New Publications are available for Electromagnetic fields
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New Publications are available now online for this publication.
Please follow the links to view the publication.Using CAEME Software Book in teaching and research
http://dl-live.theiet.org/content/conferences/10.1049/ic_19980589
The CAEME (Computer Applications in ElectroMagnetic Education) Centre, supported by the IEEE and the US National Science Foundation, has launched two volumes of the CAEME Software Book (edited by M.F. Iskander: vol. I, 1991, and vol. II, 1995) as an initiative to stimulate and accelerate the use of computers and software tools in engineering education, particularly in the electromagnetism area. The CAEME Software Book, comprising a total of 32 packages, four multimedia lessons and two videotapes, covers almost all the topics in electromagnetics education. The book is distributed on a university membership programme basis, and has been generally well received by over 500 universities in over 30 countries. This paper briefly describes the CAEME Software Book and our experience of using CAEME in teaching and research at King's College, London. It is hoped that this might result in some interest and more widespread use of the CAEME Software Book in UK universities. (5 pages)Overview of the Research and Engineering Framework (REF) for computational electromagnetics
http://dl-live.theiet.org/content/conferences/10.1049/cp_19960165
The paper presents an overview of the REF architecture, its functionality and its capabilities. Also included is a description of how the REF can be applied to the codes and requirements of the CEM community.Efficient evaluation of singular and infinite integrals using the tanh transformation
http://dl-live.theiet.org/content/journals/10.1049/ip-map_19941543
The application of the tanh transformation in the efficient and accurate evaluation of singular integrals is considered. It is shown that the transform can also be utilised in the efficient computation of infinite integrals. Several numerical examples illustrate the usefulness of the method in computational electromagnetics.Editorial: Computers and Devices for Communication (CODEC 04)
http://dl-live.theiet.org/content/journals/10.1049/ip-cds_20059073
Wavelet-based preconditioner for three-dimensional electromagnetic integral equations
http://dl-live.theiet.org/content/journals/10.1049/el_20001481
A wavelet-based method is proposed to effectively precondition 3D electromagnetic integral equations. The approximate-inverse preconditioner is constructed in the wavelet domain where both the moment matrix and its inverse exhibit sparse, multilevel finger structures. The inversion is carried out as a Frobenius-norm minimisation problem. Numerical results on a 3D cavity show that the iteration numbers are significantly reduced with the preconditioned system. The computational cost of the preconditioner is kept under <i xmlns="http://pub2web.metastore.ingenta.com/ns/">O</i>(<i xmlns="http://pub2web.metastore.ingenta.com/ns/">N</i>log<i xmlns="http://pub2web.metastore.ingenta.com/ns/">N</i>).Group theoretical approach to determine structure of complex and composite media constitutive tensors
http://dl-live.theiet.org/content/journals/10.1049/el_19980029
A group theoretical approach to the determination of the structure of the constitutive tensors of complex and composite media is suggested. The tensors are derived using the space-time symmetry of the media. Applications of the theory are discussed.The electrical stability of tubular inductance coils with deposited conductors
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1940.0065
Electro-physics
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1930.0003
The use of the Grassot fluxmeter as a quantity meter: its application to the determination of the moment of intertia of a small direct-current armature
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1935.0020
The question of the measurement of the quantity of electricty passed through a circuit in a given time is intimately connected with the magnitude of this time of passage. The paper describes the use of a Grassot fluxmeter for such measurements and gives the theory of the instrument when so used. It is shown that this instrument provides a useful intermediary when the time of passage is such that neither the ballistic galvanometer nor the ampere-hour meter can be used successfully.The determination of the moment of inertia of a small d.c. armature, using a fluxmeter, is described, and the results obtained are verified by two alternative methods of determination.Electromagnetic field near the focus of wide-angular lens and mirror systems
http://dl-live.theiet.org/content/journals/10.1049/ij-moa.1977.0015
