Inherent Magnetic Field Research Articles

Anomalous Current Steps in 3D Graphene Electrochemical Systems at Room Temperature.

In this work, we report a new phenomenon in electrochemical systems whereby uniform current steps of 1 mA per 0.5 × 0.5 × 0.1 cm3 (width × width × depth) of electrode volume occurred during the electrodeposition of gold and silver nanoparticles onto 3D microporous graphene on nickel layers (GF/Ni) at room temperature. The effect was exhibited only at specific applied electrical potentials. The experiments (magnetic interference, temperature dependence, and surface area dependence) were repeated, and the results were reproducible. Finally, we proposed classical electrochemical theory using the Butler-Volmer equation and quantum theory using the Landauer formalism to describe this new effect. Both theories could be used to explain the experimental results: temperature dependence, surface area dependence, blocking effects, and external magnetic field dependence. In addition, the stepwise current presented in this work facilitates the trapping and supplying of a large amount of electric charge via an inherent magnetic field in a sharp time step (∼1 s). A video clip of the recorded effect can be found at https://youtu.be/pPJh45w1sUQ.

Determination of the polynomial restoring force of a one DoF bistable Duffing oscillator by linear regression

A large class of energy-harvesting systems includes a bistable magnetoelastic oscillator. Due to the high complexity of the inherent magnetic field forces, those systems are commonly represented as a combination of physical and phenomenological, low-dimensional models. Therein occurring three free parameters of dissipation and restoring force are determined by the decay rate as well as constraints for the position of the equilibria and the frequency of small amplitude oscillations. As will be shown in this paper, one major disadvantage of this procedure is that high amplitude oscillations, which are most relevant in context of energy harvesting, yield the poorest consistency with experimental observations. To overcome the problem, a regression-based nonlinear system identification is performed using system responses under harmonic excitation. Models with cubic as well as quintic restoring forces are identified and compared with the experimental observations as well as a model that was built with the commonly used identification procedure. As a result, it is found that both models from the regression show a higher agreement with the experimental data. Furthermore, the quintic model is found to be more accurate than the cubic model. This shows the necessity to be able to include more than three free parameters in the model. The advantage of the applied procedure lies in the raised flexibility of model adaptation resulting in improved agreement of simulation and experimental results.

Sensitive, Efficient and Portable Analysis of Molecular Exchange Processes by Hyperpolarized Ultrafast NMR

AbstractMolecular exchange processes are ubiquitous in nature. Here, we introduce a method to analyze exchange processes by using low‐cost, portable, single‐sided NMR instruments. The inherent magnetic field inhomogeneity of the single‐sided instruments is exploited to achieve diffusion contrast of exchange sites and spatial encoding of 2D data. This so‐called ultrafast diffusion exchange spectroscopy method shortens the experiment time by two to four orders of magnitude. Furthermore, because full 2D data are measured in a single scan (in a fraction of a second), the sensitivity of the experiment can be improved by several orders of magnitude using so‐called nuclear spin hyperpolarization methods (in this case, dissolution dynamic nuclear polarization). As the first demonstration of the feasibility of the method in various applications, we show that the method enables quantification of intra‐ and extracellular exchange of water in a yeast cell suspension.

Sensitive, Efficient and Portable Analysis of Molecular Exchange Processes by Hyperpolarized Ultrafast NMR.

Molecular exchange processes are ubiquitous in nature. Here, we introduce a method to analyze exchange processes by using low‐cost, portable, single‐sided NMR instruments. The inherent magnetic field inhomogeneity of the single‐sided instruments is exploited to achieve diffusion contrast of exchange sites and spatial encoding of 2D data. This so‐called ultrafast diffusion exchange spectroscopy method shortens the experiment time by two to four orders of magnitude. Furthermore, because full 2D data are measured in a single scan (in a fraction of a second), the sensitivity of the experiment can be improved by several orders of magnitude using so‐called nuclear spin hyperpolarization methods (in this case, dissolution dynamic nuclear polarization). As the first demonstration of the feasibility of the method in various applications, we show that the method enables quantification of intra‐ and extracellular exchange of water in a yeast cell suspension.

