Magnetic Bias Research Articles

Improved path following for autonomous marine vehicles with low-cost heading/course sensors: comparative experiments

By overcoming constraints of low-cost sensors equipped on the autonomous marine vehicle (AMV), the classic path following approaches based on heading autopilot and course autopilot are improved to enhance the following accuracy of AMV, respectively. For the heading autopilot, adaptive line-of-sight (ALOS) is proposed to compensate for the generalized sideslip including the actual sideslip angle and the magnetic compass bias. For the course autopilot, extended Kalman filter (EKF) is employed to fusion the position and yaw angular rate to obtain the more precise and stable course, so as to substitute the unreliable course feedback from the satellite navigation receiver in cases of low speed and non ideal positioning. The performance and characteristics of both improved schemes are summarized through comparative experiments conducted on a low-cost AMV. Compared with the classic path following method, the straight line path following accuracy of the heading autopilot with generalized sideslip compensation and the course autopilot with EKF feedback are improved by 78.3% and 85.8% respectively. The circular path following accuracy are improved by 61.8% and 66.7% respectively. Engineers can choose the path following methods flexibly based on the hardware configuration, working environment and path type of the AMV to improve the following accuracy.

Theoretical method for the analysis and design of tunable terahertz graphene-based Faraday polarization rotators.

A theoretical method is presented that facilitates the analysis and design of graphene-based tunable terahertz polarization rotators. Most previous designs are based on a three-dimensional (3-D) full-wave electromagnetic simulation; thus, it is time-consuming to get well-tuned structural parameters. Using the proposed method, the transmission response of the polarization rotator is directly calculated for a given set of structural parameters. Hence, the need of the electromagnetic simulation is lifted. The accuracy of the proposed method is rigorously validated, as excellent agreement between the theoretical and simulation results is observed. Using the method, a rotator of 12THz central frequency with a small magnetic bias field of 0.5T and a small unit cell of 0.5 by 0.5(µm)2 is designed. It is shown that the center frequency can be increased to any desired frequency, without the need of a large magnetic bias, by reducing the unit cell size. The method presented in this work can be extended for the analysis and design of other tunable terahertz nonreciprocal devices, such as isolators, circulators, phase shifters, and switches.

An exotic uniaxial hexagonal ferrite with narrow self-biased ferrimagnetic resonance linewidths: Cu 18H hexaferrite

Traditional circulators utilize ferrites with low magnetocrystalline anisotropy driven by external magnetic bias fields. Hexagonal ferrites with a strong uniaxial anisotropy enable self-biased circulators, significantly reducing their volume, weight, and cost. Here, a unique uniaxial hexaferrite, Cu 18H hexaferrite, with narrow ferrimagnetic resonance (FMR) linewidth at zero magnetic bias field is reported. The temperature-dependent magnetic hysteresis loops show a significant decrease in coercivity from cryogenic to room temperature, indicating a transition from the hard to soft magnetic state. The crystallographic texture ensures a squareness ratio greater than 0.65 and leads to a strong internal bias field induced by the aligned easy-magnetization axes. Owing to the highly dense and oriented crystallites, the zero-field FMR exhibits excellent linewidths of ∼270–320 Oe, which are lower than those of most hexaferrites reported at the Ka-band. These results reveal the great potential of Cu 18H hexaferrite as a low-loss microwave ferrite used for self-biased circulators.

