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Showing papers on "Near and far field published in 1970"


Book
01 Jan 1970
TL;DR: In this paper, the authors discuss Electromagnetic fields and waves and their relationship with the electromagnetic field and wave propagation, and propose a method to detect electromagnetic fields and wave formation.
Abstract: Electromagnetic fields and waves , Electromagnetic fields and waves , کتابخانه دیجیتال جندی شاپور اهواز

666 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the knowledge of the incident field and the scattered far field at one frequency to determine the size, shape, and location of a perfectly conducting scatterer.
Abstract: It is demonstrated that the knowledge of the incident field and the scattered far fields at one frequency may be employed to determine the size, shape, and location of a perfectly conducting scatterer. The reconstruction of the scattering body is accomplished via an analytic continuation procedure that generates the fields in the neighborhood of the scatter from the specified far-field distribution. The geometry of the body is then determined by locating a closed surface for which the total tangential electric field, i.e., the sum of the tangential components of the incident and scattered field, is zero. Whereas exact knowledge of the entire far field is sufficient to determine the scatterer, a technique is also given for size and shape determination when only part of the far field is available. Numerical examples of several different geometries are given for ranges of ka (a the largest dimension of the body) from 0.2 to 10. Geometries considered were elliptic and circular cylinders, conducting strips, and two cylinders. Plots of the fields reconstructed from the far-field data are compared to the known solutions, and the accuracy of the procedure is demonstrated. The effects of noise in the far-field pattern is also considered, and it is shown that even with noise levels of -20 dB the scattering geometry can be recovered.

72 citations


Journal ArticleDOI
TL;DR: In this article, the determinantal equation was obtained by assuming that the strips are narrow as compared to all other linear dimensions, and the amplitudes of the space harmonics were computed and discussed in connection with the characteristic phenomena such as radiation and coupling.
Abstract: The electromagnetic waves guided by a periodically strip-loaded dielectric slab were investigated. The determinantal equation was obtained by assuming that the strips are narrow as compared to all other linear dimensions. Numerical results involving different combinations of the linear and dielectric parameters are presented in terms of k-\beta diagrams. The amplitudes of the space harmonics were computed and are discussed in connection with the characteristic phenomena such as radiation and coupling. In particular, the relations between the attenuation of the guided waves and the space-harmonic amplitudes are pointed out. As an interesting phenomenon, real solutions have been found to occur in the complex-wave region and this new result has been explained in the light of the space-harmonic amplitudes. The numerical results in the backward-radiation region have been verified experimentally by two different methods: by measuring the phase and amplitude variation in the near field and by calculation from radiation patterns. In both cases, good agreement with the theoretical results has been obtained.

54 citations



Journal ArticleDOI
TL;DR: In this paper, an analytical and closed-form expression for input admittance was obtained for an annular aperture antenna driven by a coaxial transmission line, and the effect of all higher order TM on to the admittance is found to be quite significant.
Abstract: An annular aperture antenna driven by a coaxial transmission line is studied. An analytical and closed-form expression for input admittance is obtained. The effect of all higher order TM on to the admittance is found to be quite significant. Aperture field distribution is expressed in terms of the TEM and the first five TM on modes. Higher order modes at the aperture can be estimated from the edge behavior. Near-field distribution based upon these modes is then cast into a form suitable for numerical evaluation.

26 citations



Book
01 Apr 1970
TL;DR: In this article, problems of scattering and radiation of water waves by rectangular or circular bodies are formulated within the framework of linearized potential theory, the objective is to find the far field wave amplitude due to radiation by a body oscillating in a prescribed manner or the disturbance caused by a fixed body fixed in the path of an obliquely incident train of waves.
Abstract: : Problems of scattering and radiation of water waves by rectangular or circular bodies are formulated within the framework of linearized potential theory The objective is to find the far field wave amplitude due to radiation by a body oscillating in a prescribed manner or the disturbance caused by a body fixed in the path of an obliquely incident train of waves The radiation results can be used in conjunction with Haskind's theorem to establish the forces (moment) an incident wave induces on a fixed body Further, the radiation results are useful in establishing the damping coefficients associated with forced body oscillation Specific results which are obtained are the complex reflection and transmission coefficients for two dimensional obstacles including the limiting cases of thin vertical barriers, thin surface strip, and submerged gap Also the total and differential scattering cross-sections for vertical circular cylinders are presented Radiated wave amplitudes are given for bodies oscillating in heave, sway, or roll, as well as the forces induced on fixed bodies by incident waves Comparison with experimental and theoretical results by others is included (Author)

