AC Magnetic Field Research Articles

Enhancing the geometry accuracy and mechanical properties of wire arc additive manufacturing of an Al-5%Mg alloy through longitudinal magnetic field influence

To address the issues of low deposition efficiency, poor geometric accuracy, and high porosity in wire arc additive manufacturing (WAAM) specimens, a longitudinal alternating current (AC) magnetic field-assisted WAAM method was employed. The results showed that the introduction of the longitudinal AC magnetic field significantly enhanced the geometric accuracy of the specimens. After magnetic field assistance, the porosity of the WAAM Al-5%Mg alloy specimens decreased from 0.372 % to 0.016 %. The grain size decreases from 71.95 μm to 56.3 μm, with a notable increase in the proportion of small grains (D < 30 μm) from 27.06 % to 44.57 %. The longitudinal tensile strength increased from 243 MPa to 260 MPa, while the transverse tensile strength increased from 232 MPa to 257.7 MPa. Moreover, the longitudinal and transverse tensile strengths tended to be isotropic. Therefore, the longitudinal AC magnetic field has a significant impact on the performance of AlMg alloy WAAM specimens. This study presents novel strategies and theoretical guidance for enhancing the efficiency and component performance of aluminum alloy WAAM technology.

Theoretical Analysis of a Magnetic Shielding System Combining Active and Passive Modes.

Considering the magnetic shielding requirements of both geomagnetic field and 50 Hz power-line frequency in the complex working conditions of the power grid, an electromagnetic shielding system combining active and passive modes is proposed in this article. A three-dimensional Helmholtz coil with a magnetic shielding barrel nested inside is established by the COMSOL simulation tool, and the magnetic shielding efficiency of the system is analyzed. Comparing different materials, the simulation results indicate that permalloy alloy exhibits better shielding performance than pure iron and nickel materials. Additionally, the overall shielding efficiency of the shielding barrel increases linearly with the number of multiple layers. Under the combined active and passive electromagnetic shielding conditions, the system achieves a shielding efficiency of SE = 113.98 dB, demonstrating excellent performance in shielding both AC and DC interference magnetic fields. This study provides theoretical guidance for the construction of magnetic shielding systems in electromagnetic interference environment.

Thermally Driven Untethered Swimmer Using a Convection Flow with the Eddy Current Loss Due to AC Magnetic Fields

Thermally Driven Untethered Swimmer Using a Convection Flow with the Eddy Current Loss Due to AC Magnetic Fields

A superconducting switch using induced current in the closed loop circuit

Superconducting magnets have been applied in many fields because of the high magnetic field and the low loss. In order to energize superconducting magnets and operate them in the persistent current mode, the superconducting switch is essential. Recently, a superconducting switch using the interaction between the DC transport current and induced current in a closed loop circuit has been proposed, which cannot only respond fast, but also operate efficiently. In this work, an analytical model based on equivalent circuit is proposed to explain the working principle of this type of superconducting switch. An experimental protype is built to investigate its electromagnetic behaviors and working performance. Impacting factors of the voltage across the superconducting switch have been clarified based on experimental results. The method based on asymmetric AC magnetic field is proposed to enhance the average voltage across the superconducting switch and its performance has been verified through experimental tests. Besides, the advantages and application prospects of the superconducting switch are discussed.

Wireless magnetoelectrically powered organic light-emitting diodes.

Compact wireless light sources are a fundamental building block for applications ranging from wireless displays to optical implants. However, their realization remains challenging because of constraints in miniaturization and the integration of power harvesting and light-emission technologies. Here, we introduce a strategy for a compact wirelessly powered light-source that consists of a magnetoelectric transducer serving as power source and substrate and an antiparallel pair of custom-designed organic light-emitting diodes. The devices operate at low-frequency ac magnetic fields (~100 kHz), which has the added benefit of allowing operation multiple centimeters deep inside watery environments. By tuning the device resonance frequency, it is possible to separately address multiple devices, e.g., to produce light of distinct colors, to address individual display pixels, or for clustered operation. By simultaneously offering small size, individual addressing, and compatibility with challenging environments, our devices pave the way for a multitude of applications in wireless displays, deep tissue treatment, sensing, and imaging.

