TRANSIENT ELECTROMAGNETIC RESPONSE OF AN INHOMOGENEOUS CONDUCTING SPHERE

Geophysics ◽  
1970 ◽  
Vol 35 (2) ◽  
pp. 331-336 ◽  
Author(s):  
Saurabh K. Verma ◽  
Rishi Narain Singh
Keyword(s):  
Magnetic Field ◽  
Rise Time ◽  
Mineral Deposits ◽  
Electromagnetic Response ◽  
Radial Coordinate ◽  
Induced Magnetic Field ◽  
Transient Electromagnetic ◽  
Unit Step ◽  
Analytic Expressions ◽  
The Magnetic Field

Analytic expressions for the quasi‐static electromagnetic response of a sphere in presence of unit‐step and ramp‐type time varying magnetic fields are derived. The conductivity inside the sphere is assumed to vary linearly with radius, i.e. [Formula: see text], where ρ is radial coordinate, [Formula: see text] is a constant and a is the radius of sphere. Curves showing the decay of the magnetic field for both types of fields are presented. In the case of ramp‐type applied magnetic field, the magnitudes of maxima of the induced magnetic field are found to decrease with increase in the rise time of the applied field and, hence, exciting pulses having small values of rise time should be used. It is believed that the analysis will be useful in the geoelectric exploration for highly conducting mineral deposits.

Using an induction coil sensor to indirectly measure the B-field response in the bandwidth of the transient electromagnetic method

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1489-1494 ◽  
Author(s):  
Richard S. Smith ◽  
A. Peter Annan
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Indirect Measurement ◽  
Rate Of Change ◽  
Induction Coil ◽  
Voltage Response ◽  
Magnetic Field Data ◽  
Transient Electromagnetic ◽  
Different Characteristics ◽  
The Magnetic Field

The traditional sensor used in transient electromagnetic (EM) systems is an induction coil. This sensor measures a voltage response proportional to the time rate of change of the magnetic field in the EM bandwidth. By simply integrating the digitized output voltage from the induction coil, it is possible to obtain an indirect measurement of the magnetic field in the same bandwidth. The simple integration methodology is validated by showing that there is good agreement between synthetic voltage data integrated to a magnetic field and synthetic magnetic‐field data calculated directly. Further experimental work compares induction‐coil magnetic‐field data collected along a profile with data measured using a SQUID magnetometer. These two electromagnetic profiles look similar, and a comparison of the decay curves at a critical point on the profile shows that the two types of measurements agree within the bounds of experimental error. Comparison of measured voltage and magnetic‐field data show that the two sets of profiles have quite different characteristics. The magnetic‐field data is better for identifying, discriminating, and interpreting good conductors, while suppressing the less conductive targets. An induction coil is therefore a suitable sensor for the indirect collection of EM magnetic‐field data.

scholarly journals On the Formulae for Calculating the Magnetic Field in the Source of Solar Microwave Bursts

1993 ◽  
Vol 141 ◽  
pp. 295-298
Author(s):  
Ren-Yang Zhao
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Rise Time ◽  
Peak Frequency ◽  
Nonthermal Electrons ◽  
Source Regions ◽  
Solar Microwave ◽  
Analytical Formulae ◽  
The Magnetic Field ◽  
Microwave Bursts

AbstractBased on the theory of gyro-synchrotron radiation from both thermal and nonthermal electrons, and adopting the relation between the peak frequency and the corresponding rise time of microwave bursts, we have derived several analytical formulae for calculating the magnetic field in the source regions of solar microwave bursts.

