Dynamic Magnetic Field Research Articles

Inter-strand resistance and AC loss in resin-filler impregnated ReBCO Roebel cables

In the frame of the EuCARD2 collaboration, aimed at developing the technology for 20 T class accelerator magnets, several demonstrator dipole magnets are being built using high critical current density and fully transposed ReBCO tape-based Roebel-type cables. In accelerator magnets the dynamic magnetic field quality is one of the key parameters, which is affected by the effective inter-strand resistances in the cables. For this reason, measurements of the inter-strand resistances on ReBCO Roebel cables were carried out at 4.2 and 77 K. Acquiring these data is also essential for input of cable simulation models. The cable samples are impregnated with epoxy resin to reduce the effect of transverse stress degradation due to Lorentz forces acting on the strands in the Roebel cables. The measured inter-strand resistance is used to estimate the AC coupling loss in different magnetic field orientations. Moreover, the contributions of diverse interface contact resistances to overall inter-strand resistance of Roebel cables were determined using a novel theoretical model. For validation, the AC loss of cables were examined in various orientations of applied field at 4.2 K. With three analytical models the hysteresis loss was calculated and compared to the measured data. The average inter-strand resistance of the cable samples impregnated with the unfilled epoxy CTD-101K range from 3 to 16 μΩ at 77 K and 1.5 to 9 μΩ at 4.2 K. Between the tapes the copper to copper interface resistance dominates the inter-strand resistance of impregnated Roebel cables. The calculated and measured AC loss for the CTD-101K impregnated Roebel cable lead to equivalent conclusions that the coupling loss is lower than the hysteresis loss within the range of the experiment. These observations substantially differ from earlier results extracted from a similar cable but impregnated with the alumina-filled epoxy resin CTD-101G, which showed considerable coupling loss when exposed to magnetic field parallel the wide face of the cable.

Ultrasensitive Multifunctional Magnetoresistive Strain Sensor Based on Hair‐Like Magnetization‐Induced Pillar Forests

AbstractAn ultrasensitive multifunctional sensor which integrates tactile sensing and magnetism sensing together in one device is presented. The sensor, dubbed L‐MPF, consists of two interlocking hair‐like magnetization‐induced pillar forests, which are self‐formed under a magnetic field and a loading pressure. An L‐MPF endows intelligent electronics with magnetic field reception, which is the sense of bacteria, birds, and whales, rather than human beings. It is found that the L‐MPF precisely detects the magnitude and the loading path of the dynamic load, including pressure, shear, and magnetic field, with fast response, high reversibility, excellent sensitivity, and high stability. The sensitivity coefficient can reach 1965, 1.6, and 240% T−1 under 50–60% compressive strain, 0–3.4° shear strain, and 21–170 mT magnetic field. Additionally, the strain sensitivity coefficient can be set by the external magnetic field, which affords a potential approach to realize different sensing requirements in various circumstances. For a detailed insight into the sensing element's behavior, the magnetic–mechanic–electric coupling response is also described by simplified model simulation and theoretical analysis. Furthermore, a 4 × 4 L‐MPF array exhibits contactless gesture sensing, which provides a new way for next‐generation human–electronics interface devices and artificial electronic skin.

The Seven Most Massive Clumps in W43-Main as Seen by ALMA: Dynamical Equilibrium and Magnetic Fields

Abstract Here we present new ALMA observations of polarized dust emission from six of the most massive clumps in W43-Main. The clumps MM2, MM3, MM4, MM6, MM7, and MM8, have been resolved into two populations of fragmented filaments. From these two populations we extracted 81 cores (96 with the MM1 cores) with masses between 0.9 M ⊙ to 425 M ⊙ and a mass sensitivity of 0.08 M ⊙. The MM6, MM7, and MM8 clumps show significant fragmentation, but the polarized intensity appears to be sparse and compact. The MM2, MM3, and MM4 population shows less fragmentation, but with a single protostellar core dominating the emission at each clump. Also, the polarized intensity is more extended and significantly stronger in this population. From the polarized emission, we derived detailed magnetic field patterns throughout the filaments that we used to estimate field strengths for four out of the six clumps. The average field strength estimates were found to lie between 500 μG to 1.8 mG. Additionally, we detected and modeled infalling motions toward MM2 and MM3 from single-dish and data, resulting in mass infall rates of M ⊙ yr−1 and M ⊙ yr−1. Using our estimations, we evaluated the dynamical equilibrium of our cores by computing the total virial parameter α total. For the cores with reliable field estimates, we found that 71% appear to be gravitationally bound while the remaining 29% are not. We conclude that these unbound cores, which are also less massive, are still accreting and have not yet reached a critical mass. This also implies different evolutionary timescales, which essentially suggests that star formation in high-mass filaments is not uniform.