Efficient microwave spin control of negatively charged group-IV color centers in diamond

In this paper, we provide a comprehensive overview of the microwave-induced manipulation of electronic spin states in negatively charged group-IV color centers in diamond with a particular emphasis on the influence of strain. Central to our investigation is the consideration of the full vectorial attributes of the magnetic fields involved, which are a dc field for lifting the degeneracy of the spin levels and an ac field for microwave control between two spin levels. We observe an intricate interdependence between their spatial orientations, the externally applied strain, and the resultant efficacy in spin-state control. In most studies to date the ac and dc magnetic field orientations have been insufficiently addressed, which has led to the conclusion that strain is indispensable for the effective microwave control of heavier group-IV vacancies, such as tin- and lead-vacancy color centers. In contrast, we find that the alignment of the dc magnetic field orthogonal to the symmetry axis and the ac field parallel to it can make the application of strain obsolete for effective spin manipulation. Furthermore, we explore the implications of this field configuration on the spin's optical initialization, readout, and gate fidelities. Published by the American Physical Society 2024

Nonlinear response of magnetization obeying inertial dynamics to superimposed dc and ac fields and dynamic magnetic hysteresis

The nonlinear ac stationary responses of magnetization and the dynamic magnetic hysteresis of ferromagnetic particles with uniaxial anisotropy acted on by both external dc and ac magnetic fields are evaluated by employing the inertial Landau–Lifshitz–Gilbert equation. Analytical expressions are obtained for the components of the second- and third-order nonlinear susceptibility tensors using the perturbation method. The dynamic nonlinear susceptibility strongly depends on the dc field strength. The effect of inertia on the area and slope of the dynamic magnetic hysteresis loop is demonstrated. In addition to nutation resonance, the main nonlinear effects previously observed in the ferromagnetic resonance region (frequency doubling and appearance of weak subharmonic resonance peaks) are predicted in the nutation resonance frequency region.

Boosting energy harvesting of fully flexible magnetoelectric composites of PVDF-AlN and NiO-decorated carbon nanofibers

The increasing popularity of wearable electronics has sparked interest in flexible energy harvesters as alternatives to conventional batteries. Flexible magnetoelectric (ME) composites, known for converting ambient magnetic field energy into useable power, are emerging as promising autonomous energy sources for integration into wearable devices. In this study, we prepared flexible (PVDF-AlN)–(NiO–CNF) based ME composites using two different methods: solution-casting and electrospinning techniques. The ME coupling was confirmed by measuring the ferroelectric and magnetic properties of the composite, and it was qualitatively characterized through the ME coupling coefficient. The electrospinning fibers-based ME composite exhibited an optimal value of 10.6 V/cm.Oe, significantly higher than the solution-casting films-based ME composite (1.3 V/cm.Oe) under a 1 kHz AC magnetic field (off-resonance condition). Subsequently, a flexible magneto-mechano-electric (MME) generator was designed using electrospun-derived material, harvesting a sinusoidal wave with a maximum output peak-to-peak voltage of 9.02 V. The generator displayed an optimal DC power density of 97 μW/m2 when exposed to a weak AC magnetic field of 6 Oe at a frequency of 50 Hz. Consequently, it holds great promise as an efficient autonomous power supply for medical sensing and various miniature electronic applications.

Optical Microscopy Using the Faraday Effect Reveals in Situ Magnetization Dynamics of Magnetic Nanoparticles in Biological Samples.

