Low-frequency image theory for a current dipole in front of a permeable sphere

1995 ◽  
Vol 31 (2) ◽  
pp. 954-959
Author(s):  
J.C.-E. Sten
Keyword(s):  
Low Frequency ◽  
Image Theory ◽  
Current Dipole ◽  
Permeable Sphere ◽  
A Current

The Magnetometric Resistivity Method and its Application to the Mapping of a Fault

1974 ◽  
Vol 11 (8) ◽  
pp. 1136-1156 ◽  
Author(s):  
R. N. Edwards
Keyword(s):  
Geophysical Methods ◽  
Low Frequency ◽  
Current Dipole ◽  
Field Techniques ◽  
Resistivity Method ◽  
Highly Sensitive ◽  
The Difference ◽  
Electrical Prospecting ◽  
The Magnetic Field ◽  
A Current

An electrical prospecting method, known as the Magnetometric Resistivity (MMR) method, is described both in theory and in practice. It is based on the measurement of the low level (<5 gamma), low-frequency (1–5 Hz) magnetic fields associated with noninductive current flow in the earth. The field techniques are similar to those employed in the gradient array resistivity method, except the potential electrodes are replaced by a highly sensitive component magnetometer. The horizontal component of the magnetic field, which is at right angles to the line joining the current electrodes, is usually measured. The MMR anomaly is the difference between the measured values and the 'normal' values, which are the values of the component expected at the surface of a uniform earth.It is shown that an earth composed of uniform, horizontal layers gives no MMR anomaly. But the MMR anomalies due to a current dipole, a sphere and a fault are calculated. The anomaly due to a sphere is compared with anomalies for the sphere obtained by other geophysical methods. The principal profile of the anomaly is similar to that of the vertical field anomaly of a vertically magnetised sphere.It is argued that the MMR method may be superior to the gradient-array resistivity method in mapping inhomogeneities that are embedded at depth in a conductive host or are located beneath conductive overburden. The latter is demonstrated using an analogue model.The field apparatus and the field techniques of the method are described. The data taken during a field test of the method over the Gloucester Fault, at Leitrim, Ontario, are presented and are interpreted in terms of a conductivity contrast across the fault. The contrast determined agrees quantitatively with estimates obtained using other electrical methods.

Magnetic localisation of a current dipole implanted in dogs

1987 ◽  
Vol 32 (1) ◽  
pp. 65-70 ◽  
Author(s):  
E Costa Monteiro ◽  
A C Bruno ◽  
S R W Louro ◽  
P Costa Ribeiro ◽  
A Fonseca Costa
Keyword(s):  
Current Dipole ◽  
A Current

Part II magnetic field produced by a current dipole

1976 ◽  
Vol 9 (4) ◽  
pp. 409-417 ◽  
Author(s):  
David Cohen ◽  
Hidehiro Hosaka
Keyword(s):  
Magnetic Field ◽  
Current Dipole ◽  
A Current

Short-wave low-frequency equilibrium spectra in a current-carrying plasma

1993 ◽  
Vol 50 (1) ◽  
pp. 45-50 ◽  
Author(s):  
Maxim O. Vakoulenko
Keyword(s):  
Low Frequency ◽  
Short Wave ◽  
Integrals Of Motion ◽  
Mean Values ◽  
The Mean ◽  
A Current

Short-wave (wavelengths smaller than the ion gyroradius) low-frequency (frequencies not exceeding the ion gyrofrequency) electromagnetic equilibrium spectra are found in a current-carrying plasma. Owing to cross-field correlations, the mean values of the integrals of motion increase, whereas their cascade rates are inhibited.

A CONDUCTING PERMEABLE SPHERE IN THE PRESENCE OF A COIL CARRYING AN OSCILLATING CURRENT

1953 ◽  
Vol 31 (4) ◽  
pp. 670-678 ◽  
Author(s):  
James R. Wait
Keyword(s):  
Magnetic Fields ◽  
Magnetic Permeability ◽  
Scalar Potential ◽  
Spherical Body ◽  
Primary Field ◽  
Secondary Field ◽  
Electrical Prospecting ◽  
Permeable Sphere ◽  
A Current

The analysis is carried out for the problem of a current-carrying coil in the neighborhood of a spherical body whose conductivity and magnetic permeability differ from the surroundings. The case is considered in detail where the frequency is low enough so that the primary field of the coil can be derived from a magnetic scalar potential. The secondary magnetic fields due to the sphere are then derived. The "in-phase" and "quadrature" components of the secondary field are discussed numerically and illustrated by graphs. The results have application to electrical prospecting.

Chemical reaction in electric discharge. V. Reaction kinetics in a low frequency modulated discharge

1979 ◽  
Vol 57 (7) ◽  
pp. 785-795 ◽  
Author(s):  
John N. Smith ◽  
Motilal D. Costa ◽  
Jacques M. Deckers
Keyword(s):  
Glow Discharge ◽  
Reaction Mechanisms ◽  
Low Frequency ◽  
Modulation Method ◽  
Current Modulation ◽  
Kinetic Information ◽  
Glow Discharges ◽  
Dc Discharge ◽  
A Current

A current modulation technique has been developed for the determination of kinetic information in glow discharges through flowing gases. A low frequency sinusoidal modulation superimposed on the dc discharge current produces modulations in the electron density and radical concentrations. Measurements of the amplitudes and phase shifts of radical concentrations can be used to elucidate reaction mechanisms and to determine rate constants for some reaction processes.The kinetic response of discharge chemical phenomena to an applied current modulation is discussed for several general types of reaction mechanisms. Rates of O atom production and removal measured in a current modulated O2 glow discharge are compared to rates measured in a dc glow discharge. The excellent agreement of these two sets of results provides an experimental foundation for the current modulation method.

Field and/or resistivity mapping in MT-VLF and implications for data processing

Geophysics ◽  
1994 ◽  
Vol 59 (11) ◽  
pp. 1695-1712 ◽  
Author(s):  
Roger Guerin ◽  
Alain Tabbagh ◽  
Pierre Andrieux
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Test Site ◽  
Horizontal Polarization ◽  
Resistivity Measurements ◽  
Magnetic Components ◽  
Frequency Independent ◽  
Prismatic Bodies ◽  
Lateral Variations ◽  
A Current

The ratio of the horizontal electric and magnetic components of the electromagnetic field generated by a radio transmitter in the very low frequency (VLF) range is used in MT-VLF resistivity mapping to determine the apparent resistivity of the ground. A theoretical calculation of the responses of simple 2-D and 3-D prismatic bodies shows that the measurable lateral variations in both fields are independent, uncoupled, and correspond to frequency‐independent, static variations. It is advantageous therefore to process and map the fields separately. Processing methods used in gravimetry and magnetics are especially appropriate in correcting the apparent anisotropy related to the horizontal polarization of the primary field and in integrating (upward continuation) the high‐frequency spatial variations. The different processes tested on a synthetic case and on data obtained at the Centre de Recherches Géophysiques (CRG) test site showed how to eliminate shallow features and a current channeling conductor to favor the anomaly of a fault. A third example with a hydrogeological application shows the advantages of this method over Wenner direct‐current resistivity measurements.

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