The time-averaged electric energy density near the focus of a parabolic mirror of wide-angular aperture is calculated and compared with that of an aplanatic lens system. The distributions exhibit great differences, the mirror showing a greater departure from circular symmetry, a more complicated structure and increased sidelobes. The vectorial integral representation of Wolf is derived from the Stratton-Chu formula.The stability of inductance coils for radio frequencies
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1935.0197
The paper gives an account of an investigation into the stability of inductance of coils used in radio transmitters and valve oscillators. It is shown that variation of temperature is chiefly responsible for instability, and data are obtained showing the value of the temperature coefficient of inductance for a number of modern coils of representative types, from which it is observed that this coefficient differs appreciably from the coefficient of expansion of the metal conductor.A theoretical investigation is made of the inductance variation produced by small changes in self-capacitance and in dimensions, together with an examination of the causes of mechanical distortion with temperature change. A critical study of existing methods of temperature compensation is presented and conditions for stability are established.As a result of the investigation, an experimental coil is described in which high stability is obtained by the application of these principles.The dependence on frequency of the temperature-coefficient of inductance of coils
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1939.0022
Evidence is given that the temperature-coefficient of inductance ofcoils is dependent on frequency, owing to the change with temperature of the current distribution over the conductor cross-section. The effect is of importance only over a limited range of section for any particular frequencyband. The theory1 of the effect is examined for circular-section conductors. It is shown that in all self-supporting helical coils suitable for short-wave work, where the conductor radius is greater than 0-1 cm., the effect of change of current distribution with temperature-change is such that no appreciable increase of temperature-coefficient of inductance occurs. For coils wound with very fine wire the temperature-coefficient of inductance is not affected appreciably by change of current distribution. The effect of temperature on the current distribution and consequently on the coefficient of inductance is appreciable only when the conductor radius lies between thelimits 0–001 and 0–2 cm. In such cases the coefficient has a component due to this effect which may be quite high dver an appreciable frequency band. This condition occurs in practice with deposited or sprayed-on conductors. The temperaturecoefficient of inductance of coils having a conductor section within the denned range reaches a maximum value at a particular frequencyand is less at frequencies above and below this value. Experimental verification is given of the conclusion arrived at in the theoretical discussion, together with an explanation of the behaviour of certain coils having ceramic formers. The conclusions arrived at from a study of such coils are applied to the design of coils suitable for use at high radio frequencies, and it is shown that the best type of construction from the point ofview of electrical stability is one in which the radial thickness of the conductor is small compared with the radius of the turn while the axial spacing is large.The effective inductance and resistance of screened coils
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1940.0135
In this paper an effort has been made to determine simple and workable formulae for the changes produced in the characteristics of an air-core coil by placing it in a screening container. The formulae, which have been derived empirically, are based upon the simplified case of a solenoidal coil of infinite length, placed coaxially in an infinitely long cylindrical screen. Another simplification, namely that of regarding the coil-and-screen system as a fiat band of wires placed parallel to a conducting plane, is also mentioned, and from these two simple cases it has been possible to proceed, by application of the results of measurement, to formulae for inductance and resistance change so simple that they almost amount to workshop rules. These formulae are shown to cover all practical cases of finite coils and coaxial screens to an accuracy within 2%.The effects of proximity of ends, small deformations and displacements, and temperature changes, are also examined and estimated.The shape of the curve of eddy-current distribution in the screen is examined, and it is found that the shape of curve derived from search-coil measurements is very similar to that derived from calculation on the basis of regarding the coil as a flat system.The M.K.S. system of electrical units
