Time-varying Magnetic Field Research Articles

Semi-analytical modeling AC loss of a flat stack of Y-Ba-Cu-O tapes

We propose semi-analytical models to compute alternating current (AC) power loss in a stack of N high-temperature superconductor YBa2Cu3O7−x (or Y–Ba–Cu–O) tapes subjected to a time-varying magnetic field perpendicular to the tapes with zero transport current. The models take into account screening of the interior superconducting tapes of the stack from the external magnetic field. We validate the results by experiments carried out at temperature T=77.2K under an applied magnetic field with the amplitude of its induction Bext=0.57T and frequencies up to 110 Hz. As follows from our models, the AC loss per tape in stacks of N tapes decreases with N in agreement with experiments. The approach is extended to compute the AC loss for lower temperatures, larger magnetic fields strengths, and for frequencies up to several kHz. These studies are important for understanding and predicting the AC loss for contemporary motors and generators.

An Electromagnetic Field Concentrator for Process Chambers

This paper describes selected results of the design and optimization of an electromagnetic field concentrator (MFC) for process chambers. On the basis of 2D/3D FE analysis, it was confirmed that the presented new structure for an electromagnetic field concentrator with three-phase windings and an additional DC central coil excites, in the working space of the device, a steady or time-varying magnetic field with adjustable peak value, pulsation amplitude and vector magnetic field orientation. The presented field concentrator can be used for process chambers carrying out chemical, biological, thermal and measurement processes, among others.

Electromagnetic Modeling of Superconducting Bulks in Applied Time-Varying Magnetic Field

An integrodifferential model formulated in terms of the electric vector potential is developed for the 3D numerical modeling of the electromagnetic field in superconducting bulks, for AC losses evaluation. The Newton Raphson method is applied to accelerate the convergence. The model is validated on a benchmark. The comparison results show the accuracy of the model and its performances in terms of computation time compared to classical approaches.

Analysis of Enceladus’s Time-variable Space Environment to Magnetically Sound its Interior

We provide a comprehensive study of Enceladus’s time-variable magnetic field environment and identify in measurements of the Cassini spacecraft signatures that appear to be consistent with induced fields from the moon’s interior. Therefore, we first analyze the background field Enceladus is exposed to within 21 flybys and 50 crossings of the moon’s orbit by the Cassini spacecraft. Considering magnetic field variability due to Enceladus’s eccentric orbit, Saturn’s planetary period oscillations, and local time effects within the magnetospheric current sheet, we construct predictive, time-variable background fields near Enceladus with a correlation coefficient of 0.75 and larger compared to the measured background fields. Subsequently, we build a geophysically based electrical conductivity model of Enceladus’s ocean from the equation of state for saline water and mixing laws for a porous core permeated by water. Using this conductivity model and the derived time-variable fields, we calculate expected induced fields. For close flybys, we identify within mostly plume-dominated magnetic field perturbations of 10–30 nT much smaller perturbations of 1–3 nT, which could be consistent with induction. The flybys over Enceladus’s north pole are best suited for induction studies, and the associated measurements suggest that a conductivity of the ocean with 1–3 S m–1 is not sufficient to produce an adequate induction response, but they support a highly conductive, porous core of 20–30 S m–1 and/or a more conductive ocean. Our study also provides strategies for future magnetic sounding of Enceladus.

Dynamics of paramagnetic permanent chains and self-assembled clusters under a rapidly rotating magnetic field.

We study experimentally and theoretically the dynamics of permanent paramagnetic chains and mixed clusters formed by permanent paramagnetic chains and paramagnetic particles under the influence of a time-varying magnetic field. First, we examine the dynamics of permanent chains at high frequencies (∼50 to 1000Hz). These permanent chains exhibit continuous rotational motion with a frequency several orders of magnitude lower than that of the magnetic field. We develop a theoretical model that accurately describes the dependence of the rotational dynamics of chains on their length, as well as the amplitude and frequency of the external magnetic field in this high frequency regime. Next, we examine how cluster dynamics are affected by the presence of permanent chains. We show that the rotation of clusters composed of a high proportion of permanent chains is slowed down but remains qualitatively well described by the theoretical model we developed for homogeneous clusters of isotropic particles. We propose that the decrease in angular velocity for mixed clusters is due to the hardening of the cluster's 2D elastic modulus caused by the increase of the steric interaction parameter stemming from the presence of chemical links between particles in the chains.