Dynamical Magnetic Field Accompanying the Motion of Ferroelectric Domain Walls.

The recently proposed dynamical multiferroic effect describes the generation of magnetization from temporally varying electric polarization. Here, we show that the effect can lead to a magnetic field at moving ferroelectric domain walls, where the rearrangement of ions corresponds to a rotation of ferroelectric polarization in time. We develop an expression for the dynamical magnetic field, and calculate the relevant parameters for the example of 90° and 180° domain walls, as well as for polar skyrmions, in BaTiO_{3}, using a combination of density functional theory and phenomenological modeling. We find that the magnetic field reaches the order of several μT at the center of the wall, and we propose two experiments to measure the effect with nitrogen-vacancy center magnetometry.

Magnetite‐out and pyrrhotite‐in temperatures in shales and slates

AbstractClay‐rich basins have undergone varying degrees of magnetic transformation during burial, affecting their ability to retain accurate records of Earth's dynamic magnetic field. We propose to bracket the magnetite‐out and pyrrhotite‐in temperatures in shales and slates from Taiwan and the Pyrenees by using a combination of low‐temperature magnetic transitions and geothermometers. For Tburial < 340°C, the magnetic assemblage is dominated by magnetite. Gradually with increasing burial temperature, the concentration of magnetite decreases to a few ppmv. We observe the magnetite‐out isograd at Tburial ~350°C. At Tburial >60°C and Tburial >340°C respectively, fine‐grained and coarse‐grained pyrrhotite develop. In the course of burial, a clay‐rich basin gradually loses its capability to retain a record of Earth's magnetic field. It is only during basin uplift, that coarse pyrrhotite might acquire a thermo remanent magnetization. Our results point out therefore highly contrasted magnetic properties and palaeomagnetic records between deeply buried basins and exhumed ones.

Performance optimization of magnetostrictive guided wave sensor based on waveguide wire

In this paper, an open magnetic circuit magnetostrictive guided wave sensor that allows free regulation of the static working point is proposed for ferromagnetic material waveguide wires applied to non-destructive testing of wire bars, guided wave mechanics study, magnetostrictive linear displacement sensors and other fields. The sensor was made up of an iron-gallium alloy wire, a ring-shaped permanent magnet and a concentric coil, which was used to excited a longitudinal mode guided wave on the iron-gallium alloy wire. The structural parameters of the permanent magnet were optimized, the axial relative distance between the permanent magnet and the coil was studied and the superposition of and matching between the dynamic magnetic field and the static bias magnetic field were adjusted, allowing identifying the optimal magnetization point, so that the magnetic acoustic transduction efficiency was optimized. The sensor was analyzed, by means of finite element simulation, to produce the best system combination, which improved the sensitivity of the measurement. The improvement has been experimentally verified.