21 citations


Journal ArticleDOI
TL;DR: In this article, a formal analysis for oblique incidence scattering from a radially inhomogeneous cylindrical structure is given for the scattered far field and the scattering cross-section.
Abstract: A formal analysis is first given for oblique incidence scattering from a radially inhomogeneous cylindrical structure. Then expressions for the scattered far field and the scattering cross-section of a radially inhomogeneous cylindrical shell are derived for normally incident plane waves for both polarizations. A few special profiles for the dielectric constantɛ(ϱ) are so chosen that the corresponding solution is expressible in terms of known functions. In addition, for the case of anE-polarized normally incident field, series solutions for the waves inside the inhomogeneous cylindrical region are obtained when ɛ(ϱ) also was chosen as an arbitrary polypomial.

20 citations



Patent
28 Dec 1970
TL;DR: A system for detecting the low frequency electromagnetic field radiated bylectrical and electronic equipment comprising field coils oriented perpendicularly to a missile axis is described in this article, where the electromagnetic field is modelled as a magnetic field.
Abstract: A system for detecting the low frequency electromagnetic field radiated bylectrical and electronic equipment comprising field coils oriented perpendicularly to a missile axis.

17 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that a radiating monopole can be described mathematically as two point sources located at each end of the monopole, and a microwave hologram was recorded using liquid crystals which upon optical reconstruction yielded two points as predicted by the theory.
Abstract: Microwave holography is applied to the investigation of the radiation mechanism of a monopole. It is shown that a radiating monopole can be described mathematically as two point sources located at each end of the monopole. A microwave hologram was recorded using liquid crystals which upon optical reconstruction yielded two points as predicted by the theory. Using optical techniques, one can visualize the field at the antenna plane, at a plane in the Fresnel zone, and at a plane in the far field. This technique is, however, only one example of microwave holography in the investigation of a radiator. It can be very useful in designing any type of antenna.

Journal ArticleDOI
TL;DR: In this article, a derivation of the electromagnetic generation of compressional waves in metals in static magnetic fields is given, where it is found that the acoustic amplitude varies linearly with the amplitudes of both the incident time-varying electromagnetic field and the static magnetic field.
Abstract: A derivation of the electromagnetic generation of compressional waves in metals in static magnetic fields is given. It is found that the acoustic amplitude varies linearly with the amplitudes of both the incident time-varying electromagnetic field and the static magnetic field, and inversely as the acoustic frequency. An expression is obtained for the fraction of transmitted electromagnetic power converted into acoustic power. I. IKTRODUCTIOS Ll~CTROhlAG~ETIC generation of ultrasonic waves in ttletals has been ol)served under a wide variet,y of experimctntal conditions (l). In a static magnetic field both shear anti compressional waves have heen generated where the direction of polarization de- pends upon the orientation of thc field. Theoretical di+ cussion of this phenomenon with alld without a magnetir field has been given (2). For finite magnetic fields the most gcneral trcatmcnt is tht of Quinn (a). Here, using tt self-consistent semiclassical dcsrription, Quinn explains the gencrat,iorl mechanism on tlw hayis of solutions to equations for the couplctl electron-ion system. 'The ('111- phnsis is on shc:ir-wavc gcncration and propagation. hl- though the treatment is exact,, the generation luechanism may be somewhat, ohscured hy the formalism. The tlasic mechanism for sound generation is, honc~vt~r. un(lcr- shndahle via simple classical concepts. Rlodels of this type have been given and shown to he in quantitative ngreemc.nt, with experiment (3). in the gontwll trcat- ment of Quinn, these discussions were confined to the case of shear waves. It is the purpose of this paper to present a rla4Qsic:d calculation for the generation of com- pressional waves in the presence of a static magnet,ic field (4).