Nonlinear magnetoelectric effect in a ring composite heterostructure

Objectives. The relevance of the study of magnetoelectric (ME) effect in ring ferromagnetic–piezoelectric heterostructures is due to the possibility of creating various ME devices having improved characteristics. A detailed investigation of the nonlinear ME effect in a ring composite heterostructure based on lead zirconate titanate (PZT) piezoceramics and Metglas® amorphous ferromagnetic (FM) alloy under circular magnetization is presented.Methods. The ME effect was measured by the low-frequency magnetic field modulation method. Excitation alternating- and constant magnetic bias fields were created using toroidal coils wound on a ring heterostructure for circular magnetization of the FM layer.Results. When excited with circular magnetic fields in a non-resonant mode, the ME ring heterostructure generates a nonlinear ME voltage of higher harmonics. The field and amplitude dependencies of the first three ME voltage harmonics were investigated. ME coefficients were obtained for the linear ME effect α(1) = 5.2 mV/(Oe·cm), the nonlinear ME effect α(2) = 6 mV/(Oe2·cm), and α(3) = 0.15 mV/(Oe3·cm) at an excitation magnetic field frequency f = 1 kHz. The maximum amplitudes of the 1st and 3rd harmonics were observed at a constant bias magnetic field H ~ 7 Oe, which is almost two times smaller than in planar PZT–Metglas® heterostructures.Conclusions. A nonlinear ME effect was observed and investigated in a ring heterostructure based on PZT piezoceramics and Metglas® amorphous FM alloy. Due to the absence of demagnetization during circular magnetization of the closed FM layer, nonlinear ME effects are detected at significantly lower amplitudes of the exciting alternating and constant bias magnetic fields as compared to planar heterostructures. The investigated ring heterostructures are of potential use in the creation of frequency multipliers.

A nonlinear dynamic hysteresis model with magnetic-thermal-stress-fluid coupling effect for hydraulically amplified magnetostrictive actuator

The hydraulic amplified magnetostrictive actuator (HAMA) has the advantages of large output displacement and fast response speed, but it is affected by coupling effects of electromagnetism, temperature, prestress, fluid, and other factors. In order to accurately analyze its performance, it is necessary to establish a nonlinear dynamic model including the coupling effect of eddy current loss, hysteresis, prestress, temperature, and fluid. First, a nonlinear magnetostrictive model including the magnetic-thermal-stress coupling effect is developed from the perspective of free energy. Based on the conservation of magnetization energy, the influence term of the eddy current is added to the anhysteretic magnetization and a nonlinear dynamic magnetization model including the effect of eddy current is developed. Based on the fluid transmission theory and HAMA’s equivalent dynamic model, a dynamic model of HAMA was established. Finally, a nonlinear dynamic hysteresis model with the magneto-thermal-stress-fluid coupling effect of HAMA is developed, and the performance of HAMA was studied by simulation and experiments. The results show that the output displacement is from −58.2 to 58.2 µm when the control current changes from −2 to 2 A, and the simulation results have a better agreement with the experiment result when the frequency is less than 200 Hz.

Magnetic bias field driven ferro- and antiferromagnetic semiconductors as double negative media for microwave and terahertz ranges

In this work, a theoretical study of the backward electromagnetic waves (BEMWs) existing in the bigyrotropic left-handed media controlled by a magnetic bias field is presented. The bigyrotropic media are both longitudinally and transversely magnetized ferromagnetic (FM) or antiferromagnetic (AFM) semiconductors (SCs) with electric and magnetic loss. It is shown that the BEMWs are observed both in the microwave and terahertz frequency ranges, in which the effective material parameters of the FM or AFM SCs are double negative. We demonstrate the control of the BEMW dispersion characteristics not only by changing the magnetic bias field direction and strength, but also by variation a material magnetization and thickness, an electron concentration in a solid-state plasma, as well as the electric and magnetic loss.

Controlled Polarized Optical Excitation Method on Ensembles of Nitrogen‐Vacancy Centers in Diamonds

AbstractCrystal axes must be distinguished in vector magnetic measurements of ensemble nitrogen‐vacancy (NV) centers in diamonds. However, achieving crystal axes distinction in confocal systems without a magnetic bias field is challenging. Thus, a controlled polarized optical excitation method to overcome this problem is proposed. The polarization angle of the excitation beam can be adjusted in free space using an optical pen for higher controllable degrees of freedom. Compared to previous optical excitation methods, the proposed method improves the maximum suppression by 19.2% and the maximum excitation by 42.4%. Moreover, the proposed method has a decoupling effect on NV axis resonances with a similar change trend. This method can easily replace existing optical excitation methods in NV measurement systems and is a powerful tool for ensembles of NV centers’ vector measurements without relying on magnetic bias fields.

Spontaneous exchange bias and magnetic characteristics in Ni50Mn35Sn10V5 Heusler alloy

The magnetic state transformations and exchange bias effect of Ni50Mn35Sn10V5 shape memory alloy have been studied systematically. Curie transformation and martensitic transformation of Ni50Mn35Sn10V5 alloy were observed close to room temperature. Static and dynamic magnetic measurements were performed to reveal two magnetic states of the martensitic phase, with superparamagnetic and superspin glass. In addition, two exchange bias effects were observed at low temperatures, which can be attributed to the interaction of antiferromagnetism with both ferromagnetism and superferromagnetism.

