineering applications. Necessary and sufficient conditions for solvability are found and the set of the solutions is characterized. Moreover, uniqueness is recovered by means of a finite number of supplementary conditions which are equivalent to prescribing a finite number of suitably chosen fluxes or potentials. A functional framework in which other important problems of electromagnetics naturally fit is developed.

Asymptotic methods in electromagnetics

Abstract: Ray optics search for solutions in the form of asymptotic expansions the boundary layer method spectral theory of diffraction uniform solutions integral methods surface field and physical theory of diffraction calculation of the surface impedance generalization of the notion of impedance. Appendices: canonical problems differential geometry complex rays asymptotic expansion of integrals Fock functions reciprocity principle.

Advances in complex electromagnetic materials

Abstract: I. General. II. Fundamental Issues of Bi-Anisotropic Electromagnetics. III. Continuum Modelling of Complex Media. IV. Scattering and Diffraction from Bi-Anisotropic Structures. V. Electromagnetic Modelling of Complex Particles. VI. Experiments, Measurements, Applications. List of Contributors. Index.

Challenge to Create the Space Drive

Abstract: To travel to our neighboring stars as practically as envisioned by science fiction, breakthroughs in science are required. One of these breakthroughs is to discover a self-contained means of propulsion that requires no propellant. To chart a path toward such a discovery, seven hypothetical space drives are presented to illustrate the specific unsolved challenges and associated research objectives toward this ambition. One research objective is to discover a means to asymmetrically interact with the electromagnetic fluctuations of the vacuum. Another is to develop a physics that describes inertia, gravity, or the properties of space-time as a function of electromagnetics that leads to using electromagnetic technology for inducing propulsive forces. Another is to determine if negative mass exists or if its properties can be synthesized. An alternative approach that covers the possibility that negative mass might not exist is to develop a formalism of Mach's principle or reformulate ether concepts to lay a foundation for addressing reaction forces and conservation of momentum with space drives.

A hybrid technique for the optimal design of electromagnetic devices using direct search and genetic algorithms

Abstract: Genetic algorithms (GAs) have been successfully applied to optimization problems in a variety of applications in electromagnetics. In this paper, GAs are used along with a gradient-based direct search technique. The proposed hybrid optimization procedure was found to be efficient in most of the applications. The strengths of both techniques are used at different stages of the search. A magnetizer example is presented to show the effectiveness of the proposed technique.

Electromagnetics: Theory, Techniques, and Engineering Paradigms

Abstract: Fundamentals. Elementary Solutions. Spectral Domain. Narrowband Signals and Phasor Fields. High Frequency Fields. Numerical Domain. Engineering Topics. Propagation. Engineering Topics. Radiation. Engineering Topics. Scattering. Appendices. Index.

Designing limited diffraction beams

Abstract: Theoretically, limited diffraction beams can only be produced with an infinite aperture. In practice, they can be closely approximated with a finite aperture over a large depth of field. Because of this property, these beams could have applications in medical imaging, tissue characterization, Doppler velocity estimation, and nondestructive evaluation (NDE) of materials, as well as other physics-related areas such as electromagnetics and optics. In this paper, a new method is developed to design limited diffraction beams of desired beam shapes within a finite aperture of interest. It uses previously discovered limited diffraction beams such as Bessel beams and X waves as basis functions, and constructs new beams with linear superpositions of the bases. To construct a new beam of a desired shape, coefficients of the basis functions in the linear superposition are chosen so that the difference between the new beam and a desired beam is minimized under the criterion of least-squares error within the aperture. This procedure is implemented by digitizing both the basis beams and desired beams in the aperture and solving a system of linear equations from its normal equation. The method is applied to several desired beams that are limited diffraction beams known previously. Results show that the designed beams and the desired beams are virtually identical. If the desired beams are not solutions to the wave equation, the designed beams are new limited diffraction beams that are similar in shapes to the desired beams. This suggests that the method may be a powerful and practical tool for developing new limited diffraction beams of desired properties.

Pressure Behavior of Laterally Composite Reservoirs

Abstract: This paper presents a new general method for solving the pressure diffusion equation in laterally composite reservoirs, where rock and fluid properties may change laterally as a function of y in the x-y plane. Composite systems can be encountered as a result of many different types of depositional and tectonic processes. For example, meandering point bar reservoirs or reservoirs with edgewater encroachment are examples of such systems. The new solution method presented is based on the reflection-transmission concept of electromagnetics to solve fluid-flow problems in 3D nonhomogeneous reservoirs, where heterogeneity is in only one (y) direction. A general Green`s function for a point source in 3D laterally composite systems is developed by using the reflection-transmission method. The solutions in the Laplace transform domain are then developed from the Green`s function for the pressure behavior of specific composite reservoirs. The solution method can also be applied to many different types of wells, such as vertical, fractured, and horizontal in composite reservoirs. The pressure behavior of a few well-known laterally composite systems are investigated. It is shown that a network of partially communicating faults and fractures in porous medium can be modeled as composite systems. It is also shown that the existingmore » solutions for a partially communicating fault are not valid when the fault permeability is substantially larger than the formation permeability. The derivative plots are presented for selected faulted, fractured, channel, and composite reservoirs as diagnostic tools for well-test interpretation. It is also shown that if the composite system`s permeability varies moderately in the x or y direction, it exhibits a homogeneous system behavior. However, it does not yield the system`s average permeability. Furthermore, the composite systems with distributed low-permeability zones behave as if the system has many two no-flow boundaries.« less