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1936.0040
The M.K.S. system of units
http://dl-live.theiet.org/content/journals/10.1049/jiee-1.1936.0039
Discussion on “A short modern review of fundamental electromagnetic theory”
http://dl-live.theiet.org/content/journals/10.1049/pi-b-1.1955.0138
The calculation of the magnetic field of rectangular conductors in a closed slot, and its application to the reactance of transformer windings
http://dl-live.theiet.org/content/journals/10.1049/pi-4.1951.0007
The magnetic vector potential of current-carrying conductors in a rectangular slot is the same as that due to an infinite number of images of these conductors from all the four walls of the slot. A solution of this problem can thus be obtained in the form of a Fourier series, periodic in both the <i xmlns="http://pub2web.metastore.ingenta.com/ns/">x</i>- and <i xmlns="http://pub2web.metastore.ingenta.com/ns/">y</i>-directions, the constants of the solution being determined by the boundary conditions, i.e. by the dimensions of the slot and of the conductors, and by the currents passing through them. Expressions for the magnetic vector potential due to any conductor arrangement can thus be developed, and these lend themselves to considerable simplification without undue loss of accuracy. Lines of magnetic flux density correspond to constant values of the vector potential, and this yields a ready method for plotting magnetic-flux maps. The results of this investigation can, with certain assumptions, be directly applied to transformer reactance problems and also to the equivalent problem of heat conduction of windings embedded in the slots of electrical machines. Formulae are developed for the reactance and forces in concentric-winding arrangements, showing the effects of slight asymmetries.Discussion on “A short modern review of fundamental electromagnetic theory”
http://dl-live.theiet.org/content/journals/10.1049/pi-a.1957.0024
Discussion on “A short modern review of fundamental electromagnetic theory”
http://dl-live.theiet.org/content/journals/10.1049/pi-a.1956.0051
Discussion on “A short modern review of fundamental electromagnetic theory”
http://dl-live.theiet.org/content/journals/10.1049/pi-a.1955.0138
A method of series summation and its application to the electric force in sphere-gaps
http://dl-live.theiet.org/content/journals/10.1049/pi-c.1959.0026
The paper sets out a simple procedure of general application whereby any function represented by a power series may be replaced by a sequence of rational functions, the advantage of such representation being that in many cases the rational functions converge much more rapidly than does the series. It often happens that the rational-function form continues to represent the given function accurately for values of the argument which make the series form diverge.The procedure is illustrated with a worked example, and the method is then applied to determine a simple expression for the maximum electric intensity between two equal charged spheres, when the sphere-gap is small compared with the diameters.Electromagnetic momentum and electron inertia in a current circuit
http://dl-live.theiet.org/content/journals/10.1049/pi-c.1956.0019
In the second volume of his “Treatise on Electricity and Magnetism” Clerk Maxwell developed the theory of electric current-circuits from general dynamical principles, and discussed the experimental effects which should occur if an electric current is a true motion of some substance possessing inertia. Since none of these effects had at that time been observed, Maxwell developed his general electromagnetic theory on the assumption that they do not exist, or at least that they produce no sensible effect.It is now known, however, that an electric current in a conductor consists of moving electrons, and the inertia effects which were discussed by Maxwell have been observed experimentally. They are extremely small, and have not been brought within the scope of electromagnetic theory. A conduction current is usually assumed to be due to the drifting along the conductor, with a very small mean velocity, of all the available conduction electrons, so that the kinetic energy of the electrons due to this motion is negligible in comparison with the magnetic energy of the current. Electron-inertia effects in current circuits have therefore been accepted as something outside classical electromagnetic theory—a position which is illogical if, as is usual, we identify the kinetic and magnetic energies of a free electron.It is shown in the paper that it is possible to identify the kinetic energy of the conduction electrons in a current circuit with the magnetic energy of the current, so that electron-inertia effects can be included in the general electromagnetic scheme. In