Magnetic Field Modulation Research Articles

Customized modulation on plasma uniformity by non-uniform magnetic field in capacitively coupled plasma

A two-dimensional fluid model based on COMSOL Multiphysics is developed to investigate the modulation of static magnetic field on plasma homogeneity in a capacitively coupled plasma (CCP) chamber. To generate a static magnetic field, direct current is applied to a circular coil located at the top of the chamber. By adjusting the magnetic field’s configuration, which is done by altering the coil current and position, both the plasma uniformity and density can be significantly modulated. In the absence of the magnetic field, the plasma density exhibits an inhomogeneous distribution characterized by higher values at the plasma edge and lower values at the center. The introduction of a magnetic field generated by coils results in a significant increase in electron density near the coils. Furthermore, an increase in the sets of coils improves the uniformity of the plasma. By flexibly adjusting the positions of the coils and the applied current, a substantial enhancement in overall uniformity can be achieved. These findings demonstrate the feasibility of using this method for achieving uniform plasma densities in industrial applications.

New insights into magnetic fields selective enhancement of ferrate(Ⅵ) combined with hydrogen peroxide for removal of organic pollutants

A magnetic field (MF) was applied to selectively enhance the generation of reactive species in a ferrate (Fe(VI)) water treatment system, effectively mitigating the limitations associated with the selective oxidation of Fe(VI) for organic matter. An MF was introduced into Fe(VI) and Fe(VI)/H2O2 systems, and a significant difference was observed in its enhancement of the removalefficiency of different types of contaminants. The results of radical scavenging experiments, high-valent Fe inhibition experiments, and methyl phenyl sulfoxide (PMSO) chemical probe experiments indicated that the MF promoted the production of Fe(V)/Fe(IV) in the Fe(VI) system and ·O2– in the Fe(VI)/H2O2 system, which modulated the generation of active species. Subsequently, by monitoring the change in product quantities during the decomposition of Fe(VI) and considering the theory of paramagnetism, it was hypothesized that the MF weakened the pathways for further self-reduction of Fe(V)/Fe(IV) in the Fe(VI) system and strengthened these pathways in the Fe(VI)/H2O2 system: Fe(IV) → Fe(III) → ·O2−. Furthermore, the systems enhanced by the MF were more resistant to partial anions and environmental interference in water quality experiments. This suggested that the MF modulation method may have significant potential for practical applications.

Two-electron conduction band of a graphene quantum dot and coherent spin manipulation

To get a carbon-based qubit, we pay attention to the two-electron conduction band of a graphene quantum dot (GQD) in the presence of an external magnetic field and an extrinsic Rashba spin-orbit interaction (SOI). To help understand the formation of the two-electron spectra, we first calculate the tight-binding (TB) spectra. There exist the sensitivity of the conduction band to magnetic fields and the mixing of spin states induced by a Rashba SOI. The two factors inspire the study of the magnetic-field modulation of the conduction band for realizing a spin qubit. We present the method for calculating the electronic structure of a few-electron GQD. The roles of the Coulomb interaction and the Rashba SOI in the two-electron conduction band are investigated. The Coulomb interaction contributes to a singlet-triplet level crossing and the Rashba SOI leads to a singlet-triplet mixing. The fast initialization and coherent manipulation of spin states are demonstrated by the magnetic control of singlet-triplet splitting.

Triboelectric–Electromagnetic Hybrid Energy Nanogenerator with Variable‐Frequency Effect Inspired by Magnetic Gears for Efficient Use of Low‐Speed Flow Energy

In the macrocontext of a low‐carbon and energy‐efficient economy, the rise of new energy vehicles is expected to replace traditional fuel vehicles. However, with the increasing number of new energy vehicles, the source of electricity for charging facilities faces new challenges. This study proposes a triboelectric–electromagnetic energy hybrid nanogenerator (VF‐TEMG) with a variable‐frequency effect inspired by an axial magnetic gear. The unit consists of one triboelectric nanogenerator (TENG) unit and two electromagnetic generator (EMG) units. The TENG unit employs a ternary dielectric structure to achieve kilovoltage output and reduce torque. Moreover, charging efficiency is enhanced using a mixture of high voltage from the TENG and EMG high current. Using the magnetic field modulation principle, the magnetic poles, which are produced by the low‐speed rotor permanent magnets, are modulated by a pole‐modulating piece into a magnetic pole harmonic equal to the number of pairs of high‐speed rotor permanent magnets. Consequently, when the low‐speed rotor starts to rotate, it drives the high‐speed rotor to rotate at high speed, thereby achieving variable‐frequency motion. This work establishes the theoretical and experimental basis for harvesting and effectively utilizing green energy based on frequency conversion.