Journal ArticleDOI
D. M. Milder1, W. H. Wells1
TL;DR: In this paper, an analysis of how acoustic (or microwave) holography can be applied to large masses, such as natural bodies of water or the earth, by means of a linear array of microphones and by scanning with one or more transmitters to produce holographic phase shifts.
Abstract: This paper is an analysis of how acoustic (or microwave) holography can be applied to large masses, such as natural bodies of water or the earth, by means of a linear array of microphones and by scanning with one or more transmitters to produce holographic phase shifts. This type of hologram, in which the phased array has a conical antenna pattern, is shown to be superior to the area hologram for computing images in the near field. Computer simulations are given of virtual holograms and image reconstructions for specular and diffuse reflectors; simulations are also made for the case of pulse holography, which yields geniune three-dimensional images with reduced highlight distortions.

Journal ArticleDOI
TL;DR: In this paper, various approximations to the exact formal integral representations of the near field and the impedance are considered, and a new approximate form is obtained which appears to be valid even when the dipole is near a poorly conducting earth.
Abstract: Various approximations to the exact formal integral representations of the near-field and the impedance are considered. A new approximate form is obtained which appears to be valid even when the dipole is near a poorly conducting earth. Numerical comparisons with the exact integral formula verify some of the conjectures. The result shows that the ground has a significant influence on the input impedance of the dipole, particularly for low heights.

Journal ArticleDOI
TL;DR: In this article, the design of an electromagnetic survey meter is discussed together with an analysis of the errors associated with near-field measurements, and the meter provides accurate measurements of nearfield radiation emanating from leaking microwave power devices at 915 and 2450 MHz.
Abstract: The design of an electromagnetic survey meter is discussed together with an analysis of the errors associated with near-field measurements. The meter provides accurate measurements of near-field radiation emanating from leaking microwave power devices at 915 and 2450 MHz such as consumer ovens and industrial heating devices. Measurements are not subject to polarization of the incident wave, ambient temperature, or infrared radiation. Fail-safe indications are provided in the event of damage to the sensor. The range of measurements is from 10 ?W/cm2 to 200 mW/cm2.

Journal ArticleDOI
01 Nov 1970
TL;DR: In this article, the propagation constant of the electromagnetic wave along a very thin conducting wire immersed in a magnetoplasma is obtained explicitly for a general case where the dc magnetic field is applied with an arbitrary inclination with respect to the wire.
Abstract: The propagation constant of the electromagnetic wave along a very thin conducting wire immersed in a magnetoplasma is obtained explicitly for a general case where the dc magnetic field is applied with an arbitrary inclination with respect to the wire.

Journal ArticleDOI
TL;DR: In this article, the diffracted far field of a wide-flare-angle corrugated conical horn (operating on the HE11 mode) has been obtained making use of a simpler expression for the aperture field.
Abstract: Expressions for the diffracted far field of a wide-flare-angle corrugated conical horn (operating on the HE11 mode) have been obtained making use of a simpler expression for the aperture field. Expressions for the radiation pattern and gain reduce to a closed form when the flare (semivertical) angle is less than 30°. The theoretical results are in close agreement with experiment.

Journal ArticleDOI
TL;DR: In this article, an experimental study is described, leading to the design and construction of a near-field electromagnetic radiation probe operable in the frequency band 915 to 2450 MHz.
Abstract: An experimental study is described, leading to the design and construction of a near-field electromagnetic radiation probe operable in the frequency band 915 to 2450 MHz. The study is concerned with some of the problems involved in making accurate near-field measurements, particular emphasis being placed on measurements in close proximity to potential sources of a radiation hazard. Results of the study are incorporated into the design of a microwave radiation probe, which offers significant advantages over commercially available types.