consequence, a current circuit can be said to possess an electromagnetic mass whose motion, when current flows, entails electromagnetic momentum. This momentum accounts for the known effects of electron inertia and also for the force on the end wire of a long rectangular circuit.The relativistic form of the theory indicates the possibility that electromagnetic laws may depart from the classical form, becoming non-linear in circuits where a high inductance per unit length of conductor is combined with a current greater than is usually found in practice.The inadequacy of classical theory also extends to the known electromagnetic properties of superconductors, and the present hypothesis suggests the possibility of a unified theory in which there would be no necessity to distinguish between a superconductor and a perfect conductor.M.K.S. formulae for electromagnetism
http://dl-live.theiet.org/content/journals/10.1049/jiee-3.1960.0154
Discussion on “A short modern review of fundamental electromagnetic theory” before the North-Western Centre, at Manchester, 2nd March, 1954
http://dl-live.theiet.org/content/journals/10.1049/pi-b-1.1955.0062
Discussion on “Development of the formulae of electromagnetism in the M.K.S. system” before the Measurement and Control Section, 2nd February, and the Southern Centre at Portsmouth, 24th February, 1960
http://dl-live.theiet.org/content/journals/10.1049/pi-b-2.1960.0125
The author's reply to the discussion on “Development of the formulae of electromagnetism in the M.K.S. system”
http://dl-live.theiet.org/content/journals/10.1049/pi-b-2.1960.0126
Development of the formulae of electromagnetism in the M.K.S. system
http://dl-live.theiet.org/content/journals/10.1049/pi-b-2.1960.0124
The use of metres, kilogrammes, amperes, etc., instead of centimetres, grammes, deca-amperes (the C.G.S. unit of current), etc. need not change the method of teaching electricity and magnetism, for it does not interfere with the notions of magnetic poles and point charges of electricity. A logical method of developing the theory from conventional experiments on the forces between magnets, between magnets and current-carrying loops, and between electric charges, is to proceed from magnetic poles to magnetic shells and from these to loops of current, and then bring in the definition of the ampere to evaluate the magnetic constant; consideration of the forces between electric charges follows and, together with identification of rate of change of charge and electric current, leads to the law of induction, to Maxwell's equations, and to wave propagation, which, in conjunction with the known velocity of light, gives the value of the electric constant. The theory is then extended to material media.A treatment suitable for beginners is outlined in Section 9.The use of Bessel functions for calculating the self-inductance of single-layer solenoids
http://dl-live.theiet.org/content/journals/10.1049/jiee-2.1949.0048
Diffraction of electromagnetic waves by two parallel half-planes
http://dl-live.theiet.org/content/journals/10.1049/jiee-2.1953.0236
Discussion on “A short modern review of fundamental electromagnetic theory”
http://dl-live.theiet.org/content/journals/10.1049/pi-b-1.1956.0115
Discussion on “A short modern review of fundamental electromagnetic theory”
http://dl-live.theiet.org/content/journals/10.1049/pi-b-1.1956.0250
A short modern review of fundamental electromagnetic theory
http://dl-live.theiet.org/content/journals/10.1049/jiee-2.1954.0078
Mechanical analogue of electron spin inversion and maser action with a simple description of maser operation
http://dl-live.theiet.org/content/journals/10.1049/piee.1963.0322
A simple analysis is given of phenomena such as electron spin resonance, spin-inversion processes and maser operation in paramagnetic solids. From an examination of the basic equations of motion, a mechanical analogue of these processes is conceived and a working model is described. The model constructed uses a gyroscope suitably driven by electric motors and is capable of demonstrating spin resonance, inversion processes and maser action. A discussion of further possibilities and some implications are also included.The authors' reply to the discussion on “A short modern review of fundamental electromagnetic theory”
http://dl-live.theiet.org/content/journals/10.1049/pi-1.1954.0056
A short modern review of fundamental electromagnetic theory
http://dl-live.theiet.org/content/journals/10.1049/pi-1.1954.0054
