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Showing papers on "Near and far field published in 1993"


Journal ArticleDOI
TL;DR: This work has shown how input impedance, far-field radiation pattern, radiation efficiency, and the magnitude of the near field are affected by the presence of the human body.
Abstract: This work deals with the influence the presence of a person has on the performance of antennas for hand-held portable telephones. It is shown how input impedance, far-field radiation pattern, radiation efficiency, and the magnitude of the near field are affected by the presence of the human body. The investigations have been carried out by applying the finite-difference time-domain (FDTD) technique to a model of the telephone with a lambda /4 monopole antenna and a simple hand-head model of the operator. Results from this configuration are compared with results for the telephone box and antenna alone. Measurements have been performed to verify the results obtained by simulations. The results show that a shadow effect in the far-field pattern occurs in the direction of the person and that the radiation pattern, including polarization, changes considerably from the telephone with the antenna alone. The impedance results show a change in resonance frequency when the telephone is placed next to a person. Results for radiation efficiency show that close to half of the energy is absorbed by hand and head. On average a system loss of 3-4 dB should be included in a link budget, and there is considerable fading, even in a radio-anechoic chamber, when persons move around in a natural manner. >

261 citations


Book
01 Aug 1993

147 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical analysis of the framework for near-field microscopy based on a microscopic description of the interaction between the dielectric probe and the surface is presented.

146 citations


Patent
03 Jun 1993
TL;DR: In this article, a near field scanning optical microscope (NSOM) is presented, which includes a cantilever which is aligned generally parallel to the surface of a sample, and an optical waveguide extends along the cantilevers to a tip which protrudes downward from the tip, allowing light radiation flowing through the waveguide to be directed toward the sample.
Abstract: A near field scanning optical microscope (NSOM) includes a cantilever which is aligned generally parallel to the surface of a sample. An optical waveguide extends along the cantilever to a tip which protrudes downward from the cantilever. A small aperture at the apex of the tip allows light radiation flowing through the waveguide to be directed toward the sample. The cantilever is vibrated, and variations in its resonant frequency are detected and delivered to a feedback control system to maintain a constant separation between the tip and the sample. The NSOM can also be operated as an atomic force microscope in either a contact or non-contact mode.

127 citations


Journal ArticleDOI
TL;DR: In this article, the evanescent electromagnetic wave of optically excited surface plasmons was measured directly using a scanning tunneling optical microscope (STOM) setup, and the measured intensity was increased by a factor of 30 larger than the corresponding wave intensity on a bare glass surface.

83 citations


Book ChapterDOI
01 Sep 1993

79 citations


Journal ArticleDOI
TL;DR: In this paper, a hybrid numerical technique is developed for electrically large pyramidal horn antennas radiating in free space, which is used to analyze the interior surfaces of the horn transition.
Abstract: A hybrid numerical technique is developed for electrically large pyramidal horn antennas radiating in free space. A stepped-waveguide method is used to analyze the interior surfaces of the horn transition. The electric field integral equation (EFIE) is employed on the outer surfaces of the pyramidal horn including the radiating aperture. Meanwhile, the magnetic field integral equation (MFIE) is used on the aperture to relate the aperture fields and those in the horn transition The resultant hybrid field integral equation (HFIE) is solved numerically by the method of moments. This formulation is both accurate and numerically stable so that high-gain microwave pyramidal horns can be analyzed rigorously. Far-field radiation patterns, both computed and measured, are presented for three electrically-large X-band horn antennas. The comparisons demonstrate that this method is accurate enough to predict the fine pattern structure at wide angles and in the back region. Computed far-field patterns and aperture field distributions of two smaller X-band horns are also presented along with a discussion on the validity of the approximate aperture field distributions routinely used in the analysis and design of pyramidal horns. >

70 citations


Journal ArticleDOI
TL;DR: Expressions relating far electromagnetic fields and return stroke channel base currents have been derived in the literature for various lightning return stroke models as discussed by the authors, and the use of such relations per se has been shown to be useful in the detection of lightning.
Abstract: Expressions relating far electromagnetic fields and return stroke channel base currents have been derived in the literature for various lightning return stroke models. The use of such relations per ...