Analyzing Fast-ions Trajectories in a Nuclear Fusion Reactor through Its Poincaré-Island Size and Ripple Resonance

Fast-ions confinement is a prominent subject in developing nuclear fusion reactors due to its importance in sustaining the burning plasma and keeping energy production. However, confining them has proven to be difficult until now, and one of the reasons is that the inherent discrete magnetic field produces a magnetic ripple. A better understanding of fast-ions transport using appropriate numerical calculation tools needs to be developed to overcome such a challenge in the engineering aspect. This study revisited data collection of fast ion transport simulated under the ripple presence in a nuclear fusion device. The ion trajectories were followed using two orbit-following equation schemes, and the ripple-resonance island size in the Poincaré section was compared. The result showed that the island size obtained by each scheme was different when the particle resonates with a stronger ripple field and, proportionally, the diffusion coefficients are different. The physical meaning and consequence behind this discovery were discussed in this paper.

Inherent and Local Magnetic Field Structures in Jets from Active Galactic Nuclei

In theoretical models for the electromagnetic launching of astrophysical jets, a helical magnetic (B)-field component is generated through the winding up of an initial longitudinal field component by the rotation of the cental black hole and accretion disk. This helical field component travels outward with the jet plasma. There is now abundant evidence that the jets of active galactic nuclei carry helical B fields, and the presence of such fields has been invoked to explain a wide range of phenomena observed in these jets. However, distinguishing between features associated with this inherent jet B field and with B fields generated by local phenomena such as shocks and shear can be challenging. There is now evidence that the field that is accreted is dipolar like, giving rise to a current distribution with inward currents along both jet axes and outward currents in a more extended region around the jets. Striking limb brightening has been observed for several relatively nearby active galactic nuclei; it is argued that this must be due to some intrinsic property of the jet, which is independent of the viewing angle, such as its helical B field, or mass loading and/or particle acceleration at the jet edges. Circular-polarization observations may make it possible to reconstruct the full three-dimensional B field of jets carrying a helical B-field component, and to correctly infer the direction of rotation of the central black hole and its accretion disk.

Natural convection analysis flow of Al2O3-Cu/water hybrid nanofluid in a porous conical enclosure subjected to the magnetic field

The current study investigates MHD natural convection heat transfer of a hybrid nanofluid in a truncated cone along with transparent domains having the stimulus of an inherent constant magnetic field. The governing equations subject to the physical boundary conditions are solved numerically by using the Galerkin finite element method. The effects of the various parameters involved in the problem such as the Rayleigh number Ra (ranging between 103 and 106), the Hartmann number Ha (ranging between 0 and 60), and the porosity ratio ε (0.1–0.9) are examined. Moreover, the effects of Da which represents the Darcy number (between 10‑3 and 10‑1) and the volume fraction of nanoparticles ϕ for the dissipated nanoparticles of Al2O3-Cu are reported in terms of the streamlines and isotherms distributions as well as the Nusselt number. Such parameters are critical control parameters for both the fluid flow and the rate of heat transfer of the natural convection in the annular space. The solution outcomes proof that the average Nusselt number varies directly with the dynamic field flowing through a porous media, whereas it behaves inversely with the magnetic field.

Low drift nuclear spin gyroscope with probe light intensity error suppression**Project supported by the National Key Research and Development Program of China (Grant Nos. 2016YFB0501600 and 2017YFB0503100) and the National Natural Science Foundation of China (Grant Nos. 61773043, 61673041, and 61721091).

A nuclear spin gyroscope based on an alkali-metal–noble-gas co-magnetometer operated in spin-exchange relaxation-free (SERF) regime is a promising atomic rotation sensor for its ultra-high fundamental sensitivity. However, the fluctuation of probe light intensity is one of the main technical error sources that limits the bias stability of the gyroscope. Here we propose a novel method to suppress the bias error induced by probe light intensity fluctuations. This method is based on the inherent magnetic field response characteristics of the gyroscope. By the application of a bias magnetic field, the gyroscope can be tuned to a working point where the output signal is insensitive to probe light intensity variation, referred to herein as ‘zero point’, thus the bias error induced by intensity fluctuations can be completely suppressed. The superiority of the method was verified on a K–Rb–21Ne co-magnetometer, and a bias stability of approximately 0.01 °/h was obtained. In addition, the method proposed here can remove the requirement of the closed-loop control of probe light intensity, thereby facilitating miniaturization of the gyroscope volume and improvement of reliability.

