Showing papers on "Near and far field published in 1968"
TL;DR: In this paper, the authors studied the effect of electromagnetic waves in metals in a magnetic field and found that the electromagnetic wave in metals can be modelled as a magnetic wave wave.
Abstract: (1968). Electromagnetic waves in metals in a magnetic field. Advances in Physics: Vol. 17, No. 69, pp. 605-747.
87 citations
TL;DR: In this article, the problem of the electromagnetic shielding effectiveness of a thin, plane metal sheet of infinite extent on the electromagnetic field generated by a circular loop field source with uniform current I is solved by application of the quasi-near and near field approximations to the exact integral expressions.
Abstract: The problem of the electromagnetic shielding effectiveness of a thin, plane metal sheet of infinite extent on the electromagnetic field generated by a circular loop field source with uniform current I is solved by application of the quasi-near and near field approximations to the exact integral expressions. The results are shown to be in close agreement with experimental data as well as numerical integration results. Also, they are similar to the results obtained from the plane wave shielding theory of Schelkunoff.
81 citations
TL;DR: In this paper, a perturbation theory for the interaction between free electromagnetic fields and weak gravitational fields is developed, which is applied to calculate the change in the electromagnetic field and energy density of a high-frequency plane polarized monochromatic electromagnetic wave bounced between two perfectly conducting walls.
46 citations
TL;DR: In this paper, a relativistically correct expression for the far zone electromagnetic field scattered by a perfectly conducting sphere, moving with constant velocity, through an incident plane wave is developed.
Abstract: A relativistically correct expression for the far zone electromagnetic field scattered by a perfectly conducting sphere, moving with constant velocity, through an incident plane wave is developed. It is seen that if the scattered field is expressed in a special "retarded" coordinate system, a result that is more tractible, allowing physical interpretation, is obtained. When the field is expressed in this way, the expected first-order effects are manifest, yet the higher order effects are also present. This solution may be directly applied to the finite bodies with more complicated shapes than the sphere. For the case of the sphere it is found that the form of the scattered field allows the calculation of the scattering cross section, the total scattering cross section, and the rate of exchange of electromagnetic and mechanical energies. The Special Theory of Relativity gives a rigorous means of discussing a situation involving electromagnetic scattering by a uniformly moving body, For such a situation, in free space, the theory specifies how one may restate the problem so that it is viewed with respect to an observer moving with the body. From this viewpoint the problem appears that of scattering by a stationary body. This implies that there exists a straightforward means of obtaining the field scattered by a uniformly moving body in free space, providing only that its stationary scattering properties are known. Historically, the first situation attacked by this method was that of reflection by a moving infinite mirror (Sommerfeld, 1964b; Pauli, 1958). Scattering by a moving dielectric half space also has been discussed by Tai (1965), Yeh (1965), and by Pyati (1966). Their work has been extended to a moving uniaxially anisotropic half space by Lee and Lo (1967). Recently, Lee and Mittra (1967) have considered the case of scattering by a moving conducting cylinder. It is seen that as the geometry of the scattering body becomes more complex, the original symmetry of the stationary solution is lost in the transformation between the moving systems, resulting in an expression that is awkward, yielding little physical meaning. In this paper a coordinate system is chosen to express the far field scattered by a moving finite body, a sphere, giving a solution that is relativistically correct and at the same time allows physical interpretation. Although a sphere is considered here, the method may be used to express the far field scattered by other moving finite objects or the radiation field from a finite, moving electro magnetic source.
32 citations
TL;DR: In this article, it was shown that a knowledge of a given number of near field terms suffices to determine the same number of far field terms, thus disproving the previously held contention that p+1 near fields were needed to determine p far fields.
Abstract: An explicit formula is derived expressing the low frequency expansion of the far field coefficient for any radiating electromagnetic field in terms of the low frequency expansion of the near field. It is shown that a knowledge of a given number of near field terms suffices to determine the same number of far field terms, thus disproving the previously held contention that p+1 near field terms were needed to determine p far field terms.
28 citations
TL;DR: In this paper, a GaAs junction laser with stripe contacts about 13 μ wide has been studied and it was shown that more than 80% of the diodes have approximately Gaussian intensity profiles along the junction plane.