59 citations


Journal ArticleDOI
TL;DR: In this article, a tapered GaAlAs amplifier with an output width of 320 μm is characterized by injecting an input beam with a superimposed sinusoidal intensity modulation (30 μm period, 30% peak-to-peak modulation).
Abstract: Filament formation in a tapered GaAlAs amplifier with an output width of 320 μm is characterized by injecting an input beam with a superimposed sinusoidal intensity modulation (30 μm period, 30% peak‐to‐peak modulation). Strong seeded filamentation of the output near field, and large far field side lobes are observed for powers above approximately 1 W. Time dependent decay of the main far field lobe, characterized by a time constant of several microseconds, is used to separate the effects of localized carrier density variations from the thermal contribution to intensity and phase distortion of the output beam.

55 citations


Journal ArticleDOI
TL;DR: A model of the electromagnetic radiation generated by the triggering of large-aperture biased photoconductors with ultrashort pulses is developed and the radiated fluence and intensity, as well as waveforms of the radiate electric field, are presented as a function of optical excitation fluence.
Abstract: A model of the electromagnetic radiation generated by the triggering of large-aperture biased photoconductors with ultrashort pulses is developed. In the far field, the radiated fluence and intensity, as well as waveforms of the radiated electric field, are presented as a function of optical excitation fluence.

53 citations


Journal ArticleDOI
TL;DR: This work considers the simplest quantum model for a degenerate parametric oscillator below threshold and analyze the quantum properties of the signal near field and introduces the idea of probing the emitted field by a local oscillator field of arbitrary spatial configuration to explore the spatial structure of the squeezed vacuum state emitted by the system.
Abstract: We analyze the quantum properties of the signal near field emitted by a degenerate parametric oscillator below threshold, including diffraction and its effects on the threshold for signal generation. The field is probed by a local oscillator field of arbitrary spatial configuration. The results are expressed in terms of an appropriate spectrum which describes how the level of squeezing varies with the angle from the direction of propagation. The results hold for cavities both with plane and with spherical mirrors.

Journal ArticleDOI
TL;DR: In this article, a unified theory of self-imaging and propagation invariance of three-dimensional electromagnetic fields is presented, and the properties of certain radially symmetric fields and fields with a plane-polarized electric vector are investigated to illustrate the general formalism.
Abstract: We present a unified theory of self-imaging and propagation-invariance of three-dimensional electromagnetic fields The properties of certain radially symmetric fields and fields with a plane-polarized electric vector are investigated to illustrate the general formalism

13 Sep 1993
TL;DR: A diffractive element composed of a binary phase zone-plate array that conditions the intensity distribution in the focal plane of a conventional refractive lens to generate efficiently a flattop intensity envelope on target is reported.
Abstract: The phase zone plate combines the simplicity of design and fabrication of the random phase plates with the advantage of near field target placement. The flexibility of design allows the cell structure to be easily modified to produce different focal spot shapes. The components are not specific to a particular near field intensity pattern provided several elements can be encompassed by the beam and therefore may be relevant to other laser applications requiring uniform beams on a target provided high spatial frequencies are not detrimental to the laser absorption process. >

Journal ArticleDOI
TL;DR: It is shown that by using another fiber as a detector with a polished edge placed at the surface near the fiber tip one can determine the tip-surface separation with an accuracy better than 15 nm at distances less than 1 µm.
Abstract: An experimental technique that makes use of the intensity of the interference pattern formed by light that propagates directly from the single-mode fiber tip and light that is reflected by the surface under an oblique angle of incidence is developed to control the tip–surface distance in near-field optical microscopy. It is shown that by using another fiber as a detector with a polished edge placed at the surface near the fiber tip one can determine the tip–surface separation with an accuracy better than 15 nm at distances less than 1 μm. The technique proposed is used to investigate the influence of the shape of the tip in near-field measurements.

Journal ArticleDOI
Abstract: Acoustic fields radiated by vibrating elastic bodies immersed in an infinite fluid domain are, in general, quite difficult to compute. This paper demonstrates in the two‐dimensional (2‐D) case that the radiated near field can be easily obtained using the finite element method if dipolar damping elements are attached to the mesh external circular boundary. These elements are specifically designed to absorb completely the first two components of the asymptotic expansion of the radiated field. Then, the paper provides a new extrapolation method to compute far‐field pressures from near‐field pressures, using the 2‐D Helmholtz equation and its solution obeying the Sommerfeld radiation condition. These developments are valid for any radiation problem in 2D. Finally, two test examples are described, the oscillating cylinder of order m and a finite width planar source mounted in a rigid or a soft baffle. This approach is the generalization to 2‐D problems of a previously described approach devoted to axisymmetrical and three‐dimensional (3‐D) problems [R. Bossut et al., J. Acoust. Soc. Am. 86, 1234–1244 (1989)]. It has been implemented in the ATILA code. It is well suited to the modeling of high‐frequency transducers for imaging and nondestructive testing.

