Scattered fields by a sphere present in near field of a Hertz dipole

2005 ◽  
Author(s):  
M. Amin
Keyword(s):  
Near Field ◽  
Scattered Fields

Modeling near‐field GPR in three dimensions using the FDTD method

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1114-1126 ◽  
Author(s):  
Roger L. Roberts ◽  
Jeffrey J. Daniels
Keyword(s):  
Electrical Properties ◽  
Finite Difference ◽  
Time Domain ◽  
Near Field ◽  
Characteristic Impedance ◽  
Fdtd Method ◽  
Three Dimensions ◽  
Field Pattern ◽  
Scattered Fields ◽  
Transmitting Antenna

Complexities associated with the theoretical solution of the near‐field interaction between the fields radiated from dipole antennas placed near a dielectric half‐space and electrical inhomogeneities within the dielectric can be overcome by using numerical techniques. The finite‐difference time‐domain (FDTD) technique implements finite‐difference approximations of Maxwell's equations in a discretized volume that permit accurate computation of the radiated field from a transmitting antenna, propagation through the air‐earth interface, scattering by subsurface targets and reception of the scattered fields by a receiving antenna. In this paper, we demonstrate the implementation of the FDTD technique for accurately modeling near‐field time‐domain ground‐penetrating radar (GPR). This is accomplished by incorporating many of the important GPR parameters directly into the FDTD model. These variables include: the shape of the GPR antenna, feed cables with a fixed characteristic impedance attached to the terminals of the antenna, the height of the antenna above the ground, the electrical properties of the ground, and the electrical properties and geometry of targets buried in the subsurface. FDTD data generated from a 3-D model are compared to experimental antenna impedance data, field pattern data, and measurements of scattering from buried pipes to verify the accuracy of the method.

SCATTERING OF ELECTROMAGNETIC WAVES BY COAXIAL CYLINDERS

1956 ◽  
Vol 34 (5) ◽  
pp. 510-520 ◽  
Author(s):  
Albert W. Adey
Keyword(s):  
Transmission Line ◽  
Electromagnetic Waves ◽  
Parallel Plate ◽  
Near Field ◽  
Experimental Results ◽  
Metal Cylinder ◽  
Scattering System ◽  
Coaxial Cylinders ◽  
Scattered Fields ◽  
Good Agreement

A scattering system comprising two coaxial, dielectric cylinders has been studied theoretically and experimentally. Calculations have been made of the forward and back scattered fields for several combinations of inner and outer radii. It has been found that, by covering a metal cylinder with a coaxial dielectric shield, it is possible to eliminate to some extent the deep near-field shadow. Experimental results obtained at a wavelength of 3.275 cm. using a parallel-plate transmission line are in good agreement with calculations.

scholarly journals Characteristic Mode Theory of Wavetraps for Antenna Decoupling

2020 ◽  
Author(s):  
Mikko Heino ◽  
Clemens Icheln ◽  
Pasi Ylä-Oijala ◽  
Buon Kiong Lau ◽  
Katsuyuki Haneda
Keyword(s):  
Design Method ◽  
Near Field ◽  
Full Duplex ◽  
Patch Antennas ◽  
Duplex System ◽  
Characteristic Mode ◽  
Full Wave ◽  
Receiving Antenna ◽  
Operational Frequency ◽  
Scattered Fields

This paper introduces a systematic design method for decoupling elements, which can significantly improve the isolation between two co-located antennas, e.g. between transmit and receive antennas of an in-band full-duplex system. The design method applies the theory of characteristic modes for controlling the phase and amplitude of the scattered fields of the decoupling element, in order to optimally cancel the original incident fields which couple to the receiving antenna. We describe concisely the effects that characteristic angle, modal near-field, and modal excitation of the decoupling element have on the antenna isolation. For validating the proposed method, a planar wavetrap is designed and the isolation improvement verified with full-wave simulations. When we use the proposed method to optimize a wavetrap that is placed between two co-located patch antennas, we obtain an improvement of the isolation between the antennas by 33 dB at the centre frequency of their operational frequency band, and at least 12-dB improvement across the whole 142-MHz operational bandwidth of the two antennas. As a benchmark, the wavetrap is replaced by an absorber occupying 10 times the volume of the wavetrap. The absorber gives only 6 dB of isolation improvement, substantiating the effectiveness of the proposed wavetrap method.

