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Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.


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TL;DR: In this article, the authors derived the Green's function of the magnetic field due to a single point force as a complement of previous authors' works, in which only the green's functions of the solid displacement, the relative fluid-solid displacement and the electric field were expressed.
Abstract: SUMMARY Studied in this paper are the properties of seismoelectromagnetic waves radiated by a double couple in a saturated porous medium arising from the electrokinetic effect. First, using the Pride's equations, we derive the Green's function of the magnetic field due to a single point force as a complement of previous authors’ works, in which only the Green's functions of the solid displacement, the relative fluid–solid displacement and the electric field were expressed. Furthermore, we extend these Green's functions to cater for the moment tensor sources. Then we derive the Green's functions of the solid displacement, the electric and magnetic fields in the frequency-space domain excited by a double couple source, which is frequently used in earthquake seismology. To visualize these fields, the radiation patterns are calculated and displayed. The results illustrate that the radiation pattern of the electric far field for the longitudinal (or transverse) wave is the same in shape as that of the far field of the P (or S) wave in elastodynamics. For a transverse wave, the electric and magnetic far fields share the same radiation patterns in shape, while the electric and magnetic near fields do not. For each of the four body waves, the far, intermediate and near fields are compared at different receiver-to-source distances, respectively. The electromagnetic (EM) wave has a much longer near-field-dominating distance than the seismic waves. We calculate the waveforms in the time–space domain by numerically Fourier transforming the Green's functions into the time domain. In order to validate these Green's functions and the waveforms, we calculate the waveforms again by another method. The main idea of the method is regarding the source as a displacement–stress–EM discontinuity vector. The result shows that the waveforms from those two methods are in excellent agreement. In the waveforms, there are the electric fields accompanying both the P and S waves, as well as the magnetic field accompanying the S wave. We testify that the S wave generally has a weaker capacity than the P wave in inducing an electric field. In the waveforms, there is also an independently propagating EM wave, which has a much higher speed than the seismic waves, and reaches the observation point immediately after the source launched. By comparing the waveforms at different receiving locations, we find that waveforms differ at different observation orientations.

81 citations

Journal ArticleDOI
TL;DR: In this article, the radiation emitted by electromagnetic sources placed both inside and outside of a homogeneous sphere of chiral media is studied using an exact formulation, and the radiated fields and radiation resistance are examined for a dipole located at the center of the chiral sphere.
Abstract: The radiation emitted by electromagnetic sources placed both inside and outside of a homogeneous sphere of chiral media is studied using an exact formulation. For both cases, dyadic Green’s functions are found in terms of spherical vector wave functions. The radiated fields and radiation resistance are examined for a dipole located at the center of the chiral sphere. For this case, it is shown that by choosing the sphere’s size and material parameters properly, purely circular polarization can be achieved in the far field. It is also demonstrated that the radiation resistance of the dipole can be increased.

81 citations

Journal ArticleDOI
TL;DR: In this article, a method for probe characterization based on lithography on a photosensitive polymer without film development is proposed, where the light emitted by different kinds of probes in order to distinguish in situ the near field contribution from the far field contribution of the tip.
Abstract: We propose here a method for probe characterization based on lithography on a photosensitive polymer without film development. We record in near field conditions the light emitted by different kinds of probes in order to distinguish in situ the near field contribution from the far field contribution of the tip. This information, which cannot be deduced from far field diffraction, allows an estimation of the field confinement and of the expected resolution of the microscope.

81 citations

Journal ArticleDOI
TL;DR: In this article, a finite cone, a lens, an elliptic ogive, a spindle and a finite cylinder are approximated by using radar cross-section results for bodies of revolution.
Abstract: By use of approximations based on physical reasoning radar cross-section results for bodies of revolution are found. In the Rayleigh region (wavelength large with respect to object dimensions) approximate solutions are found. Examples given include a finite cone, a lens, an elliptic ogive, a spindle and a finite cylinder. In the physical optics region (wavelength very small with respect to all radii of curvature) Kirchhoff theory and also geometric optics can be used. When the body dimensions are only moderately large with respect to the wavelength, Fock or Franz theory can be applied, and examples of the circular and elliptic cylinder are presented. In the region where some dimensions of the body are large with respect to the wavelength and other dimensions are small with respect to the wavelength, special techniques are used. One example, the finite cone, is solved by appropriate use of the wedge-like fields locally at the base. Another example is the use of traveling wave theory for obtaining approximate solutions for the prolate spheroid and the ogive. Other results are obtained for cones the base perimeter of which is of the order of a wavelength by using known results for rings of the same perimeter.

80 citations

Journal ArticleDOI
TL;DR: In this paper, a second-order asymptotic evaluation for the electric fields of an arbitrarily oriented, infinitesimal electric dipole for source and observation points located in the vicinity of the air/dielectric interface is carried out through the method of steepest descents.
Abstract: The problem of near-earth wave propagation in the presence of a dielectric layer such as a vegetation or snow covering is considered in this paper by modeling the propagation environment as a homogeneous two-layer medium (air/dielectric/ground). A number of studies have demonstrated the relevancy of the lateral wave for the case when both the transmitter and receiver are located within a simple half-space dielectric medium . Unfortunately, for the generalized two-layer model, for configurations in which the transmitter or receiver (or both) is located above the dielectric layer, far-field analytical expressions that include all propagation features do not exist. In this paper, in order to arrive at a computational efficient solution for the two-layer model, a second-order asymptotic evaluation for the electric fields of an arbitrarily oriented, infinitesimal electric dipole-for source and observation points located in the vicinity of the air/dielectric interface-is carried out through the method of steepest descents. The formulations are valid in the far field, with the limitation that the exponentially decaying pole and branch cut contributions have been ignored. It is observed that the Norton wave, though it is highly localized near the air/dielectric interface, is a significant contribution either when the dipole and observation points are both located above the dielectric layer or when one is above and the other is within the layer.

80 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023132
2022281
2021376
2020460
2019640
2018604