Normal Magnetic Component Research Articles

Fast and efficient inversion methods for crack sizing using Bz magnetic signature

AbstractFast estimation is a critical feature of the proposed modeling approach as a “forward” fast solver that has a key role in solving the “inverse” problem involved in crack sizing, especially for real‐time applications. To this end, two different inversion methods have been proposed to estimate the crack depth. The first one uses an interpolation model of the 3D direct model simulation data. The second approach is based on artificial neural networks (ANN). In this article, the rotating uniform eddy current (RUEC) probe is used to detect the normal magnetic component Bz which is defined as the characteristic signal for reconstructing the crack length and depth concurrently. Using the first approach, The Bz characteristic 3D surface is presented, and this can be modeled by a fitted polynomial interpolation equation. Thus, the crack depth can be inverted using this equation referring to the experimental or simulated Bz signal and the crack length. The ANN is outlined to determine the crack depth based on the simulated Bz signature. The move from the first inversion method to the second was flexible and useful, in which the interpolation model is used as a defect signal generator for fast building of a large and efficient database for ANN training. Both of the proposed methods proved the objectivity and accuracy of the inversion results and offered more robust engineering support for automated NDT, reducing production time and increasing productivity.

Stress-Induced Self-Magnetic Flux Leakage at Stress Concentration Zone

The residual magnetization technique is a new method for detecting stress concentration zones (SCZs) in ferromagnetic materials. Local rising of stress at SCZs, such as cracks, results in the development of local elastic and plastic deformation. The two deformation regimes produce different magnetic characteristics, which have competing effects on self-magnetic-flux-leakage signals. In the present research, samples with three different groove depths were subjected to different tensile stress levels. A surface scanning system was used to record the variation of magnetic signals at grooves of varying depth under steadily increasing stress conditions. The results show that elastic deformation increases peak-to-peak values of normal magnetic components and a maximum gradient of the normal magnetic component in the direction of applied stress, while the development of local plastic deformation reduces signal intensity at groove locations. The magnetic object (MO) model is used to explain the mechanism for excess flux leakage field at SCZs as being due to the conversion of magnetoelastic energy—introduced by the application of tensile stress up to the local yield point—into magnetostatic surface poles that are sensed as an increase in the normal component of leakage.

Математическое описание и анализ сигнала виброиндукционного преобразователя при воздействии нормальной составляющей магнитных потоков рассеяния над дефектным участком

Theoretical and experimental researches of vibration-induction transducer (VIT) outlet signal formed during exposure to normal leakage magnetic field intensity component Hn over the defective area were carried out. Theoretical research is based on an assumption that VIT signal is a trigonometric series that is limited by first five harmonics. As initial data for mathematical model creation, well-known conformities for Hn distribution over the defective area were used. Based on acquired mathematical model conformities of VIT signal harmonical composition permutation during its movement over the defective area with varying amplitudes and vibration frequency were found. Theoretical research results were proven experimentally. Moreover, additional possibilities of this way of magnetic testing are shown in comparison with conventional ones.

Acceleration of plasma in current sheet during substorm dipolarizations in the Earth's magnetotail: Comparison of different mechanisms

This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some extent electrons) can be more effectively accelerated due to the mechanism (C) than the single dipolarization (B). It is found that high-frequency electric and magnetic fluctuations accompanying multiple DFs (D) can strongly accelerate electrons e− and really weakly influence other populations of plasma. The results of modeling demonstrated clearly the distinguishable spatial and temporal resonance character of particle acceleration processes. The maximum particle energies depending on the scale of the magnetic acceleration region and the value of the magnetic field are estimated. The shapes of energy spectra are discussed.This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some exten...

Effective Nonlinear Surface Impedance of Conductive Magnetic Slabs

A new formula is developed for the surface impedance of a nonlinear magnetic conductive semi-infinite slab. The impedance expression allows for proper incorporation of the nonlinear characteristic of the magnetic material, also using an analytical expression. Thus, the usual step representation of the $B$ – $H$ curve is superseded. Normal and tangential magnetic components may simultaneously exist, avoiding the classical premise that only the tangential component exists. This way, it is possible to represent highly magnetic permeable materials where the normal component of the magnetic field is the main one. Our analytical formulation and solution can be for example used for calculation of losses in electrical machines or along with FE software code to avoid meshing of magnetic conductive regions.