Journal ArticleDOI
TL;DR: The number of points required for integration of an oscillatory function by Simpson's rule is examined and it is determined that at least 6 points per cycle are necessary to obtain 4 decimal accuracy.
Abstract: A method is presented for the computation of the far field radiation patterns of paraboloid reflector antennas by using a modified stationary phase approximation to eliminate one integration. This method is applicable to open cassegrain, offset paraboloid and horn reflector antennas. For symmetrical paraboloid antennas the modified approximation reduces to the exact expression obtained by direct integration. The errors introduced by the stationary phase and modified stationary phase approximations are investigated. Specifically the far field of an open cassegrain with a 128 wavelength aperture diameter is computed by the approximate method up to 20 degrees off-axis. The difference between these radiation patterns and those computed by double integration, is less than a few tenths of a dB up to 1.0 degree, and less than a few hundredths of a dB at larger angles off-axis. In order to estimate the computational advantage of this approximation, the number of points required for integration of an oscillatory function by Simpson's rule is also examined and it is determined that at least 6 points per cycle are necessary to obtain 4 decimal accuracy. For fewer points the error is appreciable.

Journal ArticleDOI
TL;DR: A theoretical study has been made of the effect of an apodizing screen in front of a circular aperture on the images of periodic objects with rectangular and triangular transmission profile.
Abstract: A theoretical study has been made of the effect of an apodizing screen in front of a circular aperture on the images of periodic objects with rectangular and triangular transmission profile. Irradiance distribution and contrast in the far field diffraction images have been calculated assuming the incident illumination to be completely incoherent. Object functions which give wave response similar to sine wave response (OTF) have been identified.


Journal ArticleDOI
TL;DR: In this article, a theory for the scattering by a single spherical gas bubble near a compressible spherical monopole source and a non-spherical spherical dipole source is presented.
Abstract: A gas bubble very close to an underwater sound source can have a profound influence on the sound radiated by the source. It is well known that when source and bubble are far apart, the bubble is a strong scattering centre for the incident sound, but when they are close together the bubble responds also to the near-field flow. This near field is scattered by the bubble from a non-propagating to a propagating mode so that the acoustic output of a multipole source, which has a relatively high near-field, can be considerably increased by the scattering process. A theory is developed for the scattering by a single spherical gas bubble near (a) a compressible spherical monopole source and (b) a compressible spherical dipole source, but it can be applied to non-spherical sources and bubbles by ascribing to them an 'equivalent spherical radius'. The theory is in good agreement with experiments using bubbles near a spherical monopole source and in fair agreement with experiments on bubbles near non-spherical monopole and dipole sources.

Journal ArticleDOI
TL;DR: In this article, a system consisting of a plasma column and a ring source of electromagnetic waves placed inside the column, may give rise to a radiation pattern with single or multiple narrow beams.
Abstract: It has been found that a system consisting of a plasma column and a ring source of electromagnetic waves placed inside the column, may give rise to a radiation pattern with single or multiple narrow beams. The direction of these narrow beams of electromagnetic radiation depends upon the column diameter and the plasma density. The amplitude of the peaks depends also upon the position of the ring source. The effect of varying these parameters on the radiation pattern is discussed. It is suggested that the result, presented could be used to design an electronically scannable antenna system.

Journal ArticleDOI
TL;DR: In this article, the propagation of electromagnetic radiation through a resonant medium is studied and three classes of solutions are obtained; two of them reduce to the solutions of Crisp and of McCall and Hahn when the slowly varying phase is zero.
Abstract: The propagation of electromagnetic radiation through a resonant medium is studied. The slowly varying envelope of the electromagnetic field is assumed to have a slowly varying phase in addition to a slowly varying amplitude. The nonlinear coupled equations of motion are solved exactly under rather general assumptions. Three classes of solutions are obtained; two of them reduce to the solutions of Crisp and of McCall and Hahn when the slowly varying phase is zero. Because of the gauge invariance of the equations of motion, there is a term proportional to the vector potential in addition to the terms of its space and time derivatives in the equation describing the evolution in time of the electromagnetic field. Hence, a characteristic frequency exists in the infrared region below which the wave number becomes imaginary.