Wireless Power Transmission Enabled by a Triboelectric Nanogenerator via a Magnetic Interaction

Non‐contact wireless power transmission is considered as an ideal energy supply technology due to its convenience and safety. Herein, a subtle triboelectric nanogenerator (TENG)–based non‐contact wireless energy transmission technique is invented via a dynamic magnetic field media. The electricity is first converted into the magnet's vibration. Through the interaction between a pair of magnets, TENG can then wirelessly receive the vibrational energy driven by an electrically induced magnetic field variation. The working principle and output performance of the designed device are explored by simulations and a series of demonstrations, respectively. By inserting different plates in the magnetic field and adjusting the configuration, the TENG exhibits excellent anti‐interference and desirable output performance, indicating that the energy conversion unit exhibits advantages of high efficiency and adaptability. A superior transmission and output performance of 1.5 μW can be achieved under low frequency and relatively large separation distance, at a load resistance of 80 MΩ. TENGs, which enable wireless energy transmission via magnetic field that can easily light up 12 light‐emitting diode (LED) bulbs and drive an electronic watch, provide a promising and feasible approach to energy conversion and energy supply and serve as an alternative power source for driving portable electronics.

Research on dynamic mechanical properties and transient magnetic field characteristics of composite coal and rock mass

Research on dynamic mechanical properties and transient magnetic field characteristics of composite coal and rock mass

Discrete-Time Optimal Control of Electromagnetic Coil Systems for Generation of Dynamic Magnetic Fields With High Accuracy

Electromagnetic coil systems (ECSs) have been widely used for actuation and motion control of magnetic micro/nanorobots. In this paper, two typical ECSs with different system configurations are developed: One is computer-based and uses servoamplifiers for driving the coils and the other adopts an embedded control system with home-designed circuit boards for driving the coils. For dynamic control of the two types of ECSs, a unified control scheme is proposed with two objectives: 1) to make the output magnetic field converge to the reference without steady-state error; 2) to achieve optimal transient response under tunable requirement of control effort. In the scheme, dynamic models of the two systems are described by a unified state-space form with different dimensions, which are obtained by system identification. Then, a discrete-time optimal controller is designed based on the linear quadratic with integral action method to realize the control objectives. Finally, in order to make the controller applicable to the real ECSs, the time-delayed system states are estimated by utilizing a Kalman filter, and a Smith predictor inspired compensator is designed to compensate for time delay and modeling error. Simulations and experiments using the proposed control scheme are conducted for the two ECSs with three-axis Helmholtz coils, which show the easy adaption of the control approach to different coils. Experimental results validate the significantly improved dynamic performances of the two ECSs, and tracking a three-dimensional dynamic magnetic field with high accuracy is also demonstrated.

Ferrimagnetic resonance field sensors for particle accelerators.

We report on two ferrimagnetic resonance (FMR) sensors for absolute dynamic magnetic field measurements at 36 and 100 mT. The sensors are designed to mark precisely and reproducibly the moment when a time-transient magnetic field attains a specific value. The trigger from the sensor can then be used for real-time magnetic field measurement systems, called "B-trains," which are in operation at several large synchrotron installations including five of CERN's particle accelerators. We discuss in detail the design, the operation, and the performance of the FMR sensors based on two different types of printed circuit board (PCB) resonator structures.

A New Approach to Calculate the Shielding Factor of Magnetic Shields Comprising Nonlinear Ferromagnetic Materials under Arbitrary Disturbances

To enable the realization of ultra-low magnetic fields for scientific and technological research, magnetic shielding is required to create a space with low residual magnetic field and high shielding factors. The shielding factors of magnetic shields are due to nonlinear material properties, the geometry and structure of the shields, and the external magnetic fields. Magnetic shielding is used in environments full of random realistic disturbances, resulting in an arbitrary and random external magnetic field, and in this case, the shielding effect is hard to define simply by the shielding factors. A new method to simulate and predict a dynamic internal space magnetic field wave is proposed based on the Finite Element method (FEM) combined with the Jiles-Atherton (JA) model. By simulating the hysteresis behavior of the magnetic shields and establishing a dynamic model, the new method can simulate dynamic magnetic field changes inside magnetic shields as long as the external disturbances are known. The shielding factors under an AC external field with a sine wave and certain frequencies are calculated to validate the feasibility of the new method. A real-time wave of internal magnetic flux density under an AC triangular wave external field is simulated directly with the new method versus a method that splits the triangular wave into several sine waves by a Fourier transform, divides the shielding factors, and then adds the quotients together. Moreover, real-time internal waves under some arbitrary fields are measured. Experimental internal magnetic flux density waves of a 4-layer magnetically shielded room (MSR) at the Harbin Institute of Technology (HIT) fit the simulated results well, taking experimental errors into account.