Magnetic field modulation of high spin hexa-coordinated iron sites to enhance catalytic activity

The external alternating magnetic field (AMF) strategy is the most promising research topic to solve the bottleneck of catalyst activity enhancement. However, the mechanism between the arrangement of the spin electrons under the AMF and the catalytic activity enhancement for water splitting is still unclear. Herein, we synthesize Fe3O4@CNTs heterostructure as a research model and resolve the mechanism by system theoretical analysis and in-situ Raman characterization. The multiple orbital interactions of σ(dz2, pz, s) and π(dxz-px, dyz-py) promote the hexa-coordinated Feoct for both the reductive HER and oxidative OER processes. The AMF excites the transition from low to high spin configurations of the Feoct sites, which accelerates charge transfer of unpaired d electrons and optimizes adsorption and desorption interactions to intermediates during the reaction processes, resulting in a significant enhancement of the electrocatalytic activity (HER: 32 mV at 10 mA cm−2, OER: 179 mV at 100 mA cm−2).

Strain-induced multi-band spin-wave logic gate based on alligator-type magnonic crystal/PZT structure

Here, we report the results of strain-controlled spin-wave propagation regimes in a double-period multiferroic structure. It consists of an alligator-type magnonic crystal with a period of 250 μm and a piezoelectric layer, featuring a periodic counter-pin-type electrode system with a period of 125 μm. Employing microwave measurements, we acquired the transmission and dispersion of spin waves under various external electric field configurations applied to the piezoelectric layer. The formation of bandgaps in the magnon spectrum and the variation of the spin-wave transmission when altering the configurations of the external electric field are demonstrated. A finite element method reveals that the combination of the non-uniformity in the initial internal magnetic field of the magnonic crystal, which is caused by the presence of periodic alligator-type regions, together with elastic deformations, heightens the amplitude of the modulation of the internal magnetic field. Micromagnetic modeling has demonstrated that this modulation enhancement results in the variation of the spin-wave transmission at the frequency of the magnonic bandgap center of the magnonic crystal. The proposed design of the reconfigurable magnonic crystal creates a condition for the nucleation of the spin-wave bandgap, with further enhancement of the spin-wave reflection from the periodic grating induced by strain. We demonstrate the potential use of the proposed device as a multi-band NAND/NXOR spin-wave based logic gate.

Formation of magnetic double emulsions under steady and variable magnetic fields from a 3D-printed coaxial capillary device

BackgroundDouble emulsions (DEs) have attracted researchers’ attention to be utilized as a promising platform in biomedical and chemical applications. Several actuation mechanisms have been proposed for the generation of DEs. The conventional DE formation approaches (e.g. two-stage emulsification) suffer from low monodispersity. The electric actuation (i.e. coaxial electrospray technology) has been demonstrated as a controllable method for the DE formation, while the capability of magnetic actuation has not been studied yet. ResultIn the present study, the generation of ferrofluid double emulsions (FDEs), made from water-based ferrofluid as a core and oil as a shell, under the magnetic actuation of a permanent magnet with a steady magnetic field and an electromagnet with DC and pulse width modulation (PWM) magnetic fields was investigated with a simple controllable setup fabricated using 3D printing. The effect of various parameters affecting the FDE formation, such as the fluid flow rates, the magnetic field type, the magnetic flux density, and the PWM frequency and duty cycle, on the FDE formation characteristics, including the inner and outer equivalent diameters, and the formation frequency was studied. Under the steady magnetic field, two regimes of the FDE formation were identified: inertia-dominated and magnet-dominated. SignificanceWireless power-free magnetic actuation provides better control over the FDE formation, enhancing this process by increasing the FDE formation frequency with high monodispersity. The PWM magnetic field offers excellent controllability over the FDE formation with low-volume or no, in some cases, satellite droplets by tuning the PWM frequency and the duty cycle.

