Total Magnetization Vector Research Articles

Modeling the Magnetic Field of the Inner Corona in a Radially Expanding Solar Wind

The magnetic field in the interplanetary medium is formed by the action of magnetic field sources on the photosphere of the Sun and currents in the expanding atmosphere of the Sun and the solar wind. In turn, the high-speed plasma flow changes the configuration of the magnetic field lines. The problem of determining the parameters of the magnetic field near the Sun is thus a three-dimensional problem of the interaction of the magnetic field and the plasma of the solar wind. We present analytical expressions for calculating the total magnetic field vector B→(r, θ, ϕ) (in spherical coordinates) for a radially expanding solar wind flow of finite conductivity. The parameters of the solar wind are given in the form of a dimensionless magnetic Reynolds number given as an arbitrary function of the radius, r: Rm = rσμv=ξ(r), where σ, μ, and v denote, respectively, the conductivity, magnetic permeability, and velocity of the solar wind. The solution for the magnetic field components is obtained in the form of a decomposition in spherical functions and a radial part depending on the distance from the Sun. Examples of calculations of the configuration of magnetic fields and structures of the solar corona for the solar eclipse of 21 August 2017 are given.

A new method to estimate the total magnetization direction from the magnetic anomaly: Multiple correlation

Natural remanent magnetization diverts the direction of the total magnetization vector from the earth’s magnetic field direction. It is important to determine the magnetization direction because the processing and inversion of magnetic usually need the magnetization direction as a priori information. The conventional strategy for estimating the magnetization direction is to compute the crosscorrelation between the reduced-to-the-pole (RTP) field and one magnetic magnitude transform, which is insensitive to the magnetization direction. A new theory and method are proposed that the total magnetization direction is determined by computing the multiple correlation coefficients between the RTP field and the multiple direction-insensitive magnitudes transforms, such as the total magnitude anomaly and the normalized source strength. The linear regression between the RTP field and the direction-insensitive magnitude transforms is established. Then, the correlation is computed by the RTP field and the constructed regressor. The proposed method is tested on synthetic of single and complex models, respectively. Then, the method is applied to the field data of the Yeshan region (eastern China) and the Black Hill Norite (southern Australia). The proposed multiple correlation is an extension of the conventional crosscorrelation method that provides an accurate and robust way to estimate the magnetization direction from the total field anomaly.

Magnetic radial inversion for 3-D source geometry estimation

SUMMARY We present a method for inverting total-field anomaly data to estimate the geometry of a uniformly magnetized 3-D geological source in the subsurface. The method assumes the total-magnetization direction is known. We approximate the source by an ensemble of vertically juxtaposed right prisms, all of them with the same total-magnetization vector and depth extent. The horizontal cross-section of each prism is a polygon defined by a given number of equi-angularly spaced vertices from 0° to 360°, whose polygon vertices are described by polar coordinates with an origin defined by a horizontal location over the top of each prism. Because our method estimates the radii of each polygon vertex we refer to it as radial inversion. The position of these vertices, the horizontal location of each prism and the depth extent of all prisms are the parameters to be estimated by solving a constrained non-linear inverse problem of minimizing a goal function. We run successive inversions for a range of tentative total-magnetization intensities and depths to the top of the shallowest prism. The estimated models producing the lowest values of the goal function form the set of candidate solutions. To obtain stabilized solutions, we impose the zeroth- and first-order Tikhonov regularizations on the shape of the prisms. The method allows estimating the geometry of both vertical and inclined sources, with a constant direction of magnetization, by using the Tikhonov regularization. Tests with synthetic data show that the method can be of utility in estimating the shape of the magnetic source even in the presence of a strong regional field. Results obtained by inverting airborne total-field anomaly data over the Anitápolis alkaline–carbonatitic complex, in southern Brazil, suggest that the emplacement of the magnetic sources was controlled by NW–SE-trending faults at depth, in accordance with known structural features at the study area.