Backscattering Immunity of Dipole-Exchange Magnetostatic Surface Spin Waves.

The existence of backscattering-immune spin-wave modes is demonstrated in magnetic thin films of nanoscale thickness. Our results reveal that chiral magnetostatic surface waves (CMSSWs), which propagate perpendicular to the magnetization direction in an in-plane magnetized thin film, are robust against backscattering from surface defects.CMSSWs are protected against various types of surface inhomogeneities and defects as long as their frequency lies inside the gap of the volume modes. Our explanation is independent of the topology of the modes and predicts that this robustness is a consequence of symmetry breaking of the dynamic magnetic fields of CMSSWs due to the off-diagonal part of the dipolar interaction tensor, which is present both for long- (dipole-dominated) and short-wavelength (exchange-dominated) spin waves. Micromagnetic simulations confirm the robust character of the CMSSWs. Our results open a new direction in designing highly efficient magnonic logic elements and devices employing CMSSWs in nanoscale thin films.

Signal Strength Enhancement of Magnetostrictive Patch Transducers for Guided Wave Inspection by Magnetic Circuit Optimization

Magnetostrictive patch transducers (MPT) with planar coils are ideal candidates for shear mode generation and detection in pipe and plate inspection with the advantages of flexibility, lightness and good directivity. However, the low energy conversion efficiency limits the application of the MPT in long distance inspection. In this article, a method for the enhancement of the MPT was proposed by dynamic magnetic field optimization using a soft magnetic patch (SMP). The SMP can reduce the magnetic resistance of the magnetic circuit, which increases the dynamic magnetic field intensity in the magnetostrictive patch during wave generation and restricts the induced dynamic magnetic field within the area around the coils for sensing during wave detection. Numerical simulations carried out at different frequencies verified the improvement of the dynamic magnetic fields by the SMP and influence of different affecting factors. The experimental validations of the signal enhancement in wave generation and detection were performed in an aluminum plate. The amplitude magnification could reach 12.7 dB when the MPTs were covered by the SMPs. Based on the numerical and experimental results, the SMP with a large relative permeability and thickness and close fitting between the SMP and coils were recommended when other application conditions were met.

Paramagnetic squeezing of a uniformly expanding quark-gluon plasma in and out of equilibrium

The plasma of quarks and gluons created in ultrarelativistic heavy-ion collisions turns out to be paramagnetic. In the presence of a background magnetic field, this paramagnetism thus leads to a pressure anisotropy, similar to anisotropies appearing in a viscous fluid. In the present paper, we use this analogy, and develop a framework similar to anisotropic hydrodynamics, to take the pressure anisotropy caused, in particular, by the nonvanishing magnetization of a plasma of quarks and gluons into account. We consider the first two moments of the classical Boltzmann equation in the presence of an electromagnetic source in the relaxation-time approximation, and derive a set of coupled differential equations for the anisotropy parameter $\xi_0$ and the effective temperature $\lambda_0$ of an ideal fluid with nonvanishing magnetization. We also extend this method to a dissipative fluid with finite magnetization in the presence of a strong and dynamical magnetic field. We present a systematic method leading to the one-particle distribution function of this magnetized dissipative medium in a first-order derivative expansion, and arrive at analytical expressions for the shear and bulk viscosities in terms of the anisotropy parameter $\xi$ and effective temperature $\lambda$. We then solve the corresponding differential equations for $(\xi_0,\lambda_0)$ and $(\xi,\lambda)$ numerically, and determine, in this way, the proper time and temperature dependence of the energy density, directional pressures, speed of sound, and the magnetic susceptibility of a longitudinally expanding magnetized quark-gluon plasma in and out of equilibrium.

