Magnitude Of Magnetic Field Research Articles

Bicontrollable all dielectric metasurface absorber for chemical and biosensing applications

A bi-controllable all dielectric metasurface structure is designed at terahertz, which consists of an InAs micro-cylindrical array on the gold ground plane. The maximum absorptance frequency is tunable with the help of an external magnetic field and also by geometrical rotation of the metasurface as InAs is a gyrotropic material whose property depends on the magnitude and direction of an external magnetic field. Simulation results indicate that the proposed metasurface can achieve an absorptance of more than 99 % at 9.756 THz as well as it can provide a high tunability rate of around 2.55 THz T−1 in lower band and 3.33 THz T−1 in the upper band frequency spectrum with the application of the magnetic field. Additionally, the metasurface also acts as polarization insensitive when no external magnetic field is applied. Furthermore, the maximum absorptance frequency shows sensitivity towards the change in the refractive index value of the surrounding medium, thus the metasurface can be used for chemical and biosensing applications. It shows high chemical sensitivity of around 2727 GHz/RIU for the detection of different chemicals and bio sensitivity of 787 GHz/RIU for the detection of various viruses.

Effect of magnetic field locations on thermo-magnetic convection performance of Fe3O4/H2O ferrofluid flowing in a novel dimpled tube: An experimental study

The aim of this study is to examine the hydrothermal behavior of Fe3O4 Ferrofluid flowing under the effect of uniform magnetic field (0 T ≤ B ≤ 0.3 T). In addition, magnetic field locations were changed for each experiment to observe effect of the magnetic field locations (x/D = 20, 40, 60) on the hydrothermal behavior of the proposed system. Fe3O4 Ferrofluid was prepared in φ = 1.0% volume concentration in water and flows under the laminar regime (1131 ≤ Re ≤ 2102). Comparisons of the hydrothermal behavior of the novel proposed parameters were performed according to combinations of the different magnetic field locations and magnitudes. It is concluded that the highest Nusselt number was obtained using B = 0.3 T for the magnetic field location of x/D = 20 for both in smooth and dimpled tubes. Compared to B = 0 T, the Nusselt number enhancement was detected by 64.03% for smooth tube for the magnetic field location of x/D = 20 for B = 0.3 T whereas Nusselt number wasaugmented by 45.40% for dimpled tube for the same input parameters. Furthermore, no considerable changes in friction factor was determined under magnetic field effect when the application of magnetic field locations was changed. As a result of these findings, the highest increase in Performance Evaluation Criteria belonging dimpled tube was calculated by 33.54% at Re = 2102 for B = 0.16 T for the magnetic field location of x/D = 20. As a general conclusion, this study can shed light on investigating ferrofluids behavior under magnetic field applied in variable magnetic field locations.

Asymptotically preserving particle methods for strongly magnetized plasmas in a torus

We propose and analyze a class of particle methods for the Vlasov equation with a strong external magnetic field in a torus configuration. In this regime, the time step can be subject to stability constraints related to the smallness of Larmor radius. To avoid this limitation, our approach is based on higher-order semi-implicit numerical schemes already validated on dissipative systems [3] and for magnetic fields pointing in a fixed direction [10,11,13]. It hinges on asymptotic insights gained in [12] at the continuous level. Thus, when the magnitude of the external magnetic field is large, this scheme provides a consistent approximation of the guiding-center system taking into account curvature and variation of the magnetic field. Finally, we carry out a theoretical proof of consistency and perform several numerical experiments that establish a solid validation of the method and its underlying concepts.

The influence of time varying magnetic fields on the determinations of Newton’s constant at the Bureau International des Poids et Mesures

The values of Newton’s constant of gravitation, G, reported by determinations at the International Bureau of Weights and Measures (BIPM) in Quinn et al (2001 Phys. Rev. Lett. 87 111101/1–111101/4) and in Quinn et al (2013 Phil. Trans. R. Soc. A 372 2–28) are some 200 parts per million (ppm) larger than the value of m3 kg−1 s−2 which was recommended by CODATA in Tiesinga et al (2018 J. Phys. Chem. Ref. Data 50 033105). The CODATA value has an assigned uncertainty of 22 ppm and the reported uncertainties in the BIPM values were 41 ppm and 25 ppm, respectively. The discrepancy therefore amounts to about seven times the combined uncertainty of the latest BIPM and CODATA values. We examine experimentally the hypothesis that the difference is due to a bias produced by stray alternating (AC) magnetic fields in the vicinity of the experiment. Whilst the BIPM torsion balance was located at the University of Birmingham a coil, having a similar scale to the balance, was used to generate AC magnetic fields of magnitude approximately 1 μT which in turn produced torques of magnitude approximately 0.2 % of the gravity torque. The magnitudes of these torques were compared with simple analytical models and finite element analyses. Measurements in the laboratory in Birmingham and, more recently, at BIPM give a very conservative upper limit on the rms magnitude of ambient AC magnetic fields of 100 nT. As the torque was demonstrated to vary with the square of the ambient field, these observations and our analyses suggest an upper limit to the possible bias in the BIPM determinations of the order of 20 ppm. It is therefore unlikely that torques due to ambient magnetic fields could have significantly biased values of G determined at BIPM.