The study of exogenous and endogenous nanoscale magnetic material in biology is important for developing biomedical nanotechnology as well as for understanding fundamental biological processes such as iron metabolism and biomineralization. Here, we exploit the magneto-optical Faraday effect to probe intracellular magnetic properties and perform magnetic imaging, revealing the location-specific magnetization dynamics of exogenous magnetic nanoparticles within cells. The opportunities enabled by this method are shown in the context of magnetic hyperthermia; an effect where local heating is generated in magnetic nanoparticles exposed to high-frequency AC magnetic fields. Magnetic hyperthermia has the potential to be used as a cellular-level thermotherapy for cancer, as well as for other biomedical applications that target heat-sensitive cellular function. However, previous experiments have suggested that the cellular environment modifies the magnetization dynamics of nanoparticles, thus dramatically altering their heating efficiency. By combining magneto-optical and fluorescence measurements, we demonstrate a form of biological microscopy that we used here to study the magnetization dynamics of nanoparticles in situ, in both histological samples and living cancer cells. Correlative magnetic and fluorescence imaging identified aggregated magnetic nanoparticles colocalized with cellular lysosomes. Nanoparticles aggregated within these lysosomes displayed reduced AC magnetic coercivity compared to the same particles measured in an aqueous suspension or aggregated in other areas of the cells. Such measurements reveal the power of this approach, enabling investigations of how cellular location, nanoparticle aggregation, and interparticle magnetic interactions affect the magnetization dynamics and consequently the heating response of nanoparticles in the biological milieu.

Magneto-optical characterization of TCO films using standard and enhanced configurations

Thin film samples like transparent conducting oxides (TCO) are typically investigated using measurements like Hall Effect and 4-point probe measurements. We use a sensitive AC Faraday rotation (FR) setup to study thin film samples for which a magneto-optic response is challenging to characterize. The experimental setup employs a stabilized He-Ne laser (633 nm) along with an AC magnetic field that enables lock-in detection. We investigate a series of TCO samples that are deposited on a glass substrate. The TCO samples include the more widely used Indium Tin Oxide (ITO) and the relatively newer Fluorine doped Tin Oxide films, usually referred to as FTO. These films have a magneto-optic response due to the presence of free carrier concentration and therefore measurement of this response (Verdet constant) could allow one to determine the carrier concentration of these films. Given that magneto optic responses like FR depend on the length of the sample length traveled by light, these sub-micron films pose considerable challenges in trying to extract the FR response of the film from that of the much thicker glass substrate. Furthermore, we present details of the design and FR characterization of samples using a Michelson interferometer-based measurement setup which enhances the Faraday rotation and affords a new means of studying harmonic peaks of the recorded optical signal in response to a sinusoidally-varying applied magnetic field. We compare some early results from this setup to the typical “single-pass” setup to highlight the difference in the recorded signals from the two setups. To showcase the advantages of the proposed measurements, we also include some early results from a very different type of sample, namely superparamagnetic nanoparticles (SNPs).

Frequency-tunable magnetic field sensing using continuous-wave optically detected magnetic resonance with nitrogen-vacancy centers in diamond

The nitrogen-vacancy (NV) center is a promising candidate to realize practical quantum sensors with high sensitivity and high spatial resolution at room temperature and atmospheric pressure. In conventional high-frequency AC magnetometry with NV centers, the setup requires a pulse sequence with an appropriate time synchronization and strong microwave power. To avoid these practical difficulties, AC magnetometry using continuous-wave optically detected magnetic resonance (CW-ODMR) was recently demonstrated. That previous study utilized radio frequency (RF)-dressed states generated by the coherent interaction between the electron spin of the NV center and the RF wave. However, the drawback of this method is that the detectable frequency of the AC magnetic fields is fixed. Here, we propose and demonstrate frequency-tunable magnetic field sensing based on CW-ODMR. In the new sensing scheme, we obtain RF double-dressed states by irradiation with RF fields at two different frequencies. One creates the RF-dressed states and changes the frequency of the target AC field. The other is a target AC field that induces a change in the CW-ODMR spectrum by generating the RF double-dressed states through coherent interaction with the RF-dressed states. The sensitivity of our method is estimated to be comparable to or even higher than that of the conventional method based on the RF field with a single frequency. The estimated bandwidth is 7.5 MHz, higher than that of the conventional method using the RF-dressed states. Our frequency-tunable magnetic field sensor based on CW-ODMR paves the way for new applications in diamond devices.

