Corrections to Millett’s table of electromagnetic coupling phase angles

Geophysics ◽  
1984 ◽  
Vol 49 (9) ◽  
pp. 1554-1555 ◽  
Author(s):  
R. J. Brown
Keyword(s):  
Half Space ◽  
Random Error ◽  
Electromagnetic Coupling ◽  
Inductive Coupling ◽  
Coupling Phase ◽  
Mutual Impedance ◽  
Phase Angles

Millett (1967) published tables of values of the mutual impedance due to inductive coupling between two collinear dipoles on a uniform, nonpolarizable half‐space. In the course of a recent study (Brown, 1984) I have noticed significant errors, of two different kinds, in the phase angles (ϕ) given by Millett (1967). One kind of error is evidently typographical in nature and occurs only twice, in the M = 3 table, for θ = .01 and .02. The tabled values apparently had their decimal points shifted one place. The second and more serious kind of error is an apparently random error within the range ±0.003 degrees. This is not significant for larger |ϕ|, say |ϕ| > 1 degree, but the values of |ϕ| in Millett’s tables go down to 0.006 degrees (down to 0.0045 degrees after correction) where such errors are clearly significant, particlarly if one is working with logarithmic quantities as is common.

HIGH‐FREQUENCY ELECTROMAGNETIC COUPLING BETWEEN SMALL COPLANAR LOOPS OVER AN INHOMOGENEOUS GROUND

Geophysics ◽  
1972 ◽  
Vol 37 (6) ◽  
pp. 997-1004 ◽  
Author(s):  
James A. Fuller ◽  
James R. Wait
Keyword(s):  
Half Space ◽  
High Frequency ◽  
Electromagnetic Coupling ◽  
Current Source ◽  
Vertical Axis ◽  
Loop Current ◽  
Mutual Impedance ◽  
Multiplicative Factor ◽  
The Earth ◽  
Horizontal Electric Dipole

An integral formulation is given for the fields of a loop current source which is located over a horizontally stratified half‐space and has a vertical axis. The electrical properties of the half‐space vary exponentially with the depth into the earth. An asymptotic solution is developed for the case of source and observer on the interface but separated by a large numerical distance. The approximate solution is then used to determine the mutual impedance between two small loops and between the loop and a horizontal electric dipole, when the antennas are on the interface. It is found that the effect of stratification on the mutual impedance is represented approximately by a single multiplicative factor.

MUTUAL ELECTROMAGNETIC COUPLING OF LOOPS OVER A HOMOGENEOUS GROUND—AN ADDITIONAL NOTE

Geophysics ◽  
1956 ◽  
Vol 21 (2) ◽  
pp. 479-484 ◽  
Author(s):  
James R. Wait
Keyword(s):  
Electromagnetic Coupling ◽  
Mutual Impedance ◽  
Additional Note ◽  
Homogeneous Ground

Further computations are presented for the mutual impedance between small wire loops over a semi‐infinite conductor. The cases considered are where the axes of the loops are parallel to the interface.

Cable arrangement to reduce electromagnetic coupling effects in spectral-induced polarization studies

Geophysics ◽  
2014 ◽  
Vol 79 (2) ◽  
pp. A1-A5 ◽  
Author(s):  
Myriam Schmutz ◽  
Ahmad Ghorbani ◽  
Pierre Vaudelet ◽  
Amélie Blondel
Keyword(s):  
Coupling Effect ◽  
Electromagnetic Coupling ◽  
Induced Polarization ◽  
Electrode Spacing ◽  
Coupling Effects ◽  
Array Type ◽  
Spectral Induced Polarization ◽  
Computer Codes ◽  
Lateral Offset ◽  
Phase Angles

Spectral-induced polarization (SIP) is widely used for environmental and engineering geophysical prospecting and hydrogeophysics, but one major limitation concerns the electromagnetic (EM) coupling effect. The phase angles related to EM coupling may increase even at frequencies as low as 1 Hz, depending on the ground resistivity, the array type, and the geometry. Most efforts to understand and quantify the EM coupling problem (e.g., theory and computer codes) have been developed for dipole-dipole arrays. However, we used a Schlumberger array to acquire SIP data. We found that with this array, the use of an appropriate cable arrangement during data acquisition can reduce EM coupling effects in the same proportion as for the use of a dipole-dipole array, which is the pure response of the studied earth. To measure the influence of the cable layout, four cable configurations with the same electrode spacing were compared for modeling and experimental data. We discovered that the classical DC inline array was the worst one. As soon as the cables were arranged in another shape (triangle or rectangle), the coupling effect decreased significantly. The best configuration we checked was the rectangular one with an acquisition unit located at a lateral offset of 100 m from the electrode line, even if there was still some difference between the modeled and measured data.

