Quasistatic transient electromagnetic response of a permeable nonuniformly conducting cylinder

1976 ◽  
Vol 54 (21) ◽  
pp. 2134-2139
Author(s):  
S. K. Verma ◽  
M. S. Joshi
Keyword(s):  
Distribution Pattern ◽  
Transient Response ◽  
Magnetic Permeability ◽  
Large Time ◽  
Initial Response ◽  
Pulse Response ◽  
Electromagnetic Response ◽  
Conductivity Distribution ◽  
Conducting Cylinder ◽  
Transient Electromagnetic

The step-pulse response of a permeable and a radially nonuniformly conducting cylinder is obtained. Effects of the conductivity distribution pattern and the magnetic permeability on the transient response are examined in detail. It is found that: (i) the initial response (for t → 0) remains unaffected by both the inhomogeneity and the permeability of the cylinder; (ii) the large time response is governed only by the permeability; and (iii) the conductivity inhomogeneity is reflected only during intermediate times. Finally, the implications of the results for predicting the parameters of the cylinder are discussed.

Transient electromagnetic response of a polarizable ground

Geophysics ◽  
1981 ◽  
Vol 46 (7) ◽  
pp. 1037-1041 ◽  
Author(s):  
T. Lee
Keyword(s):  
Time Constant ◽  
Transient Response ◽  
Induced Polarization ◽  
Electromagnetic Response ◽  
Relaxation Model ◽  
Reverse Polarity ◽  
Transient Electromagnetic ◽  
Show Evidence ◽  
Positive Time

When a uniform ground has a conductivity which may be described by a Cole‐Cole relaxation model with a positive time constant, then the transient response of such a ground will show evidence of induced polarization (IP) effects. The IP effects cause the transient initially to decay quite rapidly and to reverse polarity. After this reversal the transient decays much more slowly, the decay at this stage being about the same rate as a nonpolarizable ground.

The transient electromagnetic response of a magnetic or superparamagnetic ground

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 854-860 ◽  
Author(s):  
T. Lee
Keyword(s):  
Transient Response ◽  
Direct Current ◽  
Free Space ◽  
Electromagnetic Response ◽  
Time Constants ◽  
True Value ◽  
Transient Electromagnetic ◽  
Current Value ◽  
The Wire ◽  
Weakly Magnetic

The effect of superparamagnetic minerals on the transient response of a uniform ground can be modeled by allowing the permeability of the ground μ to vary with frequency ω as [Formula: see text] Here [Formula: see text] and [Formula: see text] are the upper and lower time constants for the superparamagnetic minerals and [Formula: see text] is the direct current value of the susceptibility. For single‐loop data it is found that the voltage will decay as 1/t, provided that [Formula: see text] and [Formula: see text] Here, a is the radius of the wire loop and b is the radius of the wire, t represents time and [Formula: see text] is the permeability of free space. Even if a separate transmitter and receiver are used, the transient will still be anomalous. For this case the 1/t term in the equations is less important, and more prevalent now is the [Formula: see text] term. These results show that a uniform ground behaves in a similar way to a ground which only has a thin superparamagnetic layer. A difference is that whereas the amplitude of the 1/t term could be drastically reduced by using a separate receiver, this is not the case for a uniform ground. A magnetic ground for late times will decay as [Formula: see text]. However, if the conductivity of the ground is estimated from apparent conductivities it will be found that the value of the conductivity will be incorrect by a factor that is related to the susceptibility [Formula: see text] of the ground. For a weakly magnetic ground the estimated conductivity [Formula: see text] is related to the true value of the conductivity [Formula: see text].

Transient electromagnetic response of a thin conducting plate embedded in conducting host rock

Geophysics ◽  
1985 ◽  
Vol 50 (8) ◽  
pp. 1342-1349 ◽  
Author(s):  
S. S. Rai
Keyword(s):  
Time Constant ◽  
Transient Response ◽  
Onset Time ◽  
Electromagnetic Response ◽  
Late Time ◽  
Host Medium ◽  
Transient Electromagnetic ◽  
Conducting Plate ◽  
Free Air ◽  
Em Method

The transient response of a thin, rectangular conducting plate in a conductive host medium is presented for a horizontal‐loop electromagnetic (EM) system considering both a step and pulse EM method (PEM) excitation. For a shallow plate‐like conductor, the current‐gathering effect is preceded by a blanking effect. However, for deeper plates, current gathering was not observed. The effect of increasing plate depth, the ratio of the time constant of the plate to that of the host, and the plate time constant on the temporal characteristics of blanking and current gathering are investigated. The onset time for current gathering is independent of the plate time constant and is essentially a property of the host medium. At later observations (⩾5 ms) the decay of the plate in the host resembles the decay of the plate in free air. An interpretation scheme is proposed to determine plate parameters for Crone PEM measurements using the responses in two relatively late time channels.

