Dc Bias Magnetic Field Research Articles

Dynamic resistance of a REBCO tape carrying direct current under a mixture magnetic field of AC field with DC-biased field

Abstract When the REBCO coated conductor tape carries a direct current(DC) transport current whilst exposed to the alternating current(AC) magnetic field, a DC electrical resistance can be observed, which is called “dynamic resistance”. The High Temperature Superconducting(HTS) magnet wound by the REBCO tapes is located in the HTS electrical machine as field winding carrying DC transport current. The operational environment of the HTS electrical machine involves a complex magnetic field, encompassing both AC and DC components. The interaction between the AC magnetic field and the DC transport current induces dynamic resistance and dynamic loss in the REBCO tape which is a distinctive trait of REBCO tape. Additionally, the presence of an extra DC-biased magnetic field can decrease the critical current of the REBCO tape, thereby altering its electromagnetic properties and potentially compromising its safety. As the basis of superconducting magnets, it is particularly important to study the dynamic resistance and loss distribution of the single REBCO tape under a mixture of magnetic field backgrounds, according to the real working environments in various applications. In this paper, the electromagnetic-thermal coupling model of multilayer REBCO tape based on H-formulation is built in COMSOL Multiphysics. The electromagnetic characteristics and dynamic resistance of the tape are presented when the tape is applied AC magnetic field and carries DC transport current. The effects of perpendicular and parallel DC-biased magnetic fields on the dynamic resistance and loss distribution of the REBCO tape are investigated in the paper. And the DC transport current safety margin will be observed in different applied DC-biased magnetic fields. This study comprehensively demonstrates the variation of dynamic resistance and loss distribution under a complex background magnetic field, which is significant for exploring the electromagnetic characteristics and calculating the loss of the HTS magnets in the HTS electrical machine.

Magnetoelectric effect in a Metglas–langatate ring heterostructure for current sensing

The magnetoelectric (ME) effect was observed and investigated in a planar ring-type heterostructure containing mechanically coupled rings of magnetostrictive amorphous alloy Metglas and a piezoelectric single crystal langatate. The structure was excited by a circumferential ac magnetic field in the presence of a circumferential dc bias magnetic field. Due to the absence of demagnetization and the high acoustic quality factor of the langatate, a high ME field conversion coefficient of α E ≈ 53 V (Oe cm)−1 was obtained at the frequency 221 kHz of the fundamental radial acoustic resonance mode. The structure can be used as a non-contact ac or dc current sensor. The sensitivity of the structure to the ac current was 1.6 V A−1, whereas for the dc current it reached 4.2 V A−1.

Self-Biased Magneto-Electric Antenna for Very-Low-Frequency Communications: Exploiting Magnetization Grading and Asymmetric Structure-Induced Resonance.

VLF magneto-electric (ME) antennas have gained attention for their compact size and high radiation efficiency in lossy conductive environments. However, the need for a large DC magnetic field bias presents challenges for miniaturization, limiting portability. This study introduces a self-biased ME antenna with an asymmetric design using two magneto materials, inducing a magnetization grading effect that reduces the resonant frequency during bending. Operating principles are explored, and performance parameters, including the radiation mechanism, intensity and driving power, are experimentally assessed. Leveraging its excellent direct and converse magneto-electric effect, the antenna proves adept at serving as both a transmitter and a receiver. The results indicate that, at 2.09 mW and a frequency of 24.47 kHz, the antenna has the potential to achieve a 2.44 pT magnetic flux density at a 3 m distance. A custom modulation-demodulation circuit is employed, applying 2ASK and 2PSK to validate communication capability at baseband signals of 10 Hz and 100 Hz. This approach offers a practical strategy for the lightweight and compact design of VLF communication systems.

Role of extrinsic factors on magnetoelastic resonance biosensors sensitivity

Magnetoelastic (ME) resonance devices are attractive for application as biosensors in health-related areas as they allow contactless detection of pathogenic agents with high sensitivity. After functionalization, they offer valuable diagnostic options that promote efficient capture of mass on the sensor surface through biological interactions. ME sensors are also sensitive to external factors such as temperature, magnetic fields, and variations in mass that can arise from processes unrelated to biological interactions, including corrosion and salt crystallization. This article evaluates extrinsic factors that affect the response of ME resonance sensors for diagnostic applications. In particular, the influence of heat treatments, operation temperature, applied DC magnetic field bias, and corrosive environment were studied. The control of all these factors is crucial for the design, fabrication, and functionalization of ME resonance biosensors and for the development of measuring instrumentation and effective measurement protocols. This work established maximum operating temperature and bias field variations to keep the sensor sensitivity. Heat treatment of the sensors before and after coating improved the signal-to-noise ratio and corrosion resistance. Further improvement in corrosion resistance was provided by cathodic protection, which has been proven beneficial for applications of ME resonance sensors in aqueous fluids.