Magnetic Flux Bias Compensation Based on Voltage Injection Method With an Auxiliary DC/DC Converter

DC bias will make the transformer core saturated, causing local overheating and insulation materials aging. Therefore, it is great of significance to study the suppression of DC bias in transformers. In this paper, a magnetic compensation scheme of DC bias based on a hybrid transformer (HT) integrated an auxiliary DC/DC converter is proposed. Firstly, a compensation mechanism is established by designing a novel HT topology structure, which lays the magnetic circuit foundation of DC bias compensation. Secondly, the mathematical model of transformer DC bias is established, and the DC compensation amount of HT is derived. A transient simulation model of three-phase HT is established by the finite element model, and the situation of the DC bias before and after the compensation is analyzed. Finally, the platform of the DC bias compensation scheme is built. The full compensation experiment of DC bias is simulated by two parallel HT. The experimental results show the DC bias compensation effect is obvious, the distortion of excitation current, temperature rise and flux density distribution drop obviously, which verifies the correctness of the scheme proposed in this paper. It provides a reference for solving the problem of DC bias.

A Simple and Fast Start-Up Strategy for Dual-Active-Bridge Converters With DC Bias Suppression

High power dual active bridge (DAB) converters are widely adopted in DC and hybrid AC/DC micro-grids, for which <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fast start-up dynamics</i> of DAB converters is a key requirement. Conventional start-up methods usually require complex operation stages, and a time-consuming parameter-tuning process, resulting in slow dynamics. In this work, we propose a new simple and optimal start-up method for DAB converters. Major contributions lie in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">three-folds</i> . (i) We theoretically analyze the transmission power and the peak inductor current of extended phase-shift modulation. (ii) A new Lagrange Multiplier method is proposed to solve the optimal phase-shift ratios of the underlying control problem, resulting in very fast control dynamics at maximum power transmission, fully respecting the system permissible current limit. (iii) An effective and simple strategy by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">solely</i> manipulating the gate signals in the first switching period is newly proposed to eliminate the magnetic bias. The proposed method avoids complex parameter-tuning procedures. Experimental results demonstrate the effectiveness of the proposed method. Results confirm that with the proposed solution a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">much faster</i> start-up process with a controllable inductor current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">without</i> DC bias is achieved, in comparison with the recently reported start-up methods.

Temperature Dependence of Photoluminescence Intensity and Spin Contrast in Nitrogen-Vacancy Centers.

We report on measurements of the photoluminescence properties of single nitrogen-vacancy centers in diamond at temperatures between 4K and 300K. We observe a strong reduction of the PL intensity and spin contrast between ca. 10K and 100K that recovers to high levels below and above. Further, we find a rich dependence on magnetic bias field and crystal strain. We develop a comprehensive model based on spin mixing and orbital hopping in the electronic excited state that quantitatively explains the observations. Beyond a more complete understanding of the excited-state dynamics, our work provides a novel approach for probing electron-phonon interactions and a predictive tool for optimizing experimental conditions for quantum applications.

Broadband Electromagnetic Properties of Engineered Flexible Absorber Materials

AbstractFlexible and stretchable materials have attracted significant interest in wearable electronics and bioengineering fields. Recent developments also incorporate embedded microwave circuits and systems with engineered flexible materials that operate over a broad frequency range (≈1–100 GHz). Herein, a simple flip‐chip technique is used to evaluate frequency‐dependent electromagnetic properties of flexible materials and applied to evaluate engineered microwave absorbers based on self‐biased barium hexaferrite composites. On‐wafer error correction and de‐embedding techniques are applied to determine broadband electromagnetic properties of the material‐loaded transmission lines by placing the materials on top of coplanar waveguide transmission lines. Finite‐element simulations along with broadband measurements were employed to estimate the electromagnetic material properties. To demonstrate, flexible polydimethylsiloxane (PDMS) composites are fabricated with barium hexaferrite nanoparticles and complex permittivity and permeability of the composites are quantified under zero magnetic field bias up to 110 GHz. Frequency‐dependent composite permeability is fitted to models describing the ferromagnetic resonance of the self‐biased barium hexaferrite nanoparticles in polydimethylsiloxane, and constituent nanoparticle properties are estimated using the Maxwell–Garnett mixing model. This study paves the way to exploit a wide range of engineered materials in flexible, wearable, and biomedical electronics applications and presents a convenient methodology to extract important broadband electromagnetic properties of nanoparticles for customized electromagnetic applications.