Nernst coefficient of Pt by non-local electrical measurement

The Nernst effect describes a linear relationship between orthogonal components of a magnetic field, a temperature gradient, and a resulting transverse electric field. A non-local electrical measurement, where injection and detection are physically separated on the specimen, serves as a versatile and effective platform for measuring spin and thermal effects due to the avoided interference with a charge current directly. Here, we quantify the Nernst coefficient of Pt, a common material for spin injection in non-local geometries, by a non-local electrical measurement under modulated temperature and magnetic field and finite element analysis for modeling heat transfer. We determine the Nernst coefficient of Pt from room temperature (8.56 nV K−1 T−1) to 10 K (29.3 nV K−1 T−1). Beyond the quantification of the Nernst coefficient, our results show that careful consideration of the thermal properties of the thermal sink and electrode materials is needed when making an interpretation of non-local electrical measurements.

Research Advances in Magnetic Field‐Assisted Photocatalysis

AbstractSolar‐to‐chemical energy conversion thorugh photocatalytic technology has garnered significant attention due to its potential for clean hydrogen pro duction, pollutant degradation, and carbon dioxide reduction. However, its relatively low solar‐to‐chemical conversion efficiency hinders its industrial development. External fields have currently emerged as a supplementary energy source to augment the overall catalytic efficiency. Recently, the photocatalytic performance has been considerably enhanced through magnetic field modulation, which promotes the separation and transfer of photoexcited charge carriers. This article systematically reviews the recent research progress of magnetic field–assisted photocatalysis, discussing phenomena such as the negative magnetoresistance effect, Lorentz force, and spin polarization. It comprehensively analyzes the effect of magnetic fields on critical processes in photocatalysis: light absorption, charge‐carrier separation, and surface reactions. In particular, this review focuses on the spin‐relaxation mechanism, explains how the electron lifetime is extended through spin polarization, and proposes design strategies for spin‐polarized materials. Finally, this review discusses the challenges and potential opportunities for enhancing photocatalytic efficiency. The ultimate objective of this review is to offer notable theoretical and experimental insights that can guide the design and development of high‐performance photocatalysts and photocatalytic systems.

Periodic magnetic modulation enhanced electrochemical analysis for highly sensitive determination of genomic DNA methylation

DNA methylation aberrations have a strong correlation with cancer in early detection, diagnosis, and prognosis, which make them possible candidate biomarkers. Electrochemical biosensors offer rapid protocols for detecting DNA methylation status with minimal pretreatment of samples. However, the inevitable presence of background current in the time domain, including electrochemical noise and variations, limits the detection performance of these biosensors, especially for low concentration analytes. Here, we propose an ultrasensitive frequency-domain electrochemical analysis strategy to effectively separate the weak signals from background current. To achieve this, we employed periodic magnetic field modulation of magnetic beads (MBs) on and off the electrode surface to generate a periodic electrochemical signal for subsequent frequency-domain analysis. By capturing labeled MBs with as low as 0.5 pg of DNA, we successfully demonstrated a highly sensitive electrochemical method for determination of genome-wide DNA methylation levels. We also validated the effectiveness of this methodology using DNA samples extracted from three types of hepatocellular carcinoma (HCC) cell lines. The results revealed varying genomic methylation levels among different HCC cell lines, indicating the potential application of this approach for early-stage cancer detection in terms of DNA methylation status.

MEMS miniaturized low-noise magnetic field sensor for the observation of sub-millihertz magnetic fluctuations in space exploration

The objective of this paper is to show that, using magnetic field modulation with a MEMS resonator, it is possible to reduce the noise floor of a commercial Tunneling Magnetic Resistance by one order of magnitude, in the ultra-low frequency range. Low noise at this frequency range is a strong requirement in planetary or space exploration missions like LISA (Laser Interferometer Space Antenna), where the observed gravitational waves will be in the 0.1 mHz to 0.1 Hz range. It will be shown that the noise spectral amplitude after demodulation from 0.1 mHz to 100 mHz is well below the 100 nT/Hz requirement for the future space-borne gravitational wave detector LISA – that we take as reference – being at 20 nT/Hz at 0.1 mHz, and reaching an average 1.5nT/Hz at higher frequencies, from 100 mHz to 1 Hz.