Measurement and calculation for high frequency magnetic losses of Terfenol-D alloy rod under coupled stress and DC bias fields

Compressive stress, a DC bias magnetic field, and an AC excitation field significantly affect hysteresis characteristics and magnetic energy losses of magnetostrictive materials. Therefore, studying high frequency magnetic losses of magnetostrictive materials under coupling of these three conditions is of great importance for improving the output performance of high power magnetostrictive transducers. In this paper, a magnetic property testing system for magnetostrictive materials has been constructed. It enables the magnetic property testing of Terfenol-D alloy rods under the simultaneous application of stress and DC bias at high frequency excitation (a maximum AC magnetic flux density of 0.5 T at an excitation frequency of 9 kHz). Based on Bertotti separation theory and experimental data, considering the coupling effect of stress and DC bias, a computational model for the high frequency magnetic losses of Terfenol-D materials is proposed. The model incorporates relevant parameters of stress and DC bias to modify loss coefficients, and the expressions for loss coefficients are identified using the symbolic regression method. A comparative analysis between experimental data and model calculation shows good agreement, with the maximum and average errors of 4.68% and 1.74%, respectively.

Preparation and magnetic properties of high DC-bias performance Fe-Si-Nb-B-Cu/carbonyl iron chip inductors

In this study, a gradient temperature rise technique was employed to prepare ultra-fine nanocrystalline alloy magnetic powder with excellent high-frequency and low-loss characteristics. It was found that increasing the holding time effectively refines the grain structure in the perpendicular direction of the Fe-Si-Nb-B-Cu alloy's (220) crystal plane. This refinement contributes to a reduction in eddy current losses within the soft magnetic composite material. The addition of carbonyl iron to the nanocrystalline magnetic powder resulted in further enhancements in the density, strength, and magnetic properties of soft magnetic composites under high-frequency magnetic fields. Consequently, soft magnetic composites exhibiting superior DC bias performance were successfully obtained, with a power loss of 2629.50 kW/m3 at a magnetic induction of 20 mT and a frequency of 3 MHz, and more than 70 % percent permeability in a DC biased magnetic field of 7.96 kA/m. The relationship between relative permeability and quasi-static hysteresis loops was established. Additionally, the dynamic hysteresis loops of the soft magnetic composites revealed a relaxation phenomenon, which elucidated the mechanism behind the variations in power loss with changes in magnetic induction strength and frequency. Finally, through simulations, it was determined that the number of turns and the winding method significantly influenced the internal magnetic field and inductance of the chip inductor. Utilizing this information, a chip inductor with ultra-small inductance, compact size, and excellent DC bias characteristics for 10 A circuits was successfully fabricated.

Emergence of field-induced memory effect in spin ices

Out-of-equilibrium investigation of strongly correlated materials deciphers the hidden equilibrium properties. Herein, we have investigated the out-of-equilibrium magnetic properties of polycrystalline Dy2Ti2O7 and Ho2Ti2O7 spin ices. Our experimental findings reveal the emergence of magnetic field-induced anomalous hysteresis observed solely in temperature-and magnetic field-dependent AC susceptibility measurements. The observed memory effect (anomalous thermomagnetic hysteresis) exhibits a strong dependence on both thermal and non-thermal driving variables. Owing to the non-collinear spin structure, the applied DC bias magnetic field produces quenched disorder sites in the cooperative Ising spin matrix and suppresses the spin–phonon coupling. These quench disorders create a dynamic spin correlation, having slow spin relaxation and quick decay time, which additionally contribute to AC susceptibility. The initial conditions and measurement protocol decide the magnitude and sign of this dynamical term contributing to AC susceptibility. It is being suggested that such out-of-equilibrium properties arise from the combined influences of geometric frustration, disorder, and the cooperative nature of spin dynamics exhibited by these materials.