MINERAL DISCRIMINATION AND REMOVAL OF INDUCTIVE COUPLING WITH MULTIFREQUENCY IP

Geophysics ◽  
1978 ◽  
Vol 43 (3) ◽  
pp. 588-609 ◽  
Author(s):  
W. H. Pelton ◽  
S. H. Ward ◽  
P. G. Hallof ◽  
W. R. Sill ◽  
P. H. Nelson
Keyword(s):  
Frequency Dependence ◽  
Nickel Sulfide ◽  
Electromagnetic Coupling ◽  
Spectral Response ◽  
Porphyry Copper ◽  
Massive Sulfide ◽  
Inductive Coupling ◽  
Porphyry Copper Deposits ◽  
Spectral Responses

In‐situ complex resistivity measurements over the frequency range [Formula: see text] to [Formula: see text] have been made on 26 North American massive sulfide, graphite, magnetite, pyrrhotite, and porphyry copper deposits. The results reveal significant differences between the spectral responses of massive sulfides and graphite and present encouragement for their differentiation in the field. There are also differences between the spectra of magnetite and nickeliferrous pyrrhotite mineralization, which may prove useful in attempting to distinguish between these two common IP sources in nickel sulfide exploration. Lastly, there are differences in the spectra typically arising from the economic mineralization and the barren pyrite halo in porphyry copper systems. It appears that all these differences arise mainly from mineral texture, since laboratory studies of different specific mineral‐electrolyte interfaces show relatively small variations. All of the in‐situ spectra may be described by one or two simple Cole‐Cole relaxation models. Since the frequency dependence of these models is typically only about 0.25, and the frequency dependence of inductive electromagnetic coupling is near 1.0, it is possible to recognize and to remove automatically the effects of inductive coupling from IP spectra. The spectral response of small deposits or of deeply buried deposits varies from that of the homogeneous earth response, but these variations may be readily determined from the same “dilution factor” [Formula: see text] currently used to calculate apparent IP effects.

ELECTROMAGNETIC COUPLING IN FREQUENCY AND TIME‐DOMAIN INDUCED‐POLARIZATION SURVEYS OVER A MULTILAYERED EARTH

Geophysics ◽  
1973 ◽  
Vol 38 (2) ◽  
pp. 380-405 ◽  
Author(s):  
Abhijit Dey ◽  
H. Frank Morrison
Keyword(s):  
Half Space ◽  
Time Domain ◽  
Electromagnetic Coupling ◽  
Complete Solution ◽  
Induced Polarization ◽  
Arbitrary Length ◽  
Polarization Measurements ◽  
Homogeneous Half Space ◽  
Dipole Configuration ◽  
Off Time

Electromagnetic coupling responses in frequency and time‐domain induced‐polarization measurements over a multilayered earth are evaluated. For collinear dipole‐dipole and pole‐dipole configurations over a dissipative layered subsurface, the percent frequency effects of electromagnetic coupling are seen to be as high as 60 percent for large [Formula: see text] values, where L is the length of the receiving dipole, [Formula: see text] is the conductivity of the top layer of the half‐space, and f is the higher frequency of excitation used. In both frequency and time‐domain analyses, the distinctive effects of layering compared to that of a homogeneous half‐space response are shown for different electrode configurations, layer geometry, and electrical parameters of the subsurface. The pole‐dipole configuration of electrodes, in general, exhibits higher coupling compared to the dipole‐dipole configuration. In time‐domain measurements, the late off‐time transient decays reflect almost entirely the normal polarizability of the layered subsurface, in that the coupling responses are significant only during the early off‐time of the transient. The mutual impedance between grounded dipoles of arbitrary length is computed by extension of the complete solution of the boundary‐value problem of a horizontal electric dipole situated over a multilayered half‐space. A number of nomograms are presented for various layered structures to eliminate the electromagnetic coupling response in the induced‐polarization measurements in order to obtain the true polarization effect of the subsurface.

scholarly journals Reciprocity and mutual impedance formulas within lossy cavities

2005 ◽  
Vol 3 ◽  
pp. 91-97
Author(s):  
F. Gronwald ◽  
E. Blume
Keyword(s):  
Method Of Moments ◽  
Electromagnetic Interference ◽  
Electromagnetic Coupling ◽  
Rectangular Cavity ◽  
Dipole Antennas ◽  
Mutual Impedance ◽  
Antenna Theory