A paleomagnetic and rock magnetic study of the Manicouagan impact structure: Implications for crater formation and geodynamo effects

AbstractWe report rock magnetic and paleomagnetic data from the ~214 Ma Manicouagan (Canada) impact crater based on 25 widely distributed sites of impact melt and basement rocks collected at the surface as well as from boreholes drilled to depths ≤1.5 km. Titanomagnetite and titanohematite carry the magnetic remanence in impact melts above 320 m elevation and in most basement rocks. Impact melts below 320 m contain solely titanomagnetite. Magnetic susceptibility and saturation magnetization, proxies for titanomagnetite concentration, increase more than tenfold toward the base of the thickest impact melt that underwent fractional crystallization. The titanomagnetite‐enriched zone partially contributes to a 2000 nT magnetic anomaly in the crater's center. Stepwise demagnetization reveals a single, normal polarity magnetization component in all samples regardless of the magnetic phases present. Coeval lock‐in remanence times for titanomagnetite and titanohematite indicate that the titanohematite formed >570°C during oxi‐exsolution. The average paleomagnetic direction and intensity coincide well with 214 Ma reference values. We find no evidence for an aberration of the geomagnetic field over the several thousands of years it took to cool a 481 m thick portion of the impact melt body. Hence, the energy released by the Manicouagan impact that created one of the 10 largest known craters on Earth provoked no measurable disturbance of the geodynamo. Magnetic anisotropy of clast‐free impact melts define magnetic lineation directions that are, in places, radially oriented with respect to the crater's center. Centrifugal flow of the melt within the evolving transient crater probably generated the fabric.

Formation of self‐organized shear structures in thin current sheets

AbstractSelf‐consistent kinetic (particle‐in‐cell) model of magnetotail thin current sheet (TCS) is used to understand the formation of self‐consistent sheared magnetic structures. It is shown that shear configurations appear in TCS as a result of self‐consistent evolution of some initial magnetic perturbation at the current sheet center. Two general shapes of shear TCS components are found as a function of the transverse coordinate: symmetric and antisymmetric. We show that TCS formation goes together with the emergence of field‐aligned currents in the center of the current sheet, as a result of north‐south asymmetry of quasi‐adiabatic ion motions. Ion drift currents can also contribute to the magnetic shear evolution, but their role is much less significant, their contribution depending upon the normal component Bz and the amplitude of the initial perturbation in TCS. Parametric maps illustrating different types of TCS equilibria are presented that show a higher probability of formation of symmetric shear TCS configuration at lower values of the normal magnetic component.

The Early Triassic magmatism of the Alto ParaguayProvince, Central South America: Paleomagneticand ASM data

Abstract A paleomagnetic studystudywork was carriedout on the Alto Paraguay Province (APP), a belt of alkalinecomplexes that parallel the Paraguay river for morethan 40 km at the border of Brazil and Paraguay. Theprovince is well dated by 40Ar/39Ar method giving ages inthe range 240–250 Ma with a preferred age of 241 Ma. Intrusiverocks are predominant but the stocks may be toppedby lava flows and ignimbrites. Paleomagnetic work onstocks, dikes and flows of the APP identified normal andreversed magnetic components which are carried mainlyby titanomagnetites. The calculated paleomagnetic polelocated at 319ºE 78ºS (α95 = 6º; k = 23) is in agreementwith other South American poles of Permo-Triassic age.Most of the sampling sites showed large variations in rockmagnetization, but similar patterns in the variation of thewithin-site magnetizations, mainly in dikes, suggest geomagneticpolarity transition records. The magnetizationdata along with the anisotropy of magnetic susceptibilitydeterminations suggested that the South and North areasof the province have different evolution characteristics.