Location-aware ingestible microdevices for wireless monitoring of gastrointestinal dynamics.

Localization and tracking of ingestible microdevices in the gastrointestinal (GI) tract is valuable for the diagnosis and treatment of GI disorders. Such systems require a large field-of-view of tracking, high spatiotemporal resolution, wirelessly operated microdevices and a non-obstructive field generator that is safe to use in practical settings. However, the capabilities of current systems remain limited. Here, we report three dimensional (3D) localization and tracking of wireless ingestible microdevices in the GI tract of large animals in real time and with millimetre-scale resolution. This is achieved by generating 3D magnetic field gradients in the GI field-of-view using high-efficiency planar electromagnetic coils that encode each spatial point with a distinct magnetic field magnitude. The field magnitude is measured and transmitted by the miniaturized, low-power and wireless microdevices to decode their location as they travel through the GI tract. This system could be useful for quantitative assessment of the GI transit-time, precision targeting of therapeutic interventions and minimally invasive procedures.

The effect of longitudinal static magnetic field on the radiation efficiency of high harmonics from overdense plasma

The effect of the magnetic field applied along the laser propagation direction on the radiation efficiency of high-order harmonics generated from laser-irradiated overdense plasma is investigated theoretically and numerically. We find that the external magnetic field can increase the transmittance of the overdense target, thereby dramatically enhancing the energy coupling between the laser and target. While for high-order harmonics of the laser reflected from the oscillating target, the radiation efficiency reaches the maximum when the cyclotron frequency of the electrons in the magnetized target approaches the laser frequency. This conclusion applies only to overdense plasmas targets. For targets with low reflectivity, the application of the magnetic field reduces the harmonic radiation efficiency due to the decrease of both the oscillating coherence and opacity of the target. This work provides a reasonable approach to improving the radiation efficiency of high-order harmonics and a method to estimate the magnitude of the self-generated magnetic field during intense laser–plasma interactions.

Indoor 2D Positioning Method for Mobile Robots Based on the Fusion of RSSI and Magnetometer Fingerprints.

Received signal strength indicator (RSSI)-based fingerprinting is a widely used technique for indoor localization, but these methods suffer from high error rates due to various reflections, interferences, and noises. The use of disturbances in the magnetic field in indoor localization methods has gained increasing attention in recent years, since this technology provides stable measurements with low random fluctuations. In this paper, a novel fingerprinting-based indoor 2D positioning method, which utilizes the fusion of RSSI and magnetometer measurements, is proposed for mobile robots. The method applies multilayer perceptron (MLP) feedforward neural networks to determine the 2D position, based on both the magnetometer data and the RSSI values measured between the mobile unit and anchor nodes. The magnetic field strength is measured on the mobile node, and it provides information about the disturbance levels in the given position. The proposed method is validated using data collected in two realistic indoor scenarios with multiple static objects. The magnetic field measurements are examined in three different combinations, i.e., the measurements of the three sensor axes are tested together, the magnetic field magnitude is used alone, and the Z-axis-based measurements are used together with the magnitude in the X-Y plane. The obtained results show that significant improvement can be achieved by fusing the two data types in scenarios where the magnetic field has high variance. The achieved results show that the improvement can be above 35% compared to results obtained by utilizing only RSSI or magnetic sensor data.

