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.

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.

Aftereffects in the Transient Electromagnetic Method: Inductively Induced Polarization

2021 ◽  
Vol 62 (12) ◽  
pp. 1440-1448
Author(s):  
N.O. Kozhevnikov ◽  
E.Yu. Antonov
Keyword(s):  
Transient Response ◽  
Electric Polarization ◽  
Induced Polarization ◽  
Point Of View ◽  
Electromagnetic Method ◽  
Time Range ◽  
General Point ◽  
Transient Electromagnetic Method ◽  
Transient Electromagnetic ◽  
Tem Method

Abstract —Inductively induced electric polarization (IIP) is one of the aftereffects inherent in the geologic materials and affecting results of the transient electromagnetic method. Its effect on the inductive transient response manifests itself as a nonmonotonic EMF decay, including the polarity reversal. The dependence of IIP on many conditions makes it difficult to study the basic regularities in its manifestation. One of the ways to address this problem is to present the simulation results as a normalized transient response. From the most general point of view, the intensity and time range of the IIP manifestation are controlled by the competition between induction and induced polarization phenomena. Induced polarization manifests itself differently, depending on the transmitter used for the excitation of the ground response. Therefore, when studying polarizable ground, the results of the conventional IP method and those of the TEM method do not always correlate.

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].

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.

scholarly journals 3D Numerical Modeling of Induced-Polarization Grounded Electrical-Source Airborne Transient Electromagnetic Response Based on the Fictitious Wave Field Methods

2020 ◽  
Vol 10 (3) ◽  
pp. 1027 ◽  
Author(s):  
Yanju Ji ◽  
Xiangdong Meng ◽  
Weimin Huang ◽  
Yanqi Wu ◽  
Gang Li
Keyword(s):  
Time Domain ◽  
Maxwell Equations ◽  
Integral Transformation ◽  
Induced Polarization ◽  
Response Amplitude ◽  
Electromagnetic Response ◽  
Low Resistance ◽  
Transient Electromagnetic ◽  
The Time Domain ◽  
Electrical Source

The grounded electrical-source airborne transient electromagnetic (GREATEM) system is widely used in mineral exploration. Meanwhile, the induced polarization (IP) effect, which indicates the polarizability of the earth, is often found. In this paper, the Maxwell equations in the frequency domain are transformed into fictitious wave domain, where Maxwell equations are solved by the time domain finite difference method. Then, an integral transformation method is used to convert the calculation results back to the time domain. A three-dimensional (3D) numerical simulation in a polarizable medium is presented. The accuracy of this method is proven by comparing it with the analytical solution and the existing method, and the calculation efficiency is increased five-fold. The simulation results show that the GREATEM system has a higher response amplitude in the conductive region, while IP effects cannot be identified in the conductive area. The GREATEM system has a higher response amplitude in the low-resistance region, but IP effects cannot be identified in the low-resistance area, and the detection of IP effects is more suitable for the high-resistance area. Therefore, it is necessary to improve the detection ability of the GREATEM system in the low-resistance area.

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.

The Cole‐Cole model in time domain induced polarization

Geophysics ◽  
1981 ◽  
Vol 46 (6) ◽  
pp. 932-933 ◽  
Author(s):  
T. Lee
Keyword(s):  
Equivalent Circuit ◽  
Time Domain ◽  
Induced Polarization ◽  
Relaxation Model ◽  
Trivial Case ◽  
Alternative Expression ◽  
Transient Voltage ◽  
Transient Voltages ◽  
Cole Model ◽  
The Given

Recently Pelton et al. (1978) used a Cole‐Cole relaxation model to simulate the transient voltages that are observed during an induced‐polarization survey. These authors took the impedance of the equivalent circuit Z(ω) to be [Formula: see text]They then gave the expression for the transient voltage [Formula: see text] as [Formula: see text]In equation (2), [Formula: see text] was misprinted as [Formula: see text]. In these equations, [Formula: see text] and [Formula: see text], [Formula: see text] and τ are constants to be determined for the given model. [Formula: see text] is the height of the step current that will flow in the transmitter. A disadvantage of equation (2) is that it is only slowly convergent for large t/τ. Pelton et al. (1978) used a τ which ranged from [Formula: see text] to [Formula: see text]. The purpose of this note is to provide an alternative expression for [Formula: see text] that is valid only at the later stages but which does not have this disadvantage. The trivial case of c = 1.0 is ignored.

Mapping of induced polarization using natural fields

Geophysics ◽  
2001 ◽  
Vol 66 (1) ◽  
pp. 137-147 ◽  
Author(s):  
Erika Gasperikova ◽  
H. Frank Morrison
Keyword(s):  
Electric Field ◽  
Surrounding Medium ◽  
Low Frequency ◽  
Induced Polarization ◽  
The Body ◽  
Electromagnetic Response ◽  
Frequency Dependent ◽  
Finite Body ◽  
Electric Field Profile ◽  
Measured Response

The observed electromagnetic response of a finite body is caused by induction and polarization currents in the body and by the distortion of the induction currents in the surrounding medium. At a sufficiently low frequency, there is negligible induction and the measured response is that of the body distorting the background currents just as it would distort a direct current (dc). Because this dc response is not inherently frequency dependent, any observed change in response of the body for frequencies low enough to be in this dc limit must result from frequency‐dependent conductivity. Profiles of low‐frequency natural electric (telluric) fields have spatial anomalies over finite bodies of fixed conductivity that are independent of frequency and have no associated phase anomaly. If the body is polarizable, the electric field profile over the body becomes frequency dependent and phase shifted with respect to a reference field. The technique was tested on data acquired in a standard continuous profiling magnetotelluric (MT) survey over a strong induced polarization (IP) anomaly previously mapped with a conventional pole‐dipole IP survey. The extracted IP response appears in both the apparent resistivity and the normalized electric field profiles.

Sign in / Sign up

Export Citation Format

Share Document