Sustained multiferroicity in liquid crystal induced by core/shell quantum dots

Sustained multiferroicity along with the ferromagnetic ordering in a ferroelectric liquid crystal (FLC) on incorporation of Co-ZnO/ZnO core/shell (CZZ) quantum dots (QDs) is confirmed by ferroelectric (P-E) and ferromagnetic (M-H) hysteresis measurements. An appropriate amount of CZZ QDs was added into pure FLC (KCFLC 7S) material to study its ferroelectric and ferromagnetic properties. Increased cobalt concentration in the core of CZZ QDs enhances the magnitude of saturation magnetization. The inherent magnetic field of core/shell QDs is coupled with the director field of the FLC molecules without altering the intrinsic properties of host FLC and dopant QDs, which reveals sustained multiferroic behavior. Notably, the optimized concentration of QDs does not disturb the intrinsic ferroelectric nature of the host as confirmed by ferroelectric and helical pitch measurements. The outcome of this work would be beneficial for future QD based liquid crystal displays that exhibit both electric and magnetic memory within itself.

Investigation of the inherent magnetic field influence on corrosion resistance of Nd – Fe – B permanent magnets

Investigation of the inherent magnetic field influence on corrosion resistance of Nd – Fe – B permanent magnets

The construction of rod-like polypyrrole network on hard magnetic porous textile anodes for microbial fuel cells with ultra-high output power density

This study attempts to prompt the formation of microorganism films on flexible textile-based anodes and enhances the performance of living microorganisms by introducing magnetic properties to the anodes. A magnetic and electrically conductive anode for a microbial fuel cell is designed and fabricated by encapsulating uniformly dispersed SrFe12O19 nanoparticles into the poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibers and forming a three-dimensional (3D) polypyrrole (PPy) network on the surface of flexible composite nanofiber based fabric. A dual-chamber MFC equipped with the magnetized anode shows a maximum power density of 3317 mW m−2, which is significantly larger than that of the non-magnetized anode (2471 mW m−2). This study demonstrates that the hard-magnetic anode providing an inherent magnetic field can greatly promote bio-electrochemical reaction rates of E. coli, and decrease the anode charge transfer resistance in a MFC system.

Hybrid Excitation Stator PM Vernier Machines With Novel DC-Biased Sinusoidal Armature Current

Stator permanent magnet (PM) machines are gaining more research interest in recent decades. Since the permanent magnets (PMs) are moved from the rotor side to the stator side and the salient rotor structure is adopted, it is claimed that the stator permanent magnet machines exhibit several promising features, such as simple and robust rotor, and good ability of heat dissipation as the main losses are located in the stator. On the other hand, to improve the shortcomings of the inherent limited magnetic field adjustment ability, and the low efficiency and power factor of stator dc current excited machines, hybrid excitation PM machines with additional field windings are proposed. However, the complexity of the machine structure is increased inevitably. At present, it is found that both the stator PM and the stator dc current excited Vernier machines operate with the flux modulation principle, and generally, the armature windings of the stator PM machines are fed with pure sinusoidal current. In this paper, a novel hybrid excitation stator PM Vernier machine is analyzed. In addition to the features of the salient rotor structure, stator located PMs, and concentrated armature windings, the novelty of this machine is dc-biased sinusoidal phase current, which contains an ac component and a dc component. The fundamental theories of stator PM machines fed with dc-biased current are researched, operation principle and slot/pole combination is concluded, and the optimal current configuration is studied theoretically and by finite element analysis. Finally, a prototype was designed and manufactured; the experimental tests were done to validate the proposed analysis.