Slow Magnetic Relaxation of Ni(III) Complexes toward Molecular Spin Qubits

AbstractMolecule‐based magnetic materials are promising candidates for molecular spin qubits, which utilize spin relaxation behavior. Various kinds of transition metal complexes with S=1/2 have been reported to act as spin qubits with long spin‐spin relaxation times (T2). However, the spin qubit properties of low‐spin Ni(III) complexes are not as well known since Ni(III) compounds are often unstable. We report here the slow magnetic relaxation behavior and T2 values for three kinds of low‐spin Ni(III) based complexes with S=1/2 under magnetically diluted conditions. [Ni(cyclam)X2]Y (cyclam=1,4,8,11‐tetraazacyclotetradecane) with octahedral structures and [Ni(mnt)2]− (mnt=maleonitriledithiolate) with a square‐planar structure underwent slow magnetic relaxations in the presence of a dc magnetic bias field. From electron spin resonance (ESR) spectroscopy, the Ni(III) complexes exhibited observable T2, indicating that Ni(III) complexes are promising candidates for use as molecule‐based spin qubits.

Examination of Thickness Evaluation of Steel Plate Using DC Bias Magnetic Field by 3-D FEM Analysis Considering Minor Loop Magnetic Characteristics

Thickness evaluation of steel plates and large-diameter steel pipes in various plant structures is considered important for plant safety. In this paper, an electromagnetic inspection method that can evaluate this thickness using a pulsed magnetic field is investigated. When a steady square-wave pulse magnetic field with DC bias is applied from the surface of the steel plate, the relationship between the leakage flux on the steel plate and the plate thickness is investigated. The inspection principle is evaluated by electromagnetic field analysis considering eddy current and minor loop magnetic property of the steel plate and verification experiments. In addition, it is also confirmed that the calculation results considering the hysteresis curve in the steel plate are more useful than those considering only the initial magnetization curve.

Tunable self-biased magnetoelectric effect in magnetization-graded magnetoelectric composites

Magnetoelectric (ME) composites, which are magnetostrictive-piezoelectric composites, have garnered attention for use in various application fields owing to their large ME coupling compared with single-phase multiferroic materials. The maximum ME coupling is observed when an increased DC magnetic bias field is applied, which results in large devices with degraded sensitivity due to electromagnetic noise. To address this problem, a strong self-biased ME composite that generates the maximum ME response in a zero-bias field was proposed in this study. Highly self-biased ME composites were prepared by combining soft magnetic Ni and highly permeable Metglas magnetostrictive layers with a Pb(Mg1/3Nb2/3)O3–PbZrTiO3 piezoelectric single-crystal laminate structure and inducing a magnetization gradient. The maximum ME voltage value without a DC bias field was evaluated to be 4.2 V/cm∙Oe for an MMNPNMM (M: Metglas foil, N: nickel, P: PMN-PZT) structure, which is 625 % higher than that of conventional ME composites. Therefore, the relatively bulky means of the DC-bias application on ME materials could be eliminated, resulting in a simple ME device with a small volume using the magnetization gradient concept.

Магнитоимпеданс в планарной магнитоэлектрической гетероструктуре аморфный ферромагнетик-пьезоэлектрик: модуляция электрическим полем

The magnetoimpedance effect and the converse magnetoelectric effect in a planar heterostructure consisting of mechanically bonded layers of amorphous ferromagnet FeBSiC and piezoelectric lead zirconate titanate are studied. Magnetoimpedance was observed in the frequency range of 0.1-40 MHz and bias dc magnetic field of 0-300 Oe; the maximum magnitude of the effect at a frequency of 10 MHz reached 12%. The converse magnetoelectric effect was observed in magnetic fields of 0-50 Oe; the maximum value of the effect at the structure acoustic resonance frequency of 40 kHz was 1.45 G/(V/cm). Amplitude modulation of the magnetoimpedance by an electric field at the resonance frequency of the structure with a coefficient of ~1∙10─2 is found. Modulation occurs as a result of a combination of the piezoelectricity and magnetostriction of the layers, which leads to a change in the transverse magnetic permeability and the thickness of the skin-layer of the ferromagnet.

Thermally stable multi-directional magnetoelectric based embedded magnetic sensor

Owing to the multifunctional behavior possessed by magnetoelectric (ME) composites, they are sought-after materials for various magnetic field sensing applications. This article proposes a three-directional ME-based embedded magnetic sensor that has been fabricated using the press-fit technique. The employed fabrication method negates the use of epoxy in the ME sensor, thus enabling its use at elevated temperatures in excess of 100 ∘C. The fabricated sensor is tested using an experimental setup capable of producing ac and dc bias magnetic fields in three coordinate directions. Experiments are performed for various dc magnetic field conditions, including x, y, z directions, their simultaneous combinations, and magnetic field aligned at an angle with the sensor. Under all testing conditions, the embedded sensor shows a significantly high output voltage response. Additionally, the effect of the magnetic field generated by the double magnet system and single magnet system on the sensor performance has also been demonstrated, wherein the embedded sensor is observed to be marginally affected by magnetic field due to the presence of only one magnet. Finally, quasi-static ME measurements are performed at elevated temperatures up to 100 ∘C, and it is observed that the novel embedded sensor has reliable sensing capabilities in aggravated thermal environments even in excess of 100 ∘C. Thus, the proposed three-directional embedded magnetic sensor offers reliable response under all conditions of magnetic field and temperature and can thus be a reliable alternative for the traditionally used layered-based counterparts.

