Magnetic Flux Gradient Research Articles

Power enhancement of vibration energy harvesters by way of magnetic flux gradient analysis of electromagnetic induction

This study proposes strategies to enhance the conversion of mechanical energy to electrical energy in cylindrical electromagnetic induction-type vibration energy harvesters (VEH) using disc or ring-shaped magnets and ring-shaped coils. The rationale behind these strategies has been substantiated by an analysis of magnetic flux gradients based on simulations. In particular, the utilization of a repulsive magnet pair and a yoke has been proposed to maximize the magnetic flux gradient at the coil winding position by manipulating the magnetic flux path. Simulation results confirm that the use of a yoke can produce a nearly 5.8-fold increase in power consumption at the external load. Additionally, the study demonstrates that the positioning and thickness settings of the coil are critical for improving the electrical output based on the spatial distribution of the magnetic flux gradient. Within the same magnet topology, points where power generation is not feasible due to a zero magnetic flux gradient are identified, besides a nearly 5.3-fold increase in observed power generation depending on coil placement. Given the structural feasibility of VEH implementation, a design for a moving magnet VEH utilizing ring magnets with a yoke enclosure is proposed, demonstrating that it can generate power at nearly 85% of the level attributed to using disc magnets.

Enhancing the magnetic field gradient between two superconductors with rotational motion under a background DC field

The ability of bulk high-temperature superconductors to trap magnetic flux densities up to one order of magnitude larger than the saturation magnetization of conventional ferromagnetic materials offers the prospect of generating large magnetic flux density gradients. Combining multiple superconductors, akin to assembling a Halbach array of permanent magnets, may increase the generated gradient even further. The associated challenge is that superconductors are prone to demagnetization when exposed to field components perpendicular to their main magnetization direction. In the present work, we investigate the magnetic flux density gradient achieved with a pair of cubic, bulk, large-grain melt-textured superconductors in the presence of a background DC magnetic field at 77 K. We investigate the increase of the performance when decreasing the temperature down to 59 K. The studied configuration consists in two facing cubic YBa2Cu3O 7−x superconductors of 6 mm side with anti-parallel magnetization directions. It is obtained after the simultaneous magnetization of the samples followed by a rotation of 180∘ of the top superconductor. Although the background field reduces the trapped field ability of individual samples, it is shown that this phenomenon is significantly mitigated at 65 K and at 59 K compared to 77 K. The results reveal that a sample-to-sample distance ( ∼16 mm) of the order of their size is sufficient to avoid any mutual demagnetization effect during the rotational motion. Furthermore, it is shown that decreasing the temperature is not only beneficial in increasing the field and field gradient achieved but also in extending the range of background fields in which the superconductor can be rotated without demagnetization. This superconducting assembly yields a magnetic flux density gradient exceeding that of an isolated superconductor and has the potential to surpass the capabilities of permanent magnets.

Mixed convection by buoyancy and magnetothermal forces

The magnetic force in the paramagnetic fluid depends on the local gradient of magnetic flux density and the temperature-dependent magnetic susceptibility. In the presence of the gravity, the buoyant force due to the temperature difference additionally overlaps, and the resultant flow becomes a mixed convection. In this study, the effect of the temperature-dependent magnetic force (magnetothermal force) on the natural convection was numerically investigated. The magnetic field formed by the permanent-magnet array was employed and effective one was discussed in terms of the heat transfer. A three-dimensional Rayleigh-Benard convection simulation was conducted with the magnet array below the bottom hot wall. It was found that the magnetothermal force enhances the convection not only where the magnet locates but also away from the magnet due to the force profile.

Impact behavior of a novel magnetorheological energy absorber based on wedge-shaped squeeze flow model

Magnetorheological (MR) energy absorbers (MREAs) have been extensively investigated as a means of dissipating impact energy and decreasing injury as well as used in a wide range of applications. When applied as an accidental collision buffer, however, problems can arise owing to the inertia of the sudden impact. In this study, a novel MREA with a gradient resistance gap structure working in a wedge-shaped squeeze flow model of a high-viscosity linear polysiloxane-based MR fluid was developed. The MREA has a continuously changing working gap and internal magnetic flux density gradient distribution representing a wedge-shaped structure. A Power-Law model inclusive of fluid minor losses (PLM)- of the damping force of an MREA with a wedge-shaped resistance gap was built to study the impact behavior. A second model also considered the effects of inertia (PLMI). The wedge angle was defined to quantitatively and comprehensively characterize the effects of the wedge-shaped resistance gap because of its significant influence on the dynamic characteristics. Two MREAs with wedge-shaped and equidistant working gaps were fabricated and tested using a drop tower facility with a mass of 600 kg. The experimental results show that the maximum damping force of the MREA with a wedge-shaped resistance working gap reached to as high as 235.8 kN and the dynamic range is increased by 6.5% compared to that with an equidistant working gap. The relative errors of the peak force for impact velocities between 2.8 and 4.2 m s−1 with no applied current were 1.84%–3.67% (PLM) and 0.63%–1.91% (PLMI), and with 3 A applied current were 2.35%–4.99% (PLM), and 1.24%–2.72% (PLMI), demonstrating that the PLMI-based model is capable of accurately predicting the dynamic behavior of the MREA.

