A Comparative Study on the Difference between the Multi-dipole Sources and Vector Synthesis Source

2020 ◽  
Vol 25 (4) ◽  
pp. 529-543
Author(s):  
Xian-Xiang Wang ◽  
Ju-Zhi Deng
Keyword(s):  
Electromagnetic Field ◽  
Near Field ◽  
Electromagnetic Response ◽  
Dipole Source ◽  
Mountainous Area ◽  
Field Zone ◽  
Specific Direction ◽  
Single Dipole ◽  
The Difference ◽  
Dipole Sources

CSAMT exploration generally adopts a single dipole as the transmitter. The single dipole source has the apparent disadvantages–there are weak areas for all components, Ey and Hx are weak in the area where Ex and Hy are reliable. Moreover, it is hard to deploy the source with a specific direction in a rugged mountainous area. Given the shortcomings of the single dipole source, multi-dipole sources are introduced into CSAMT exploration. Although the dipole sources follow the principle of vector synthesis, the length of the source in actual exploration can last for several kilometers and the offset is generally a few kilometers. In this case, the source can no longer be regarded as a single dipole in the near-field zone. The electromagnetic field in this region becomes relatively complicated. We first compare the similarities and differences of electromagnetic field generated by vector synthesis source and multi-dipole source through the Ex radiation patterns. Then, we study the factors that affect electromagnetic response due to the substitution of the double-dipole source with the vector synthesis source. The measured EM fields is affected by the source length, frequency, the source angle, the offset, and the resistivity.Finally, we apply the double-dipole source to the 1D and 3D geological model and compare the difference between the electromagnetic field generated by the double-dipole source and that generated by the vector synthesis source. Usually, the difference is very obvious in the near-field zone, and is almost negligible in the far-field zone.

The effects of source polarization in CSAMT data over two massive sulfide deposits in Australia

Geophysics ◽  
1993 ◽  
Vol 58 (12) ◽  
pp. 1764-1772 ◽  
Author(s):  
Richard Kellett ◽  
John Bishop ◽  
Emmett Van Reed
Keyword(s):  
Structural Information ◽  
Near Field ◽  
Real Data ◽  
Black Shales ◽  
Electromagnetic Response ◽  
Resistivity Structure ◽  
Field Zone ◽  
Controlled Source ◽  
Source Field ◽  
Eastern Australia

Since the advent of the controlled‐source audio‐magnetotelluric method it has been recognized that the location and orientation of the bipole source is important in determining the response of the earth at the receiver. In this study, two‐dimensional (2-D) far‐field modeling has been used to illustrate the frequency-domain electromagnetic response of a simple conductive dike for two orthogonal polarizations of the source field. The current gathered from the surrounding media by the dike, when the electric field is parallel to the strike direction (E‐polarization), produces a strong anomaly not seen in the perpendicular H‐polarization. This model response has been identified in real data sets over the Rosebery and Flying Doctor orebodies of eastern Australia. In the case of Rosebery the E‐polarization data yielded little structural information because the penetration of the signal was reduced by strong current channeling in the orebody and adjacent black shales. At the Flying Doctor prospect the model predictions held but changes in the extent of the near‐field zone, for the two bipole locations, dominate the data. The changes in the source field observed over the Flying Doctor prospect are interpreted as evidence for anisotropy in the regional resistivity structure. The controlled‐source is a fundamental component of the CSAMT system, and the choice of the bipole location and orientation must be made considering the geology of the target region and the surrounding regional resistivity structure.

An Investigation Into Acoustic Dipole Source Calibration Methods for Turbomachinery Sound Radiation in Reverberant Fields

2016 ◽  
Author(s):  
Michael L. Jonson ◽  
Steven D. Young
Keyword(s):  
Near Field ◽  
Dipole Source ◽  
Acoustic Source ◽  
In Situ Calibration ◽  
Calibration Methods ◽  
Penn State ◽  
Radiated Sound ◽  
Reverberant Field ◽  
Dipole Sources

In-situ calibration methods using a single spherical-shaped transmitting hydrophone (idealized as a monopole acoustic source) have traditionally been used for radiated sound measurements of turbomachinery performed in the Garfield Thomas 1.22-m diameter water tunnel located at The Pennsylvania State University’s Applied Research Laboratory (ARL Penn State). In this reverberant field, the monopole source containing known transmitting characteristics was used to calibrate acoustic sensors that were either near or far from the source. This method typically works well when the type of source is monopole in nature; however, many acoustics sources can be dipole or quadrupole in nature. In this study we investigated the applicability of using dipole sources in a space such as a well-characterized reverberant tank, and we found through a virtual dipole method that the radiation still appears monopole in the reverberant field. The method was extended for the vibration of a panel (a known dipole source) and once again the monopole assumption for the in-situ calibration for a near-field hydrophone and conventional reverberant hydrophones remained consistent.