Ballooning instability‐induced plasmoid formation in near‐Earth plasma sheet

The formation of plasmoids in the near‐Earth magnetotail is believed to be a key element of the substorm onset process. Previous work has identified a new scenario in MHD simulations where the nonlinear evolution of a ballooning instability is able to induce the formation of plasmoids in a generalized Harris sheet with finite normal magnetic component. In present work, we further examine this novel mechanism for plasmoid formation and explore its implications in the context of substorm onset trigger problem. For that purpose, we adopt the generalized Harris sheet as a model proxy to the near‐Earth region of magnetotail during the substorm growth phase. In this region the magnetic component normal to the neutral sheet Bn is weak but nonzero. The magnetic field lines are closed, and there are no Xlines. Simulation results indicate that in the higher Lundquist number regime , the linear axial tail mode, which is also known as “two‐dimensional resistive tearing mode,” is stabilized by the finite Bn, hence cannot give rise to the formation of X lines or plasmoids by itself. On the other hand, the linear ballooning mode is unstable in the same region and regime, and its nonlinear development leads to the formation of a series of plasmoid structures in the near‐Earth and middle magnetotail regions of plasma sheet. This new scenario of plasmoid formation suggests a critical role of ballooning instability in the near‐Earth plasma sheet in triggering the onset of a substorm expansion.

Plasmoid formation in current sheet with finite normal magnetic component.

Current sheet configurations in natural and laboratory plasmas are often accompanied by a finite normal magnetic component that is known to stabilize the two-dimensional resistive tearing instability in the high Lundquist number regime. Recent magnetohydrodynamic simulations indicate that the nonlinear development of ballooning instability is able to induce the formation of X lines and plasmoids in a generalized Harris sheet with a finite normal magnetic component in the high Lundquist number regime where the linear two-dimensional resistive tearing mode is stable.

Magnetic transitions and spin-glass reentrance in two-dimensional [MnII(TCNE)(NCMe)2]X (X = PF6,AsF6,SbF6) molecular magnets

The structural, spectroscopic and magnetic properties of the two-dimensional (2D) molecule-based magnets of [MnII(TCNE)(NCMe)2]X (X = PF6, AsF6, SbF6; TCNE = tetracyanoethylene, NCMe = acetonitrile) composition are reported. It is shown that the alteration of the interlayer distance by increasing the anion size has little effect on the critical magnetic ordering temperature, Tc, suggesting that it depends predominantly on the intra-plane magnetic exchange. The observed field-induced irreversibility in static magnetization, a slow decay of isothermal remanence below Tc, and the dynamic susceptibility data are in accord with a re-entrant spin-glass nature of the ground state of all materials. In contrast to the isostructural Fe-based magnets, in which strong magnetocrystalline anisotropy facilitates the finite temperature magnetic ordering with the magnetization easy axis perpendicular to the μ4-TCNE•− plane, in the studied Mn-based magnets the easy axis is canted away from the normal direction, due to a small magnetocrystalline anisotropy. The two magnetic transitions observed on cooling are assigned to the ferrimagnetic long-range ordering of the normal magnetization component followed by the re-entrant spin-glass type transition resulting from a random freezing of the in-plane magnetization component.

Spin Diffusion Coefficient of A Phase of Liquid 3He at Low Temperatures and Stability of Half Quantum Vortex

We theoretically investigate the spin diffusion coefficient tensor in the A phase of liquid 3He in term of quasiparticle life-time by using the Kubo formula approach at low temperatures. In general, the coefficient is a fourth rank tensor for the anisotropic states and can be defined as a function of both normal component of spin-current and magnetization. The quasiparticle life-time is obtained by using the Boltzmann equation. We find that components of the spin diffusion coefficient are proportional to T−2 at low temperatures. The normal components of spin current, hence, are strongly diffusive and one can ignore the contribution of these components to the stability of half quantum vortices (HQVs) in the equal-spin-pairing of 3He — A state. Hence to make a stable HQV, it is enough for one to consider weak interaction plus the effects of Landau Fermi liquid.