Time-dependent Aharonov-Bohm type topological effects on dipoles

Exploring the time-dependent characteristics of AB-type effects holds significant importance in contemporary physics and its practical applications. Here, we delve into the investigation of time-dependent topological effects emerging in AB-type experimental setups. We first analyse the topological effects on magnetic dipoles moving in closed trajectories around the time-varying magnetic field source solenoid, then on electrical dipoles around a time-varying electric field source in 2+1 dimensions without any approximation. Last, we discuss the characteristics of the topological effects by considering the identity and dualities between phases from an integrated perspective.

Effect of magnetic anisotropy and interaction on spatial focused hyperthermia for rotating and oscillating fields

The behavior of magnetic nanoparticles in a time-varying magnetic field has several practical applications. One of these is hyperthermia used in the treatment of cancer. The nanoparticles injected in the tumor cells release the energy absorbed from the time dependent external magnetic field in the form of heat to its environment in a well-localized way. The aim of the research in this area is to maximize the amount of the dissipated energy. Using a combination of an oscillating and static magnetic field, this dissipated energy can be more focused in space. In this article, we investigated whether this spatial focusing is also present using a rotating and static field together. Furthermore, we investigated the effects of anisotropy and interaction between nanoparticles on this spatial focusing effect using the jump-diffusion model for Néel relaxation in both cases. This kinetic Monte Carlo (MC) method was validated and compared with the stochastic Landau-Lifshitz-Gilbert (SLLG) equation based model. We have shown that the spatial focusing effect is also present for these non-idealized experimentally realizable cases. Also, the effect of rotating magnetic field on magnetic nanoparticles was not investigated in kinetic Monte Carlo simulations before.

Non-Newtonian behaviors of ferrofluid Couette–Poiseuille flows in time-varying magnetic fields

We analyze the fully developed Couette–Poiseuille flows of ferrofluids between two parallel flat walls subject to three types of time-varying magnetic fields. In these scenarios, ferrofluids exhibit diverse non-Newtonian characteristics such as distinct flow velocity distribution, apparent viscosity and shear stress compared to ordinary Couette–Poiseuille flows. The influence of spin viscosity is explored first through the solution of the governing equations with zero and non-zero spin viscosities. It shows that although the value of the spin viscosity is very small, its inviscid limit would have great influence over the velocity and spin velocity distributions. The assumption of zero spin viscosity leads to an exaggerated non-Newtonian behavior induced by time-varying magnetic fields in the ferrofluid Couette–Poiseuille flows. Then the solutions of equations with non-zero spin viscosity are utilized to delve into non-Newtonian behaviors of ferrofluid Couette–Poiseuille flow under the application of the three time-varying magnetic fields. The results indicate that negative rotational viscosity will occur if the dimensionless frequency lies in the range 1–10, which is a distinguishing feature compared with Newtonian flows. At this point, non-Newtonian flow induced by magnetic field arises, although this effect is very tiny. Within the same frequency range, reversed tangential stress appears in strong uniform alternating magnetic fields. The minimum negative rotational viscosity may arrive at up to 20 % of the intrinsic viscosity in the rotating magnetic field when the magnetization relaxation time is 4 ms.

Depinning of domain walls in a notched ferromagnetic nanostrip: role of inertial and nonlinear damping effects

Abstract In this work, we investigate theoretically the static and kinetic depinning field of a domain wall in a notched magnetic nanostrip under the generalized framework of the Landau–Lifshitz-Gilbert equation, which combines inertial and nonlinear viscous-dry friction damping effects. We assume a head-to-head transverse domain wall configuration and analyzed its motion subject to a time-varying external magnetic field. To deduce the equation ruling the spatio-temporal evoution of the magnetic domain wall, we adopt the Schryer and Walker trial function approach. The results show that static and kinetic depinning fields increase as the dry friction dissipation increases. Moreover, viscous dissipation exhibits a weak dependence on the kinetic depinning field and saturated domain wall velocity, while inertial damping due to the relaxation time of angular momentum significantly impacts the kinetic depinning field, depinning time, and breakdown velocity. Our numerical results are in good qualitative agreement with the recent observations reported in the literature.