Generation of High-Power Terahertz Waves in a Collisional and Magnetized Plasma by Two-Color Femtosecond Laser Beams

Terahertz (THz) radiation generation based on a nonlinear induced electron current density in the interaction of two-color femtosecond laser beams with collisional and magnetized plasma is investigated. The nonlinear electron current density that is responsible for THz radiation includes a share from nonlinear ponderomotive force and a part from relativistic term. In this work, relativistic effects along with the effects of variation of interacting plasma density, external magnetic field, and electron collision frequency on THz wave generation have been considered. The reduction of electron collision frequency along with rising in the magnitude of the external magnetic field generates more power without any deformation of radiation patterns. The angular distribution showing the radiation pattern of THz radiation in the forward direction is obtained and the effect of laser pulse second harmonic and variation of electric field on the directivity of generated waves is examined. The change in two-color laser beam intensities both in relativistic and nonrelativistic regimes leads to the generation of THz wave electric fields with different orders of magnitude. The numerical analysis indicated that the utilization of laser pulse second harmonic in a two-color scheme enhances the THz electric field leading to more intense radiation compared to single-color mechanism. The model also shows the effect of external magnetic field and electron collision frequency on the radiation efficiency of THz generation for linear and circular polarizations of two-color laser pulses.

A Numerical Analysis of the Hybrid Nanofluid (Ag+TiO2+Water) Flow in the Presence of Heat and Radiation Fluxes

The hydrothermal characteristics of (Ag+TiO2+H2O) hybrid nanofluid three dimensional flow between two vertical plates, in which the right permeable plate stretches as well as rotates, are investigated by employing varying magnetic, heat and radiation fluxes. The motion is governed by coupled PDEs (nonlinear) obeying suitable boundary conditions. The PDEs coupled system is transformed to a coupled set of nonlinear ODEs employing appropriate similarity transformation relations. The resultant equations are numerically solved through the bv4c solver. The impact of the changing strength of associated parameters on the flow is investigated graphically and through tables. It has been found that the velocity gradient and velocity initially increase and then decrease with increasing Grashof number values in both the suction and injection cases. The enhancing magnetic field first augments and then lowers the velocity gradient in the presence of radiation source of maximum strength. The increasing strength of injection parameter drops the velocity. The temperature distribution in the fluid increases with the increasing Eckert number, radiation flux and heat strength and nanomaterial concentration, and depreciates with the enhancing injection parameter values and Prandtl number. The Cfx increases with a higher magnetic field magnitude and nanomaterial concentration, and declines with an increasing Grashof number. The results obtained are compared with the available literature in the form of tables.

Evaluation and analysis of Voyager 1 48-s resolution magnetic field data

The aim of this paper is to provide information on the radial dependence of turbulence quantities as input for ab initio numerical cosmic-ray modulation models. We present an evaluation and analysis of 48-s resolution Voyager 1 data for the normal component of the magnetic field. These data were preprocessed to fill in data gaps and filter out spurious peaks. The effectiveness of this process is illustrated for a sample data set, for which we show that the underlying spectrum is indeed Kolmogorov. We use a second-order structure function to find correlation times, and also the spectral index and spectral level in the inertial range from expressions derived by Huang et al. (2010). The usefulness of the second-order structure function for data with significant gaps is illustrated by using synthetic data. Gaps up to 68% cause changes of less than 5% in the quantities that we calculate. We show that beyond about 20 au there are significant changes in the behaviour of the magnetic field magnitude and the inertial range spectral index, neither of which has a reasonable explanation. We find that the ratio δBN/BN remains almost constant out to 20 au, that the correlation times is consistent with results from other studies, and that the spectral index in the inertial range is consistent with the Kolmogorov value. A new result is that we could infer that the break between the energy- and the inertial range has a radial dependence that is consistent with that of the correlation scale.

Influence of an external magnetic field on laser-induced plasma and cavitation bubbles in submerged targets

A pulsed Nd:YAG laser is tightly focussed on a metal target immersed in distilled de-ionized water. The resultant laser-induced plasma and subsequent cavitation bubble behavior are studied under the influence of an external magnetic field that is varied from 700 to 1000 Gauss. The study is conducted using a beam deflection probe arrangement. In addition, laser-induced breakdown spectroscopy is also employed to study the plasma spectrum. Furthermore, three different magnetic materials are employed for this investigation: ferromagnetic nickel, paramagnetic gadolinium, and diamagnetic copper. The studies revealed that cavitation bubble radii and collapse durations increased considerably as the magnitude of the external magnetic field was increased. This effect was prominent in the case of nickel and less so in the case of gadolinium and copper. For nickel, collapse times increase when the magnetic field was applied, whereas for gadolinium and copper, significant changes were not observed. The differences observed in collapse times showed that magnetic properties of the targets played a vital role in this phenomenon. The process of pulsed laser ablation in liquid also led to the respective generation of metallic nanoparticles from individual materials. Characterization of the generated nanoparticles revealed size reduction when synthesized under the influence of an external magnetic field. These characterizations were performed using transmission electron microscopy and UV-Vis spectroscopy.