Gyrator Operation Using Josephson Mixers

Nonreciprocal microwave devices, such as circulators, are useful in routing quantum signals in quantum networks and protecting quantum systems against noise coming from the detection chain. However, commercial, cryogenic circulators, now in use, are unsuitable for scalable superconducting quantum architectures due to their appreciable size, loss, and inherent magnetic field. We report on the measurement of a key nonreciprocal element, i.e., the gyrator, which can be used to realize a circulator. Unlike state-of-the-art gyrators, which use a magneto-optic effect to induce a phase shift of $\pi$ between transmitted signals in opposite directions, our device uses the phase nonreciprocity of a Josephson-based three-wave-mixing device. By coupling two of these mixers and operating them in noiseless frequency-conversion mode, we show that the device acts as a nonreciprocal phase shifter whose phase shift is controlled by the phase difference of the microwave tones driving the mixers. Such a device could be used to realize a lossless, on-chip, superconducting circulator suitable for quantum-information-processing applications.

Magnetic annihilation of the dark mode in a strongly coupled bright-dark terahertz metamaterial.

Dark mode in metamaterials has become a vital component in determining the merit of the Fano type of interference in the system. Its strength dictates the enhancement and suppression in the amplitude and Q-factors of resulting resonance features. In this work, we experimentally probe the effect of strong near-field coupling on the strength of the dark mode in a concentrically aligned bright resonator and a dark split ring resonator (SRR) system exhibiting the classical analog of the electromagnetically induced transparency effect. An enhanced strong magnetic field between the bright-dark resonators destructively interferes with the inherent magnetic field of the dark mode to completely annihilate its effect in the coupled system. Moreover, the observed annihilation effect in the dark mode has a direct consequence on the disappearance of the SRR effect in the proposed system, wherein under the strong magnetic interactions, the LC resonance feature of the split ring resonator becomes invisible to the incident terahertz wave.

The Mars crustal magnetic field control of plasma boundary locations and atmospheric loss: MHD prediction and comparison with MAVEN

AbstractWe present results from a global Mars time‐dependent MHD simulation under constant solar wind and solar radiation impact considering inherent magnetic field variations due to continuous planetary rotation. We calculate the 3‐D shapes and locations of the bow shock (BS) and the induced magnetospheric boundary (IMB) and then examine their dynamic changes with time. We develop a physics‐based, empirical algorithm to effectively summarize the multidimensional crustal field distribution. It is found that by organizing the model results using this new approach, the Mars crustal field shows a clear, significant influence on both the IMB and the BS. Specifically, quantitative relationships have been established between the field distribution and the mean boundary distances and the cross‐section areas in the terminator plane for both of the boundaries. The model‐predicted relationships are further verified by the observations from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Our analysis shows that the boundaries are collectively affected by the global crustal field distribution, which, however, cannot be simply parameterized by a local parameter like the widely used subsolar longitude. Our calculations show that the variability of the intrinsic crustal field distribution in Mars‐centered Solar Orbital itself may account for ∼60% of the variation in total atmospheric loss, when external drivers are static. It is found that the crustal field has not only a shielding effect for atmospheric loss but also an escape‐fostering effect by positively affecting the transterminator ion flow cross‐section area.

A position measurement method for 3-degree-of-freedom motion based on magnetic detection

Generally, optical methods for precision measurement have limitations when rotation of large angle (larger than 10°) and translation of large range occur simultaneously. To deal with the problem, an improved method based on spatial magnetic detection is proposed for planar 3-degree-of-freedom position measurement with large ranges in this article. The position-solving algorithm of the method calculates position by decoupling 3 degrees of freedom with the magnetic flux densities of the inherent magnetic field of the permanent-magnet synchronous planar motor detected by the proposed Hall-sensor array. On the basis of previous work, the calculation approach of decoupling is improved; as a result, the calculations for solving position are simplified. The characteristics of the sensor topology are exploited further, and a new calculation approach of decoupling is introduced to compensate the original one, achieving better robustness to noise. The ability of solving 3-degree-of-freedom position and the robustness to noise and magnetic-field imperfections are evaluated by simulation; the results show that the accuracies of translational and rotational motions are 10 µm scale and 0.1° scale in the case with noise of 0.01% of signal amplitude, while they are 100 µm scale and 10° scale in the case with the magnetic-field imperfections caused by parameter deviations. Comparison experiments with commercial sensors are conducted on a self-developed testing platform to verify the feasibility of the method, and the results show that the method can achieve sensing a large rotational angle and a large translational range with a simple implementation.