A paradigm shift in magnetic data interpretation: Increased value through magnetization inversions

Magnetic data are sensitive to both the induced magnetization in rock units caused by the present earth's magnetic field and the remanent magnetization acquired by rock units in past geologic time. Susceptibility is a direct indicator of the magnetic mineral content, whereas remanent magnetization carries information about the formation process and subsequent structural movement of geologic units. The ability to recover and use total magnetization, defined as the vectorial sum of the induced and remanent magnetization, therefore enables us to take full advantage of magnetic data. The exploration geophysics community has achieved significant advances in inverting magnetic data affected by remanent magnetization. It is now feasible to invert any magnetic data set for total magnetization. We provide an overview of the state of the art in magnetization inversion and demonstrate the informational value of inverted magnetization through a set of case studies from mineral exploration problems. We focus on the methods that recover either the magnitude of the total magnetization or the total magnetization vector itself.

Influence of length of partitions on the generation of transit flow in MHD-channel

The process of the transit flow generation in the magnetohydrodynamic channel of the pump is investigated. Its design provides for the variation of the flow-rate of the liquid metal without changing the current in the channel. The pressure in the pump channel creates by an electromagnetic force through the interaction of a longitudinal electric current with its own magnetic field. C-shaped ferromagnetic cores are put on the channel. The current generates its own magnetic field which magnetizes the cores. The total magnetic induction vector of the current’s magnetic field and the field of the cores is orthogonal to the channel plane. The arising electromagnetic force generates a transit flow through the channel which is caused by the presence of flow partitions in it. The pump is tested on the gallium circuit. The pressure drop at the locked mode and variable flow rate mode for different values of channel overlapping by C-cores and their different numbers has been measured in the experiment. The pressure drop — flow-rate characteristics of the channel are determined at different values of overlap the channel.

Extracting Induced and Remanent Magnetizations From Magnetic Data Modeling

AbstractTo investigate the crustal magnetic structure, it is important to assess the susceptibility and remanence properties of rocks and ores. In this paper, we propose a method to extract the contributions of induced and remanent magnetization from modeling of magnetic anomalies. We first estimate the direction of the total magnetization vector by studying the reduced‐to‐pole anomaly and its correlation with different magnitude magnetic transforms. Then we invert the magnetic data to obtain the volumetric distribution of the magnetization intensity. As the third step, based on a priori information about the Koenigsberger ratio derived from petrophysical measurements, we extract the distributions in the source volume of the induced and remanent magnetization intensities, based on a generalized relationship involving the total and remanent magnetizations, and the true susceptibility. In this way, we are able to produce separate maps of the anomaly fields attributed to the physical magnetic source parameters: remanent and induced magnetization. After validating the method with synthetic data, we analyze the data relative to the Mesozoic and Cenozoic igneous rocks in Yeshan region, eastern China. The analysis of the separated magnetization components reveals that the intrusion of dioritic and basaltic rocks occurred at different geological periods, and the basaltic rocks were magnetized by a reversed geomagnetic field. The uncertainty analysis shows that a larger Koenigsberger ratio is beneficial to extract more reliable remanence and susceptibility information.

3D Magnetization Vector Inversion of Magnetic Data: Improving and Comparing Methods

Magnetization vector inversion is an useful approach to invert for magnetic anomaly in the presence of significant remanent magnetization and self-demagnetization. However, magnetizations are usually obtained in many different directions under the influences of geophysical non-uniqueness. We propose an iteration algorithm of magnetization vector inversion (M-IDI) that one couple of magnetization direction is iteratively computed after the magnetization intensity is recovered from the magnitude magnetic anomaly. And we compare it with previous methods of (1) three orthogonal components inversion of total magnetization vector at Cartesian framework (MMM), (2) intensity, inclination and declination inversion at spherical framework (MID), (3) directly recovering the magnetization inclination and declination (M-IDCG) and (4) estimating the magnetization direction using correlation method (M-IDC) at the sequential inversion frameworks. The synthetic examples indicate that MMM returns multiply magnetization directions and MID results are strongly dependent on initial model and parameter weights. M-IDI computes faster than M-IDC and achieves a constant magnetization direction compared with M-IDCG. Additional priori information constraints can improve the results of MMM, MID and M-IDCG. Obtaining one magnetization direction, M-IDC and M-IDI are suitable for single and isolated anomaly. Finally, M-IDI and M-IDC are used to invert and interpret the magnetic anomaly of the Galinge iron-ore deposit (NW China) and the results are verified by information from drillholes and physical properties measurements of ore and rock samples. Magnetization vector inversion provides a comprehensive way to evaluate and investigate the remanent magnetization and self-demagnetization.