Impact of the mutual direction of Polarizer and Free Layer on the auto-oscillation mode of magnetic tunnel junctions (MTJs) of different geometry

In this work we studied the auto-oscillation mode of structures based on magnetic tunnel junctions. During the experiment we studied how different values and orientation of the magnetic field affect the efficiency of the auto-oscillations regime for samples of various shapes. The auto-oscillation mode in samples was observed near the transition from one state of magnetization of the free layer to another. It was found that the maximum value of the power spectral density and its position relative to the frequency axis can be controlled by changing the magnitude and orientation of the external magnetic field. Keywords: Magnetic tunnel junction (MTJ), auto-oscillations, power spectral density, nanooscillator.

Влияние взаимного направления поляризатора и свободного слоя на автогенерацию магнитных туннельных переходов (МТП) разной геометрии

In this work we studied the auto-oscillation mode of structures based on magnetic tunnel junctions. During the experiment we studied how different values and orientation of the magnetic field affect the efficiency of the self-generation regime for samples of various shapes. The auto-oscillation mode in samples was observed near the transition from one state of magnetization of the free layer to another. It was found that the maximum value of the power spectral density and its position relative to the frequency axis can be controlled by changing the magnitude and orientation of the external magnetic field.

Small Signal Magnetic Compensation Method for UAV-Borne Vector Magnetometer System

Aeromagnetic surveys using UAVs (Unmanned Aerial Vehicle) have attracted extensive interest, and aeromagnetic compensation is indispensable to improve the quality of magnetic field. For the vector magnetic sensors fixed on the drone, existing compensation methods are based on that the magnitude of vector magnetic field is a constant, but in theory, even if the center position of the UAV remains unchanged during rotation, the magnitude of the measured vector magnetic field is time-varying, because the interference field generated by the drone is related to its attitude, resulting in residual error after compensation. This paper creates a novel small signal model (SSM) based on the measured results of the vector magnetometer, compensating the permanent and induced interference magnetic field generated by the drone. A high-pass filter is used to separate the UAV interference field from the outputs of a vector magnetic sensor, and compensation parameters are estimated by the least square method. Meanwhile, compensation flight is the UAV-borne vector magnetometer system flying multiple lines in a small area, no need to keep the center of the system fixed while performing rotation operations in the air. Field experiments have been conducted, and the root mean square error of the compensated magnetic field is less than 1 nT. In addition, the subsequent test flight and detection experiment were carried out, showing that the SSM compensation can improve the quality of magnetic field.

Analysis and improvement of the uniformity of magnetic field coil based on the cylindrical magnetic shield in atomic magnetometers

The magnetic field performance of the uniform coils will be affected by magnetic shields and produce errors in the atomic magnetometer. It is necessary to analyze the influencing factors and guide the coil design. Aiming at the above shortcomings, this paper analyzes the coupling effect of magnetic shield and coil and proposed a Lee-Whiting coil design method based on the linearly decreasing inertia weight particle swarm optimization (LDW-PSO) algorithm. Firstly, the magnetic field model under the ferromagnetic boundary is established, and the effects of the size, thickness and permeability of the magnetic shield on the magnitude and uniformity of the Lee-Whiting coil magnetic field are analyzed. The results show that the coupling coefficient of the coil changes monotonically with the change of the size of the magnetic shield, while the uniformity error has a minimum value with the change of the size of the shield. In addition, an improved Lee-Whiting coil is designed by combining the LDW-PSO algorithm, which improves the uniformity of the coil. Compared with the original coil, the measured uniformity error of the improved coil is reduced from 8.39 × 1 0 − 4 to 2.81 × 1 0 − 4 . The accuracy of the theoretical analysis is verified by experiments. This paper is of great significance to study the coupling and optimization design of the coil based on the magnetic shields in atomic magnetometers. • The influence of magnetic shield parameters on coil uniformity is analyzed. • The optimal coil size for the uniformity in magnetic shield is given by analysis and testing. • The improved Lee-Whiting coil is designed by intelligent optimization algorithm. • Improved Lee-Whiting coil overcomes the coupling effect between coil and magnetic shield. • The correctness of the analysis and the effectiveness of the design are proved by experiments.

Motion of a Piston Separating Magnetic and Non-Magnetic Fluids in a Magnetic Field

The pumping of non-magnetic fluid by a dosing pump that is based on a magnetic fluid with an immersed body made of a magnetizable material is studied theoretically and experimentally. The process of fluid pumping in an applied vertical uniform magnetic field is investigated. The time dependences of the rise of the piston between the magnetic and non-magnetic fluids are calculated and measured in constant and stepwise magnetic fields. A good agreement between theory and experiment is obtained. The dependence of the rise time of the piston on the magnitude of the constant magnetic field is calculated. The motion of piston is theoretically investigated after the magnetic field is switched off.

