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.

Response characteristics of coincident loop transient electromagnetic systems

Geophysics ◽  
1982 ◽  
Vol 47 (9) ◽  
pp. 1325-1330 ◽  
Author(s):  
P. Weidelt
Keyword(s):  
Step Function ◽  
Voltage Response ◽  
Complex Frequency ◽  
Induced Voltage ◽  
Response Characteristics ◽  
Transient Electromagnetic ◽  
Driving Current ◽  
Occasional Occurrence ◽  
Frequency Independent ◽  
Independent Distribution

The occasional occurrence of persistent sign reversals in coincident loop transient electromagnetic (TEM) measurements stimulates an investigation of possible causes for this effect. By examining the response in the complex frequency plane near the spectrum of freely decaying current modes, it is shown that for any physically reasonable frequency‐independent distribution of electrical conductivity and magnetic permeability the voltage response to a step function driving current is of one sign only. Moreover, under the conditions mentioned above, the logarithm of the induced voltage is a decreasing convex function of time. These characteristics are retained for more general time functions of the driving current. The conservation of sign for frequency‐independent material parameters supports the assumption of IP effects as a possible mechanism for sign reversals. The latter point is illustrated by a simplified example.

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.

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 use and misuse of apparent resistivity in electromagnetic methods

Geophysics ◽  
1986 ◽  
Vol 51 (7) ◽  
pp. 1462-1471 ◽  
Author(s):  
Brian R. Spies ◽  
Dwight E. Eggers
Keyword(s):  
Apparent Resistivity ◽  
Early Time ◽  
Asymptotic Formulas ◽  
Voltage Response ◽  
Late Time ◽  
Induced Voltage ◽  
Resistivity Curve ◽  
Transient Electromagnetic ◽  
Electromagnetic Methods ◽  
Tem Method

Problems and misunderstandings arise with the concept of apparent resistivity when the analogy between an apparent resistivity computed from geophysical observations and the true resistivity structure of the subsurface is drawn too tightly. Several definitions of apparent resistivity are available for use in electromagnetic methods; however, those most commonly used do not always exhibit the best behavior. Many of the features of the apparent resistivity curve which have been interpreted as physically significant with one definition disappear when alternative definitions are used. It is misleading to compare the detection or resolution capabilities of different field systems or configurations solely on the basis of the apparent resistivity curve. For the in‐loop transient electromagnetic (TEM) method, apparent resistivity computed from the magnetic field response displays much better behavior than that computed from the induced voltage response. A comparison of “exact” and “asymptotic” formulas for the TEM method reveals that automated schemes for distinguishing early‐time and late‐time branches are at best tenuous, and those schemes are doomed to failure for a certain class of resistivity structures (e.g., the loop size is large compared to the layer thickness). For the magnetotelluric (MT) method, apparent resistivity curves defined from the real part of the impedance exhibit much better behavior than curves based on the conventional definition that uses the magnitude of the impedance. Results of using this new definition have characteristics similar to apparent resistivity obtained from time‐domain processing.

MINIMIZING THE EFFECTIVE AREA OF SCATTERING BY MEANS OF CHANGING THE RELATIVE MAGNETIC PERMEABILITY

2021 ◽  
pp. 85-88
Author(s):  
А.В. Володько ◽  
С.М. Фёдоров ◽  
Е.А. Ищенко ◽  
М.А. Сиваш ◽  
Л.В. Сопина ◽  
...  
Keyword(s):  
Magnetic Permeability ◽  
Dielectric Material ◽  
Threshold Value ◽  
Effective Area ◽  
Large Object ◽  
Frequency Dependent ◽  
Relative Magnetic Permeability ◽  
Effective Scattering Area ◽  
Maximum Value ◽  
Simulation Results

Исследуется зависимость эффективной площади рассеяния (ЭПР) от относительной магнитной проницаемости материала, из которого изготавливается структура. В качестве тела моделирования был выбран шар, который изготовлен из диэлектрического материала, у которого возможно выполнять изменение относительной магнитной проницаемости. По полученным результатам моделирования построены графики зависимости максимального значения моностатической ЭПР от частоты, а также от относительной магнитной проницаемости среды. Было показано, что с увеличением относительной магнитной проницаемости материала изготовления происходит увеличение значения ЭПР объекта, а также обнаружена зависимость эффективной площади рассеяния от соотношения размеров шара и длиной волны, так при превышении порогового значения, после которого шар становится крупным объектом, ЭПР резко возрастает. По результатам исследования был построен график зависимости эффективной площади рассеяния шара от относительной магнитной проницаемости материала изготовления. Доказана возможность применения материала с частотозависимой относительной магнитной проницаемостью в качестве стелс-покрытия. В статье содержится исследуемая модель, графики полученных результатов, по которым можно легко определить зависимость ЭПР от частоты и от относительной магнитной проницаемости материала изготовления The article investigates the dependence of the effective scattering area (ESA) on the relative magnetic permeability of the material from which the structure is made. We chose a sphere as the modeling body, which is made of a dielectric material, in which it is possible to change the relative magnetic permeability. Based on the obtained simulation results, graphs of the dependence of the maximum value of monostatic ESA on frequency, as well as on the relative magnetic permeability of the medium, were constructed. It was shown that with an increase in the relative magnetic permeability of the material of manufacture, an increase in the value of the ESA of the object occurs, and the dependence of the effective scattering area on the ratio of the size of the ball and the wavelength was found, so when the threshold value is exceeded, after which the ball becomes a large object, ESA rises sharply. Based on the results of the study, a graph of the dependence of the effective scattering area of the sphere on the relative magnetic permeability of the material of manufacture was built. The possibility of using a material with a frequency-dependent relative magnetic permeability as a stealth coating was proven. The article contains the investigated model, graphs of the results obtained, by which it is easy to determine the dependence of the ESA on the frequency and on the relative magnetic permeability of the material of manufacture

Manifestation of Сoncentration Quenching of Fluoroaluminate Glasses Doped with Erbium

2019 ◽  
Vol 822 ◽  
pp. 871-877
Author(s):  
Victor Klinkov ◽  
Aleksander Semencha ◽  
Evgenia Tsimerman ◽  
Artem Osipov ◽  
Margarita G. Dronova
Keyword(s):  
Quantum Yield ◽  
Decay Curve ◽  
Emission Spectra ◽  
Luminescence Spectra ◽  
Ion Energy ◽  
Maximum Value ◽  
Absolute Quantum Yield ◽  
Concentration Dependences ◽  
Yield Values ◽  
Absolute Quantum

Fluoroaluminate glasses of the composition 2Ва (РО3)2–98MgCaSrBaYAl2F14-xErF3, where x=0, 0.1, 0.5, 1.0 mol. % have been prepared by melt quenching technique and characterized by optical absorption, emission spectra and decay curve analysis. Measured transmission spectra indicate the high practical relevance of the composition of glasses under investigation for photonics and optoelectronics products. In the region of 500–700 nm, luminescence spectra with peaks at about 522, 550, and 665 nm were obtained. The positions of the luminescence bands have been described using an erbium ion energy scheme. The concentration dependences of the absolute quantum yield values for the series of Er3+-doped fluoroaluminate glasses were also established. The maximum value of absolute quantum yield was found for a sample with Er3+ concentration 0.21∙1020 сm-3. The main reason for reducing the values of absolute quantum yield is concentration quenching.

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.

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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