Abstract: Far‐field patterns from GaAs junction lasers with stripe contacts about 13 μ wide have been studied. At room temperature, more than 80% of the diodes have approximately Gaussian intensity profiles along the junction plane. Intensity measurements show that the profiles are stable for currents exceeding threshold by 60% in some diodes. These experimental results indicate that the lasers oscillate predominantly in the lowest‐order mode. Previously, with 50 μ stripe widths it was impossible to predetermine the dominant mode or to insure its stability for current variations greater than about 5%. In contrast to the symmetric behavior along the junction plane the radiation patterns perpendicular to the plane are asymmetric. Infrared photographs show a major lobe along with several minor lobes, the latter always appearing on the n side of the junction plane. The main features of the asymmetry are essentially the same for similarly fabricated diodes. Differences are found in the intensity distributions or widths of the minor lobes.
25 citations
01 Oct 1968
TL;DR: In this article, the scattering of plane waves from perfectly conducting cylinders is studied, using the condition that the total field inside the cylinders must be zero, and it is shown that the surface current density can always be expressed as a sum of proper modes.
Abstract: The scattering of plane waves from perfectly conducting cylinders is studied, using the condition that the total field inside the cylinders must be zero. It is shown that the surface current density can always be expressed as a sum of proper modes. In general, fewer modes are required for calculating the scattered far field than are required for calculating the surface current density to the same accuracy. Two new approximate methods are introduced. These methods complement the method of physical optics, and the more accurate of them is suitable for calculating the scattering over a wide range of bistatic angles.
23 citations
TL;DR: In this paper, the near field pattern of each mode passed through the wire-cloth mesh mirror is obtained by sliding a Golay cell behind the mirror, and it is shown that the pattern of mode has usually complex structures and is largely changed when the mirror is tilted.
Abstract: Experimental results on time behavior of pulsed output, transverse mode pattern, and polarization characteristics of the 311 or 337 µm CN lasers are presented. According to the behavior of the current pulse of discharge in a static gas filling, it is possible to find the conditions where the laser oscillation starts or ceases. The near field pattern of each mode passed through the wirecloth mesh mirror is obtained by sliding a Golay cell behind the mirror, and it is shown that the pattern of mode has usually complex structures and is largely changed when the mirror is tilted. The polarization characteristics of the laser light are determined by anisotropies in the cavity, and the polarization azimuth is changed by inserting an one-dimensional grid into the cavity. The polarization flip is observed by tuning through the line center of 311 and 337 µm, when the electroformed or wirecloth mesh mirror is used.
22 citations
TL;DR: In this article, the far field patterns of large circular loop antennas of circumferences up to two and one-half wavelengths were calculated using Storer's theory for the current distribution on the antenna.
Abstract: Far field patterns of large circular loop antennas of circumferences up to two and one-half wavelengths were calculated using Storer's theory for the current distribution on the antenna. To verify the theory, radiation pattern measurements were made at 3 GHz; the experimental results are in good qualitative agreement with theory.
20 citations
TL;DR: In this article, exact numerical solutions for the interaction of a plane, electromagnetic wave with a cylindrical plasma are given for the application of microwave diagnostics, including a new bistatic method.
Abstract: Exact numerical solutions are given for the interaction of a plane, electromagnetic wave with a cylindrical plasma. The incident wave is normal to the plasma axis and both TE and TM polarizations are considered. The electron density profile is represented by a Gaussian curve consistent with flow-field calculations for wakes and jets. Transmitted and scattered amplitudes are evaluated as functions of the polar angle and plasma parameters. The data are compared with previous theoretical and experimental work. [17],[18] Parabolic electron density profiles are also investigated and contrasted with the Gaussian results. The sharp cutoff in a parabolic profile has a significant effect on the electromagnetic interaction. Applications to microwave diagnostics are discussed including a new bistatic method.
19 citations
TL;DR: An analogue model for studying electromagnetic variations for an overhead oscillating line current is described in this paper, where measurements of electric and magnetic fields for model earth-sea interfaces are discussed and compared with results reported earlier for an overcast sheet current.
