EM Theory Research Articles

A functional scaling approach to electromagnetic scattering by particulates: theory and algorithms for spheres and cylinders

A functional scaling approach to computing the electromagnetic (em) scattering coefficients ( a n , b n ) is described and used to develop a unified theory of em scattering for infinite cylinders and spheres. Scattering algorithms based on the unified theory and scaled Bessel functions are described.

Parabolic function expansion and its application to EM theory

A parabolic function expansion for an arbitrary function in L 2 space is derived with the aid of the classical eigenfunction expansion theory of Titchmarsh. The Green's function in free space in terms of the parabolic function is expanded as an example. The theory is then applied to the integral transform of the Helmholtz equation in paraboloidal coordinates.

Unusual boundary conditions at an interface (EM theory)

The derivation of electromagnetic boundary conditions at an interface by applying Gauss' divergence theorem to a flat pillbox or Stokes' curl theorem to a narrow contour is considered for two types of unusual boundary condition. One is an electric field discontinuity and the other is a double layer of current. It is suggested that the usual continuity proofs, based on pillboxes and contours of vanishing dimension, must be handled with care. Specifically, a ' delta function' behavior of certain components along the normal is possible. >

Measurement of the microwave conductivity of a polymeric material with potential applications in absorbers and shielding

The microwave conductivity of a new material, the polymer poly-p-phenylene-benzobis-thiazole (PBT) made conductive by ion-implantation doping with iodine, is measured at 9.89 GHz as a function of temperature using the cavity perturbation technique applicable to thin films of arbitrary shape. The DC and microwave conductivities of PBT are seen to approach asymptotically the low-temperature limit predicted by Mott's energy-dependent hopping model. The potential utilization of conductive polymers in microwave absorbers and electromagnetic interference (EMI) shielding is examined using layered media EM theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Emergency and operational low and medium frequency band radio communications system for underground mines

A minewide low and medium-frequency radio system has been developed and installed in coal and metalliferous mines. The radio system utilizes two robust radio signal transmission modes to establish underground radio coverage areas. The seam transmission mode occurs when layers in the ground form a natural waveguide. The conductor transmission line mode waveguide occurs when electrical conductors, such as AC power distribution cables, are in place in mine passageways. The author describes the development history of MF band technology during the past five decades in South Africa, Europe, and the United States. How EM wave theory guided the design and development of the conductor transmission line repeater network and associated mobile radio equipment is discussed. The safety and cost reduction benefits of a practical radio system are also described. >

On the relationship between the MoM and the GMT [EM theory

The method of moments (MoM) is compared with the generalized multipole technique (GMT), which has been shown to be very efficient. Although the GMT can be considered to be a variant of the MoM, it is based on a completely different philosophical foundation. Both the foundation and concrete implementations are considered. It is shown how the MMP code, based on the GMT, can profit from MoM concepts, and how MoM codes can profit from GMT ideas. >

Electromagnetic polarization and its expression

AbstractBefore 1950, Maxwell's phenomenological theory was used widely in the study of electromagnetics. In spite of the number of works published, none of them adopted electron theory to the study of electromagnetics.Not until after 1950 did the electron theory become popular among electromagnetic researchers. The author has developed an axiomatic electromatic theory (hereafter called EM theory) in which Lorentz' electron theory was taken as one of the axioms.This paper clarifies the problem in the old definitions of polarization and proposes a new definition using formulas which hold rigorously at the microscopic level. Based on this definition, the physical and mathematical meanings of polarization are clarified to establish firmly the EM theory.

Reply to J.R. Waits 'In defense of Stratton' (EM theory)

Additional comments on an ongoing controversy on Maxwell's equations are presented. Harmuth (see ibid., vol.EMC-30, no.1, p.90, 1988) claims that three scientists searching through Stratton's (1941) book could not find equations for the magnetic field strength associated with an electric excitation force or the electric field strength associated with a magnetic excitation force. >

Case histories and modelling interpretation in CSAMT

Two CSAMT case history studies are presented in which modelling has been applied to data in order to produce geo-electric depth sections. These sections then assist in developing an idealized geologic model used as part of a geological exploration programme. At the geological planning level, one can define certain key geologic features which need to be identified as part of an exploration programme. Modelling may give some indication as to the success of a particular planned geophysical programme.At the interpretation level, modelling can be used to confirm or disprove geologic ideas previously developed, and aid in quantifying features that survive the test. In addition, modelling may give new insights on how to get more information from the geophysical data and give rise to new ideas.The case history information comes from the Golden Cross mine development programme near Waihi, New Zealand, and from the Togi exploration programme conducted near Kanazawa on the island of Honshu, Japan. While the distance separating the two survey sites is great, they are both epithermal gold prospects. CSAMT was used to obtain high resolution structural mapping both for near-surface geology and geology at depth, which are two important tasks.Modelling of the CSAMT data obtained at Golden Cross and Togi is provided by three different computer programmes: CSINV is a one-dimensional general EM field approach using a finite number of layers where the survey geometry is specified; a variation of CSINV uses an infinite number of one-dimensional layers; and EM2D is a two-dimensional approach using a finite number of bodies/layers based on plane-wave EM theory. All three modelling approaches provide resistivity values varying as a function of depth, however useful results with EM2D are limited to modelling frequencies where data satisfies plane-wave criteria.Modelling at Golden Cross provides cross-sectional geoelectric information which extends known drill-hole geology. This provides broader detail to known information, and suggests additional potentially interesting features. Modelling at Togi was directed at providing plan view coverage of certain geologic structures. Here one survey objective of the CSAMT survey was to provide structurally related control to be used with interpretation of geochemical data.Even though targets are geologically similar, planning and interpretational goals differed. CSAMT modelling optimized the interpretational use of CSAMT data in each case history.