Inversion of magnetic anomaly on rugged observation surface in the presence of strong remanent magnetization

We study the inversion of magnetic data acquired over a rugged observation surface and where the buried source bodies have strong remanent magnetization that leads to unknown total magnetization directions. These factors pose significant challenges for processing and inversion of such data. To tackle the challenges from both a rugged observation surface and an unknown magnetization direction, we propose a strategy through the joint use of the equivalent source technique and 3D amplitude inversion to obtain 3D magnetization strength. We use equivalent source processing to calculate the amplitude data in the space domain because the use of the wavenumber-domain method is invalid due to large variations in the data elevation. We then carried out an amplitude inversion to generate a 3D subsurface distribution of the magnitude of the total magnetization vector. The results from a synthetic example and aeromagnetic data in Daye Mine in China showed that this approach is effective and images the magnetic units whose contact zones with the limestone country rock host the mineralization. The method is general and can be applied to a variety of cases with similar challenges.

Formulation for shielding effectiveness analysis of a rectangular enclosure with an electrically large aperture

Since electric components and printed circuit board in the enclosure can be destroyed by electromagnetic pulse weapons through “front door and back door” coupling, which is a great threat to the operational security, the study of the shielding effectiveness is of important significance. A formulation for shielding effectiveness analysis of a rectangular enclosure with an electrically large aperture is proposed in this paper. Firstly, the plane wave with oblique incidence and polarization is decomposed. Secondly, based on the Cohn model, the equivalent electric and magnetic dipole of the electrically large aperture is computed. Thirdly, the total Hertz electric and magnetic vector potential is obtained through mirror procedure. Finally, the electric field inside an enclosure with electrically large aperture is formulated, which is used for shielding effectiveness calculation. Five verification experiments are designed. Simulation result shows that the mean square error and absolute error of this method compared to computer simulation technology (CST) microwave studio are 11.565 dB and 8.015 dB respectively, the correlation coefficient is 0.921, through which the accuracy of this method is verified. The simulation time of this method is 0.183 s, which is only 1/7530 times of CST, so its efficiency is obvious.

Electromagnetic field of worm coils for electromechanical integrated toroidal drive

In this paper, based on electromagnetic theory and geometrics, the electromagnetic field of the worm coils for the drive is researched. A coordinate system is established and equations of the toroidal helical slots for three phase coils on worm are presented. By means of equation for magnetic vector at any point near coil, magnetic vector near single phase toroidal worm coils is introduced. Hence, the total magnetic vector near three phase toroidal worm coils is obtained as well. Simulation results show: near toroidal worm, as a static current is applied to its one toroidal coil, a toroidal electromagnetic field is formed; when the 3-phase source is connected to the coils of the worm, a toroidal circular rotating electromagnetic field will drive several planets rotate about their own axial. And by means of magnetic forces between teeth of the planet and stator or worm, the rotor will be driven to rotate about its own axial and an output of low speed and large torque can be obtained.

Estimating the magnetization direction of crustal structures by means of an equivalent source algorithm

The estimation of the direction of the total magnetization vector of a magnetic source is the first step of a reliable modelling of a magnetic anomaly when remanent magnetization is not negligible. We present a new method to obtain the magnetization direction of a crustal body, based on an iterative equivalent layer inversion of a magnetic anomaly. The main advantage of the proposed approach is that no a priori information about the source is needed. The method is suitable for the interpretation of isolated magnetic sources for which magnetization is expected to be uniform in direction, but not necessarily in intensity. We have verified the success of the technique with synthetic data and with the magnetic anomaly of El Hierro volcanic island.

