Orthogonal Magnetic Field Research Articles

The Expected but Well-Hidden EMF in the Jumping Wire Experiment and its Unexpected Role

As presented in physics textbooks, as well as in a few papers, the typical example of an induced motional electromotive force εmot = Blv consists of a conductive rod of length l frictionlessly sliding with speed v along parallel wires within an orthogonal and constant uniform magnetic field of magnitude B. End-of-chapter problems, variants of that sliding rod, are additionally posed in those textbooks. The horizontal jumping wire of length l carrying a current i that is tossed upward by a magnetic force, in a transverse horizontal magnetic field B, is an important variant, as evidenced by its popularity as a demonstration experiment (with numerous videos and blogs posted on the web). A simplistic account of the wire-jump experiment is often given exclusively in terms of the well-known magnetic force F = i l × B that propels the wire upward. The jumping wire is an eye-catching demonstration for both students and the public, and it indeed deserves to be analyzed in greater detail, since as shown below it hides fundamental and interesting physics, certainly much more than what the eye catches.

Analysis and Simulation of Flight Effects on an Airborne Magnetic Gradient Tensor Measurement System

A magnetic tensor gradiometer is used to measure the spatial derivatives of three orthogonal magnetic field components. Being relatively insensitive to the geomagnetic field affords it the capability of being loaded onto flying platforms to conduct an airborne geophysical survey. It is especially suitable for exploring shallow buried mines and moving magnetic targets. The aerodynamic model was provided by the open source flight simulator, FlightGear. Estimations of the magnetic gradient tensor model of the magnetic dipole, the magnetic interference model of the aircraft, and the error model of the measuring device were all used to investigate the effects of flight on the airborne magnetic gradient tensor measurement system (AMGTMS). A thorough analysis of its causes, such as the vibration of the aircraft, the different rotating sequences of the coordinate system, and the reasonable sequence of data processing, was also done. The results can be applied to the guide design, integration, calibration, and data processing of the AMGTMS, thus reducing the research and development risk.

Nonreciprocal Phase Error Caused by Orthogonal Magnetic Field in a Polarization-Maintaining Fiber-Optic Gyro

This paper aims to investigate the nonreciprocity caused by orthogonal magnetic field (OMF) vertical to the light direction propagating in a polarization-maintaining fiber-optic gyro (PM-FOG). In orthogonal magnetic field, the nonreciprocal phase error (NPE) results from the small change of the propagation constants of the two opposite light waves propagating in the fiber coil. Even using a PM fiber coil, the pressure, twist, and other imperfections will change the polarization state, which may lead to an instable drift in PM-FOGs. This phenomenon was observed in the 0°-coupling regime which is commonly used for PM-FOG systems. Theoretical analysis and experimental results show and confirm that the instability of the NPE can be evidently reduced by taking a double-45°-coupling scheme. In this case, the NPE appears to be linear to the OMF and can therefore be compensated via later processes.

Magneto-transport from momentum dissipating holography

We obtain explicit expressions for the thermoelectric transport coefficients of a strongly coupled, planar medium in the presence of an orthogonal magnetic field and momentum-dissipating processes. The computations are performed within the gauge/gravity framework where the momentum dissipation mechanism is introduced by including a mass term for the bulk graviton. Relying on the structure of the computed transport coefficients and promoting the parameters to become dynamical functions, we propose a holography inspired phenomenology open to a direct comparison with experimental data from the cuprates.

Magnetic-field strength measurements in ferromagnetic materials for determining the orthogonal biasing effect

The mutual influence of orthogonal magnetic fields on ferrite magnetic characteristics was experimentally studied. Experiments were performed in a pulse mode using a compound specimen. An induction probe positioned in the gap between its parts was used in magnetic-field measurements. A numerical simulation showed that the field strength in the central part of the gap corresponds to the field inside the ferromagnetic material with an accuracy of 5–7%, if the gap width is substantially smaller than its length. The analysis of the measurement results demonstrates a substantial difference (by 30–50%) in the dependences of the magnetic permeabilities on the magnetizing-field strength in the collinear and orthogonal directions.

Effect of magnetic field inhomogeneity on ion cyclotron motion coherence at high magnetic field.