Magneto electric sensor based on cantilever coated galfenol/ AlN structure

Ultrasensitive magnetic field sensors based on magnetoelectric (ME) structures have many applications in bio-magnetic sensors and magnetoencephalography (MEG) scanners. Enhance the sensitivity, limit of detection and main frequency of these sensors need simulation process by accurate methods such as finite element method (FEM). To get good sensitivity and efficient benefit, we use a cantilever-type composite structures including galfenol alloy as a magnetostrictive layer and AlN as a piezoelectric layer. Galfenol is an alloy of iron and gallium and its Fe0.83Ga0.17 structure has a high magnetostriction coefficient and can be used as a thin film. This simulated sensor can measure an AC magnetic field with field resolution in the order of 1pT. This sensor has the best performance in the bias DC magnetic field of 2.3 mT and resonance frequency of 2521.8 Hz and has a magnetoelectric coefficient of 4865 (V/cm.Oe).

Magnetoelectric coupling at room temperature in LaTiO3/SrTiO3 heterojunctions

This work focuses on LaTiO3 (LTO) thin films synthesized by the polymeric precursor method and deposited onto SrTiO3 (STO) substrates via spin coating. The results show interesting coexisting ferromagnetic (Mr≈2.85 emu/g) - ferroelectric (Pr≈18.5 μC/cm2) responses at room temperature. Magnetoelectric coupling can be observed under DC bias magnetic field (14 V/cm.Oe), and its dielectric constant is affected by the coupling between magnetic and electric dipoles at room temperature as well as oxygen octahedra distortion along direction a. Little film-substrate mismatch significantly influences the system dielectric properties. Our results suggest the possibility to induce ferromagnetic/ferroelectric phases in the LTO/STO heterojunctions using an electric/magnetic field, respectively, due to the magnetoelectric coupling. This study also helps comprehend oxygen vacancy dynamics when applying a tensile strain or an external electric field, which is fundamental for actuators, switches, magnetic field sensors, and new types of electronic memory devices.

Ultra-low anisotropy magnetoelectric sensor in ferrite/piezoelectric toroidal composites

An ultra-low anisotropy magnetoelectric (ME) magnetic field sensor consisting of strictly concentric toroidal nickel-zinc ferrite/piezoelectric composite with toroidal solenoid was developed, and its sensitivity and resolution under different angles of planar AC/DC magnetic field were systemically characterized. The experimental results demonstrate that the induced voltage output strength was constant along the angles between the ME magnetic sensor and the planar DC/AC magnetic field due to toroidal structure had ultra-low shape-induced anisotropy. Consequently, for the DC case its sensitivity and resolution could reach about 15 mV/Oe and 2 × 10−7T under a low excitation of ƒ=111.42 kHz circumferential AC magnetic field, respectively. Correspondingly, for the AC case its sensitivity and resolution could reach about 56.9 mV/Oe and 7 × 10−9T under a 2.25Oe circumferential DC bias magnetic field. These findings provided more flexibility of the device design for weak magnetic field detection.

Influence of the conductivity of the magnetoelectric composites electrode under resonance frequency and its validation by laser vibrometer system

Magnetic sensor based on functional dielectric with high-efficiency energy property is projected to stimulate technological advancement in the fields of energy internet, power engineering materials, energy harvesting and storage, touchless human–machine interface, and magnetoreception for artificial intelligence (AI). At present, the research and development of hypersensitive magnetic sensors remain extraordinarily challenging. The effects of magnetoelectric (ME) composite electrodes with different conductivities and their electromechanical resonance frequency of Metal/PZT/Metal laminates were investigated in this paper. The results of calculations and experiments showed that the magnetoelectric coupling in the magnetoelectric composite (Metal/PZT/Metal) was mostly caused by the piezoelectricity effect in the radial direction and Ampere force under DC bias magnetic fields. According to the radial strain measurement, it can be further indicated that the capping layer with high conductivity produced a larger magnetoelectric voltage at the range of resonance frequency. Therefore, the ME voltage coefficient of the silver electrodes was higher than that of the gold electrodes, and they were 77.8 mV/(cm Oe) and 58.3 mV/(cm Oe) at a DC magnetic field of 3000 Oe, respectively. The ME coupling in the ME composite was mostly connected to the piezoelectricity effect and Ampere force, as well as the conductivity of the electrode layer of the ME composite. The optimization of the electrode structures of magnetoelectric composites provides a vital reference for the development of energy storage, information storage and sensing technology in new power systems.