RESPONSE OF DYKE TO OSCILLATING DIPOLE

Geophysics ◽  
1958 ◽  
Vol 23 (1) ◽  
pp. 128-133 ◽  
Author(s):  
James Paul Wesley
Keyword(s):  
Magnetic Field ◽  
Closed Form ◽  
Scalar Potential ◽  
Three Dimensions ◽  
Electromagnetic Response ◽  
Dipole Source ◽  
First Approximation ◽  
Sulfide Ore ◽  
Infinite Conductivity ◽  
The Magnetic Field

A dyke of sulfide ore may be geophysically prospected by observing its electromagnetic response to a slowly oscillating magnetic dipole source. An excellent first approximation of the fields generated is obtained by considering the idealized case of a dyke of infinite conductivity and vanishing thickness in a vacuum. Surprisingly, this idealized problem can be solved exactly in terms of a newly discovered Green’s function for Laplace’s equation (in three dimensions) which is simply expressed in closed form. The magnetic scalar potential and the magnetic field are given for final results.

scholarly journals On the magnetic field of OH 231.8+4.2

2011 ◽  
Vol 7 (S283) ◽  
pp. 418-419
Author(s):  
Marcelo L. Leal-Ferreira ◽  
Wouter H. T. Vlemmings ◽  
Philip J. Diamond ◽  
Athol Kemball ◽  
Nikta Amiri ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spherical Symmetry ◽  
Planetary Nebula ◽  
Initial Mass ◽  
Induced Magnetic Field ◽  
Tidal Forces ◽  
Star Binary ◽  
The Magnetic Field

AbstractDuring the transition from an AGB star to a planetary nebula, a large number of low/intermediate initial mass stars loses its spherical symmetry. The process responsible for that change of morphology is, so far, not well understood. The candidates responsible for shaping these objects are (i) a companion to the star (binary/heavy planet) and its tidal forces, (ii) disk interaction and (iii) magnetic fields - or a combination of these. In particular a binary induced magnetic field is a promising option. To study this we observed the polarization of H2O masers in the known binary pre-Planetary Nebula (pPN) OH231.8+4.2. Our results show a magnetic field B|| of ~45 mG is present in the H2O maser region of this pPN.

scholarly journals Analysis of Juno perijove 1 magnetic field data using the Jovian paraboloid magnetospheric model

2018 ◽  
Author(s):  
Ivan A. Pensionerov ◽  
Elena S. Belenkaya ◽  
Stanley W. H. Cowley ◽  
Igor I. Alexeev ◽  
Vladimir V. Kalegaev ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Field Model ◽  
Outer Edge ◽  
Optimal Parameters ◽  
Magnetic Field Data ◽  
Analytic Expressions ◽  
Magnetic Field Model ◽  
Current Systems ◽  
The Magnetic Field

Abstract. One of the main features of Jupiter's magnetosphere is its equatorial magnetodisc, which significantly increases the field strength and size of the magnetosphere. Juno measurements of the magnetic field during the perijove 1 pass have allowed us to determine optimal parameters of the magnetodisc using the paraboloid magnetospheric magnetic field model, which employs analytic expressions for the magnetospheric current systems. Specifically within the model we determine the size of the Jovian magnetodisc and the magnetic field strength at its outer edge.

scholarly journals On the Bottom Magnetic Fields of Millisecond Pulsars

2004 ◽  
Vol 218 ◽  
pp. 47-48
Author(s):  
Chengmin Zhang
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Accretion Rate ◽  
Induced Magnetic Field ◽  
Radio Observations ◽  
Millisecond Pulsars ◽  
Low Field ◽  
Field Evolution ◽  
Field Decay ◽  
The Magnetic Field

The magnetic field strengths of most millisecond pulsars (MSPs) are about 108–9 gauss. The accretion-induced magnetic field evolution scenario here concludes that field decay is related to the accreted mass, that the minimum or bottom field stops at about 108 gauss for Eddington-limited accretion, and scales with the accretion rate as M1/2. The possibility of low field (∼ 107 gauss) MSPs has been proposed for future radio observations.

scholarly journals Noise-induced magnetic field saturation in kinetic simulations

2020 ◽  
Vol 86 (4) ◽  
Author(s):  
J. Juno ◽  
M. M. Swisdak ◽  
J. M. Tenbarge ◽  
V. Skoutnev ◽  
A. Hakim
Keyword(s):  
Magnetic Field ◽  
Sampling Error ◽  
Kinetic Equations ◽  
Particle Methods ◽  
Induced Magnetic Field ◽  
Particle Count ◽  
Particle In Cell ◽  
Broad Array ◽  
The Magnetic Field ◽  
Kinetic Instabilities

