ELECTRIC DIPOLE OVER AN ANISOTROPIC AND INHOMOGENEOUS EARTH

Geophysics ◽  
1967 ◽  
Vol 32 (4) ◽  
pp. 652-667 ◽  
Author(s):  
Ajit Kumar Sinha ◽  
Prabhat K. Bhattacharya
Keyword(s):  
Electric Dipole ◽  
Principal Axis ◽  
Low Frequency ◽  
Transversely Isotropic ◽  
Vector Potentials ◽  
The Earth ◽  
Longitudinal Conductivity ◽  
Asymptotic Expressions ◽  
Special Cases ◽  
Horizontal Electric Dipole

The electromagnetic fields of a low‐frequency horizontal electric dipole placed over a two‐layer earth have been derived. The overburden is considered to be transversely isotropic with respect to the conductivity. The unequal principal axis of the conductivity tensor is normal to the layers. The substratum is taken as isotropic. The vector potentials at the surface of the earth have been evaluated and expressed in such a way that the fields may be easily calculated. We have considered the special cases of a perfectly conducting, a perfectly insulating, and a substratum whose conductivity is very close to the longitudinal conductivity of the overburden. Asymptotic expressions for the fields have also been calculated. All the results are given in terms of known functions, and some numerical results have been included.

On modeling a well casing for resistivity and induced polarization

Geophysics ◽  
1984 ◽  
Vol 49 (11) ◽  
pp. 2061-2063 ◽  
Author(s):  
James R. Wait
Keyword(s):  
Electrical Properties ◽  
Electric Dipole ◽  
Free Space ◽  
Eddy Currents ◽  
Interfacial Polarization ◽  
Induced Polarization ◽  
Mutual Impedance ◽  
The Earth ◽  
Horizontal Electric Dipole ◽  
Displacement Currents

In a previous communication I proposed an analytical model to simulate the electromagnetic (EM) and induced polarization (IP) response of a metal well casing (Wait, 1983). To facilitate the analysis, the earth was idealized as a homogeneous conducting half‐space of electrical properties (σ, ε, μ). The well casing was represented as a filamental vertical conductor of semiinfinite length that was characterized by a series axial impedance to account for eddy currents and interfacial polarization. A further basic simplification was to neglect displacement currents in the air; this was justified when all significant distances were small compared with the free‐space wavelength. Initially, the source was taken to be a horizontal electric dipole or current element I ds on the air‐earth interface. By integration of the results, the mutual impedance between two grounded circuits could be ascertained. In the absence of the vertical conductor (i.e., the well casing) the results reduced to those given by Sunde (1968) and Ward (1967).

Effect of a Conducting Overburden on the Fields of a Buried Dipole Source

1975 ◽  
Vol 53 (6) ◽  
pp. 598-609 ◽  
Author(s):  
V. Ramaswamy ◽  
H. W. Dosso
Keyword(s):  
Magnetic Fields ◽  
Electromagnetic Fields ◽  
Analytical Solutions ◽  
Electric Dipole ◽  
Lower Layer ◽  
Low Frequency ◽  
Dipole Source ◽  
Vertical Electric Dipole ◽  
Electric And Magnetic Fields ◽  
Horizontal Electric Dipole

Analytical solutions for the low frequency electromagnetic fields of a dipole source situated in the lower layer of a two layer conductor are derived. The sources considered are a vertical electric dipole, a horizontal electric dipole, and a horizontal magnetic dipole. The numerical results discussed in this paper describe the general behavior of the electric and magnetic fields for various upper layer conductivities, upper layer thickness, and source depths. The results are of interest in the application of electromagnetic techniques to locate miners trapped underground following a mine disaster.

THE INFLUENCE OF THE IONOSPHERE ON THE VERTICAL FORCE EXCITED BY A HORIZONTAL ELECTRIC DIPOLE

2020 ◽  
pp. 68-76
Author(s):  
P. E. Tereshchenko
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Vertical Component ◽  
Low Frequency ◽  
Vertical Force ◽  
Frequency Range ◽  
The Earth ◽  
Horizontal Electric Dipole ◽  
Lower Frequency Range ◽  
The Magnetic Field

An analytical expression for the vertical component of the magnetic field has been obtained, with the help of which calculations have been made showing the effect of the ionosphere on the low-frequency field in the Earth-ionosphere waveguide. At distances from the source that are less than the doubled waveguide height, in ELF, and a lower frequency range, noticeable changes in the field strength caused by the state of the ionosphere are found.

ELECTROMAGNETIC FIELDS OF AN OSCILLATING MAGNETIC DIPOLE OVER AN ANISOTROPIC EARTH

Geophysics ◽  
1968 ◽  
Vol 33 (2) ◽  
pp. 346-353 ◽  
Author(s):  
Ajit K. Sinha
Keyword(s):  
Wave Propagation ◽  
Electromagnetic Wave ◽  
Magnetic Dipole ◽  
Electromagnetic Fields ◽  
Isotropic Medium ◽  
Electromagnetic Wave Propagation ◽  
Vector Potentials ◽  
The Earth ◽  
Longitudinal Conductivity ◽  
Vertical Magnetic Dipole

The problem of electromagnetic wave propagation from an oscillating magnetic dipole placed over a uniaxially anisotropic earth has been considered. Formal expressions for the vector potentials inside the earth have been derived. It has been shown that for a vertical magnetic dipole, the field components are identical to those in the case of an isotropic medium in which the conductivity is the “horizontal or longitudinal conductivity.” For a horizontal dipole, directed along the x axis, it has been shown that the vector potential inside the earth will have a y component as well as x and z components. Formal expressions for the vector potentials in air have been obtained for the case of a horizontal magnetic dipole. However when the conductivity of air is considered to be negligibly small, the field components are not affected by the anisotropy.

Foreshock ULF fluctuations near the Moon: THEMIS observations

2021 ◽  
Author(s):  
Anna Salohub ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Rest Frame ◽  
Low Frequency ◽  
Solar Wind Plasma ◽  
Turbulent Plasma ◽  
Bow Shock ◽  
Ulf Waves ◽  
The Moon ◽  
Shock Surface ◽  
The Earth

<p>The foreshock is a region filled with a turbulent plasma located upstream the Earth’s bow shock where interplanetary magnetic field (IMF) lines are connected to the bow shock surface. In this region, ultra-low frequency (ULF) waves are generated due to the interaction of the solar wind plasma with particles reflected from the bow shock back into the solar wind. It is assumed that excited waves grow and they are convected through the solar wind/foreshock, thus the inner spacecraft (close to the bow shock) would observe larger wave amplitudes than the outer (far from the bow shock) spacecraft. The paper presents a statistical analysis of excited ULF fluctuations observed simultaneously by two closely separated THEMIS spacecraft orbiting the Moon under a nearly radial IMF. We found that ULF fluctuations (in the plasma rest frame) can be characterized as a mixture of transverse and compressional modes with different properties at both locations. We discuss the growth and/or damping of ULF waves during their propagation.</p>

WORKING DEPTHS FOR LOW FREQUENCY ELECTRICAL PROSPECTING

Geophysics ◽  
1945 ◽  
Vol 10 (1) ◽  
pp. 63-75 ◽  
Author(s):  
William Bradley Lewis
Keyword(s):  
Low Frequency ◽  
Electrical Measurements ◽  
The Earth ◽  
Electrical Prospecting

Electrical measurements were made on the surface of the earth with low frequency commutated current using nineteen separate frequencies and six electrode separations. Analysis of the data indicates that there is an effect of appreciable magnitude attributable to an interface 6000 feet below the surface.

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