A Novel Counter-Rotating AFPM Machine Based on Magnetic-Field Modulation for Underwater Propulsion System

The underwater propulsion system (UPS) with two counter-rotating propellers is very popular now. In tradition, it needs two electric machines or additional gears, which greatly increases the volume and weight of the system. Therefore, a novel counter-rotating axial-flux permanent magnet (AFPM) machine based on magnetic-field modulation (MFM) for the UPS is proposed. It contains a more pole (MP) rotor and a less pole (LP) rotor on two sides. The MFM is achieved through the split teeth on the stator. Based on the MFM, the two rotors can rotate in opposite directions. The principle of MFM and the relationships of rotary speeds between two rotors are analyzed. Furthermore, the effects of split tooth shape and dimensions on the performances of the proposed machine are also evaluated. The triangular skew fan-shaped split teeth are adopted in the counter-rotating AFPM machine. Finally, the prototype is manufactured and an experiment is conducted to validate the performance. The results show the consistency of analysis and experiment.

3D Host Design Strategies Guiding “Bottom–Up” Lithium Deposition: A Review

AbstractLithium metal batteries (LMBs) have the potential to be the next‐generation rechargeable batteries due to the high theoretical specific capacity and the lowest redox potential of lithium metal. However, the practical application of LMBs is hindered by challenges such as the uncontrolled growth of lithium dendrites, unstable solid electrolyte interphase (SEI), and excessive volume change of Li metal. To solve these issues, the design of high‐performance lithium metal anodes (LMAs) with various 3D structures is critical. Targeting at realizing the “bottom–up” Li deposition to fully utilize the 3D architecture, in recent years, strategies such as gradient host materials construction, magnetic field modulation, SEI component design, and so on have attracted intensive attention. This review begins with a fundamental discussion of the Li nucleation and deposition mechanism. The recent advances in the aspects of construction strategies and modification methods that enable the “bottom–up” Li deposition within advanced 3D host materials, with a particular emphasize on their design principles are comprehensively overviewed. Finally, future challenges and perspectives on the design of advanced hosts toward practical LMAs are proposed.

A Magnetic-Geared Machine With Improved Magnetic Circuit Symmetry for Hybrid Electric Vehicle Applications

Magnetic-geared machine (MGM) has been widely investigated as the power split device for hybrid electric vehicles with the inherently high-integration of multi-mechanical ports. It is revealed that the magnetic circuits of armature winding in MGM are essentially asymmetrical for different phases under the magnetic field modulation effect. This inevitably results in unbalanced phase back electromotive force (EMF) waveforms, severe torque ripples, acoustic noise, and difficulty for precise control. To alleviate the asymmetry problem, a generic winding design model is presented for MGMs in this paper, which allows for consideration of all potential winding configurations. Firstly, a novel back EMF harmonic factor is proposed to account for both the harmonic content and asymmetric level in MGM. The genetic algorithm (GA) is further employed to optimize the winding in terms of minimizing the back EMF harmonic factor, armature magnetomotive force harmonic contents, and phase winding resistance. The proposed winding layout exhibits superior filtering capability for three-phase asymmetric magnetic field harmonics. As compared with the conventional integral-slot distributed winding, the MGM with the proposed winding exhibits improved back EMF waveform symmetry, suppressed torque ripple, and reduced core losses. Finally, an experimental prototype is manufactured to validate the effectiveness of asymmetric magnetic field suppression for MGMs. The results show the investigated winding design method is an effective solution to the asymmetric issue of MGMs, paving the way to research opportunities for further improvements.

Transformation of topological states in three-dimensional photonic crystal under magnetic field modulation

The realization and modulation of high-order topological states in three-dimensional (3D) photonic crystals (PCs) hold great significance for practical applications in optical communication, optical information processing, and optical computing. However, they have encountered technological challenges due to the difficulty in achieving a complete bandgap in 3D PCs. To address this issue, we introduce a design for a 3D PC based on the Su–Schrieffer–Heeger (SSH) model that exhibits distinctive topological surface states, topological hinge states, and topological corner states. Furthermore, these three types of topological states can be interconverted through the modulation of magnetic field because the topological states are closed and extremely sensitive to the structure, which are modulated by the magnetic field. This intriguing capability holds potential applications in the manipulation of optical flow, optical signal storage, and magnetic field sensors.

Magnetic field modulation effect on photoelectric effect and its explanation in BiFe0.9Ni0.1O3/n-Si multiferroic heterojunction

This paper reports a heterojunction laminate consisting of Ni doped BiFeO3 thin film and n-type single crystal silicon semiconductor, in which the repeatable modulation effect on the photoelectric properties were achieved by applying external magnetic fields. More obviously, the response of photocurrent and photovoltage to the magnetic field is perfectly linear. This functional effect of sensing is mainly related to the guidance of the magnetic field to the photogenerated carrier transfer process in the heterojunction. The linear relationships between magnetic field and photocurrent, magnetic field and photovoltage have been proved through the derivation of the formulas. The heterojunction perfectly combines the functions of the sensor and the controller to reflect both the intensity of the magnetic field and the intensity of the light in the environment. This work provides an alternative and facile way to realize the multi-degree of freedom control for electrical signal and practicability of multifunctional devices.