Abstract: An analogue model for studying electromagnetic variations for an overhead oscillating line current is described. Measurements of electric and magnetic fields for model earth–sea interfaces are discussed and compared with results reported earlier for an overhead sheet current. A truncated cone representing a circular sea, a graphite wedge representing an ocean coastline, and a graphite wedge underlain by a graphite block representing an upwelling conducting zone in the earth's mantle near a sea coast are considered. In some cases the results for the line current model differ appreciably from those for the sheet current model, indicating that the nature of the source field can be an important factor in determining the behavior of the field components. The model measurements indicate that land–sea interfaces produce no appreciable anomalous magnetic fields at frequencies below 0.01 cps and hence the presence of the sea alone cannot account for coastal magnetic field anomalies. The results obtained for the mo...
TL;DR: In this article, a standard photographic film was proved to be applicable to a quick and easy direct mapping of an electromagnetic field using selective development of the film in accordance with the thermo-image produced by the electromagnetic field.
Abstract: A standard photographic film was proved to be applicable to a quick and easy direct mapping of an electromagnetic field. The method utilises selective development of the film in accordance with the thermo-image produced by the electromagnetic field. The method would be most useful for preparing microwave holograms.
23 Jul 1968
TL;DR: A general engineering technique by which the shielding effectiveness of solid single-layer shields may be analytically evaluated, using the transmission-line approach of Schelkunoff.
Abstract: This paper presents a general engineering technique by which the shielding effectiveness of solid single-layer shields may be analytically evaluated. Shielding equations applicable to any homogeneous isotropic material are developed using the transmission-line approach of Schelkunoff. Corresponding limitations are discussed. Necessary information regarding near-field wave impedance is presented in normalized graphs. A useful computer program (FORTRAN IV) is given, together with application information. Calculated results are compared with corresponding test data.
TL;DR: In this article, an exact formal solution for the fields due to an axial electric dipole in the presence of a homogeneous isotropic infinite circular cylinder is obtained in integral form.
Abstract: Using the differential equation approach an exact formal solution for the fields due to an axial electric dipole in the presence of a homogeneous isotropic infinite circular cylinder is obtained in integral form. An asymptotic expansion of the integral yields the far field. Patterns for different choices of the parameters are given. It is seen that for dielectric cylinders in particular, drastic departures from the perfectly conducting case can be obtained leading to more directive patterns. This in turn may have application in the design of arrays.
TL;DR: In this article, the Fourier transform of the dyadic Green's function is used to model the VLF electromagnetic radiation through an ionized gas in a permanent magnetic field (magnetoionic medium).
Abstract: We examine VLF electromagnetic radiation through an ionized gas in a permanent magnetic field (magnetoionic medium). Such a medium can be taken as a model of the ionosphere. We work from the Fourier transform of the dyadic Green's function which relates the current density and the electric field. Asymptotic expansions of the function are obtained for both small and large separation. The expansions for small separation can be used to discuss the power radiated by a current distribution (antenna). Special attention is given to the power radiated by a Hertzian dipole, and a conflict in the literature (Staras, 1964; Lee and Papas, 1965) is resolved. The expansion for large separation can be used to discuss the far field. The radiated far field is shown to propagate most strongly along the field lines of the permanent magnetic field. The far field radiated by a Hertzian dipole is considered.
01 Jan 1968
TL;DR: In this article, the high-frequency backscattered field produced by a plane electromagnetic wave incident on an inverse square-power dielectric lens is determined in terms of reflected field, creeping wave, and evanescent wave contributions.
Abstract: The high-frequency backscattered field produced by a plane electromagnetic wave incident on an inverse-square-power dielectric lens is determined in terms of reflected field, creeping wave, and evanescent wave contributions.
TL;DR: In this paper, the authors have given a quantitative analytical investigation of the interesting concept of the modulation of an electromagnetic wave by its propagation along an alternating magnetic field in a semiconductor or a plasma.
Abstract: In this paper the authors have given a quantitative analytical investigation of the interesting concept of the modulation of an electromagnetic wave by its propagation along an alternating magnetic field in a semiconductor or a plasma. Numerical results, presented at the end, show that this phenomenon is appreciable.