A three-dimensional code based on the particle-in-cell algorithm modified to account for the inhomogeneity of the magnetic field was applied to determine the effect of Z(1), Z(2), Z(3), Z(4), X, Y, ZX, ZY, XZ(2) YZ(2), XY and X(2)-Y(2) components of an orthogonal magnetic field expansion on ion motion during detection in an FT-ICR cell. Simulations were performed for magnetic field strengths of 4.7, 7, 14.5 and 21 Tesla, including experimentally determined magnetic field spatial distributions for existing 4.7 T and 14.5 T magnets. The effect of magnetic field inhomogeneity on ion cloud stabilization ("ion condensation") at high numbers of ions was investigated by direct simulations of individual ion trajectories. Z(1), Z(2), Z(3) and Z(4) components have the largest effect (especially Z(1)) on ion cloud stability. Higher magnetic field strength and lower m/z demand higher relative magnetic field homogeneity to maintain cloud coherence for a fixed time period. The dependence of mass resolving power upper limit on Z(1) inhomogeneity is evaluated for different magnetic fields and m/z. The results serve to set the homogeneity requirements for various orthogonal magnetic field components (shims) for future FT-ICR magnet design.

Research on High Resolution Stress Corrosion Crack Detection Based on Remote Field Eddy Current Non-Destructive Testing

Although remote field eddy current had achieved successive application in pipes and tubes non-destructive testing, the poor ability and sensitivity to axial crack such as stress corrosion crack prevented its further application. A novel high resolution remote field eddy current detection method which can be suitable for axial crack especially stress corrosion crack detection was proposed and verified by simulation and experiment. First of all, conventional detection ability of remote field eddy current for crack in different directions was researched with detail. Aside from this, applicability of orthogonal magnetic filed in remote field eddy current was analyzed and simulated by finite element method, and appropriate configuration using to generating orthogonal magnetic fields for tubular structure was discussed and verified. Thirdly, design of detection system including key parameters selection and detection coil mode were researched. At last, proposed high resolution detection system were verified experimentally using various type defects, such as parallel axial crack and real stress corrosion crack. From the above research, conclusions were drawn as followed: the detection ability and sensitivity of proposed remote field eddy current detection system could be improved significantly compared with conventional system, especially for axial crack which was not easily to detect, and real stress corrosion crack could be detected and evaluated successively.

Unified Topological Response Theory For Gapped and Gapless Free Fermions

We derive a scheme for systematically enumerating the responses of gapped as well as gapless systems of free fermions to electromagnetic and strain fields starting from a common parent theory. Using the fact that position operators in the lowest Landau level of a quantum Hall state are canonically conjugate, we consider a massive Dirac fermion in $2n$ spatial dimensions under $n$ mutually orthogonal magnetic fields and reinterpret physical space in the resulting zeroth Landau level as phase space in $n$ spatial dimensions. The bulk topological responses of the parent Dirac fermion, given by a Chern-Simons theory, translate into quantized insulator responses, while its edge anomalies characterize the response of gapless systems. Moreover, various physically different responses are seen to be related by the interchange of position and momentum variables. We derive many well-known responses, and demonstrate the utility of our theory by predicting spectral flow along dislocations in Weyl semimetals.

Photon propagation in noncommutative QED with constant external field

We find dispersion laws for the photon propagating in the presence of mutually orthogonal constant external electric and magnetic fields in the context of the $\theta $-expanded noncommutative QED. We show that there is no birefringence to the first order in the noncommutativity parameter $% \theta .$ By analyzing the group velocities of the photon eigenmodes we show that there occurs superluminal propagation for any direction. This phenomenon depends on the mutual orientation of the external electromagnetic fields and the noncommutativity vector. We argue that the propagation of signals with superluminal group velocity violates causality in spite of the fact that the noncommutative theory is not Lorentz-invariant and speculate about possible workarounds.

Size-dependent axial dynamics of magnetically-sensitive strain gradient microbars with end attachments

The multi-parameter Sturm–Liouville eigenvalue problems, associated with the size-dependent longitudinal vibration of a finite micro-scale bar embedded in orthogonal transverse magnetic fields, are addressed in this study. Derived as a fourth-order partial differential equation, and augmented by enriched higher-order boundary conditions, the mathematical model of the micro-scale bar is predicated on the duo of the strain gradient theory of elasticity and the extended Hamilton׳s principle. The derived model is tackled with the computation scheme of the power series method. A thorough validation of the simplified form of the model is presented with benchmark results published in the literature. Presented along with the validation study is a comprehensive parametric examination of the influence of the aspect ratio, the material length scale, the mass and stiffness ratios of attachments and the magnetic field strength. Results from the analyses affirm that in the case of a lightweight mass attached to the end of the microbar, the axial resonant frequencies approach that of a microbar with a fixed–free boundary condition. However, in the case of an attachment with a heavy mass the fundamental resonant frequency of the microbar tends to zero. A Pareto analysis of the order of influence of the model׳s variables unmasks the ratio of the stiffness of the microbar and an attached elastic spring as having the most significant effect on the fundamental axial natural frequency, in the absence of the magnetic field. In the presence of the magnetic field, however, the effects of the end attachments are totally overshadowed by the influence of the magnetic field strength.

A novel high sensitivity sensor for remote field eddy current non-destructive testing based on orthogonal magnetic field.