Monte Carlo methods are often employed to numerically integrate kinetic equations, such as the particle-in-cell method for the plasma kinetic equation, but these methods suffer from the introduction of counting noise to the solution. We report on a cautionary tale of counting noise modifying the nonlinear saturation of kinetic instabilities driven by unstable beams of plasma. We find a saturated magnetic field in under-resolved particle-in-cell simulations due to the sampling error in the current density. The noise-induced magnetic field is anomalous, as the magnetic field damps away in continuum kinetic and increased particle count particle-in-cell simulations. This modification of the saturated state has implications for a broad array of astrophysical phenomena beyond the simple plasma system considered here, and it stresses the care that must be taken when using particle methods for kinetic equations.

scholarly journals Modulationof The Recirculation Region Within Two Inline Square Rib Due toMagnetohydrodynamic FlowUsingComputational Fluid Dynamics

2020 ◽  
pp. 331-336
Author(s):  
Sayahnya Roy ◽  
Gunasekaran N ◽  
Krishnendu Barman ◽  
Koustuv Debnath ◽  
Prantik Sinha
Keyword(s):  
Magnetic Field ◽  
Hartmann Number ◽  
Turbulent Transport ◽  
Mhd Flow ◽  
Recirculation Region ◽  
Wake Region ◽  
Induced Magnetic Field ◽  
Tke Dissipation Rate ◽  
Vorticity Generation ◽  
The Magnetic Field

This study presents the turbulent flow around two square ribs. The numerical computations performed using k–ε model at Reynolds number (Re) = 60000 to quantify the turbulent transport measures. The magnetic field has been applied by Hartmann number (Ha) to generate the magnetohydrodynamic (MHD) flow. The reduction of recirculation region was observed due to the application of magnetic field in the flow. The weak recirculation has an effect on small vorticity generation, which leads to small turbulent kinetic energy (TKE) and TKE dissipation rate generation in the wake region behind the rib. The induced magnetic field is capable of controlling the vortex structures around the square ribs. Results in decreasing magnitude of turbulence level around and between the spaces of the square ribs. It may be hypothesized that by introducing magnetic field, the unwanted vibrations (due to vortex shedding behind the rib) of fully submerged structures can be controlled.

scholarly journals Research on Airborne Electromagnetic Whole-area Apparent Resistivity Imaging Algorithm in the Detection of Goaf in Rail Transit

2021 ◽  
Vol 2083 (4) ◽  
pp. 042072
Author(s):  
Yajuan Jia ◽  
Jianbo Zheng ◽  
Hongfang Zhou
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Apparent Resistivity ◽  
Electromagnetic Method ◽  
Transient Electromagnetic Method ◽  
Resistivity Imaging ◽  
Transient Electromagnetic ◽  
Air System ◽  
The Magnetic Field

Abstract Depth apparent resistivity imaging is an important process of data processing and analysis in the aviation transient electromagnetic method. It can provide reference value of conductor depth, vertical extension, and other information, and can accurately provide the measurement of each aviation transient electromagnetic measurement system. The structural section of the apparent conductivity of the one-dimensional layered medium on the line. As an advanced geophysical exploration technology, the aerial transient electromagnetic method has been applied significantly in the exploration of polymetallic minerals abroad in recent years. In this paper, based on the theory of ground-to-air transient electromagnetic method with multiple radiation sources, a corresponding multi-component global apparent resistivity definition method is established. The advantages of using the magnetic field strength to define the global apparent resistivity of the multi-radiation field source ground-air system are analysed. For each component of the magnetic field strength, respective global apparent resistivity algorithms are proposed to realize the multi-component, full-time, and full-space visual resistivity. The resistivity is calculated, and the influence of the offset on the global apparent resistivity is analysed. By adjusting the relative position of the source and the current direction and other parameters, the multi-radiation source transient electromagnetic ground-air system can not only strengthen the signal strength of different components, weaken random interference, but also better distinguish the location of underground anomalies

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