scholarly journals Modeling ferrite electromagnetic response in the time-domain

2003 ◽  
Author(s):  
J. Johnson ◽  
J.F. DeFord ◽  
G.D. Craig
Keyword(s):  
Time Domain ◽  
Electromagnetic Response ◽  
The Time Domain

On: “Crone pulse electromagnetic response of a conducting thin horizontal sheet—Theory and application,” by S. S. Rai (GEOPHYSICS, 50, 1350–1354, August 1985).

Geophysics ◽  
1987 ◽  
Vol 52 (3) ◽  
pp. 373-374
Author(s):  
David C. Bartel
Keyword(s):  
Time Domain ◽  
Simple Formula ◽  
Thin Sheet ◽  
Step Response ◽  
Electromagnetic Response ◽  
The Subject ◽  
The Time Domain ◽  
Airborne Em

Rai uses a simple formula for the step response of a conducting, horizontal thin sheet in the time domain and applies it to the Crone pulse electromagnetic (PEM) system. He also uses this formulation to interpret some field results. The idea of an infinite, horizontal, conductive thin sheet is valid in some cases for both ground and airborne EM systems. However, I disagree with some of the derivations of the thin‐sheet equation as presented in the subject paper. The applicability of the study is not questioned; but the interpretation of the field example may be different.

The time-domain electromagnetic response of wedge-like structures

2004 ◽  
Vol 2004 (1) ◽  
pp. 1-4
Author(s):  
David Annetts ◽  
Art Raiche ◽  
Fred Sugeng
Keyword(s):  
Time Domain ◽  
Electromagnetic Response ◽  
Time Domain Electromagnetic ◽  
The Time Domain

Three-dimensional modeling of IP effects in time-domain electromagnetic data

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. E303-E314 ◽  
Author(s):  
David Marchant ◽  
Eldad Haber ◽  
Douglas W. Oldenburg
Keyword(s):  
Frequency Dependence ◽  
Time Domain ◽  
Electromagnetic Coupling ◽  
Electromagnetic Response ◽  
Implicit Time ◽  
Full Time ◽  
Electromagnetic Data ◽  
Rational Series ◽  
Time Domain Electromagnetic ◽  
The Time Domain

Understanding the effects of induced-polarization (IP) effects on time-domain electromagnetic data requires the ability to simulate common survey techniques when taking chargeability into account. Most existing techniques preform this modeling in the frequency domain prior to transforming their results to the time domain. Even though this technique can allow for chargeable material to be easily incorporated, its application for some problems can be computationally limiting. We developed a new technique for forward modeling the time-domain electromagnetic response of chargeable materials in three dimensions. The frequency dependence of Ohms’ law translates to an ordinary differential equation when considered in the time domain. The system of ordinary-partial differential equations was then discretized using an implicit time-stepping algorithm, that yielded absolute stability. This approach allowed us to operate directly in the time domain and avoid frequency to time-domain transformations. Although this approach can be applied directly to materials exhibiting Debye dispersions, other Cole-Cole dispersions resulted in fractional derivatives in time. To overcome this difficulty, Padé approximations were used to represent the frequency dependence as a rational series of integer order terms. The resulting method was then simplified to generate a reduced time-domain model that can be used to forward model the IP decay curves in the absence of any electromagnetic coupling. We found numerical examples in which the method produced accurate results. The potential application of the method was demonstrated by modeling the full time-domain electromagnetic response of a gradient array IP survey, and the occurrence of negative transients in airborne time-domain electromagnetic data.

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.

On closed-form expressions for the approximate electromagnetic response of a sphere interacting with a thin sheet — Part 1: Theory in the frequency and time domain

Geophysics ◽  
2019 ◽  
Vol 84 (3) ◽  
pp. E189-E198 ◽  
Author(s):  
Jacques K. Desmarais
Keyword(s):  
Closed Form ◽  
Time Domain ◽  
Mineral Exploration ◽  
Thin Sheet ◽  
Electromagnetic Response ◽  
Uniform Field ◽  
Electromagnetic Modeling ◽  
The Time Domain ◽  
Glacial Clays ◽  
Metamorphic Terranes

In mineral exploration and geologic mapping of igneous and metamorphic terranes, the background is often dominantly resistive. The most important electromagnetic interaction is between a discrete conductor and an overlying sheet of conductive overburden (e.g., glacial clays or weathering products of the basement rocks). To enable the electromagnetic modeling of these common situations, here I provide closed-form expressions for the approximate electromagnetic response of a sphere embedded in highly resistive rocks and interacting with an overlying thin sheet. The sphere is assumed to be dipolar and excited by a locally uniform field. The expressions in the time and frequency domains are represented as sums of complete and incomplete cylindrical functions. New asymptotic approximations are provided for the efficient evaluation of the required incomplete cylindrical functions. The frequency-domain formulas are validated by numerical transformation to the time domain and comparison to the time-domain solution.

An experimental study of the time-domain electromagnetic response of a buried conductive plate

Geophysics ◽  
2005 ◽  
Vol 70 (1) ◽  
pp. G1-G7 ◽  
Author(s):  
Mark E. Everett ◽  
Alfonso Benavides ◽  
Carl J. Pierce
Keyword(s):  
Experimental Study ◽  
Time Domain ◽  
Metal Plate ◽  
Electromagnetic Response ◽  
Late Time ◽  
Conductive Plate ◽  
Spatial Response ◽  
Time Domain Electromagnetic ◽  
The Time Domain ◽  
Cultural Noise

It is important to understand the effects of a buried metal object on electromagnetic data, whether the object is a source of cultural noise or a target of interest. The time-domain electromagnetic response of a buried metal plate exhibits several remarkable properties. An experimental study has been undertaken to confirm these properties. The spatial response of a shallow-buried plate is temporally self-similar and exhibits a late-time dipolelike response. Clutter-generated noise can be significant if the plate is poorly coupled to the primary transmitter flux. A vertical plate exhibits a transition from a horizontal to a vertical mode of eddy current induction.

Apodisation in the time domain

1992 ◽  
Vol 2 (4) ◽  
pp. 615-620
Author(s):  
G. W. Series
Keyword(s):  
Time Domain ◽  
The Time Domain
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