Bifurcation to complex dynamics in largely modulated voltage-controlled parametric oscillator

An experimental demonstration of a parametric oscillation of a magnetization in a ferromagnet was performed recently by applying a microwave voltage, indicating the potential to be applied in a switching method in non-volatile memories. In the previous works, the modulation of a perpendicular magnetic anisotropy field produced by the microwave voltage was small compared with an external magnetic field pointing in an in-plane direction. A recent trend is, however, opposite, where an efficiency of the voltage controlled magnetic anisotropy (VCMA) effect is increased significantly by material research and thus, the modulated magnetic anisotropy field can be larger than the external magnetic field. Here, we solved the Landau–Lifshitz–Gilbert equation numerically and investigated the magnetization dynamics driven under a wide range of the microwave VCMA effect. We evaluated bifurcation diagrams, which summarize local maxima of the magnetization dynamics. For low modulation amplitudes, the local maximum is a single point because the dynamics is the periodic parametric oscillation. The bifurcation diagrams show distributions of the local maxima when the microwave magnetic anisotropy field becomes larger than the external magnetic field. The appearance of this broadened distribution indicates complex dynamics such as chaotic and transient-chaotic behaviors, which were confirmed from an analysis of temporal dynamics.

Winding-MMF-based design and investigation of dual-winding hybrid-tooth vernier permanent magnet motor with reduced torque ripple and improved power factor

In this paper, in order to further reduce torque ripple and improve power factor, a new vernier permanent magnet motor is proposed, in which the design concept of dual-winding hybrid-tooth configuration is incorporated. In order to clarify motor torque ripple and power factor, the winding-magnetomotive-force-based design and analysis method is proposed, in which harmonic characteristics are considered as key factors during the magnetic field modulation process. The relationship between harmonics generated by winding MMF, torque ripple, and power factor are investigated. In addition, the split-tooth vernier permanent magnet motor is also investigated as a referenced motor. Detailed comparisons between the DWHT-VPM motor and ST-VPM motor are carried out, including air gap magnetic field, torque, and power factor. Both theoretical and simulation results verify the reasonability of the proposed DWHT-VPM motor, and the effectiveness of the proposed winding-MMF-based analysis method, which provide a new potential research path for the design and analysis of flux modulation motors.

Optical 2-bit nanoscale multiplier using MIM waveguides.

The plasmonic 2-bit multiplier is designed at a 1310nm operating wavelength and a 65% transmission threshold (T t h r e s h o l d ). Using the finite element method (FEM) with the COMSOL version 15 software, we simulated the suggested 2-bit multiplier, based on the principle of the constructive and destructive interferences between the input light waves. The results were delivered in graphs containing the transmission level (T) versus an operating wavelength range between 800 and 2000nm, magnetic field distribution, modulation depth (MD), contrast ratio (CR), and insertion loss (IL). The modulation depth was 99.91%, the CR was 14.75dB, and the IL was -1.2d B.

Oscillatory nonlinear thermal instability in nanoliquid under gravity modulation within Hele-Shaw cell

Abstract The effect of gravity-field modulation is investigated in a nano liquid-confined Hele-Shaw cell. This study aims to finish the work described in (S. N. Rai, B. S. Bhadauria, K. Anish, and B. K. Singh, “Thermal instability in nanoliquid under four types of magnetic-field modulation within Hele-Shaw cell,” Int. J. Heat Mass Transfer, vol. 145, no. 7, p. 072501, 2023) for oscillatory convection. The existence of the complex Ginzburg-Landau equation (CGLE) model is constrained by the requirement ω 2 > 0. The magnetic fluxes in the Hele-shaw cell are governed by CGLE with g-jitter. The quantity of heat-mass transfer is examined in the presence of a g-jitter. In addition, the findings of our research on transport analysis indicate that oscillatory mode is preferable to stationary mode. It is also found that the gravity-driven Hele-Shaw layer has lower transport properties. Further, the transport analysis is compared to previous research and shown to have improved results.