On the electromagnetic response of a resistive cylinder buried in a conductive host

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. E341-E351 ◽  
Author(s):  
Andrei Swidinsky
Keyword(s):  
Electric Dipole ◽  
Mineral Exploration ◽  
Skin Depth ◽  
Hydrocarbon Exploration ◽  
Electromagnetic Response ◽  
Dipole Source ◽  
Additional Information ◽  
Dipole System ◽  
Single Dipole ◽  
Current Systems

The frequency-domain electromagnetic response of a confined conductor buried in a resistive host has received much attention, particularly in the context of mineral exploration. In contrast, the problem of the electromagnetic response of a confined resistor buried in a conductive host has been less thoroughly studied. However, resistive targets are important in geotechnical and hydrologic studies, archaeological prospecting, and, more recently, offshore hydrocarbon exploration. I analytically address the problem of the electromagnetic response of a completely resistive cylindrical cavity buried in a conductive host in the presence of a simplified 2D electric dipole source. In contrast to the confined conductor, which channels and induces current systems, the confined resistor deflects current and produces additional eddy current systems in the conductive host. I apply this theory to model the response of a grounded electric dipole-dipole system operating over a range of frequencies from 0 Hz to 10 kHz, in the presence of a horizontal 5-m radius insulating cylinder located 1-m beneath the surface of a uniform earth. This represents a common hazard encountered during mining and civil engineering operations. Results show that such an insulating cavity increases the recorded electric field amplitude and phase delay at all transmitted frequencies. These observations suggest that a broadband electromagnetic prospecting system may provide additional information about the location and extent of a void, over and above a standard dipole-dipole resistivity survey. When the host skin depth is much larger than all other length scales, the response can be approximated by an equivalent single dipole unless the cylinder’s radius is much larger than its distance from the transmitter. This result provids a useful rule of thumb to determine the acceptable range over which a resistive target can be modeled by a distribution of dipoles.

The scattering of multipole near-field sound by a gas bubble

1970 ◽  
Vol 314 (1518) ◽  
pp. 363-385 ◽  
Keyword(s):  
Near Field ◽  
Dipole Source ◽  
Gas Bubble ◽  
Underwater Sound ◽  
Near Field Sound ◽  
Acoustic Output ◽  
Scattering Centre ◽  
Strong Scattering ◽  
Dipole Sources ◽  
Good Agreement

A gas bubble very close to an underwater sound source can have a profound influence on the sound radiated by the source. It is well known that when source and bubble are far apart, the bubble is a strong scattering centre for the incident sound, but when they are close together the bubble responds also to the near-field flow. This near field is scattered by the bubble from a non-propagating to a propagating mode so that the acoustic output of a multipole source, which has a relatively high near-field, can be considerably increased by the scattering process. A theory is developed for the scattering by a single spherical gas bubble near ( a ) a compressible spherical monopole source and ( b ) a compressible spherical dipole source, but it can be applied to non-spherical sources and bubbles by ascribing to them an ‘equivalent spherical radius’. The theory is in good agreement with experiments using bubbles near a spherical monopole source and in fair agreement with experiments on bubbles near non-spherical monopole and dipole sources.

scholarly journals Localization of Alternating Magnetic Dipole in the Near-Field Zone with Single-Component Magnetometers

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Gao Xiang ◽  
Du Bo-cheng ◽  
Wang Qi-long
Keyword(s):  
Magnetic Field ◽  
Magnetic Dipole ◽  
Near Field ◽  
Vertical Component ◽  
Low Frequency ◽  
Single Component ◽  
Dipole Source ◽  
Magnetic Field Measurement ◽  
Field Zone ◽  
Theoretical Simulation

Tri-axis magnetometers are widely used to measure magnetic field in engineering of the magnetic localization technology. However, the magnetic field measurement precision is influenced by the nonorthogonal error of tri-axis magnetometers. A locating model of the alternating magnetic dipole in the near-field zone with single-component magnetometers was proposed in this paper. Using the vertical component of the low-frequency magnetic field acquired by at least six single-component magnetometers, the localization of an alternating magnetic dipole could be attributed to the solution for a class of nonlinear unconstrained optimization problem. In order to calculate the locating information of alternating magnetic dipole, a hybrid algorithm combining the Gauss–Newton algorithm and genetic algorithm was applied. The theoretical simulation and field experiment for the localization of alternating magnetic dipole source were carried out, respectively. The positioning result is stable and reliable, indicating that the locating model has better performance and could meet the requirements of actual positioning.

Scattering by a two-layer spherical dielectric object in a lossy medium illuminated by a loop carrying an arbitrary azimuthal mode

1989 ◽  
Vol 67 (6) ◽  
pp. 617-623
Author(s):  
A. Sebak ◽  
L. Shafai
Keyword(s):  
Current Distribution ◽  
Scattered Field ◽  
Near Field ◽  
Electromagnetic Response ◽  
Field Zone ◽  
Spherical Object ◽  
Azimuthal Mode ◽  
Low Frequencies ◽  
Circular Loop ◽  
Lossy Medium

The electromagnetic response of a circular loop antenna in the vicinity of a two-layer dielectric spherical object located in a lossy medium is investigated analytically. For a loop carrying an azimuthally dependent current distribution, a technique based on the dyadic Green's functions is employed to determine the fields in all regions. The formulation is general and can be applied to a wide variety of electromagnetic sources. Numerical results are presented in the near field zone and at low frequencies to determine the effect of the coating on the scattered field and its influence on the degree of detectability of a coated object.

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