TL;DR: In this paper, a generalized refractive index profile permitting exact transcendental solutions for the radial variation of fields of the electric type has been presented, which is the state-of-the-art.
Abstract: The general electromagnetic field can be resolved into two components represented by electric and magnetic Hertz vectors, both vectors being parallel to the radial direction. Very few exact solutions for the radial variation of fields of the electric type have been found hitherto. Generalised refractive-index profiles permitting exact transcendental solutions are presented.
TL;DR: In this article, the radiation characteristics of a horizontal antenna embedded in a conducting half space and illuminated by a refracted electromagnetic wave are investigated, and asymptotic expressions of the far fields are given in two regions: the horizontal plane of the interface at large radial distances from the vertical axis and the upper hemisphere far from the origin.
Abstract: The radiation characteristics of a horizontal antenna embedded in a conducting half space and illuminated by a refracted electromagnetic wave are investigated. Asymptotic expressions of the far fields are given in two regions: the horizontal plane of the interface at large radial distances from the vertical axis and the upper hemisphere far from the origin. Due to the interference of the fields generated by the currents in different parts of the antenna, the groundwave and spacewave radiation patterns are different from those due to an infinitesimal horizontal dipole.
TL;DR: The general electromagnetic field, when independent of axial distance, may be expressed as the sum of E parallel and H parallel partial fields as mentioned in this paper, and exact solutions of the wave equation for the radial variation of the H parallel field are not numerous Generalised refractive index profiles are presented which permit transcendental solutions to be made
Abstract: The general electromagnetic field, when independent of axial distance, may be expressed as the sum of E parallel and H parallel partial fields Exact solutions of the wave equation for the radial variation of the H parallel field are not numerous Generalised refractive-index profiles are presented which permit transcendental solutions to be made
TL;DR: In this paper, it was shown that static electromagnetic fields have nonlinear energy and momentum due to the interaction between sources, while the apparent nonlinearity in energy and energy momentum densities of electromagnetic waves generated by noninteracting sources merely reflects a hitherto unsuspected degree of freedom of the energy-momentum four-tensor Tμν, which can undergo the following transformation without changing its physical meaning.
Abstract: It is shown that static electromagnetic fields have nonlinear energy and momentum due to the interaction between sources, while the apparent nonlinearity in energy and momentum densities of electromagnetic waves generated by noninteracting sources merely reflects a hitherto unsuspected degree of freedom of the energy-momentum four-tensor Tμν, which can undergo the following transformation without changing its physical meaning: Tμν→ T′μν = Tμν + Kμν, where the symmetric four-tensor Kμν is arbitrary except for the constraint δνKμν = 0. The force density fμ = δνTμν is preserved in this transformation. The implication of this transformation on fields everywhere satisfying the homogeneous wave equations is discussed.
TL;DR: The relation between the retarded Green's function and second-order correlation tensors of electromagnetic potential for a pure electromagnetic radiation in thermal equilibrium is derived in this article, and the relation holds also for a long wavelength electromagnetic radiation, so long as the radiation is in thermal equilibria.
Abstract: The relation between the retarded Green's function and second-order correlation tensor of electromagnetic potential for a pure electromagnetic radiation in thermal equilibrium is derived. This relation holds also for a long wavelength electromagnetic radiation in media, so long as the radiation is in thermal equilibrium. The electromagnetic second-order correlation tensors for blackbody radiation is obtained, using the relation mentioned above. Upon following Abrikosov, Gorkov and Dzyaloshinski the retarded Green's function for a electromagnetic radiation interacting with matter is expressed in terms of the complex dielectric constant which is necessarily introduced for carrying out a macroscopic formulation. With the assumption of spatial homogeneity of media the electromagnetic second-order correlation tensors for an optical field are obtained. These correlation tensors are also expressed in tems of the complex dielectric constant. This retarded Green's function is simply related to the temperature Gree...
01 Jun 1968
TL;DR: In this article, the tensor of time averaged stresses arising in a magnetoactive plasma under the the effect of an oscillating electromagnetic field was derived, and it was proved that the radiation pressure need not arise on the plasma-vacuum boundary even if the electromagnetic wave falling from vacuum is reflected substantially.