Remote field eddy current is an effective non-destructive testing method for ferromagnetic tubular structures. In view of conventional sensors' disadvantages such as low signal-to-noise ratio and poor sensitivity to axial cracks, a novel high sensitivity sensor based on orthogonal magnetic field excitation is proposed. Firstly, through a three-dimensional finite element simulation, the remote field effect under orthogonal magnetic field excitation is determined, and an appropriate configuration which can generate an orthogonal magnetic field for a tubular structure is developed. Secondly, optimized selection of key parameters such as frequency, exciting currents and shielding modes is analyzed in detail, and different types of pick-up coils, including a new self-differential mode pick-up coil, are designed and analyzed. Lastly, the proposed sensor is verified experimentally by various types of defects manufactured on a section of a ferromagnetic tube. Experimental results show that the proposed novel sensor can largely improve the sensitivity of defect detection, especially for axial crack whose depth is less than 40% wall thickness, which are very difficult to detect and identify by conventional sensors. Another noteworthy advantage of the proposed sensor is that it has almost equal sensitivity to various types of defects, when a self-differential mode pick-up coil is adopted.

Anomalous cross-field diffusion in a magnetic trap.

We numerically simulated the diffusion of a charged Brownian particle confined to a plane under the action of an orthogonal magnetic field with intensity depending on the distance from a center. Despite its apparent simplicity, this system exhibits anomalous diffusion. For positive field gradients, radial and angular dynamics are asymptotically subdiffusive, with exponents given by simple analytical expressions. In contrast, when driven by a weakly decaying field, the particle attains normal diffusion only after exceedingly long superdiffusive transients. These mechanisms can be related to Bohm diffusion in magnetized plasmas.

Shot noise suppression due to a magnetic field in disordered conductors

We investigate the effect of an orthogonal magnetic field on a 2-D disordered wire, by means of a numerical model based on the recursive Green's function technique. We discuss the resulting behavior of the shot noise suppression factor and of the conductance in terms of the interplay among the relevant transport quantities, i.e. the mean free path, the localization length, the average separation between impurities and the cyclotron radius. We find that, starting from a diffusive or quasi-diffusive behavior, shot noise is increasingly suppressed as the magnetic field is turned on, up to a noiseless condition typical of the disappearance of backscattering for edge states.

Optical compensation technology for magnetic drift in depolarized FOG induced by orthogonal magnetic field

A magnetic drift that linear to orthogonal magnetic field (OMF) is induced by OMF which is parallel to the sensitive axis of the depolarized FOGs. As winding a fiber coil causes the refractive index near the center to increase and away from the center to decrease, by placing a short segment of special fiber at the end of the coil, the magnetic drifts induced by OMF in the special fiber and that in the single-mode fiber (SMF) are equal in magnitude but opposite in signs, which means the summation of the two magnetic drifts is zero. Therefore the goal of compensating magnetic drift induced by OMF in depolarized FOG is successfully achieved.

Electrostatic focal spot correction for x-ray tubes operating in strong magnetic fields.

A close proximity hybrid x-ray/magnetic resonance (XMR) imaging system offers several critical advantages over current XMR system installations that have large separation distances (∼5 m) between the imaging fields of view. The two imaging systems can be placed in close proximity to each other if an x-ray tube can be designed to be immune to the magnetic fringe fields outside of the MR bore. One of the major obstacles to robust x-ray tube design is correcting for the effects of the MR fringe field on the x-ray tube focal spot. Any fringe field component orthogonal to the x-ray tube electric field leads to electron drift altering the path of the electron trajectories. The method proposed in this study to correct for the electron drift utilizes an external electric field in the direction of the drift. The electric field is created using two electrodes that are positioned adjacent to the cathode. These electrodes are biased with positive and negative potential differences relative to the cathode. The design of the focusing cup assembly is constrained primarily by the strength of the MR fringe field and high voltage standoff distances between the anode, cathode, and the bias electrodes. From these constraints, a focusing cup design suitable for the close proximity XMR system geometry is derived, and a finite element model of this focusing cup geometry is simulated to demonstrate efficacy. A Monte Carlo simulation is performed to determine any effects of the modified focusing cup design on the output x-ray energy spectrum. An orthogonal fringe field magnitude of 65 mT can be compensated for using bias voltages of +15 and -20 kV. These bias voltages are not sufficient to completely correct for larger orthogonal field magnitudes. Using active shielding coils in combination with the bias electrodes provides complete correction at an orthogonal field magnitude of 88.1 mT. Introducing small fields (<10 mT) parallel to the x-ray tube electric field in addition to the orthogonal field does not affect the electrostatic correction technique. However, rotation of the x-ray tube by 30° toward the MR bore increases the parallel magnetic field magnitude (∼72 mT). The presence of this larger parallel field along with the orthogonal field leads to incomplete correction. Monte Carlo simulations demonstrate that the mean energy of the x-ray spectrum is not noticeably affected by the electrostatic correction, but the output flux is reduced by 7.5%. The maximum orthogonal magnetic field magnitude that can be compensated for using the proposed design is 65 mT. Larger orthogonal field magnitudes cannot be completely compensated for because a pure electrostatic approach is limited by the dielectric strength of the vacuum inside the x-ray tube insert. The electrostatic approach also suffers from limitations when there are strong magnetic fields in both the orthogonal and parallel directions because the electrons prefer to stay aligned with the parallel magnetic field. These challenging field conditions can be addressed by using a hybrid correction approach that utilizes both active shielding coils and biasing electrodes.

