scholarly journals Opposing-coils transient electromagnetic method focused near-surface resolution

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. E279-E285 ◽  
Author(s):  
Zhenzhu Xi ◽  
Xia Long ◽  
Long Huang ◽  
Sheng Zhou ◽  
Gang Song ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Free Space ◽  
Theoretical Calculations ◽  
Field Work ◽  
Induction Effect ◽  
Near Surface ◽  
Enhanced Sensitivity ◽  
Optimal Separation ◽  
Transient Electromagnetic ◽  
Mutual Induction

The transient electromagnetic (TEM) method is a commonly used, nonintrusive, geophysical method, but inherent mutual induction between the transmitter (TX) and receiver (RX) coils strongly influences the measurements. We have developed an opposing-coils configuration to greatly reduce this effect. Three coils are used in this system. The upper opposing coil is physically the same as the lower TX coil, and they are concentric and parallel to the middle RX coil. A pair of currents with equal amplitudes but reverse directions is injected into the opposing and TX coils. Theoretical calculations in free space show that the received magnetic field by the RX coil is zero, which indicates that the mutual induction effect could be largely reduced. Physical experiments prove that an almost-pure secondary field could be acquired using this system. We have studied an optimal separation between the TX and opposing coils to guarantee that the primary magnetic field is powerful and the instrument is compacted for field work. Then, the efficient exploration depth of this system for typical geoelectric models was simulated to be approximately 15–50 m. Comparisons of simulated responses over highly conductive thick plates in free space and a field test over a culvert structure between this system and EM-47 showed that the system has enhanced sensitivity and lateral resolution. This system can be used in near-surface investigations, e.g., groundwater, environmental, and engineering investigations.

scholarly journals Colossal anomalous Nernst effect in a correlated noncentrosymmetric kagome ferromagnet

2021 ◽  
Vol 7 (13) ◽  
pp. eabf1467
Author(s):  
T. Asaba ◽  
V. Ivanov ◽  
S. M. Thomas ◽  
S. Y. Savrasov ◽  
J. D. Thompson ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electronic Structure ◽  
Theoretical Calculations ◽  
Zero Magnetic Field ◽  
Nernst Effect ◽  
Nodal Lines ◽  
Transverse Response ◽  
Narrow Bands ◽  
Strong Spin ◽  
Anomalous Nernst Effect

The transverse voltage generated by a temperature gradient in a perpendicularly applied magnetic field, termed the Nernst effect, has promise for thermoelectric applications and for probing electronic structure. In magnetic materials, an anomalous Nernst effect (ANE) is possible in a zero magnetic field. We report a colossal ANE in the ferromagnetic metal UCo0.8Ru0.2Al, reaching 23 microvolts per kelvin. Uranium’s 5f electrons provide strong electronic correlations that lead to narrow bands, a known route to producing a large thermoelectric response. In addition, uranium’s strong spin-orbit coupling produces an intrinsic transverse response in this material due to the Berry curvature associated with the relativistic electronic structure. Theoretical calculations show that in UCo0.8Ru0.2Al at least 148 Weyl nodes, and two nodal lines, exist within 60 millielectron volt of the Fermi level. This work demonstrates that magnetic actinide materials can host strong Nernst and Hall responses due to their combined correlated and topological nature.

Influences of the Earth’s Magnetic Field on the Transient Electromagnetic Process in the Geoelectric Field: an Experimental Study

2021 ◽  
Vol 62 (12) ◽  
pp. 1430-1439
Author(s):  
V.S. Mogilatov ◽  
V.V. Potapov ◽  
A.N. Shein ◽  
V.A. Gur’ev
Keyword(s):  
Magnetic Field ◽  
Hall Effect ◽  
Field Experiments ◽  
Geoelectric Field ◽  
Earth’S Magnetic Field ◽  
Electromagnetic Process ◽  
Transient Electromagnetic ◽  
Schematic Layout ◽  
Earth's Magnetic Field ◽  
Tem Method

Abstract —A mathematical model of the influence of the Earth’s magnetic field (the Hall effect) on results of the controlled source transient electromagnetic (TEM) method has been elaborated. For identification of this effect, we propose a schematic layout of the experimental grounded system with a pulsed loop source and signals recording by radial receive lines equally spaced relative to the loop. The 2018–2019 special field experiments were conducted in the Tatar region of the West Siberian Lowland with an aim to estimate the Hall effect contributions to the TEM method. To detect the Hall effect, transient electromagnetic responses were measured mainly by four receive lines radiating from a 500×500 m square loop. Analysis of the TEM results processing aimed at improving the signal quality and reducing the interference revealed a great similarity in signals from the radial lines, which is theoretically possible only under the Hall effect. Comparison of the field signals with the theoretical ones enabled estimation of the components caused by the Hall effect, in particular, conductivity at ~0.002 S/m.