Paleomagnetic determinations on Lanzarote from magnetic and gravity anomalies: Implications for the early history of the Canary Islands

The Bouguer and aeromagnetic anomaly maps of Lanzarote show a gravity high and a dipolar magnetic anomaly over the central part of the island, indicating one isolated source. Assuming that the structure responsible for both anomalies is the same, a methodology has been designed to estimate the total magnetization vector of the source, which is interpreted as a large intrusive body (mafic core) positioned as a result of magma rising to the surface during the early stages of growth of Lanzarote. Considering its geometry to be known from a previous three‐dimensional (3‐D) gravity model, the approach proposed in this paper is based on the delineation of magnetic contacts through analysis of the horizontal gradient of the reduced‐to‐the‐pole anomaly map, comparison between the gravity and the pseudogravity anomalies, and 3‐D forward magnetic modeling. The total magnetization vector obtained by this method is defined by a module of 4.5 A m−1 and a direction D = −20° and I = 30°. Comparing the paleomagnetic pole, obtained from this direction, with the apparent polar wander path of Africa for the last 160 Myr, it is concluded that the main component of the total magnetization vector is probably a primary natural remanent magnetization (NRM) which could have been acquired between 60 and 100 Ma. This result suggests that the emplacement of magmas at shallow depths linked to the beginning of volcanism in Lanzarote took place during the Upper Cretaceous, thus providing the first evidence of a timeline for the early formative stages of this volcanic island.

Current density and forces for a current loop moving parallel over a thin conducting sheet

An analytical expression for the eddy current forces on a circular current loop moving with constant velocity over a thin conducting sheet is derived in this paper. This calculation is based on using the boundary conditions across the conducting sheet to solve for the total magnetic vector potential. The eddy currents in the sheet and the forces on the sheet are first presented in the ‘quasi-static’ limit and the perfect conductor limit. Finally, an analytical expression for both the drag and lift force is derived.

Coronal magnetograms of solar active regions

A series of coronal magnetograms, related to the active region NOAA 9068 is derived using the effects of the quasi-transverse (QT-) propagation at microwaves. In the assumption that the product of the electron density N and the scale of magnetic divergence Ld is constant and equal to 10 18 cm −2 , the sensitivity of the measurements peaks at B(G) ≈ 180 λ −4/3 (cm), where λ is the observational wavelength. The radio maps of the Sun taken with the Solar Siberian Radio Telescope (SSRT) at λ =5 .2 cm were sampled and converted into the 2D coronal magnetograms supplying absolute values of the total magnetic vector � B in the range 10 - 30 G. Each coronal magnetogram covers the portion of the microwave source in the active region affected by the QT-propagation conditions in the corona.

Antimagnons in ferrimagnets

Purely antiferromagnetic intrinsic oscillations of magnetic ions in a tetragonal ferrimagnet are considered. The magnetic ions occupy two double positions (forming four magnetic sublattices) so that the center of symmetry for each position is not a closed element. Not involving the total magnetization vector, the oscillations are not excited by the magnetic field; however, the oscillations can be excited by an alternating electric field or by a combination of a constant electric field and the alternating magnetic field of a certain frequency. This phenomenon is a dynamic manifestation of the magnetoelectric interaction. These oscillations, representing a new special type of spin waves (magnons), were called antimagnons. The intrinsic frequencies of antimagnons, as well as the corresponding susceptibilities, were determined. Quantitative estimates were obtained for a Mn2Sb-based ferrimagnetic phase in both easy-axis and easy-plane orientation states.

Effect of tensile stress on the 3D reversible and irreversible differential magnetic susceptibilities

Magnetic hysteresis loops in three orthogonal directions are measured for a line pipe steel sample while the external magnetic field is applied in a direction perpendicular to the tensile stress direction. The total magnetization vector is calculated. This tends to the stress direction when tensile stress is applied. The reversible and irreversible differential magnetic susceptibilities are derived. It is found that the susceptibilities in all three directions are enhanced with increasing tensile stress, although the increase in the stress direction is much larger than in the other directions.