Unity-order magnetochiral effects exhibited by a single metamolecule.

A numerical study predicts that a single metamolecule with magnetism and chirality has giant magnetochiral (MCh) effects at microwave frequencies. The magnetism is provided by the ferromagnetic resonance of ferrite under dc bias magnetic fields, while the chirality is provided by the spiral arrangement of dielectric cubes with Mie resonance. The dielectric and magnetic resonances interfere in the metamolecule, resulting in a two-order of magnitude enhancement of the MCh effect compared with that reported in previous studies. This prediction is verified experimentally. A unity-order directional difference in the refractive index caused by the MCh effect is also demonstrated. This study is a significant milestone in the practical use of the MCh effect.

Comparative study of energy harvesting performance of magnetoelectric composite-based piezoelectric beams subject to varying magnetic field

Magnetostrictive materials with good mechanical properties can effectively convert the alternating magnetic energy in the environment into mechanical vibrations via the magnetostriction effect. Few studies exist on the working mechanism and the effect on the performance of magnetoelectric (ME) composite components in complex magnetic field environments. This work first investigated the magnetoelectric conversion process of two types of ME composite components under the action of DC magnetic field alone and the DC–AC coupled magnetic field using COMSOL simulation. When coupled with AC magnetic field, the DC bias magnetic field can enhance the magnetization by AC field for the Galfenol alloy component and negate the magnetization for the nickel component. Then, two types of ME composite components made from Galfenol alloy and nickel bonded with piezoelectric transducer are prototyped and tested for energy harvesting. The experimental results show that, under a harmonic excitation of 3 Oe magnetic field, the DC bias magnetic field of 120 Oe can increase the open-circuit voltage of the Galfenol alloy based harvester from 0.495 V to 10.68 V, and the output power from 1.6 μW to 42 μW by 2525% with a matched external resistance of 50 kΩ. Under the same amplitude of AC magnetic field, the DC bias magnetic field increases the open-circuit voltage of the nickel based harvester from 0.117 V to 0.837 V, and the output power from 2.6 μW to 23 μW by 784.6% with a matched resistance of 1000 kΩ. The findings of this work reveal the effect of the coupled magnetic field for the magnetostriction for different magnetostrictive materials and provide the guideline for the design of magnet electric energy harvesters.

Optimal magnetoelectric coupling performance of Terfenol-D/PZT composites in resonance state under bias magnetic field

Laminated magnetoelectric (ME) composites with various thickness ratios were optimized, fabricated and experimentally investigated in this work. The Terfenal-D/PZT specimens with optimal thickness ratio between the magnetostrictive phase and piezoelectric phase, and two other values were tested for their ME coupling performance. The coupling voltage output increases linearly with the increase of DC bias magnetic field. The ME voltage coefficient increases more than 100 times in the resonance state for the optimal laminate. The DC bias magnetic field affects the ME voltage coefficient significantly, and also has little effect on the resonant frequency. The strength of AC magnetic field also slightly affects the ME voltage coefficient in resonance state, but does not affect the resonant state under which the same DC magnetic field is required. The experimental results can help understand the coupling performance of ME composite under bias magnetic field and prompt the application of ME devices.

Gyro-magnetically induced transparency and opaqueness at microwave frequency

The ferrite’s permeability is a second-rank tensor, depending on the saturation magnetization, the dc bias magnetic field, and the operating frequency. The permeability tensor can be manipulated by adjusting the applied bias magnetic field, changing the wave’s propagating properties. Here we proposed a coaxial structure with a toroidal ferrite. At frequencies around 2.45 GHz, the incident wave can transmit or reflect by merely adjusting the bias magnetic field. The coaxial-ferrite structure can serve as a switch. The variation of 62 Oe of the bias magnetic field in the experiment changed the device’s state from transparent to opaque. The derived equations explain the underlying physics, which provides a solid ground for designing similar switches at other frequency bands.