scholarly journals Movement of the Ward Hunt Ice Shelf, Ellesmere Island, N.W.T., Canada

1971 ◽  
Vol 10 (59) ◽  
pp. 211-225 ◽  
Author(s):  
E. Dorrer
Keyword(s):  
Power Flow ◽  
Field Work ◽  
Ellesmere Island ◽  
Ice Shelf ◽  
Surface Layers ◽  
Atmospheric Refraction ◽  
Near Surface ◽  
Angle Measurements ◽  
Ice Velocity ◽  
Ice Forces

AbstractThe movement at a marginal location on the Ward Hunt Ice Shelf, northern Ellesmere Island, was determined by repeated survey measurements with theodolite and geodimeter. The purpose and duration of the field work, and reduction of the observational data are described, and the resulting mean ice velocity of 0.53 m year-1is discussed. Strain-rates of a 1 km by 1 km deformation figure are determined. The parametersnandBof Glen’s power flow law are determined by using the equations given by Nye and Weertman. The results are compared with experimental data. Computed ice stresses show that the “ridge-and-trough" structure on the ice shelf surface is not originated by internal ice forces. The elevations of all survey markers have been determined from vertical-angle measurements, and the peculiarities of atmospheric refraction in near-surface layers are discussed.

A New Magnetooptical Effect Discovered on Magnetic Multilayers: The Magnetorefractive Effect

1995 ◽  
Vol 384 ◽  
Author(s):  
J. C. Jacquet ◽  
T. Valet
Keyword(s):  
Magnetic Field ◽  
Optical Transmission ◽  
Theoretical Calculations ◽  
Wavelength Region ◽  
Magnetic Multilayers ◽  
Light Wavelength ◽  
Metallic Multilayers ◽  
Magnetooptical Effect ◽  
Transmission Measurements ◽  
Magnetorefractive Effect

ABSTRACTWe show theoretically that the change in the magnetization structure of magnetic metallic multilayers under the application of a magnetic field shall be generally associated with a significant change of the refractive index. This constitutes a new magnetooptical effect: the magnetorefractive effect.Optical transmission measurements under an applied magnetic field through [Ni80Fe20/Cu/Co/Cu] multilayers, in the light wavelength region between 2 μm and 20 μm, clearly demonstrate the existence of the predicted effect and are found in reasonnable agreement with the theoretical calculations.

Using an induction coil sensor to indirectly measure the B-field response in the bandwidth of the transient electromagnetic method

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1489-1494 ◽  
Author(s):  
Richard S. Smith ◽  
A. Peter Annan
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Indirect Measurement ◽  
Rate Of Change ◽  
Induction Coil ◽  
Voltage Response ◽  
Magnetic Field Data ◽  
Transient Electromagnetic ◽  
Different Characteristics ◽  
The Magnetic Field

The traditional sensor used in transient electromagnetic (EM) systems is an induction coil. This sensor measures a voltage response proportional to the time rate of change of the magnetic field in the EM bandwidth. By simply integrating the digitized output voltage from the induction coil, it is possible to obtain an indirect measurement of the magnetic field in the same bandwidth. The simple integration methodology is validated by showing that there is good agreement between synthetic voltage data integrated to a magnetic field and synthetic magnetic‐field data calculated directly. Further experimental work compares induction‐coil magnetic‐field data collected along a profile with data measured using a SQUID magnetometer. These two electromagnetic profiles look similar, and a comparison of the decay curves at a critical point on the profile shows that the two types of measurements agree within the bounds of experimental error. Comparison of measured voltage and magnetic‐field data show that the two sets of profiles have quite different characteristics. The magnetic‐field data is better for identifying, discriminating, and interpreting good conductors, while suppressing the less conductive targets. An induction coil is therefore a suitable sensor for the indirect collection of EM magnetic‐field data.