Journal ArticleDOI
TL;DR: In this paper, the design and theory of operation of a new form of near field polarizing optical microscope are presented, which uses electro-optic premodulation of light to generate two simultaneous complementary images of samples.
Abstract: The design and theory of operation of a new form of near field polarizing optical microscope are presented. The system uses electro‐optic premodulation of light to generate two simultaneous complementary images of samples. This affords the capability to obtain a final output signal which is a linear representation of the sample birefringence, and is independent of the sample transmissivity/reflectivity. A number of images are presented.

Journal ArticleDOI
TL;DR: In this paper, the authors examined an inverse problem for time-harmonic electromagnetic waves in an inhomogeneous medium and showed with integral equation techniques that the resulting direct transmission problem is uniquely solvable.
Abstract: In this paper we examine an inverse problem for time-harmonic electromagnetic waves in an inhomogeneous medium. Outside of a bounded domain D we assume that the medium is dielectric and homogeneous with constant electric permittivity and constant magnetic permeability. These quantities and the electric conductivity change discontinuously across delta D and are inhomogeneous in D. We show with integral equation techniques that the resulting direct transmission problem is uniquely solvable. Then, using a method suggested by Kirsch and Kress (1993), we prove that delta D is uniquely determined by a knowledge of the far field patterns for all incoming plane waves. Finally, we give conditions so that the parameters epsilon , mu and sigma are uniquely determined in D by these far field patterns. Here we use special solutions of the Maxwell equations which were constructed by Colton and Paivarinta (1992).

Patent
06 Jan 1993
TL;DR: In this paper, an optical system useful for near-field scanning optical microscopy is provided, which consists of a tapered and partially metallized portion of a single-mode optical fiber.
Abstract: An optical system useful, e.g., for near-field scanning optical microscopy is provided. The system incorporates a probe having improved properties. In one embodiment, the probe comprises a tapered and partially metallized portion of a single-mode optical fiber.

Journal ArticleDOI
TL;DR: In this paper, an account of the three-dimensional structure of the sound field produced by a spinning sinusoidal distribution of thickness or loading sources is given, with particular attention paid to the creeping evanescent waves in the near field and their physical interpretation as trapped edge waves; an exponentially small amount of energy leaks or tunnels through them to emerge as far-field acoustic radiation (as it does through the inhomogeneous waves carried by a waveguide in a cylindrically layered medium).
Abstract: An account is given of the three-dimensional structure of the sound field produced by a spinning sinusoidal distribution of thickness or loading sources. Particular attention is paid to the creeping evanescent waves in the near field and their physical interpretation as trapped edge waves; an exponentially small amount of energy leaks or tunnels through them to emerge as far-field acoustic radiation (as it does through the inhomogeneous waves carried by a waveguide in a cylindrically layered medium). The dependence of the structure on three parameters is investigated in detail: the Mach number M at the outermost radius of the source; the harmonic number n, defined so that the source strength is a function of n$\theta $, where $\theta $ denotes azimuthal angle; and the type of source, i.e. thickness or loading. Parameter values considered include those for subsonic, sonic and supersonic motion, and for high and low harmonics. The field is calculated by reducing a special case of Rayleigh's double integral to a single integral containing a function related to the Chebyshev polynomials, then integrating numerically to give contour plots of pressure as a function of position on various plane and cylindrical sections. These show that the evanescent waves occupy a spherical or ellipsoidal region, and consist of crescents of alternating high and low pressure, shaped and arranged like the segments of an orange; its `peel' marks the transition to the propagating spiral waves of the far field, i.e. the radiation zone. Contour plots on meridional sections are similar to those for the oscillating hertzian electric dipole, suggesting that the field is approximately that produced by a suitably phased arrangement of its acoustic counterpart. When M > 1, the source distribution straddles both the evanescent and the radiation zone; at high supersonic M, the meridional contour plots display an intense beaming pattern, with side-lobes between the main beam and source plane. The results of the paper agree with previous work on propeller acoustics, especially the asymptotic theory.