Positivity of the coincident loop transient electromagnetic response

Geophysics ◽  
1984 ◽  
Vol 49 (2) ◽  
pp. 194-194 ◽  
Author(s):  
D. Guptasarma
Keyword(s):  
Magnetic Permeability ◽  
Decay Curve ◽  
Electromagnetic Response ◽  
Field Observations ◽  
Induced Voltage ◽  
Linear Medium ◽  
System A ◽  
Transient Electromagnetic ◽  
Maximum Value ◽  
Frequency Independent

Field observations with a coincident loop transient EM frequently show that the measured decaying voltage changes its sign during the decay, reaches a maximum value with this changed sign, and then decays to zero. This change of sign has been ascribed to special distributions of magnetic permeability or conductivity (Spies, 1980), as well as to the presence of electrochemical polarizability (Lee, 1975, 1981). Gubatyenko and Tikshayev (1979) showed, however, that for any frequency‐independent linear medium the induced voltage caused by a step current excitation is always of one sign. Weidelt (1982) extended the results of Gubatyenko and Tikshayev (1979), and established further constraints on the slope and curvature of the decay curve. It is thus quite clear that with a coincident loop system a change of the polarity of the decaying voltage cannot be caused by any distribution of conductivity or permeability in the ground.

The harmonic and transient electromagnetic response of a thin dipping dike

Geophysics ◽  
1983 ◽  
Vol 48 (7) ◽  
pp. 934-952 ◽  
Author(s):  
P. Weidelt
Keyword(s):  
Formal Solution ◽  
Harmonic Excitation ◽  
Electromagnetic Response ◽  
Approximate Determination ◽  
Finite Conductivity ◽  
Circular Loop ◽  
Decay Modes ◽  
Transient Electromagnetic ◽  
Free Decay

An exact solution is given for the electromagnetic induction in a dipping dike of finite conductivity, represented as a thin half‐sheet in a nonconducting surrounding. The problem is formulated for arbitrary dipole or circular loop [Formula: see text] configurations. The formal solution obtained by the Wiener‐Hopf technique is cast into a rapidly convergent triple integral suitable for an effective numerical treatment. A good agreement is found between numerical results and analog measurements available for harmonic excitation. The transient response is obtained as a superposition of the half‐sheet free‐decay modes and is illustrated by some numerical examples for coincident loops, including a diagram for the approximate determination of conductance and depth of a vertical dike.

scholarly journals Diagnosis for Conductor Breaks of Grounding Grids Based on the Wire Loop Method of the Transient Electromagnetic Method

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Shengbao Yu ◽  
Guanliang Dong ◽  
Nannan Liu ◽  
Xiyang Liu ◽  
Chang Xu ◽  
...  
Keyword(s):  
Topological Structure ◽  
Electromagnetic Response ◽  
Height Difference ◽  
Measuring Point ◽  
Wire Loop ◽  
Loop Method ◽  
Transient Electromagnetic ◽  
Grounding Grid ◽  
Grounding Grids ◽  
The Wire

The wire loop method of the transient electromagnetic (TEM) method is used to nondestructively detect conductor breaks of grounding grid. For this purpose, grounding grids serve as an underground wire loop, and the measuring points are arranged on the ground. At each measuring point, a receiving loop is employed to detect the electromagnetic response generated by transmitting the current of the transmitting loop. Conductor breaks can be diagnosed by analyzing the slices of the electromagnetic response. We study the effect of loop size and height difference through the simulation of an intact 2×2 grounding grid, confirming that it is easier to obtain the topological structure using a small transmitting loop and a small height difference. Furthermore, simulations of an intact 4×4 grounding grid and grids with different locations of conductor breaks are also conducted with a small transmitting loop. It is easy to distinguish the topological structure of the grounding grid and the locations of conductor breaks. Finally, the detection method is applied experimentally. The experimental results confirm that the proposed method is an effective technique for conductor break diagnosis.

scholarly journals Numerical Simulation of Transient Electromagnetic Response of Unfavorable Geological Body in Tunnel