Preparation of stable colloidal dispersion of surface modified Fe3O4 nanoparticles for magnetic heating applications

The effect of surface modification on enhancing the magnetic heating behavior of magnetic nano fluids were investigated, for this purpose Fe3O4 nanoparticles were synthesized using co-precipitation method and surface modification was done using citric acid, ascorbic acid, tetraethyl orthosilicate (TEOS), polyvinyl alcohol (PVA) and polyethylene glycol (PEG). Experimental heating tests using AC magnetic field were done in the frequency of 100 kHz and different magnetic field (H) intensities. Theoretically the specific absorption rate (SAR) in magnetic nano fluids is independent of nanoparticles concentration but the experimental results showed different behavior. The theoretical SAR value @ H = 12kA.m–1 for Nano fluids containing bare Fe3O4 nanoparticles was 11.5 W/g but in experimental tests the obtained value was 9.72 W/g for nano fluid containing 20,000 ppm of dispersed nanoparticles. The experimental SAR calculation was repeated for sample containing 10,000 ppm of nanoparticles and the results showed increase in experimental SAR that is an evidence of nanoparticles agglomeration in higher concentrations. The surface modification has improved the dispersion ability of the nanoparticles. The Ratio of SAR, experimental, 20000ppm to SAR, experimental, 10000ppm was 0.85 for bare Fe3O4 nanoparticles dispersion but in case of surface modified nanoparticles this ratio has increased up to 0.98 that shows lower agglomeration of nanoparticles as a result of surface modification, although on the other hand the surface modification agents were magnetically passive and so it is expected that in constant concentration the SAR for bare Fe3O4 nanoparticles to be higher than this variable for surface modified nanoparticles. At lower concentrations the dispersions containing bare Fe3O4 nanoparticles showed higher SAR values but at higher concentrations the surface modified Fe3O4 nanoparticles showed better results although the active agent amount was lower at them. Finally, it should be noted that the nanoparticles that were surface modified using polymeric agents showed the highest decrease in experimental SAR amounts comparing theoretical results that was because of the large molecules of polymers comparing other implemented surface modification agents.

Enhanced dielectric, magnetic and magnetoelectric properties in 0.5BaFe12O19 - xBaTiO3 - (0.5-x)CoFe2O4 composites

(0.5)BaFe12O19 - xBaTiO3 - (0.5-x)CoFe2O4; (x = 0.1, 0.2, 0.3 & 0.4) composite system was developed through conventional solid-state technique. XRD with Rietveld refinement confirmed pure tri-phasic composites with no impurity. The microstructure of samples has inhomogeneous grain packing with average size of grains ∼0.5 μm and typically decreased with BaTiO3 increment. The dielectric constant showed low-frequency dispersion and increased with BaTiO3 increment, hence maximum at 400 °C for composite x = 0.4 (∼2.8 × 103 at 1 kHz). Composites are ferrimagnetic in nature along with presence of firm exchange coupling among BaFe12O19/CoFe2O4 ferrite phases. The samples are multiferroic owing to typically high magnetoelectric coupling coefficient which increased with BaTiO3 increment, thus composite x = 0.4 attains highest value of 4.56 mV/cm.Oe on application of ac magnetic field (Hac = 45 Oe). The results indicate that the composites are suitable for magnetic field sensors and memory storage devices.

High frequency magnetometry with an ensemble of spin qubits in hexagonal boron nitride

Sensors based on spin qubits in 2D crystals offer the prospect of nanoscale proximities between sensor and source, which could provide access to otherwise inaccessible signals. For AC magnetometry, the sensitivity and frequency range are typically limited by the noise spectrum, which determines the qubit coherence time. We address this using phase modulated continuous concatenated dynamic decoupling, which extends the coherence time towards the T1 limit at room temperature and enables tuneable narrowband AC magnetometry. Using an ensemble of negatively charged boron vacancies in hexagonal boron nitride, we detect out-of-plane AC fields in the range of ~ 10 − 150 MHz, and in-plane fields within ± 150 MHz of the electron spin resonance. We measure an AC magnetic field sensitivity of sim 1,mu {{{rm{T}}}}/sqrt{{{{rm{Hz}}}}} at ~ 2.5 GHz, for a sensor volume of ~ 0.1 μm3. This work establishes the viability of spin defects in 2D materials for high frequency magnetometry, with wide-ranging applications across science and technology.

Beyond Newton's law of cooling in evaluating magnetic hyperthermia performance: a device-independent procedure.