Magnetic field distribution in the flare productive active region NOAA 10720

Association of the active region NOAA 10720 magnetic flux and flare appearance is investigated. Distributions of the normal magnetic component in the active region are calculated in the potential approximation using SOHO MDI line-of-sight magnetic measurements. During traveling along the solar disk the magnetic flux of the active region increases up to 4×1022Mx. The X class solar flares appear, when the magnetic flux reaches ∼3×1022Mx. It is shown that the magnetic flux and the magnetic field distribution in the active region in the long duration X3.8 flare January 17, 2005 do not reveal considerable change. During the flare X3.8 magnetic energy flow from the photosphere is not observed. The obtained results show that flare energy released in the corona has been accumulated during the preflare time. This conclusion supports the flare model based on the conception of flare energy accumulation in the magnetic field of a coronal current sheet.

Magneto-optics of heterostructures with an InGaAs/GaAs quantum well and a ferromagnetic delta-layer of Mn

Magneto-optics of heterostructures with an InGaAs/GaAs quantum well (QW) and a 3–5 nm spaced ultra-thin ferromagnetic δ-layer of Mn in the GaAs barrier is investigated in detail. While nonmagnetic structures demonstrate very low degree of circular polarization PC of QW photoluminescence, the existence of the close Mn δ-layer gives rise to high values of PC even above its Curie temperature TC ∼ 35 K. Fast growth of PC and Zeeman splitting of the QW emission band, observed at low B < 0.2 T, is followed by a slow linear increase at B > 0.5 T in heterostructures with strictly oriented GaAs (001) substrates. The characteristic fast increase slows down with temperature and disappears above TC. The effect depends non-monotonically on QW depth and is explained by the model of strong QW fluctuation potential caused by the highly charged Mn δ-layer. The spin polarization of carriers is believed to be related to the effective (p–d)-exchange interaction of holes in the QW with the ferromagnetic δ-layer and to appear due to a normal-to-plane magnetization emerging from the plane of the δ-layer with saturation of the normal component of magnetization at high magnetic fields.

Model for electromagnetic field analysis of superconducting power transmission cablecomprising spiraled coated conductors

Since the superconductor layers of YBCO-coated conductors are very thin, the acloss of coated conductors is dominated by the magnetic flux density normal tothe conductor face. In cables, most of the normal magnetic flux component isgenerated near gaps between coated conductors. Although the effects of gaps aresignificant, there are few reports on the electromagnetic field analysis of cables withspiral structures carried out while taking the gap effect into consideration. In afinitely long cable with a spiral structure, the electromagnetic field is naturallyperiodic along the cable axis. In a two-layer cable, the simplest period along thecable axis is the least common multiple of the spiral pitches in the inner andouter layers. However, we verified that there is a shorter period, and the sameelectromagnetic field distribution appears in all conductors of the same layer. Usingthese periodicities, we developed a three-dimensional model for the analysis oftwo-layer cables with a spiral structure. Current distributions of cables were analyzedusing this model, and ac losses were calculated. In addition, these results werecompared with ac losses calculated by two-dimensional analysis performed on thecross section of a cable. It was verified that the ac loss in a cable is correctlycalculated by the 2D model when the spiral pitch is long enough. However, in thecase of a tightly twisted cable, the ac losses calculated by the 2D model includesome errors caused by an approximation in which the spiral structure is ignored.

Paleomagnetism and rock magnetism of the Neoproterozoic Itajaí Basin of the Rio de la Plata craton (Brazil): Cambrian to Cretaceous widespread remagnetizations of South America

A detailed rock magnetic and paleomagnetic study was performed on samples from the Neoproterozoic Itajaí Basin in the state of Santa Catarina, Brazil, in order to better constrain the paleogeographic evolution of the Rio de la Plata craton between 600 and 550 Ma. However, rock magnetic properties typical of remagnetized rocks and negative response in the fold test indicated that these rocks carried a secondary chemical remanent magnetization. After detailed AF and thermal cleaning, almost all samples showed a normal polarity characteristic remanent magnetization component close to the present geomagnetic field. The main magnetic carriers are magnetite and hematite, probably of authigenic origin. The mean paleomagnetic pole of the Itajaí Basin is located at Plat = − 84°, Plong = 97.5° (A95 = 2°) and overlaps the lower Cretaceous segment of the apparent polar wander path of South America, suggesting a cause and effect with the opening of the South Atlantic Ocean. A compilation of remagnetized paleomagnetic poles from South America is presented that highlights the superposition of several large-scale remagnetization events between the Cambrian and the Cretaceous. It is suggested that some paleomagnetic poles used to calibrate the APWP of Gondwana at Precambrian times need to be revised; the indication of remagnetized areas in southern South America may offer some help in the selection of sites for future paleomagnetic investigations in Precambrian rocks.