Genetic algorithm coupled with a deterministic method for optimization in electromagnetics

Abstract: In this paper, a hybrid technique for global optimization based on the genetic algorithm and a deterministic method is presented. A potential advantage of the hybrid method compared to the genetic algorithm is that global optimization can be performed more efficiently. An intrinsic problem of the hybrid techniques is related to the moment of stopping the stochastic routine to launch the deterministic one. This is investigated using some natural criteria for the commutation between the two methods. The results show that it is possible to gain in efficiency and in accuracy but the criterion is usually problem dependent. Finally, to show the solution of a real problem, the hybrid algorithm is coupled to a 2D code based on the boundary element method to optimize a connector of 145 kV GIS.

Active microwave signatures of snow covers at 5.3 and 35 GHz

Abstract: During the last 3 years we performed in situ backscattering measurements on various natural snow covers at 5.3 and 35 GHz (C and Ka band, respectively). Most of the measurements were made at a test site above Davos in the Swiss Alps at 2540 m above sea level (asl), but studies were conducted also at other test sites in Switzerland and Austria at heights between 500 and 2200 m asl. The backscattering coefficient γ was measured at hh, vv, hv and vh polarization, together with physical parameters of the snow cover, like snow height, stratification, temperature, density, and permittivity. On the basis of ground information and on a simple distribution of γ, we identified signatures of object classes. The signatures were used in order to evaluate the capability of active microwave sensors at 5.3 and 35 GHz for the classification of snow covers. In addition, semiempirical algorithms for the retrieval of physical parameters of the snow cover, such as water equivalent, liquid water content, and thickness of the refrozen crust, were defined.

DC resistivity mapping of old landfills: two case studies

Abstract: Geophysical investigations were carried out on two old waste disposal sites, Lernacken and Lackalanga, both situated in the province of Scania in southern Sweden. The objectives of the surveys were to map the internal structure and to delineate the extent of deposited waste, as well as to gain information about the local geology. The methods used were 2D DC resistivity, frequency domain electromagnetics (FDEM) and magnetics. The resistivity data sets were interpreted with 2D smoothness constrained inversion, and the FDEM and the magnetic data sets were contoured. The objectives were successfully met, including delineation of sludge ponds, a coastal saltwater front and geological structures, and identification of the positions of buried metal objects. In addition, at Lernacken leakage plumes were identified by the resistivity survey. The slingram EM equipment was rapid, whereas the 2D DC resistivity surveys provided valuable depth information that allowed the construction of quasi 3D models of the ground. The in-phase component in slingram measurements was especially good at localising individual metal objects, but the total field magnetic measurements also worked well.

Nonlethal Weapons: Terms and References.

Abstract: : The purpose of this paper is to promote an understanding of and research into a new category of weapons, designated nonlethal by military services, and less than lethal or less lethal by law enforcement agencies. The intent is to create an initial term and reference listing to help support joint force and dual use initiatives focused on identifying the potential drawbacks of integrating nonlethal weapons into our military services and law enforcement agencies. The paper is split into two sections: a list of terms that describes nonlethal weapons along with the concepts both surrounding and inhibiting their use, and a comprehensive listing of references to facilitate further research. Nonlethal weapons are listed under the categories of acoustics, opticals, antilethals, antiplant agents, barriers, batons, biotechnicals, electricals, electromagnetics, entanglers, holograins, markers, obscurants, projectiles, reactants, and riot control agents. Nonlethal weapons concepts are divided by the following categories: ethical, functional, operational, physiological, and theoretical.

Introduction to Optics and Optical Imaging

Abstract: Preface. ELECTROMAGNETICS FOR OPTICS: THREE VIEWPOINTS. Foundations of the Diffraction Integral Method. Foundations of the Plane Wave Spectrum Method. Foundations of Geometrical Optics. LENS ACTION FROM THREE VIEWPOINTS. Focusing and Imaging Properties of Lenses: Ray Optical Viewpoint. Focusing and Imaging Properties of Lenses: Diffraction Integral Viewpoint. Focusing and Imaging Properties of Lenses: The Plane Wave Spectrum Viewpoint. REFLECTIVE AND REFRACTIVE OPTICS. Classical Optical Imaging Instruments. Other Common Optical Components. Aberration Theory. OPTICAL INTERFERENCE PHENOMENA. Applications of the Plane Wave Spectrum Concept: Introduction to Diffraction Gratings. Introduction to Optical Moire Techniques. Interference and Interferometers. Introduction to Holography. INTRODUCTION TO OPTICAL INFORMATION PROCESSING. A Sampling of Optical Information Processing Systems Based on Fourier Plane Filtering. APPENDIXES. Appendix A: Elements of Vector Analysis. Appendix B: Theorems and Relations from Fourier Analysis. Appendix C: Vector Calculations in Source and Field Coordinates. Singularity Functions. Fresnel Integrals. Bessel Functions of Integer Order. Index. About the Author.