Modelling and analysis of LCC‐HVDC converter station for harmonic coupling of AC/DC power grid during geomagnetic storm

AbstractIn this paper, the problem of harmonic coupling between the converter transformer and the converter under the action of geomagnetically induced current (GIC) is proposed to be investigated. Firstly, a model of a 12‐pulse line commutated converter high voltage direct current (LCC‐HVDC) converter station based on harmonic state space (HSS) theory is established. Secondly, the harmonic components of the interaction between the AC‐side harmonic current and the DC‐side harmonic voltage are qualitatively analyzed by using the harmonic modulation theory. Through the simulation model and harmonic state space (HSS) calculation model, the harmonic coupling characteristics of power grid are analyzed. Finally, the harmonic current and voltage amplitude of AC / DC power grid under different GIC are calculated, and the characteristics and rules of AC / DC harmonic propagation are revealed. Among them, the amplitude of the 2nd harmonic current on the AC side and the 3rd harmonic current on the DC side increases linearly with the GIC. In addition, the 3rd and 9th harmonics on the AC side are also greatly affected by the magnetic bias of the converter.

Design and Manufacture of a Test Cryostat With MgB2 Superconducting Magnet Significantly Reducing Helium Consumption

A test cryostat equipped with a conduction-cooled MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> high-temperature superconducting bias magnet has been designed, manufactured, and demonstrated. This cryostat is more environmental-friendly and user-friendly than the conventional cryostat with an immersion-cooled NbTi superconducting magnet. Liquid helium consumption is reduced by almost half of that of a previous conventional cryostat because the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet does not need liquid helium for cooling itself. A ramp-up rate of the bias magnet has also been improved to 1 A/s, which is almost 10 times faster than that of the previous NbTi magnet, due to the high stability of the superconducting MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnet. A maximum bias magnetic field is 1 T at the center of the magnet. A helium vessel of the cryostat is 212 mm in inner diameter so that various superconducting samples such as bulks, short samples of wires, and small coils, could be immersion-cooled by cryogen and tested in it. A performance demonstration was also successfully conducted.

Field-free spin-orbit-torque switching of a single ferromagnetic layer with fourfold in-plane magnetic anisotropy

We present the observation of field-free spin-orbit-torque (SOT) switching of magnetization in a ferromagnetic semiconductor (Ga,Mn)As film with four-fold in-plane magnetic anisotropy. Magnetization switching is demonstrated between two orthogonal in-plane easy axes through planar Hall resistance measurements as a current is scanned in the absence of a magnetic field. The chirality of the switching of the current hysteresis loop is consistent with SOT arising from spin polarization caused by Dresselhaus- and Rashba-type spin-orbit-induced effective magnetic fields in the (Ga,Mn)As film. The chirality of magnetization switching can be reversed either by changing the direction of the initial magnetization or by applying a constant external magnetic field bias. The SOT magnetization switching between two states was consistently repeated by applying sequential current pluses with alternating polarities, indicating the potential for developing a field-free SOT device.

A high-efficiency magnetic suspension actuator with reluctance-balanced permanent magnet biasing and flux-based control

A high-efficiency magnetic suspension actuator with reluctance-balanced permanent magnet biasing and flux-based control

Super-broadband terahertz absorber: an optimized and magnetized graphene-embedded 1D disordered photonic system