The velocity-space signature of transit-time damping

Transit-time damping (TTD) is a process in which the magnetic mirror force – induced by the parallel gradient of magnetic field strength – interacts with resonant plasma particles in a time-varying magnetic field, leading to the collisionless damping of electromagnetic waves and the resulting energization of those particles through the perpendicular component of the electric field, $E_\perp$ . In this study, we utilize the recently developed field–particle correlation technique to analyse gyrokinetic simulation data. This method enables the identification of the velocity-space structure of the TTD energy transfer rate between waves and particles during the damping of plasma turbulence. Our analysis reveals a unique bipolar pattern of energy transfer in the velocity-space characteristic of TTD. By identifying this pattern, we provide clear evidence of TTD's significant role in the damping of strong plasma turbulence. Additionally, we compare the TTD signature with that of Landau damping (LD). Although they both produce a bipolar pattern of phase-space energy density loss and gain about the parallel resonant velocity of the Alfvénic waves, they are mediated by different forces and exhibit different behaviours as the perpendicular velocity $v_\perp \to 0$ . We also explore how the dominant damping mechanism varies with ion plasma beta $\beta _i$ , showing that TTD dominates over LD for $\beta _i > 1$ . This work deepens our understanding of the role of TTD in the damping of weakly collisional plasma turbulence and paves the way to seek the signature of TTD using in situ spacecraft observations of turbulence in space plasmas.

Pulsed-Mode Magnetic Field Measurements with a Single Stretched Wire System.

In synchrotrons, accurate knowledge of the magnetic field generated by bending dipole magnets is essential to ensure beam stability. Measurement campaigns are necessary to characterize the field. The choice of the measurement method for such campaigns is determined by the combination of magnet dimensions and operating conditions and typically require a trade-off between accuracy and versatility. The single stretched wire (SSW) is a well-known, polyvalent method to measure the integral field of magnets having a wide range of geometries. It, however, requires steady-state excitation. This work presents a novel implementation of this method called pulsed SSW, which allows the system to measure rapidly time-varying magnetic fields, as is often needed, to save power or gain beam time. We first introduce the measurement principle of the pulsed SSW, followed by a combined strategy to calculate the absolute magnetic field by incorporating the classic DC SSW method. Using a bending magnet from the Proton Synchrotron Booster located at the European Organization for Nuclear Research as a case study, we validate the pulsed SSW method and compare its dynamic measurement capabilities to a fixed induction coil, showing thereby how the coil calibration must be adjusted according to the field level. Finally, we assess the method's measurement accuracy using the standard SSW as a reference and present an analysis of the primary noise contributors.

Toward Programmable Quantum Processors Based on Spin Qubits with Mechanically Mediated Interactions and Transport.

Solid-state spin qubits are promising candidates for quantum information processing, but controlled interactions and entanglement in large, multiqubit systems are currently difficult to achieve. We describe a method for programmable control of multiqubit spin systems, in which individual nitrogen-vacancy (NV) centers in diamond nanopillars are coupled to magnetically functionalized silicon nitride mechanical resonators in a scanning probe configuration. Qubits can be entangled via interactions with nanomechanical resonators while programmable connectivity is realized via mechanical transport of qubits in nanopillars. To demonstrate the feasibility of this approach, we characterize both the mechanical properties and the magnetic field gradients around the micromagnet placed on the nanobeam resonator. We demonstrate coherent manipulation of a spin qubit in the proximity of a transported micromagnet by utilizing nuclear spin memory and use the NV center to detect the time-varying magnetic field from the oscillating micromagnet, extracting a spin-mechanical coupling of 7.7(9)Hz. With realistic improvements, the high-cooperativity regime can be reached, offering a new avenue toward scalable quantum information processing with spin qubits.

High-Dynamic-Range Integrated NV Magnetometers

High-dynamic-range integrated magnetometers demonstrate extensive potential applications in fields involving complex and changing magnetic fields. Among them, Diamond Nitrogen Vacancy Color Core Magnetometer has outstanding performance in wide-range and high-precision magnetic field measurement based on its inherent high spatial resolution, high sensitivity and other characteristics. Therefore, an innovative frequency-tracking scheme is proposed in this study, which continuously monitors the resonant frequency shift of the NV color center induced by a time-varying magnetic field and feeds it back to the microwave source. This scheme successfully expands the dynamic range to 6.4 mT, approximately 34 times the intrinsic dynamic range of the diamond nitrogen-vacancy (NV) center. Additionally, it achieves efficient detection of rapidly changing magnetic field signals at a rate of 0.038 T/s.