Abstract. We discuss the validity of reciprocity and mutual impedance formulas within lossy cavities. Mutual impedance formulas are well-known from antenna theory and useful to describe the electromagnetic coupling between electromagnetic interference sources and victims. As an example the mutual impedance between two dipole antennas within a lossy rectangular cavity is calculated from a system of coupled Hallén's equations that efficiently is solved by the method of moments.

scholarly journals Noninvasive real-time assessment of intracranial pressure after traumatic brain injury based on electromagnetic coupling phase sensing technology

BMC Neurology ◽  
2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Gen Li ◽  
Wang Li ◽  
Jingbo Chen ◽  
Shuanglin Zhao ◽  
Zelin Bai ◽  
...  
Keyword(s):  
Traumatic Brain Injury ◽  
Brain Injury ◽  
Intracranial Pressure ◽  
Electromagnetic Coupling ◽  
Characteristic Curve ◽  
Test System ◽  
Adaptive Boosting ◽  
Change Rate ◽  
Coupling Phase ◽  
Sensing Technology

Abstract Background To investigate the feasibility of intracranial pressure (ICP) monitoring after traumatic brain injury (TBI) by electromagnetic coupling phase sensing, we established a portable electromagnetic coupling phase shift (ECPS) test system and conducted a comparison with invasive ICP. Methods TBI rabbits’ model were all synchronously monitored for 24 h by ECPS testing and invasive ICP. We investigated the abilities of the ECPS to detect targeted ICP by feature extraction and traditional classification decision algorithms. Results The ECPS showed an overall downward trend with a variation range of − 13.370 ± 2.245° as ICP rose from 11.450 ± 0.510 mmHg to 38.750 ± 4.064 mmHg, but its change rate gradually declined. It was greater than 1.5°/h during the first 6 h, then decreased to 0.5°/h and finally reached the minimum of 0.14°/h. Nonlinear regression analysis results illustrated that both the ECPS and its change rate decrease with increasing ICP post-TBI. When used as a recognition feature, the ability (area under the receiver operating characteristic curve, AUCs) of the ECPS to detect ICP ≥ 20 mmHg was 0.88 ± 0.01 based on the optimized adaptive boosting model, reaching the advanced level of current noninvasive ICP assessment methods. Conclusions The ECPS has the potential to be used for noninvasive continuous monitoring of elevated ICP post-TBI.

Approximate calculations of the transient electromagnetic response from buried conductors in a conductive half‐space

Geophysics ◽  
1984 ◽  
Vol 49 (7) ◽  
pp. 918-924 ◽  
Author(s):  
J. D. McNeill ◽  
R. N. Edwards ◽  
G. M. Levy
Keyword(s):  
Half Space ◽  
Free Space ◽  
Target Location ◽  
Electromagnetic Coupling ◽  
Practical Interest ◽  
Electromagnetic Response ◽  
Galvanic Current ◽  
Transient Electromagnetic ◽  
Space Modeling ◽  
Space Response

The transient electromagnetic (TEM) response from a conductive plate buried in a conductive half‐space and energized by a large‐loop transmitter is investigated in a heuristic manner. The vortex and galvanic components are each calculated directly in the time domain using an approximate procedure which ignores the electromagnetic coupling present in the complete solution. In modeling the vortex and galvanic current flows, the plate is replaced with a single‐turn wire loop of appropriate parameters and a distribution of current dipoles, respectively. The results of calculations of the transient magnetic field at the surface of the earth are presented for a few selected cases of practical interest. The relative importance of the vortex and galvanic components varies with the half‐space resistivity. The vortex component dominates if the half‐space is resistive, in which case free‐space algorithms suffice for numerical modeling. Furthermore the measured responses give much useful information about the target, and large depths of exploration should be achieved. As the half‐space resistivity decreases, a significant half‐space response is observed, caused by currents induced in the half‐space itself. This response can be very large. Spatial variations in it caused by relatively small changes in resistivity, i.e., geologic noise, obscure the response from deep targets making them difficult to detect. The effect of the half‐space is also to delay, distort, and reduce the vortex component in comparison with the free‐space response. The behavior of the galvanic component is determined by the haft‐space current flow. The presence of this component explains the large enhancement of overall target response seen at early times over relatively resistive ground and the departure from an exponential decay seen over more conductive ground, again with respect to responses predicted by free‐space modeling. In more conductive ground the galvanic component completely dominates the vortex component, resulting in the loss of useful diagnostic information. Although target location and depth can still be determined, target shape and orientation are poorly defined. Because of galvanic current saturation good conductors are difficult to distinguish from poor ones.

Sign in / Sign up

Export Citation Format

Share Document