COMPARATIVE ANALYSIS ON NUMERICAL MODELLING AND EXPERIMENTS OF THE CUTTING TEMPERATURE IN MAGNETIC ABRASIVE FINISHING PROCESS

In Magnetic Abrasive Finishing (MAF) process the cutting temperature is generated from two sources, from the electromagnetic flux (electrical heat), and from magnetic abrasive brush due to the friction force (mechanical heat). The cutting temperature has significant effects upon the condition of the surface, whereas it is less studied than the other parameters. In this study, an attempt has been made to simulate and investigate the influence of cutting parameters on the cutting temperature, to improve the thermal effect by MAF process. The aims of this study was to determine the distribution of the cutting temperature in the working gap, numerically and experimentally, then compared the results. In addition, to determine the most influence parameters affecting on the cutting temperature for Brass alloy CuZn28. Two dimensional Finite Element Models (FEM) with two software’s were developed to predict the temperature by dynamic electric and magnetic field, the first was DEFORM 10.2 used to calculate the mechanical heat and the second was COMSOL5.2 used to calculate the electrical heat. Sixteen tests designed according to Taguchi matrix through the orthogonal array (OA) L16 (). There are four various parameters that, have a large impact on cutting temperature, with four levels (rotational speed (A), working time (B), current (C), and working gap (D)). The analysis of the variance (ANOVA) technique was utilized to analysis the results, by using the statistical software (MINITAB-17). From the results, it is concluded that the Numerical modeling gives a very good comparison with the values of experimental tests. The maximum difference between the numerical and experimental temperature for brass CuZn28 is less than (9%).

Demagnetization-based axial magnetized magnetostrictive patch transducers for locating defect in small-diameter pipes using the non-axisymmetric guided wave

The propagation of the non-axisymmetric guided wave in the small-diameter pipe is complicated, which makes the circumferential position of the defect difficult to be determined. This article reports on the design of a segmented axially magnetized magnetostrictive patch transducer array for efficient transduction of non-axisymmetric L(M,2) modes to determine defect’s axial and circumferential positions in the small-diameter pipe. First, the background of the magnetostrictive patch transducer and non-axisymmetric guided wave in the pipe was presented. Moreover, the theoretical background to the influence of the length-to-width ratio of the magnetized rectangular patch on the demagnetizing factors was introduced. Second, the method of the pipe health monitoring using the designed segmented axially magnetized magnetostrictive patch transducer array was proposed. Third, the most suitable multi-belts of the flexible printed coils were chosen to provide the dynamic magnetic field by the comparison experiments. Then the signal amplitudes of the segmented axially magnetized magnetostrictive patch transducer array with different length–width ratios of magnetostrictive materials were compared with each other to prove the principle of demagnetization. Another two magnetostrictive patch transducer arrays employing permanent magnets were compared with the proposed segmented axially magnetized magnetostrictive patch transducer array. The experiments of pipe health monitoring were carried out to prove that the proposed method can realize pipe health monitoring over time. Fourth, the defect orientation experiments in a 304 stainless steel pipe with 48 mm inner diameter and 2 mm thickness were performed using the proposed segmented axially magnetized magnetostrictive patch transducer array at 650 kHz. The prediction of the circumferential position of the defects correlated well with the defect’s true location through matching the angular profiles of the experimental results and the modulated numerical analysis for several axial distances. The experimental results for the segmented axially magnetized magnetostrictive patch transducer array demonstrated that the proposed segmented axially magnetized magnetostrictive patch transducer array could potentially be applied to detect the axial and circumferential positions of the defect in a small-diameter pipe.

Novel design of a smart and harmonized flexible printed coil sensor to enhance the ability to detect defects in pipes