2011 ◽  
Vol 90-93 ◽  
pp. 37-40 ◽  
Author(s):  
Lu Bo Meng ◽  
Tian Bin Li ◽  
Zheng Duan
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Electromagnetic Field ◽  
Electromagnetic Response ◽  
Detection Distance ◽  
Geological Body ◽  
Response Characteristics ◽  
Finite Element Software ◽  
Transient Electromagnetic ◽  
Field Decay

To investigate the transient electromagnetic method of response characteristics in the tunnel geological prediction, the finite element numerical simulation of unfavorable geological body of different location, different resistivity sizes, different shapes, and different volume size were carried out by ANSYS finite element software. The results show that secondary electromagnetic field of different location of unfavorable geological body have same decay rate, when detection distance from 30m to 70m, transient electromagnetic responses are strongest, followed distance from 10m to 30m and from 70m to 90m. The shape, volume and resistivity of unfavorable geological body have strong influence on transient electromagnetic response, unfavorable geological body more sleek, the greater the volume and the smaller the resistivity of unfavorable geological body, the secondary electromagnetic field decay slower.

On the theory of sea‐floor conductivity mapping using transient electromagnetic systems

Geophysics ◽  
1987 ◽  
Vol 52 (2) ◽  
pp. 204-217 ◽  
Author(s):  
S. J. Cheesman ◽  
R. N. Edwards ◽  
A. D. Chave
Keyword(s):  
Half Space ◽  
Magnetic Dipole ◽  
Transient Response ◽  
System Response ◽  
Sea Floor ◽  
Closed Form Solutions ◽  
Dipole System ◽  
Transient Electromagnetic ◽  
A Minor ◽  
Resistive Zone

The electrical conductivity of the sea floor is usually much less than that of the seawater above it. A theoretical study of the transient step‐on responses of some common controlled‐source, electromagnetic systems to adjoining conductive half‐spaces shows that two systems, the horizontal, in‐line, electric dipole‐dipole and horizontal, coaxial, magnetic dipole‐dipole, are capable of accurately measuring the relatively low conductivity of the sea floor in the presence of seawater. For these systems, the position in time of the initial transient is indicative of the conductivity of the sea floor, while at distinctly later times, a second characteristic of the transient is a measure of the seawater conductivity. The diagnostic separation in time between the two parts of the transient response does not occur for many other systems, including several systems commonly used for exploration on land. A change in the conductivity of the sea floor produces a minor perturbation in what is essentially a seawater response. Some transient responses which could be observed with a practical, deep‐towed coaxial magnetic dipole‐dipole system located near the sea floor are those for half‐space, the layer over a conductive or resistive basement, and the half‐space with an intermediate resistive zone. The system response to two adjoining half‐spaces, representing seawater and sea floor, respectively, is derived analytically. The solution is valid for all time, provided the conductivity ratio is greater than about ten, or less than about one‐tenth. The analytic theory confirms the validity of numerical evaluations of closed‐form solutions to these layered‐earth models. A lateral conductor such as a vertical, infinite, conductive dike outcropping at the sea floor delays the arrival of the initial crustal transient response. The delay varies linearly with the conductance of the dike. This suggests that time delay could be inverted directly to give a measure of the anomalous integrated conductance of the sea floor both between and in the vicinity of the transmitter and the receiver dipoles.

A finite‐element solution for the transient electromagnetic response of an arbitrary two‐dimensional resistivity distribution

Geophysics ◽  
1986 ◽  
Vol 51 (7) ◽  
pp. 1450-1461 ◽  
Author(s):  
Y. Goldman ◽  
C. Hubans ◽  
S. Nicoletis ◽  
S. Spitz
Keyword(s):  
Finite Element ◽  
Sparse Matrix ◽  
Equation System ◽  
Electromagnetic Response ◽  
Implicit Time ◽  
Two Dimensional ◽  
Time Step ◽  
Transient Electromagnetic ◽  
Exact Boundary ◽  
The Time Domain

We present a numerical method for solving Maxwell’s equations in the case of an arbitrary two‐dimensional resistivity distribution excited by an infinite current line. The electric field is computed directly in the time domain. The computations are carried out in the lower half‐space only because exact boundary conditions are used on the free surface. The algorithm follows the finite‐element approach, which leads (after space discretization) to an equation system with a sparse matrix. Time stepping is done with an implicit time scheme. At each time step, the solution of the equation system is provided by the fast system ICCG(0). The resulting algorithm produces good results even when large resistivity contrasts are involved. We present a test of the algorithm’s performance in the case of a homogeneous earth. With a reasonable grid, the relative error with respect to the analytical solution does not exceed 1 percent, even 2 s after the source is turned off.

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