Journal ArticleDOI
TL;DR: In this article, the effect of cracks on the surface of reflectors that can result from the imperfect fitting together of panels to form large reflectors was investigated. But the results were limited to three models of cracks, and significant pattern effects were found, depending on the model and orientation of the cracks.
Abstract: Incremental length diffraction coefficients (ILDCs) for the half-plane are integrated around the rim of a paraboloid reflector antenna to obtain well-behaved far fields of the nonuniform current for all angles of observation. These far fields, when added to the physical optics far field, produce a more accurate total far field of the reflector. Excellent agreement with the far fields obtained from a method-of-moments solution to the electric field integral equation applied to a 20-wavelength-diameter reflector shows that the cross polarization, farther-out sidelobes, and fields near nulls of reflector antennas can be appreciably modified by the fields of the nonuniform currents. ILDCs are also used to investigate the effect of cracks on the surface of reflectors that can result from the imperfect fitting together of panels to form large reflectors. Three models of cracks are studied. Significant pattern effects are found, depending on the model and orientation of the cracks. >

Patent
28 Jul 1993
TL;DR: In this article, an antenna device is used for emitting a beam of optical radiation to irradiate a remote target area. But, at least one characteristic of the beam being controlled by the hologram pattern in the path of the beacon is observed.
Abstract: A device, particularly an antenna device, for emitting a beam of optical radiation to irradiate a remote target area. The device includes an optical source (10) having a limited wavelength band, and a hologram pattern (14) positioned in the path of a light beam originating from the source, the pattern being selected to produce a composite beam (20) having a predetermined shape or far field pattern conforming to the target area and/or a predetermined distribution of light intensity in the target area. Where the optical source is a point source, the hologram pattern (10) selectively retards the phase of respective components of the incident wavefront to produce a composite beam having a far field pattern that precludes focusing of the beam into a single small spot. The device has particular application in a telecommunication system wherein a data signal is transmitted through free space by an optical beam, at least one characteristic of the beam being controlled by the hologram pattern in the path of the beam.

Journal ArticleDOI
TL;DR: In this paper, a selfconsistent macroscopic approach based on the Maxwell equations in two-dimensional geometry is developed to describe tip-surface interaction in external-reflection near-field microscopy.
Abstract: The self-consistent macroscopic approach based on the Maxwell equations in two-dimensional geometry is developed to describe tip–surface interaction in external-reflection near-field microscopy. The problem is reduced to a single one-dimensional integral equation in terms of the Fourier components of the field at the plane of the sample surface. This equation is extended to take into account a pointlike scatterer placed on the sample surface. The power of light propagating toward the detector as the fiber mode is expressed by using the self-consistent field at the tip surface. Numerical results for trapezium-shaped tips are presented. We show that the sharper tip and the more confined fiber mode result in better resolution of the near-field microscope. Moreover, it is found that the tip–surface distance should not be too small so that better resolution is ensured.

Journal ArticleDOI
TL;DR: In this paper, a new method for the calibration of the refractive index is proposed, which allows simultaneous measurement of the transmitted near field at 1300 nm and 1550 nm, and the refracted near fields at 820 nm.
Abstract: An experimental setup is presented which permits, in a routine way for R&D purposes, simultaneous measurement of the transmitted near field at 1300 nm and 1550 nm, and the refracted near field at 820 nm. A new method for the calibration of the refractive index is proposed. The obtained accuracy for the refractive index is dn+or-0.0002. The reproducibility of measurements of geometrical parameters like the mode field diameter, the core and cladding diameters, and concentricity error, is +or-0.1 mu m. Measurements of the mode field as a function of polarization state for four different hi-bi fiber are presented. >

Patent
17 Nov 1993
TL;DR: In this paper, an amplitude modulated radio frequency carrier is used to monitor the level of signal at a test point in a system for susceptibility to electromagnetic fields, and a voltage can be injected, using a voltage injection probe, into the system at another point to recreate the detected signal at the test point from the electromagnetic field.
Abstract: Apparatus and method for low cost monitoring the level of signal at a test point in a system for susceptibility to electromagnetic fields. A probe, including a detector diode, and a non-metallic, electrically overdamped conductor, which is transparent to the electromagnetic field, is used to monitor the signal level at a test point as an amplitude modulated radio frequency carrier. The carrier is transmitted to a monitor outside of the range of the electromagnetic field using a transmission link, such as an optical waveguide transmitter, that is transparent to the electromagnetic field when the system under test fails. The system under test can then be removed from the electromagnetic field and, for each frequency at which the system failed, a voltage can be injected, using a voltage injection probe, into the system at another point to recreate the detected level of signal at the test point that was coupled into the system from the electromagnetic field. This stimulates the effect of the susceptibility to the electromagnetic field, and permits testing of a suitable filter or other expedient applied to the system, even though the system is not exposed to the electromagnetic field. Thus, the system may be tested for susceptibility inside a shielded enclosure and subjected to a controlled electromagnetic field, and the susceptibility may be recreated and solved outside of the shielded enclosure.