Moments and force densities of the electrodynamic levitation system

Theoretical predictions of the moments and the force density distributions on the superconducting magnet and on the conducting sheet guideway are given for the reference levitation system design proposed for the Canadian Maglev vehicle. The theoretical method is based on the Lorentz force, \tilde{J} \times \tilde{B} and the solution follows from a combination of the dynamic circuit theory and the EM field theory already developed. Very good correlations are found with the moments measurements already published. The data from the predictions are important for vehicular mechanics analysis and for mechanical structural design of fastenings and bracings.

Teaching Electromagnetic Theory to Electrical Engineering Undergraduates

Electromagnetic theory is usually an integral part of the undergraduate curriculum in Electrical Engineering in our universities. It is also usually the subject least-liked by students. For a long time, EM theory has been taught to undergraduates with an overwhelming bias towards communication. Unfortunately, in a first EM theory course, it is difficult to bring out interesting and practical communication engineering examples to motivate the students and sustain their interest So it turns out that the major portion of the first basic course in EM theory becomes mainly the exposition of physical concepts through mathematical manipulations. Many concepts in EM theory are taught without any reference to their applications and students have to wait till much later to learn these applications. This does not make good engineering teaching.If the first course in EM theory is taught in its own right without being made an appendage of communication engineering, it can be made interesting by bringing into the course the numerous practical applications from electro-mechanics and magneto-mechanics.Several observations have been made here which may be useful in making the first course in electromagnetics an interesting one for electrical engineering undergraduates.

Computer-Managed Instruction in Electromagnetic Field Theory

This paper discusses the application of computer-managed instructional techniques in an introductory electromagnetic field theory course being taught to all undergraduate students in the College of Engineering at The University of Iowa. In the process of preparing the various computer lessons, we found ourselves faced first with the need to carefully appraise what we wished the students to learn and then to consider appropriate teaching strategies for achieving the desired objectives. Our approach to computer assisted instruction takes several different forms, including use of drill and practice modules, tutorial segments, computer-administered quizzes, and field visualization through interactive computer graphics. Our computer-managed instructional materials complement the more traditional forms of instruction being used in EM theory, rather than replacing them. In this way we seek to provide alternatives designed to suit the different learning needs of our students.

Variational formulation of the relativistic theory of microelectromagnetism

By adjoining a set of adequate potentials to the classical electromagnetic potential, it is possible to formulate a variational principle that yields the equations of the micromorphic EM theory proposed by Eringen and Kafadar [J. Math. Phys. 11, 1984 (1970)]. The energy-momentum law for micromorphic EM fields is obtained and constitutive equations are derived for relativistic EM-elastic fields.

Obsolete Factors in the International Economy or Why Tortoises Never Beat Mechanical Rabbits

Mr. Hudson's paper attempts a sweeping explanation of what still the modern world's greatest problem: the relative stagnation in destitu? tion of a third to a half of mankind. Such a paper must of necessity have its faults, some serious, but no critique of them, however justified, can be a substitute for or be allowed to obscure a confrontation of the main argument. Unfortunately, Mr. Hudson, himself, too diverting with irreverent swipes at received classical and neo-classical trade theory. I tend to share his iconoclasm, but in view of the strong opposition, which, I presume, his Obsolescence and Ghetto theses invite, a more irenic challenge would have been more effective. Theorists who apparently accept for their analytical framework the Heckscher-Ohlin-Stolper-Samuelson (HOSS) model are simply not as naive and do not believe it has as much hoss power, at least in policy matters, as Hudson implies. In G. M. Meier's The International Economics of Development,1 probably the best and most recent compendium of the literature, one finds extremely judicious and cautious reasoning from theory and little neglect of em? pirical findings, such as they are. Still, in fairness to Mr. Hudson, the new conventional subtleties are ever so gently, but naggingly persistent, if not biased, in reminding poor countries of the dangers of ill-afforded losses from trade restrictions, of the logically valid, but . infant economy case, and so on. Neo-classical theorists may admit, though not entirely, to the justice of Mr. Hudson's critique of the HOSS model, but they typically retreat to a methodological citadel which to them seems impregnable whereas it may be more an indication of intellectual impermeability. As Harry G. Johnson puts it, Fundamentally, the theorem, what I call the HOSS model, is not a prediction concerning the real world. Rather it must be interpreted as an enumeration, deduced by the process of theo? retical abstraction, of the factors that are present in the real world and prevent the realization of factor-price equality, an equality which would characterize world economic efficiency.2 In effect, the economist's mis 153

On calculating transient electromagnetic fields of a small current-carrying loop over a homogeneous earth

The basic theory of airborne EM surveying, in the time domain, is considered. Rather than resorting to tediousdouble numerical integration, a more direct approach is adopted. This method, valid in the quasi-static regime, is illustrated for a homogeneous flat earth. The results exhibit a number of clear-cut features that are relevant to remote sensing. For example, a vertical co-axial loop system has a desirable transient response from the standpoint of yielding conductivity data without requiring accurate information on the height of the device above the ground.