Are spine–sheath polarization structures in the jets of active galactic nuclei associated with helical magnetic fields?

One possible origin for polarization structures across jets of Active Galactic Nuclei (AGNs) with a central "spine" of orthogonal magnetic field and a "sheath" of longitudinal magnetic field along one or both edges of the jet is the presence of a helical jet magnetic field. Simultaneous Very Long Baseline Array (VLBA) polarization observations of AGN displaying partial or full spine--sheath polarization structures were obtained at 4.6, 5.0, 7.9, 8.9, 12.9 and 15.4 GHz, in order to search for additional evidence for helical jet magnetic fields, such as transverse Faraday rotation gradients (due to the systematic change in the line-of-sight magnetic-field component across the jet). Results for eight sources displaying monotonic transverse Faraday rotation gradients with significances $\geq 3\sigma$ are presented here. Reversals in the directions of the transverse RM gradients with distance from the core or with time are detected in three of these AGNs. These can be interpreted as evidence for a nested helical magnetic field structure, with different directions for the azimuthal field component in the inner and outer regions of helical field. The results presented here support the idea that many spine--sheath polarization structures reflect the presence of helical magnetic fields being carried by these jets.

Calibration of SQUID vector magnetometers in full tensor gradiometry systems

Measurement of magnetic vector or tensor quantities, namely of field or field gradient, delivers more details of the underlying geological setting in geomagnetic prospection than a scalar measurement of a single component or of the scalar total magnetic intensity. Currently, highest measurement resolutions are achievable with superconducting quantum interference device (SQUID)-based systems.Due to technological limitations, it is necessary to suppress the parasitic magnetic field response from the SQUID gradiometer signals, which are a superposition of one tensor component and all three orthogonal magnetic field components. This in turn requires an accurate estimation of the local magnetic field. Such a measurement can itself be achieved via three additional orthogonal SQUID reference magnetometers. It is the calibration of such a SQUID reference vector magnetometer system that is the subject of this paper.A number of vector magnetometer calibration methods are described in the literature. We present two methods that we have implemented and compared, for their suitability of rapid data processing and integration into a full tensor magnetic gradiometry, SQUID-based, system.We conclude that the calibration routines must necessarily model fabrication misalignments, field offset and scale factors, and include comparison with a reference magnetic field. In order to enable fast processing on site, the software must be able to function as a stand-alone toolbox.

Research of Magnetic Fluid under the Orthogonal Stationary Magnetic Field

The nonlinear characteristic is the one of essential characteristics about the magnetic fluid. The orthogonal stationary magnetic field is caused by the mutual orthogonal DC. According to the grads of magnetic field in the area filled with magnetic fluid, the magnetic density of magnetic fluid changes with the grads of magnetic field. With the increasing magnitude of DC, the magnetic density of magnetic fluid can be increased. Error of the measured voltage wll be increased as the volume of the changing rate of DC increasing.

Coherent nonlinear quantum model for composite fermions

Originally proposed by Read [1] and Jain [2], the so-called "composite-fermion" is a phenomenological attachment of two infinitely thin local flux quanta seen as nonlocal vortices to two-dimensional (2D) electrons embedded in a strong orthogonal magnetic field. In this letter, it is described as a highly-nonlinear and coherent mean-field quantum process of the soliton type by use of a 2D stationary Schroedinger-Poisson differential model with only two Coulomb-interacting electrons. At filling factor $\nu={1}{3}$ of the lowest Landau level, it agrees with both the exact two-electron antisymmetric Schroedinger wave function and Laughlin's Jastrow-type guess for the fractional quantum Hall effect, hence providing this later with a tentative physical justification based on first principles.

On developing a magnetorheological transformer that operates in orthogonal magnetic fields

The operation of a magnetorheological transformer in which choke channels are replaced with a cylindrical clearance between two coaxial cylinders is considered. The cylindrical clearance, as well as the working and compensation chambers, are filled with a magnetorheological fluid. It has been shown that this design of the magnetorheological transformer is preferable for damping impact loads.