scholarly journals Characteristic Mode Theory of Wavetraps for Antenna Decoupling

2020 ◽  
Author(s):  
Mikko Heino ◽  
Clemens Icheln ◽  
Pasi Ylä-Oijala ◽  
Buon Kiong Lau ◽  
Katsuyuki Haneda
Keyword(s):  
Design Method ◽  
Near Field ◽  
Full Duplex ◽  
Patch Antennas ◽  
Duplex System ◽  
Characteristic Mode ◽  
Full Wave ◽  
Receiving Antenna ◽  
Operational Frequency ◽  
Scattered Fields

This paper introduces a systematic design method for decoupling elements, which can significantly improve the isolation between two co-located antennas, e.g. between transmit and receive antennas of an in-band full-duplex system. The design method applies the theory of characteristic modes for controlling the phase and amplitude of the scattered fields of the decoupling element, in order to optimally cancel the original incident fields which couple to the receiving antenna. We describe concisely the effects that characteristic angle, modal near-field, and modal excitation of the decoupling element have on the antenna isolation. For validating the proposed method, a planar wavetrap is designed and the isolation improvement verified with full-wave simulations. When we use the proposed method to optimize a wavetrap that is placed between two co-located patch antennas, we obtain an improvement of the isolation between the antennas by 33 dB at the centre frequency of their operational frequency band, and at least 12-dB improvement across the whole 142-MHz operational bandwidth of the two antennas. As a benchmark, the wavetrap is replaced by an absorber occupying 10 times the volume of the wavetrap. The absorber gives only 6 dB of isolation improvement, substantiating the effectiveness of the proposed wavetrap method.

Near-field scanning optical microscopy

1986 ◽  
Vol 44 ◽  
pp. 642-643
Author(s):  
E. Betzig ◽  
A. Harootunian ◽  
M. Isaacson ◽  
A. Lewis
Keyword(s):  
Near Field ◽  
Optical Microscope ◽  
Visible Radiation ◽  
Field Methods ◽  
Optical Elements ◽  
Optical Region ◽  
Order Of Magnitude ◽  
Nondestructive Imaging ◽  
Scanning Optical Microscopy ◽  
Near Field Scanning

In general, conventional methods of optical imaging are limited in spatial resolution by either the wavelength of the radiation used or by the aberrations of the optical elements. This is true whether one uses a scanning probe or a fixed beam method. The reason for the wavelength limit of resolution is due to the far field methods of producing or detecting the radiation. If one resorts to restricting our probes to the near field optical region, then the possibility exists of obtaining spatial resolutions more than an order of magnitude smaller than the optical wavelength of the radiation used. In this paper, we will describe the principles underlying such "near field" imaging and present some preliminary results from a near field scanning optical microscope (NS0M) that uses visible radiation and is capable of resolutions comparable to an SEM. The advantage of such a technique is the possibility of completely nondestructive imaging in air at spatial resolutions of about 50nm.

Principles of Planar Near-Field Antenna Measurements

2007 ◽  
Author(s):  
Stuart Gregson ◽  
John McCormick ◽  
Clive Parini
Keyword(s):  
Near Field ◽  
Antenna Measurements

Immobilization of Radionuclides on Iron Canister Material at Simulated Near-field Conditions

2008 ◽  
Author(s):  
Daqing Cui ◽  
Ylva Ranebo ◽  
Jeanett Low ◽  
Vincenzo Rondinella ◽  
Jinshan Pan ◽  
...  
Keyword(s):  
Near Field ◽  
Field Conditions
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