In this study, a broadband terahertz absorber was designed and numerically demonstrated. The optical features were computed using 4×4 transfer matrix formalism. The broadband absorption is attained by optimizing the Fermi levels of graphene, the magnetic field, and the thickness of the dielectric layers using the differential evolution algorithm. The results demonstrated that the WMF-optimized scenario offered greater than 90% absorption over a bandwidth of 4.18 THz, and the WoMF&amp;SL scenario provided the shortest bandwidth of 0.89 THz. These findings reveal the significance of the spacer layer to achieve broad absorption. Moreover, the absorption band is tailored to the required spectral range by careful choice of the structural and electrical parameters of the spacer layer; changing the refractive index to 1.2 offers a bandwidth of 4.42 THz and altering the thickness to 12 µm provides a bandwidth of 5.5 THz. The broadband absorption was attained due to the impedance matching provided by the optimized structure over a wide spectral range. Furthermore, the average absorption and bandwidth were enhanced, while fluctuations in the selected absorption band were minimized by engineering the magnetic biasing. The reported super-broadband absorber offers numerous applications in terahertz imaging, terahertz communications, and photodetectors.

Tunable non-reciprocal waveguide using spoof plasmon polariton coupling to a gaseous magnetoplasmon.

We experimentally demonstrate non-reciprocal (one-way) waveguiding in a microstrip transmission line tailored to support the propagation of spoof plasmon polaritons. Time-reversal symmetry is broken by coupling the microstrip fields to a magnetized gaseous plasma discharge column thereby exciting non-reciprocal magnetoplasmons at the interface between the plasma and a surrounding quartz envelope. The magnetic bias introduces asymmetry in the dispersion of the surface plasmon polaritons at the gaseous plasma-dielectric interface, resulting in a breaking of the bidirectionality of the wave propagation in the microstrip. The isolation generated at conditions of modest magnetic bias is measured to be nearly 60 dB, and tunable by varying the plasma density through the voltage applied to the discharge. The advantage of using magnetized gaseous plasmas to produce this unidirectional waveguide structure is that it can be turned on or off at rates limited by the production and recombination of the plasma.

Deterministic Magnetization Reversal in Synthetic Antiferromagnets using Natural Light.

Traditional current-driven spintronics is limited by localized heating issues and large energy consumption, restricting their data storage density and operation speed. Meanwhile, voltage-driven spintronics with much lower energy dissipation also suffers from charge-induced interfacial corrosion. Thereby finding a novel way of tuning ferromagnetism is crucial for spintronics with energy-saving and good reliability. Here, a visible light tuning of interfacial exchange interaction via photoelectron doping into synthetic antiferromagnetic heterostructure of CoFeB/Cu/CoFeB/PN Si substrate is demonstrated. Then, a complete, reversible magnetism switching between antiferromagnetic (AFM) and ferromagnetic (FM) states with visible light on and off is realized. Moreover, a visible light control of 180° deterministic magnetization switching with a tiny magnetic bias field is achieved. The magnetic optical Kerr effect results further reveal the magnetic domain switching pathway between AFM and FM domains. The first-principle calculations conclude that the photoelectrons fill in the unoccupied band and raise the Fermi energy, which increases the exchange interaction. Lastly, a prototype device with visible light control of two states switching with a 0.35% giant magnetoresistance ratio change (maximal 0.4%), paving the way toward fast, compact, and energy-efficient solar-driven memories is fabricated.

Bias-free very low frequency magnetoelectric antenna

A rapid surge in the research on very low frequency (VLF) antennas is occurring due to the demand for radio navigation and special environment communications such as underwater and underground applications. Among them, magnetoelectric (ME) antennas have recently proven to be a prospective solution for miniaturization of VLF communication systems. However, the essential magnetic bias fields (Hdc) lead to challenges of miniaturization, electromagnetic interference, and noise sources for ME antenna application. Here, a bias-free VLF ME antenna based on the magneto-gradient ME composite (i.e., annealed Metglas/Metglas/PZT/Metglas/annealed Metglas) has been designed. Owing to the interaction effect between multi-unannealed/annealed Metglas, the magneto-gradient ME composite exhibits a large direct and converse ME response (αDME = 107 V/cm Oe and αCME = 9 Gs/V at resonance) at bias-free, which is about 63% and 33% of the maximum value under optimal magnetic bias for unannealed ME composites. Moreover, a digital amplitude shift keying (ASK) modulation method is proved suitable for the as-made bias-free VLF ME antenna. Such a bias-free ME antenna provides a practicable strategy for miniaturization of VLF communication.