The interaction between the static and dynamic magnetic fields generated from a conventional magnetostrictive sensor (MsS) is an important factor in the sensitivity of defect detection. Normally, the dynamic magnetic field of an MsS is generated by its electric coils, whereas the static magnetic field is generated by permanent magnets. The magnitude of the generated fields and their interactions significantly affect the amplitude of the induced guided-wave signals. The conventional hard coil-based MsS is usually bulky and is not sufficiently flexible to fit pipes of various sizes. Such inflexibility limits the use of conventional MsS in practical situations. To overcome these limitations, the authors designed an innovative type of coil, called the flexible printed coil (FPC), to replace the inflexible hard coil. Because the FPC is a thin film, it can be easily wrapped around any size pipe, whereas the conventional hard coil–based MsS requires modification with changes in the size of pipes. Although the smart FPC-MsS can work as expected, due to the design of the flexible coils, the interference caused by the coils exerted an uneven magnetostrictive force on the tested pipe. This increases the sensitivity required to detect defects, which differ at each circumferential location of the inspected pipe. Hence, the smart FPC-MsS generates different results at different circumferential locations even though the sizes of the cracks are the same at each circumferential location. To address this deficiency, we designed a smart and harmonized FPC-MsS, called smart HFPC-MsS, which can generate an even magnetostrictive force regardless of the circumferential location of the crack. Ultimately, an evenly distributed amplitude of guided waves can be emitted into the entire pipe, which improves the accuracy of crack detection. In this paper, the theoretical foundation of designing the smart HFPC-MsS is explained, and its working principles are introduced. Both the simulated and experimental results prove the effectiveness of such a novel HFPC-MsS, and the results show that it can generate even amplitude of the guided waves to the pipe regardless of the circumferential location of the crack, resulting in more accurate crack detection than that provided by the author's previously designed smart FPC-MsS.

Study of Surface Character of Micrometer-Scale Dipole-Exchange Spin Waves in an Yttrium Iron Garnet Film

We demonstrate that micrometer-scale spin waves can be excited in a thin film of the ferrimagnetic material yttrium iron garnet (YIG) using patterned, multi-element antennas. The magnitude of the dynamic magnetic field generated by such antennas decays exponentially along the thickness direction, and this leads to an enhanced coupling to modes having a surface-like character as opposed to a more sinusoidal bulk-like character. We have used this property to identify spin waves having a mixed bulk/surface character.

Investigation of the magnetic field sensing properties of a magnetic fluid clad microfiber knot sensor

The performance of a magnetic fluid clad microfiber knot–based magnetic field sensor was experimentally investigated in the presence of static and dynamic magnetic fields. In addition, the dependence of the sensor response on the orientation of the externally applied magnetic field has been evaluated. The results show that the proposed sensor provides simultaneous measurements of magnetic field strength and orientation by monitoring the resonant wavelength of microfiber knot. When the magnetic field was increased to 220 Gs, the maximum wavelength shift reached nearly 130 pm. To avoid rectification for alternating current magnetic field input, a direct current magnetic field bias was introduced to the sensor. Using this approach, the unipolar response was converted into a bipolar form, which produced an acceptable replica of the input sinusoidal waveform. These results provide great promise for the development of practical magnetic fluid-based fiber-photonic magnetic field devices.

Optimization of RFX-mod2 gap configuration by estimating the magnetic error fields due to the passive structure currents

A major refurbishment of the toroidal complex of the RFX-mod device is in progress and will include the removal of the Inconel vacuum vessel and a modification of the stainless steel supporting structure to be made vacuum tight. The plasma facing graphite tiles will be mounted onto the inner surface of the copper shell so as to increase the plasma proximity factor. New operation regimes are expected to provide a significant reduction of the amplitude of RFP tearing modes with magnetic chaos mitigation and confinement improvement. On the other hand, due to the shorter distance from the passive structures, the plasma is expected to be even more sensitive to magnetic field errors at the plasma boundary, produced by the induced currents near the cuts of the same structures. In preparation to the new RFX-mod2 experiments, a thorough revision of the conditions triggering the error fields due to the eddy currents was undertaken. An analysis of the static and dynamic equilibrium magnetic field has been carried out in RFX-mod and RFX-mod2 to estimate the magnetic field driving the shell eddy currents. A lower equilibrium magnetic field should be required in RFX-mod2. Analyses of different configurations of the poloidal gap were also carried out by a specialized computational tool. A solution with a spaced poloidal gap and a more extended overlapping was envisaged capable of maintaining the same error fields at the closer plasma boundary with the same forcing field and meeting the more stringent insulation and assembly requirements of RFX-mod2.