Multimedia Modules for Electromagnetics Education.

Abstract: Multimedia technology provides a valuable resource to enhance the teaching and learning experience. The ability to combine practical applications, visualization of complex mathematical and abstract subjects, virtual labs, and guided use of simulation software is among the advantages of technology-based education. In this article we describe the main features of several multimedia tutorials for electromagnetics education developed by the Computer Applications in Engineering Education Center at the University of Utah. The electromagnetics CD-ROM includes lessons on vectors and coordinate systems, electrostatics, Maxwell's equations, electromagnetic waves, dielectric materials, and transmission lines. Several virtual labs were developed and software packages on electrostatic, transient and steady-state analysis of transmission lines, and two-dimensional finite-difference time-domain (FDTD) simulation code are included. Tutorials can be used both as standalone tutors and as demonstrations to complement classroom lectures. © 1997 John Wiley & Sons, Inc. Comput Appl Eng Educ 5: 257–267, 1997

Progressive wave expansions and open boundary problems

Abstract: In this paper we construct progressive wave expansions and asymptotic boundary conditions for wave-like equations in exterior domains, including applications to electromagnetics, compressible flows and aero-acoustics. The development of the conditions will be discussed in two parts. The first part will include derivations of asymptotic conditions based on the well-known progressive wave expansions for the two-dimensional wave equations. A key feature in the derivations is that the resulting family of boundary conditions involve a single derivative in the direction normal to the open boundary. These conditions are easy to implement and an application in electromagnetics will be presented. The second part of the paper will discuss the theory for hyperbolic systems in two dimensions. Here, the focus will be to obtain the expansions in a general way and to use them to derive a class of boundary conditions that involve only time derivatives or time and tangential derivatives. Maxwell’s equations and the compressible Euler equations are used as examples. Simulations with the linearized Euler equations are presented to validate the theory.

Finding sphalerite at Broken Hill with drillhole magnetometric resistivity

Abstract: Lode horizons north and south of the Broken Hill, New South Wales orebody contain a number of zones rich in sphalerite and poor in galena. One example is Pasminco Mining's new opencut Potosi Mine, which averages 8.5% Zn and 2% Pb with little other sulphide. The mineralisation at the Potosi Mine has been well defined by applied potential and induced polarisation (IP) surveys, but different techniques are required for deeper, downplunge exploration. Drillhole electromagnetics (DHEM) is routinely used but may miss those zones where sphalerite is almost the only sulphide. It was therefore decided to try a series of drillhole magnetometric resistivity (DHMMR) surveys, since this method responds to contrasting, rather than absolute, conductivity. The results were very successful with the known sulphides (and some previously unsuspected zones) responding at downhole depths of more than 600 m. The method has detected mineralisation at distances greater than 150 m from the drillhole and has given clear responses to sulphides where DHEM has failed. The method has less resolving capability than DHEM, although it has proven to be more definitive where sulphide lenses occur both above and below the drillhole. The results also suggest that the magnetic field, which responds to changes in resistivity, has a much larger search radius than the phase angle, which measures the IP effect. DHMMR is expected to play a wider role in the Broken Hill district and elsewhere, in the search for sphalerite-rich orebodies.

Calibration and use of EMC antennas.

Abstract: The documentation addresses the calibration of electromagnetic compatibility (EMC) antennas in the frequency range 30 Hz to 40GHz. Guidance is given on the assessment of uncertainties in their use for EMC radiated emission measurement.

Combustion driven pulsed linear generators for electric gun applications

Abstract: Energy storage and pulse forming for electromagnetic and electro-thermal chemical guns has historically been accomplished through the use of complex power trains. Such power trains typical involve a prime power source, electrical or mechanical power conversion devices, capacitive or flywheel energy storage devices, and sophisticated switching and control elements. Kaman Electromagnetics (KEC) has developed concepts for simpler pulse power systems where chemical energy is converted more directly into an electrical output which can be utilized by an electric gun load without further conditioning. One family of devices which has shown considerable promise is the linear flux compressor. Early work with flux compressors used explosives and was suited only for microsecond duration pulses. More recent efforts utilizing propellants and even conventional hydrocarbon fuels can provide millisecond duration pulses which are well suited for electric gun type loads. Internally funded efforts indicate linear flux compressor pulse power supplies can be considerable smaller and lighter than conventional systems. This paper presents the operational principles and design issues of linear flux compressors suitable for EM guns. Point designs, performance simulations and general scaling relationships are also presented.