Patent
18 Jun 1970
TL;DR: In this article, a method of forming and utilizing a hologram by placing a Fresnel diffraction pattern and a Fourier transform lens in the reference beam during the formation of the hologram was proposed.
Abstract: The present invention relates to a method of forming and utilizing a hologram by placing a Fresnel diffraction pattern and a Fourier transform lens in the reference beam during the formation of the hologram. An object pattern is placed in the object beam. A hologram of the near field or the far field of the object beam is formed by interfering the object beam and the reference beam at a recording medium in the focal plane of the Fourier transform lens. A reconstruction of the object pattern is produced from the hologram by passing the reference beam through the Fresnel diffraction pattern, the Fourier transform lens, the hologram, and a reconstruction lens.

Journal ArticleDOI
TL;DR: In this article, the authors study the reduction of the wave function which transforms as electromagnetic fields to the irreducible representation of proper, inhomogeneous, orthochronous Lorentz group.
Abstract: In the present paper we study the reduction of the wave function which transforms as electromagnetic fields to the irreducible representation of proper, inhomogeneous, orthochronous Lorentz group The electromagnetic fields are expanded into the modes with the amplitudes as wave functions for massless particles of spin 0 and 1 The values of electromagnetic fields in terms of these expansions are calculated as the solution of Maxwell's equations in free space with and without the source In the presence of source, we derive the expansions for longitudinal and transverse electric and magnetic fields and prove that in electromagnetic waves the horizontal component of the magnetic field is always zero, while in the absence of source we discuss the two types of circular polarizations of electromagnetic waves by proving that only spin-1 wave functions contribute to the electromagnetic fields in this case In the end we study the second quantization of the electromagnetic fields on replacing the wave function and their complex conjugates by destruction and the construction operators respectively

Patent
Richard William Teale1
19 Oct 1970
TL;DR: A device for detecting and/or recording electromagnetic radiation which employs as an active element one which responds to the electromagnetic radiation by changing a magnetic parameter thereof such as anisotropy, coercivity or permeability.
Abstract: A device for detecting and/or recording electromagnetic radiation which employs as an active element one which responds to the electromagnetic radiation by changing a magnetic parameter thereof such as anisotropy, coercivity or permeability. The active element contains metal ions of which two different energy states as regards a free electron can exist. Ions in one state can absorb energy from electromagnetic radiation to transfer across an energy threshold to the other energy state.

Journal ArticleDOI
TL;DR: In this article, the exact vector solution of far-field diffraction by a conducting strip is verified experimentally and an approximate solution based upon Kirchhoff's theory is compared with the vector formulation.
Abstract: The exact vector solution of far-field diffraction by a conducting strip is verified experimentally. Strips of 0.015- and 0.37-λ thickness were investigated. Results for both polarizations are compared for a strip of 2.85-λ width irradiated by a plane wave incident at glancing angles of 64°, 44°, and 24°. An approximate solution based upon Kirchhoff’s theory is compared with the vector formulation.

Journal ArticleDOI
TL;DR: In this article, the near radiation field of a microwave-illuminated aperture is mapped by a perturbation element and processed to yield a microwave hologram, and optical signal processing of the hologram yields an image of the aperture and its associated far-field pattern.
Abstract: The near radiation field of a microwave-illuminated aperture is mapped by a perturbation element and processed to yield a microwave hologram. Optical signal processing of the hologram yields an image of the aperture and its associated far-field pattern.

Journal ArticleDOI
TL;DR: In this paper, the situation where a normally incident plane monochromatic electromagnetic wave is reflected by an expanding dielectric slab is analyzed by means of the invariant-imbedding concept.
Abstract: The situation where a normally incident plane monochromatic electromagnetic wave is reflected by an expanding dielectric slab is analyzed by means of the invariant‐imbedding concept. An approximate expression for the spectrum of the reflected radiation is obtained.