Journal ArticleDOI
TL;DR: Numerical simulations of the propagation of the field emitted by laser arrays consisting of a small number of elements show how propagation transforms part of an amplitude modulation into a phase modulation.
Abstract: We present numerical simulations of the propagation of the field emitted by laser arrays consisting of a small number of elements. Our computations show how propagation transforms part of an amplitude modulation into a phase modulation. This fact can be used to enhance the central lobe energy in the far field of high-power laser arrays by means of a simple corrective optical element. We discuss optimal filtering conditions and prove that the quarter-Talbot distance generally used in previous studies is not the best choice.

Journal ArticleDOI
TL;DR: An approach based on a waveguide model for analyzing the uniform and nonuniform dielectric leaky-wave structures is proposed for which the Galerkin solution method is applied.
Abstract: An approach based on a waveguide model for analyzing the uniform and nonuniform dielectric leaky-wave structures is proposed for which the Galerkin solution method is applied. In the first part of the paper the far-field radiation of the uniform antenna is determined theoretically and experimentally in the Ku band and also the dependence of beamwidth and sidelobe level as function of strip width and frequency is demonstrated. In addition, an analysis of the antenna with a tapered-strip distribution-is presented. The second part describes a novel tapering procedure, performed by changing the width of the uniform antenna, for obtaining the radiation pattern with lower sidelobe levels. Sinusoidally and exponentially shaped dielectric leaky-wave structures are analyzed as nonuniform antennas. Finally, the radiation and scanning characteristics of these antennas are theoretically presented. >

Patent
07 Apr 1993
TL;DR: In this article, an amplitude modulated radio frequency carrier is used to monitor the level of signal at a test point in a system for susceptibility to electromagnetic fields, and the system under test can then be removed from the electromagnetic field and, for each frequency at which the system failed, a voltage can be injected, using a voltage injection probe, into the system at another point to recreate the detected signal at the test point.
Abstract: Apparatus and method for low cost monitoring the level of signal at a test point in a system for susceptibility to electromagnetic fields. A probe, including a detector diode, and a non-metallic, electrically overdamped conductor, which is transparent to the electromagnetic field, is used to monitor the signal level at a test point as an amplitude modulated radio frequency carrier. The carrier is transmitted to a monitor outside of the range of the electromagnetic field using a transmission link, such as an optical waveguide transmitter, that is transparent to the electromagnetic field when the system under test fails. The system under test can then be removed from the electromagnetic field and, for each frequency at which the system failed, a voltage can be injected, using a voltage injection probe, into the system at another point to recreate the detected level of signal at the test point that was coupled into the system from the electromagnetic field. This simulates the effect of the susceptibility to the electromagnetic field, and permits testing of a suitable filter or other expedient applied to the system, even though the system is not exposed to the electromagnetic field. Thus, the system may be tested for susceptibility inside a shielded enclosure and subjected to a controlled electromagnetic field, and the susceptibility may be recreated and solved outside of the shielded enclosure. The probe may include a plurality of detector diodes mounted on a printed circuit board in a shielded structure that is directly connected to the test wire of the circuit to be monitored.

Journal ArticleDOI
TL;DR: In this paper, the influence of spatial inhomogeneity of the gain, gain saturation, finite aperture and roughness of the mirrors on the performance of diode-array pumped solid-state laser is considered.

Journal ArticleDOI
TL;DR: In this paper, a modal method is used for the determination of the near field weighting functions related to the power transmitted from a rectangular waveguide aperture towards a lossy material and, by reciprocit...
Abstract: A modal method is used for the determination of the near field weighting functions related to the power transmitted from a rectangular waveguide aperture towards a lossy material and, by reciprocit...

Book ChapterDOI
01 Jan 1993
TL;DR: In this paper, a partially metal-coated tetrahedral tip is considered to be a structure fulfilling these functions, and first results of tests of their optical properties are reported.
Abstract: In scanning near field optical microscopy (SNOM), a tip whose dimensions are small compared with the wavelength serves as a light-emitting antenna. Light is transmitted from a source via a waveguide structure to this antenna. An important part of an SNOM probe — apart from the detailed structure of the tip — is the link between the macroscopic waveguide and the antenna of subwavelength dimensions. A partially metal-coated tetrahedral tip is considered to be a structure fulfilling these functions. Motivations for the choice of this structure are models of metal waveguide structures without cutoff and the fact that surface plasmons can be excited on planar metal films and along edges as well as on tips. Aspects of probe fabrication and first results of tests of their optical properties are reported.