Solar wind entry via flux tube into magnetosphere observed by Cluster measurements at dayside magnetopause during southward IMF

By analyzing hot ion and electron parameters together with magnetic field measurements from Cluster, an event of magnetopause crossing of the spacecraft has been investigated. At the latitude of about 40° and magnetic local time (MLT) of 13:20 during the southward interplanetary magnetic field (IMF), a transition layer was observed, with the magnetospheric field configuration and cold dense plasma features of the magnetosheath. The particle energy-time spectrograms inside the layer were similar to but still a little different from those in the magnetosheath, obviously indicating the solar wind entry into the magnetosphere. The direction and magnitude of the accelerated ion flow implied that reconnection might possibly cause such a solar wind entry phenomenon. The bipolar signature of the normal magnetic component BN in magnetopause coordinates further supported happening of reconnection there. The solar wind plasma flowed toward the magnetopause and entered the magnetosphere along the reconnected flux tube. The magnetospheric branch of the reconnected flux tube was still inside the magnetosphere after reconnection and supplied the path for the solar wind entry into the dayside magnetosphere. The case analysis gives observational evidence and more details of how the reconnection process at the dayside low latitude magnetopause caused the solar wind entry into the magnetosphere.

Mixed magnetooptical contrast induced by an inhomogeneous magnetic field in metal films with planar anisotropy

Magnetooptical (MO) images induced by a strongly inhomogeneous external magnetic field in magnetic metal films with planar anisotropy have been studied. In the polar Kerr effect geometry, MO images created by the normal magnetization component is observed. In the meridional Kerr effect geometry, a superposition of the MO images (mixed MO contrast) is observed, which is determined by the distribution of the normal and horizontal magnetization components. Calculation of distribution of magnetization in a film is carried out, a field of magnetic system corresponding to coordinate dependence and are simulated corresponding MO images and the corresponding MO images have been simulated, which demonstrate satisfactory agreement between the theory and experiment.

Experimental investigations into forces acting during a magnetic abrasive finishing process

A magnetic abrasive finishing (MAF) process is the one in which material is removed in such a way that surface finishing and deburring are performed simultaneously with the applied magnetic field in the finishing zone. Knowledge of forces acting during MAF is important to understand the mechanism of material removal. Forces have direct influence on the generation of a finished surface and accuracy of the workpiece. This paper reports the experimental findings about the forces acting during MAF and provides correlation between the surface finish and the forces. The resistance type force transducer (ring dynamometer) has been designed and fabricated. It is used to measure the normal magnetic force component responsible for microindentation into the workpiece and tangential cutting force component producing microchips. The force data have been recorded on-line by making use of virtual instruments (using Lab-View software). It is concluded that forces and change in surface roughness (ΔRa) increase with increase in current to the electromagnet (or magnetic flux density) and decrease in the working gap.

Unexpected vertical current sheets in the magnetotail associated with northward IMF

Fast magnetic field polarity changes detected in the quiet magnetotail by a spacecraft are usually attributed to thin cross-tail current sheet crossings. On September 14, 2001, Cluster registered several such events. However the IMF was northward for the previous 24 h and the formation of a thin current sheet was very unlikely. The multi-point analysis revealed that these sheets were almost vertically oriented, had strong shear and vanishing normal magnetic components and therefore should be interpreted as boundaries between two independent magnetic field domains (flux tubes), rather than crossings of the main cross-tail current sheet. We suggest that such anomalous configuration might form in the course of high-latitude reconnection of geomagnetic lobe and interplanetary field lines when IMF is northward.