Combined Marangoni and Buoyancy Convection in a Porous Annular Cavity Filled with Ag-MgO/Water Hybrid Nanofluid

Background: This article numerically examines the effect of buoyancy and Marangoni convection in a porous enclosure formed by two concentric cylinders filled with Ag-MgO water hybrid nanofluid. The inner wall of the cavity is maintained at a hot temperature, and the outer vertical wall is considered to be cold. The adiabatic condition is assumed for the other two boundaries. The effect of the magnetic field is considered in radial and axial directions. The Brinkman-extended Darcy model has been adopted in the governing equations. Methods: The finite difference scheme is employed to work out the governing Navier-Stokes equations. The numerically simulated outputs are deliberated in terms of isotherms, streamlines, velocityand average Nusselt number profiles for numerous governing parameters. Results: Except for a greater magnitude of axial magnetic field, our results suggest that the rate of thermal transport accelerates as the nanoparticle volume fraction grows. Also, it is observed that there is an escalation in the profile of average Nusselt numberwith an enhancement in Marangoni number. Conclusion: Furthermore, the suppression of heat and fluid flow in the tall annulus is mainly due to the radial magnetic field whereas in the shallow annulus, the axial magnetic field profoundly affects the flow field and thermal transfer.

Управление свойствами магнитоупругих волн в слоистых антиферромагнитных гетероструктурах

In this work we present a model explaining the properties of magnetoelastic waves propagation in the heterostructure containing an antiferromagnetic layer on a non-magnetic elastic substate. The dispersion characteristic of magnetoelastic waves in such structure was obtained, and the effect of variation of the thickness of the antiferromagnetic layer and the external magnetic field on the frequency of the magnetoelastic resonance on the elastic structure was also studied. It was found that an increase in the magnetic field magnitude leads to the increase with pressure of the magnetoelastic resonance frequency, and, on the contrary, with an increase in the thickness of the AFM layer the magnitude of the magnetoelastic resonance frequency decreases. The results obtained can be used to create devices for generating and processing signals in the gigahertz and terahertz frequency ranges.

Feasibility study of magnetic sensing for detecting single-neuron action potentials

Understanding the magnitude of the local magnetic fields generated by neurons is critical to assessing the feasibility of novel magnetic field sensors to record in vivo neuronal activities at cellular resolution. However, the strength of the magnetic fields induced by individual neurons and neuronal networks has not been systematically studied. This step is critical for evaluating and benchmarking the ability of different magnetic field sensors to record neuronal activities with far better spatial and temporal resolution. Herein, FEM exemplary models and open-source computational libraries are used to calculate the magnetic fields generated by individual neurons and neuronal networks at micrometer distances. Our theoretical results show that the magnetic field generated by a single-neuron action potential can be detected by ultra-high sensitivity sub-pT magnetic field sensors, which opens the door to future in vivo decoding of neuronal activities through custom neural networks. We anticipate that the identification of single-neuron signals with high-sensitivity magnetic devices will allow the interface of nanoscale devices to interpret biological signals supported by machine-learning techniques capable of monitoring and predicting the localized activities underlying brain computations.

Magnetoelectric effect in three-layered gradient LiNbO3/Ni/Metglas composites

The effect of annealing in a permanent magnetic field on the magnitude of magnetoelectric coefficient in three-layered gradient magnetoelectric LiNbO3/Ni/Metglas composites has been studied. A method of electrochemical nickel deposition on bidomain lithium niobate crystals has been demonstrated. We show that the optimum annealing temperature in a permanent magnetic field for the generation of the highest remanence in the Ni layer is 350 °C. The specimens annealed at this temperature exhibit the greatest shift of the magnetoelectric coefficient dependence on external magnetic field magnitude relative to the value Hdc = 0. The quasi-static magnetoelectric coefficient in the absence of an external magnetic field proves to be 1.2 V/(cm ∙ Oe). The highest magnetoelectric coefficient that has been achieved at a bending structure resonance frequency of 278 Hz proves to be 199.3 V/(cm ∙ Oe) without application of an external magnetic field. The experimental magnetoelectric coefficient figures for three-layered gradient LiNbO3/Ni/Metglas composites are not inferior to those for most magnetoelectric composite materials reported earlier.