Nature-inspired position determination using inherent magnetic fields

Many creatures in nature, including butterflies, newts, and mole rats, use the Earth's inherent magnetic field for navigation. They use magnetic field lines and variations in field intensity to determine their geographical position. This paper seeks to apply similar techniques to measure the positions of individual ferromagnetic objects found all around us in everyday life. Ferromagnetic objects have inherent magnetic fields around them. We show here that the magnetic field variation around a ferromagnetic object can be modeled using purely the geometry of the object under consideration. By exploiting this model, the position of the object can be measured quite accurately using a small inexpensive magnetic sensor. Further, the use of just one additional redundant magnetic sensor can eliminate the need to calibrate the position measurement system. As demonstrated in the paper through a series of experimental results, the developed measurement system is applicable to accurate position measurement of small and large ferromagnetic objects, including cars on highways, oscillating pistons in internal combustion engines, pneumatic cylinders, hydraulic cylinders, as well as moving parts in many machines.

Non-Intrusive Piston Position Measurement System Using Magnetic Field Measurements

This paper proposes a novel sensing system for the non-intrusive real-time measurement of piston position inside a cylinder. The proposed sensor exploits the principle that any ferromagnetic object has an inherent magnetic field which varies as a function of position around the object. Through modeling the magnetic field as a function of position and using sensors to measure magnetic field intensity, the position of the object can be estimated. This principle is used to measure the piston position in a free piston engine without requiring any sensors inside the engine cylinder. The piston is approximated as a rectangular metallic object and the variation of the magnetic field around it is modeled. A challenge arises from the fact that the parameters of the model vary from engine to engine and are cumbersome to calibrate for each engine. This challenge is addressed by utilizing two magnetic field sensors with known longitudinal separation between them. A number of estimation methods are proposed that identify and update magnetic field parameters in real time without requiring an additional linear variable differential transformer (LVDT) sensor for calibration. The advantages and performance of these estimation methods are compared. Experimental results from a free piston engine setup show that the proposed sensor can provide 0.4 mm accuracy in position estimates. The proposed sensing concept can be utilized for piston position measurement in multi-cylinder SI and diesel engines, hydraulic cylinders, pneumatic cylinders, and in many other position measurement applications.

Controlling heat input in non-consumable electrode arc welding

Analysis of the existing heating force control modes at non-consumable electrode arc welding of groove faces is carried out. Methods and experimental investigation results allowing for determining application field of the arc attitude positioning due to changing characteristic of its inherent magnetic field at non-consumable electrode argon-arc welding by current up to 200 A are covered.

Preliminary assessment of the effects of the application of an axial magnetic field during GMA welding of Al-6063-T6

Plates of Al 6063-T6 (6.35mm thick) were welded using an ER-5356 filler wire. The aim of the experiments was to assess the effects that yield the induction of an axial magnetic field (AMF) during gas metal arc (GMA) welding on the grain structure of the weld metal and on the mechanical properties of the welded joint. Magnetic fields between 0 to 15mT were induced by using a coil which was fed with different current intensities by an external power source. Plots of the grain size distribution showed that applying low magnetic fields homogenizes the grain structure of the weld metal and suppresses the typical columnar-dendritic growth from partially melted grains at the fusion line. The mechanisms involved in these phenomena are discussed with the aid of finite element analysis. Transverse microhardness profiles of the welds revealed a reduction in the loss of hardening in the heat affected zone (HAZ). The loss of hardening after fusion welding in heat treatable aluminum alloys is known as overaging and it is the result of coarsening and transformation of the strengthening phase [1]. It is thought that an electromagnetic interaction between the external magnetic field applied and the inherent magnetic field generated by the direct current of the welding process alters the diffusion process delaying over aging kinetics in the HAZ.