Enhancing thermal stability of optimal magnetization reversal in nanoparticles

Energy-efficient switching of nanoscale magnets requires application of a time-varying magnetic field characterized by microwave frequency. At finite temperatures, even weak thermal fluctuations induce perturbations in the magnetization that can accumulate in time, disrupt the phase locking between the magnetization and the applied field, and eventually compromise magnetization switching. It is demonstrated here that the magnetization reversal is mostly disturbed by unstable perturbations arising in a certain domain of the configuration space of a nanomagnet. The instabilities can be suppressed and the probability of magnetization switching enhanced by applying an additional stimulus such as a weak longitudinal magnetic field that ensures bounded dynamics of the perturbations. Application of the stabilizing longitudinal field to a uniaxial nanomagnet makes it possible to reach a desired probability of magnetization switching even at elevated temperatures. The principle of suppressing instabilities provides a general approach to enhancing thermal stability of magnetization dynamics. Published by the American Physical Society 2024

Planar microcoil arrays for in vitro cellular-level micromagnetic activation of neurons

In the treatment of neurodegenerative disorders, a potential cure at a single neuron cell resolution is still lacking. Micromagnetic neurostimulation, although in its infancy, is one of the most promising techniques that offer spatially selective activation of neurons through micrometer-sized coils or microcoils (μcoils). Time-varying current drives these μcoils and generates a time-varying magnetic field which in turn induces an electric field to activate the neural tissues. In this work, we report the design and fabrication of planar μcoil arrays, termed Magnetic Patch (MagPatch), for activating single neurons. Using numerical calculations on ANSYS-Maxwell and NEURON, we report an optimized MagPatch array design that exploits the directionality of the induced electric field from the μcoils to enhance spatial selectivity. Each μcoil has an outer dimension of 190 × 190 μm2 and one MagPatch array contains 8 μcoils. For proof-of-concept design and development, the MagPatch array has been fabricated on Si-substrates using Ti, Au, and Si3N4 to ensure preliminary biocompatibility. They were then encapsulated in Parylene-C, a waterproof, anti-leakage current coating, thereby ensuring basic surface biocompatibility. Human neuroblastoma cells were cultured directly on the surface encapsulated MagPatch, and calcium fluorescence imaging was used to assess cell functionality. The impact of scaling the dimensions of the μcoil in the MagPatch array on electrical characteristics, Q-factor, and thermal effects on neural tissues from these μcoils have also been discussed.

Dynamics of the atom-polyatomic molecule conversion with quantum decoherence

Based on the mean-field approximation and the two-mode Bose–Hubbard model, we investigate the dynamical properties of atom-polyatomic molecule conversion systems under dissipation and dephasing. For such a many-body system problem, we partition phase space based on the states of fixed points, study the movement of fixed points and the transition to attractors in an open system. Additionally, for all the atoms that constitute a molecule, depending on whether the species of these atoms are identical or not, we introduce the innovative concepts of unbiased and biased systems. We discover that in biased conversion systems under particle losses, the evolution trajectories are distributed on a three-dimensional Bloch sphere with an internal structure. There exists a significant difference from the two-dimensional Hilbert space of an unbiased system. Finally, we discuss the sweeping rate of the time-varying magnetic field applied externally to the conversion system, and analyze a feasible scheme for the quantum coherent synthesis of triatomic molecules.

The method for noninvasive investigation of the boundaries of homogeneous magnetizable inclusions inside a biological object

Currently, in modern medicine and related areas of medical technology, the problem of noninvasive investigation of the internal structure of a biological object with the aim of detecting and subsequently visualizing hidden metallic foreign inclusions in the body is becoming increasingly important. Determining the spatial position and identifying the boundaries of such inclusions in the body can be a rather time-consuming process, as solving this problem is mainly done through noninvasive methods of introscopy, which require very careful application. Thus, a method for noninvasive investigation of hidden differently oriented homogeneous inclusions that allow for magnetization by an externally periodically time-varying magnetic field inside a biological object, is proposed in the study. This is achieved by representing the investigated volume as a set of parallel sections and measuring the distribution of the vector function of magnetic field induction in each of them using a working element in the form of spatially oriented contours based on a pair of inductance coils with an equal number of turns and opposing winding inclusion. This allows for non-invasive tomographic scanning of a biological object aimed at detecting the refraction effect of the altered vector field of magnetic field induction, followed by the reconstruction of inclusions based on projection data. The reconstruction is carried out using the back-projection method with prior spatial filtering in the original area through convolution of projection data with a convolution function.