Equation of motion of the magnetization vector in materials with fluctuating valence

In micromagnetics, it is common practice to describe the motion of the magnetization vector in terms of the Landau–Liftshitz–Gilbert equations. In these, the strength of the dissipative torque is measured by a phenomenological parameter, and the form of the torque is chosen so as to lead to a reversion of the magnetic vector to a stable or metastable position. The microscopic origin of the parameter, as well as the correct form of the torque is not generally discussed. Retaining the mathematical description of all the degrees of freedom to which the magnetization vector is coupled, would give correct results. However, it is obviously desirable to formally eliminate these degrees of freedom, resulting in equations for the magnetization vector alone. In this article, the necessary procedure is carried out for the particular case in which the loss mechanism arises from valence fluctuations changing electron occupation numbers, and thereby the magnetic moments, of the various sites. Since the fluctuations are not instantaneous, the total magnetization vector develops time lags that manifest themselves as a loss mechanism. Apart from a numerical measure of this damping, we find that the structure of the torque term does not, in general, have one of the familiar forms. Furthermore, this results in certain changes in the switching characteristics of small magnetic particles. This particular origin of dissipation was discussed in the early 1950’s by Clogston, Gate, and others in the context of domain wall motion and small-signal ferromagnetic resonance, but no attempt was made at that time to re-express the entire process in terms of an equation of motion of the magnetization vector alone.

High field magnetization and spin reorientation in Sm 2(Fe 1− xAl x) 17 single crystals

High field magnetization measurements have been performed for single crystals of Sm 2(Fe 1− x Al x ) 17, with x = 0.075, 0.093, 0.114, 0.145. The spontaneous magnetization at room temperature lies in the hexagonal c plane. Appreciable anisotropy within the c plane was observed at 4.2 K with the magnetization along the a axis being more than 3% smaller than that along the b axis, even in a field of 10 T. The c axis curve has been found to show a smaller spontaneous magnetization, indicating that the total magnetization vector is not within the c plane but in the plane spanned by the b and c axes. The angle between the magnetization direction and the b axis increases linearly with increasing x. The results are analyzed on the basis of crystalline electric field theory.

Spin reorientation transition in HoFe10Si2 compound

The second order magnetic phase transition (spin reorientation) was indicated near TSR = 52 K in HoFe10Si2 compound by temperature dependence of the ac susceptibility and resistivity measurements. Crystal field Hamiltonian up to the sixth order with isotropic exchange term was applied to calculate temperature dependence of the angle between the total magnetization vector and tetragonal c-axis. Estimation of the crystal field coefficients indicates clearly the crucial role of the highest order crystal field terms in Hamiltonian.

Properties of the fluctuating magnetic helicity in the inertial and dissipation ranges of solar wind turbulence

We investigated the inertial and dissipation ranges of the reduced magnetic helicity spectrum of solar wind fluctuations and have found that this spectrum appears insensitive to solar cycle variations and changes in solar wind flow parameters. In the inertial range of the spectrum, the reduced helicity is large but random and independent of heliocentric distance between 0.3 and 10 AU. At small scales, in the dissipation range of the spectrum, a correlation appears to exist between the average value of the normalized reduced magnetic helicity and the polarity of magnetic sectors, suggesting that these fluctuations, if outward propagating, are predominantly right‐hand polarized. In the inertial range the statistical properties of the normalized magnetic helicity are well approximated by a simple model of the magnetic field in which the total magnetic field vector randomly walks with only small variations in magnitude. The behavior of the inertial range spectrum is very similar to that seen in three‐ and two‐and‐a‐half‐dimensional simulations of the incompressible and compressible equations describing magnetohydrodynamic turbulence, consistent with the paradigm that the solar wind is a turbulent magnetofluid.