The paper is concerned with the teaching of the fundamentals of electromagnetism; it is divided into three parts.Part 1 deals with a method of presenting electromagnetic concepts to the student which takes the inverse square law of force between magnetic poles or electric charges as its starting points. This method is considered to result in a more satisfying sequence of thought than that usually adopted, because the symmetry of magnetic and electrical relations is stressed.Part 2 is a detailed discussion of the teaching of Faraday's laws of electromagnetic induction.Part 3 is a presentation of Maxwell's equations in terms of electric and magnetic flux density.The calculation of the magnetic field of rectangular conductors in a closed slot, and its application to the reactance of transformer windings
http://dl-live.theiet.org/content/journals/10.1049/pi-2.1951.0178
Derivation of the relation between the vector potential and the current in electromagnetic theory
http://dl-live.theiet.org/content/journals/10.1049/piee.1976.0108
Discussion on “A short modern review of fundamental electromagnetic theory” before the Institution, 11th February, 1954
http://dl-live.theiet.org/content/journals/10.1049/pi-1.1954.0055
The use of Bessel functions for calculating the self-inductance of single-layer solenoids
http://dl-live.theiet.org/content/journals/10.1049/pi-3.1949.0028
This paper is a continuation of the paper on “The Field of a Coil between two Parallel Metal Sheets.” It was pointed out in Section 6 of that paper that the general expressions, which had been developed therein, made it possible to calculate both the self-inductance and the high-frequency resistance of any circular coil enclosed in a closed screening-can. This solution was not then developed, but the work is in progress now. As a preliminary to this said new work it seemed desirable to show first that the Bessel function treatment did yield the correct result for the self-inductance of a single-layer solenoid. This exploration has shown that the old problem can be attacked with great elegance by the Bessel process and that it has definite merits of its own. This is perhaps not surprising, since the form of a solenoid suggests that Bessel functions are more appropriate to it than the integral of elliptic functions. This paper sets out the solution of an old problem by a new means.The first stage shows that the extremely general Bessel formulae do lead to the well-known expression <i xmlns="http://pub2web.metastore.ingenta.com/ns/">H</i> = 4π<i xmlns="http://pub2web.metastore.ingenta.com/ns/">IT</i> cos ϕ for the magnetic field at the centre of a solenoid. To obtain this result, use has to be made of formulae for the infinite integral of products of Bessel functions, and in particular to one formula due originally to Heaviside. The Bessel treatment turns out to have special advantages for calculating the strength of the field just inside the winding: this evaluation is necessarily peculiarly cumbersome by Legendre functions because they are in a series which is verging on becoming divergent at this radius. Formulae typified by eqn. (10) in the paper have a certain element of novelty and are valuable for calculating the high-frequency resistance of a coil having only one turn. The inductance of the isolated solenoid is derived in Section 2, and the results are tabulated and compared with values derived by Dr. A. Russell: also it is shown that the results can be expressed as t the sum of two integrals, the one or other of which becomes relatively unimportant when the coil is either long or short. The process of addition is exhibited graphically in Fig. 2; this Figure exposes very clearly the structure of the whole calculation, which otherwise remains obscure right up to the final result. Section 3 is devoted to calculating the inductance of any solenoid placed symmetrically between a pair of infinite sheets of metal, perpendicular to its axis. The tabulated results are useful for estimating the order of magnitude of the effect of a large metal sheet; and also they establish that the inductance of a long, isolated solenoid may be calculated by means of a rapidly convergent series without resort to the much more cumbersome process of using the definite integral.Though most of the results are old, the process of deriving them is believed to be novel. The new method is found to have some advantages over the old, and moreover it will solve many problems which are insoluble by the old. It is hoped that the new solutions will follow shortly; this paper is a necessary preliminary to the exposition of them.Diffraction of electromagnetic waves by two parallel half-planes
http://dl-live.theiet.org/content/journals/10.1049/pi-3.1953.0072
The field of a plane wave diffracted by two parallel, thin, highly conducting sheets, equivalent to semi-infinite planes, has been measured close to the diffracting edges for various spacings between the sheets. For one spacing, experimental results are compared with values derived from the theory of Clemmow for two parallel, infinitely thin, perfectly conducting half-planes.The inductance of wires and tubes
http://dl-live.theiet.org/content/journals/10.1049/ji-1.1947.0032