Resonant inductive coupling network for human-sized magnetic particle imaging.

In magnetic particle imaging, a field-free region is maneuvered throughout the field of view using a time-varying magnetic field known as the drive-field. Human-sized systems operate the drive-field in the kHz range and generate it by utilizing strong currents that can rise to the kA range within a coil called the drive field generator. Matching and tuning between a power amplifier, a band-pass filter, and the drive-field generator is required. Here, for reasons of safety in future human scanners, a symmetrical topology and a transformer called an inductive coupling network are used. Our primary objectives are to achieve floating potentials to ensure patient safety while attaining high linearity and high gain for the resonant transformer. We present a novel systematic approach to the design of a loss-optimized resonant toroid with a D-shaped cross section, employing segmentation to adjust the inductance-to-resistance ratio while maintaining a constant quality factor. Simultaneously, we derive a specific matching condition for a symmetric transmit-receive circuit for magnetic particle imaging. The chosen setup filters the fundamental frequency and allows simultaneous signal transmission and reception. In addition, the decoupling of multiple drive field channels is discussed, and the primary side of the transformer is evaluated for maximum coupling and minimum stray field. Two prototypes were constructed, measured, decoupled, and compared to the derived theory and method-of-moment based simulations.

BIOIMPACT OF HYPOMAGNETIC FIELDS

Hypomagnetic fields (HMF), or nearly zero magnetic fields, are fields with a value of magnetic flux density lower than the Earth's geomagnetic field. The effects of these so-called weak magnetic fields can manifest in living organisms by influencing biological functions such as the circadian system, calcium balance in cells, DNA methylation, concentration of reactive oxygen species, as well as changes in metabolic and developmental processes. This article describes how HMF affects selected cellular structures through specific exposure parameters, whose selective impact has been verified on the proliferative activity of the yeast strain Saccharomyces cerevisiae. In 25 experiments, the inhibitory effect of a time-varying magnetic field at a level of 0.365 µT was confirmed, which corresponds to the magnitude of magnetic flux density in the vicinity of 100 kV power lines. Global organizations also point out the possible correlation between HMF generated by 50 Hz power lines and various diseases, particularly childhood leukemia.

Analytical analysis of the generation of a rotating driving magnetic field on the outer surface of a magnetic pinch load with a helical return current post

A recently emerging approach adopts a directionally time-varying (rotating) magnetic field to drive a pinch load, aiming to mitigate the inherent magneto-Rayleigh-Taylor instability in dynamic Z pinches. A helical return current post (RCP) serves as a functional structural element capable of generating the requisite driving magnetic field for this purpose in the load region. This paper first calculates the current azimuthally induced on the outer surface of a magnetically pinched load within this type of RCP using a zero-dimensional lumped-parameter circuit model. The results show that the induced current deviates significantly from the presumed “perfect” induced current (100% amplitude) as reported in the literature [S. A. Sorokin, ); P. F. Schmit , ); G. A. Shipley , ); and P. C. Campbell , ], with an effective coefficient of current induction considerably less than 1. However, even when the load is fully compressed to the axis, the effective coefficient does not approach zero but rather converges to a finite value that solely depends on the aspect ratio of the RCP. This is quite favorable for the suppression of magneto-Rayleigh-Taylor instability in the Z pinch. As for the pointlike X pinch, the axial magnetic field does not tend to zero but a finite value, though the effective coefficient tends to zero, and this result may be used to suppress the instability in X pinch and improve the time stability and spatiotemporal unity of hot spots. In addition, the anode and cathode plates have the potential to enhance the current induced in the load. This paper then analyzes the axial distribution and time behavior of the induced current adopting an approximate analytical method and numerical integration and finds an approximate invariance that can be well characterized by δt, the product of the normalized skin depth and time. Similar values of δt indicate similar axial distribution characteristics. When δt is lower than, at, or higher than the critical region (∼0.1–0.3), the axial distribution appears dumbbell shaped, nearly flat, and arched, respectively. These distributively induced currents can be exploited to achieve quasispherical, near flat, and dumbbell-shaped implosions, respectively. Published by the American Physical Society 2024