Evaluation of the Equivalent Lumped Element Parameters of Modified Microstrip Ring Resonator

2015 ◽  
Vol 735 ◽  
pp. 278-281
Author(s):  
Yi Lung Then ◽  
Kok Yeow You ◽  
Mohamad Ngasri Dimon ◽  
Wei Ying Lai
Keyword(s):  
Magnetic Field ◽  
Free Space ◽  
Ring Resonator ◽  
Element Model ◽  
Network Analyzer ◽  
Simulation Data ◽  
Lumped Element ◽  
Lumped Element Model ◽  
Microstrip Ring ◽  
Microstrip Ring Resonator

Microstrip ring resonator (MRR) sensor was modeled by simple equivalent lumped element circuits in free space based on simulation data obtained from Microwave Office (AWR) simulator and comparison was made with the measurements using the E5071C Network Analyzer. The calculated reflection coefficient, |G| and complex input impedanceZinusing lumped element model were compared with the measurements results. Both results showed well agreement with a little discrepancy, basically due to imperfect soldering. The MRR was designed to have operating frequencies between 0.5 GHz and 4.5 GHz. The maximum surrounding of magnetic field,Hϕis within 15 A/m in free space.

scholarly journals A parallel finite‐difference approach for 3D transient electromagnetic modeling with galvanic sources

Geophysics ◽  
2004 ◽  
Vol 69 (5) ◽  
pp. 1192-1202 ◽  
Author(s):  
Michael Commer ◽  
Gregory Newman
Keyword(s):  
Magnetic Field ◽  
Finite Difference ◽  
Electric Field ◽  
Electric Fields ◽  
Time Derivative ◽  
Stable Solution ◽  
Parallel Computer ◽  
Staggered Grid ◽  
Electromagnetic Modeling ◽  
Transient Electromagnetic

A parallel finite‐difference algorithm for the solution of diffusive, three‐dimensional (3D) transient electromagnetic field simulations is presented. The purpose of the scheme is the simulation of both electric fields and the time derivative of magnetic fields generated by galvanic sources (grounded wires) over arbitrarily complicated distributions of conductivity and magnetic permeability. Using a staggered grid and a modified DuFort‐Frankel method, the scheme steps Maxwell's equations in time. Electric field initialization is done by a conjugate‐gradient solution of a 3D Poisson problem, as is common in 3D resistivity modeling. Instead of calculating the initial magnetic field directly, its time derivative and curl are employed in order to advance the electric field in time. A divergence‐free condition is enforced for both the magnetic‐field time derivative and the total conduction‐current density, providing accurate results at late times. In order to simulate large realistic earth models, the algorithm has been designed to run on parallel computer platforms. The upward continuation boundary condition for a stable solution in the infinitely resistive air layer involves a two‐dimensional parallel fast Fourier transform. Example simulations are compared with analytical, integral‐equation and spectral Lanczos decomposition solutions and demonstrate the accuracy of the scheme.

Magnetic modulation of Fano resonances in optically thin terahertz superlattice metasurfaces

2021 ◽  
Author(s):  
Subhajit Karmakar ◽  
Ravi Varshney ◽  
Dibakar Roy Chowdhury
Keyword(s):  
Magnetic Field ◽  
Free Space ◽  
Skin Depth ◽  
Electromagnetic Energy ◽  
Magnetic Control ◽  
Fano Resonances ◽  
Electromagnetic Responses ◽  
On Chip ◽  
Magneto Resistance ◽  
Sub Wavelength

Abstract Optically thin metasurfaces operating at sub-skin depth thicknesses are intriguing because of its associated low plasmonic losses (compared to optically thick, beyond skin-depth metasurfaces). However, their applicability has been restricted largely because of reduced free space coupling with incident radiations resulting in limited electromagnetic responses. To overcome such limitations, we propose enhancement of effective responses (resonances) in sub-skin depth metasurfaces through incorporation of magneto-transport (Giant Magneto Resistance, GMR) concept. Here, we experimentally demonstrate dynamic magnetic modulation of structurally asymmetric metasurfaces (consisting of superlattice arrangement of thin (~ 10 nm each) magnetic (Ni)/ nonmagnetic (Al) layers) operating at terahertz (THz) domain. With increasing magnetic field (applied from 0 to 30 mT approximately, implies increasing superlattice conductivity), we observe stronger confinement of electromagnetic energy at the resonances (both in dipole and Fano modes). Therefore, this study introduces unique magnetically reconfigurable ability in Fano resonant THz metamaterials, which directly improves its performances operating in the sub-skin depth regime. Our study can be explained by spin-dependent terahertz magneto-transport phenomena in metals and can stimulate the paradigm for on-chip spin-based photonic technology enabling dynamic magnetic control over compact, sub-wavelength, sub-skin depth metadevices.

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