Stability problem in electromagnetic systems and possible solutions
http://dl-live.theiet.org/content/journals/10.1049/el_19690271
The letter is concerned with dispersion relations of active electromagnetic systems which are polynomial functions of either frequency or wavenumber. In this case, the search for saddle and branch points needed for stability analysis can be performed by 2-dimensional rather than 4-dimensional search.Teaching the principles of electromagnetism: quagmires and stepping-stones
http://dl-live.theiet.org/content/journals/10.1049/esej_19990508
It is acknowledged that electromagnetism is a very difficult subject, but reasons are given why its principles should be taught in all relevant degree and diploma courses. These reasons are based on the unifying influence of the principles and the help they give to professional engineers to change between specialisms during their careers. Maxwell's advice on how to teach the subject is discussed and endorsed, particularly as regards the role of physical analogies which enable new concepts to be explored. Some of the difficulties arising in teaching the subject are discussed in a series of twelve questions and outline answers. The central role of energy distribution is stressed. The conclusion suggests that the principles of electromagnetism should be taught in the manner of a spiral staircase which revisits the same view at repeated higher levels. It is suggested that there should be courses in electromagnetism for professional engineers in mid-career. The importance of applications is mentioned.Evaluation of some aspects of relativity
http://dl-live.theiet.org/content/journals/10.1049/piee.1969.0211
Calculation of the electric field and the capacitance of a charged spherical bowl by means of toroidal co-ordinates
http://dl-live.theiet.org/content/journals/10.1049/piee.1970.0126
Mathematical expressions for the potential function and the electric capacitance of a charged spherical bowl with respect to infinity are derived. Some numerical calculations of the potential field are presented for a charged spherical bowl of different openings and for the limiting case of a circular disc to illustrate the derived results. The mathematical expressions derived for the charged density on the concave and the convex sides of the spherical bowl are identical to those given by Kelvin, who employed the method of inversion.Evaluation of some aspects of relativity
http://dl-live.theiet.org/content/journals/10.1049/piee.1968.0323
If the relativity theory is to predict experimental results about the rates of clocks, the time intervals must be defined in such a way that they are capable of measurement. When this is done the confusion which has been associated with the theory is explained. The theory is shown to be self-consistent up to a point, but an error is then made in the course of a ‘thought experiment’. The result given does not follow from the ‘experiment’ but from an additional assumption made implicitly. The same kind of error is made in the ‘thought experiments’ in Einstein's later papers. The results again follow from implicit assumptions and not from the ‘experiments’. His final assumptions that time dilatation is a consequence of acceleration or gravitational potential are supported by the results of recent experiments.Absolute velocity of d.c. energy transmission by an electromagnetic field between two conductors and implications of relativity
http://dl-live.theiet.org/content/journals/10.1049/piee.1969.0038
The inductance of wires and tubes
http://dl-live.theiet.org/content/journals/10.1049/ji-2.1946.0115
Formulae are developed from Maxwell's equations of the electromagnetic field for the inductance of a single-phase system of wires or tubes arranged side by side or concentrically.Tables are given, so that the numerical evaluation of the formulae is very simple, and the formulae are shown to give values in good agreement with experimental figures.Modelling of a Litz-wire planar winding geometry for an accurate reactance evaluation
http://dl-live.theiet.org/content/journals/10.1049/iet-smt.2009.0118
A rigorous analytical electromagnetic model of a Litz-wire planar winding geometry is presented here. The main objective was the analytical description of the internal structure achieved by setting up a three-dimensional model with parametrical equations. The Litz-wire geometry is used to develop the electromagnetic model of the structure, obtaining a simple circuit formulation of the problem, whose numerical solution allows tocompute all the currents in every strand and also the structure reactance. The comparison with solid-wire spiral is also presented in order to highlight the advantages of the rigorous modelling of Litz-wire structure. To validate this model, different configurations were simulated and compared with measurements.