Accurate knowledge of the heating performance of magnetic nanoparticles (MNPs) under AC magnetic fields is critical for the development of hyperthermia-mediated applications. Usually reported in terms of the specific loss power (SLP) obtained from the temperature variation (ΔT) vs. time (t) curve, such an estimate is subjected to a huge uncertainty. Thus, very different SLP values are reported for the same particles when measured on different equipment/in different laboratories. This lack of control clearly hampers the further development of nanoparticle-mediated heat-triggered technologies. Here, we report a device-independent approach to calculate the SLP value of a suspension of magnetic nanoparticles: the SLP is obtained from the analysis of the peak at the AC magnetic field on/off switch of the ΔT(time) curve. The measurement procedure, which itself constitutes a change of paradigm within the field, is based on the heat diffusion equation, which is still valid when the assumptions of Newton's law of cooling are not applicable, as (i) it corresponds to the ideal scenario in which the temperature profiles of the system during heating and cooling are the same; and (ii) it diminishes the role of coexistence of various heat dissipation channels. Such an approach is supported by theoretical and computational calculations to increase the reliability and reproducibility of SLP determination. Furthermore, the new methodological approach is experimentally confirmed, by magnetic hyperthermia experiments performed using 3 different devices located in 3 different laboratories. Furthermore, the application of this peak analysis method (PAM) to a rapid succession of stimulus on/off switches which results in a zigzag-like ΔT(t), which we term the zigzag protocol, allows evaluation of possible variations of the SLP values with time or temperature.

The impact of cross-linker distribution on magnetic nanogels: encapsulation, transport and controlled release of the tracer.

Magnetic nanogels (MNGs) are highly attractive for biomedical applications because of their potential for remote control of the rheology and internal structure of these soft colloids with biocompatible magnetic fields. In this contribution, using molecular dynamics simulations, we investigate the impact of the cross-linker distribution in the body of a MNG on the shape and magnetic response to constant and AC magnetic fields and relate those properties to the behaviour of non-magnetic tracers placed in the MNGs and left to escape. We find that if no AC magnetic field is applied, although the escape times of the tracer particles barely depend on morphology, the highest degree of subdiffusion is observed for the gels with a non-uniform cross-linkerer distribution. We also find how the eigen frequency at which particles relax locally in the polymer matrix affects the dynamic magnetic response of the gel. We show that a magnetic field-induced wobbling can facilitate drug release from gels.

Investigation of Heat Treatment Effect of Amorphous Magnetic Materials in AC Magnetic Field

Investigation of Heat Treatment Effect of Amorphous Magnetic Materials in AC Magnetic Field

Harmonic response of Gd-doped Mn-ferrite nanoparticles under AC magnetic field and optimization of Gd doping for MPI applications

This study synthesized Gd-doped Mn-ferrite nanoparticles for magnetic particle imaging (MPI) applications with doping levels (x) of 0, 0.05, 0.07, and 0.10. Analyses using X-ray diffraction measurements unequivocally confirmed the presence of a spinel-type crystal structure in the synthesized particles and X-ray absorption fine-structure spectroscopy confirmed the incorporation of Gd atoms in place of Mn within the crystal lattice. Magnetization and harmonic measurements under an AC magnetic field revealed that particles with a high initial permeability and low coercivity showed a high response intensity. Notably, particles possessing a Gd doping level of x = 0.07 displayed the highest response and were considered promising as MPI materials.

Investigation of the effects of AC magnetic fields on locomotion and brain matter in small laboratory animals

Investigation of the effects of AC magnetic fields on locomotion and brain matter in small laboratory animals

Magnetostrictive-piezocatalytic CoFe2O4@UiO-66 nanohybrid and its potential for deep-seated tumor treatment.

Magnetostrictive CoFe2O4 (CFO) nanoparticles were encapsulated within a UiO-66 metal-organic-framework layer to form a CFO@UiO-66 nanohybrid. The deforming of CFO, in response to a high-frequency AC magnetic field, initiates the piezocatalytic property of UiO-66 to generate ˙OH radicals, which can kill cancer cells buried in thick tissues, showcasing bright potential for deep-seated tumor treatment.