Design, development, and performance analysis of plate-plate hybrid magneto rheometer considering uniform radial magnetic flux

The current study presents a magnetic numerical simulation of a plate-plate magnetorheometer using the finite-element method. In this study, a magnetorheometer with the least number of coil turns has been proposed and developed to obtain a high and consistent magnetic flux density (0.68 T at 3A) along the radius of the magnetorheological fluid (MRF) zone. The possibility of radial migration of MRF is eliminated by the lack of a magnetic flux gradient along the MRF zone’s radius. After comparing the temperature rise in the magnetorheometer caused by resistive and viscous heating in the simulation and the experiment, it has been found that the temperature rise has a negligible effect on the MR fluid. When we conducted studies in hybrid mode—that is, shear plus compression mode—we found that, under the same operating conditions, the shear stress was significantly higher compared to when we only used shear mode. In the combined shear plus compression mode, it has been observed that the effects of particle concentration and compression velocity have a significant impact on the shear stress value.

Non-contact embedded sensing by Magnetostrictive Carbon Fiber Reinforced Polymer (MagCFRP): A smart material for early inter-lamina localized damage detection

Although failure mechanics and plasticity of composite materials is a relatively new and volatile field, it has been long realized in the composite materials community that a composite’s true integrity lies in the constituents’ interfacial health. Composite materials allow scientists and engineers to design structural architectures with directional stress, strain, and thermal fields in mind while simultaneously reducing the system’s overall weight. While there are advantages to using composite materials like carbon fiber reinforced polymers (CFRPs), designing and implementing long-term sustainable aerospace structures out of CFRPs is bottlenecked by the brittle catastrophic failure mechanism high strength carbon composites exhibit. As the demand for these materials in critical loading regimes increases, it is paramount that scientists and engineers understand how CFRPs will behave in real-time and in predictive models for load profiles. This research’s motivation comes from the US Army’s future vertical lift vehicle initiative to transition from interval-based maintenance to condition-based maintenance (CDB). This paper explores a real-time, non-contact, and non-destructive evaluation (NDE) method for composite materials by performing localized magnetic flux scans (32 mm2 field of view) of CFRP embedded with Terfenol-D ([Formula: see text] microns in diameter), a magnetostrictive material. For Magnetostrictive Carbon Fiber Reinforced Polymer (MagCFRP) elastic regime testing, there was an observed localized magnetic flux gradient of more than 5 mT (4%) with a reversible flux of 100%. For MagCFRP elastic-plastic regime testing, a localized magnetic flux gradient of more than 3 mT (2%) with a reversible flux of only 25% was observed. Terfenol-D embedded CRFPs have shown promising results for detecting instantaneous stress and strain levels and detecting deviations in inter-lamina residual stress after critical loading. Acoustic emission (AE), Digital Image Correlation (DIC), and X-ray computed tomography (CT) scanning were used to validate the observed results.

Footstep-powered floor tile: Design and evaluation of an electromagnetic frequency up-converted energy harvesting system enhanced by a cylindrical Halbach array

Energy harvesting floor systems use the mechanical energy generated by human weight to produce electrical energy, providing sustainable power sources for low-power systems at pedestrian crossings. They also have the potential to serve as renewable energy solutions on a larger scale. This study evaluates the design and performance of a kinetic energy harvester floor tile. The system design employs a frequency up-conversion technique to utilize the force exerted by the weight of humans for creating vibrational movement. In addition, the use of the cylindrical Halbach array improves the magnetic flux gradient, leading to an increased power output. A semi-analytical model is presented to evaluate the system performance, which is then validated through available experimental analysis and finite element simulations. A sensitivity analysis is performed to assess the impact of various factors on system performance, ultimately determining the optimal configuration. The optimal modular system is then used to create a 30 × 30 cm2 tile. This tile is capable of generating energy while walking, running, jogging, slow running, and fast running, with power outputs of 0.57, 0.85, 1.11, and 1.42 W (0.57, 0.86, 1.11, and 1.58 mW/cm2) respectively. Additionally, it is estimated that 511 mJ (568 mJ/cm2) of energy is generated per step. Additionally, an assessment is conducted on the energy production capabilities and environmental advantages of a specific site, such as a subway station.

Magnetic field patterns as a tool for stress estimation in steel samples

In this work, steel square samples were subjected to varying degrees of compression, resulting in a distribution of simultaneous compressive and tensile stresses within the samples. The tangential component of the surface magnetic flux density was mapped along both the direction of compression and perpendicular to it, using a magnetic sensor, for each level of compression. The results show that the maps of the relative difference of magnetic flux density for different levels of applied stress, with respect to the flux density at zero stress, exhibited a diagonal stripes pattern. This pattern was discovered thanks to the particular surface stress distribution in square samples. The formation of these patterns could be attributed to the re-orientation of magnetic domains due to stress and the magneto-elastic effect, which was confirmed by the change in orientation of the magnetic flux density vectors obtained from the measurement of two of their components. Additionally, the maps showed an increase in contrast between high and low values with an increase in applied stress. Finally, the maps of the module of the gradient of magnetic flux density displayed a distinct diagonal chessboard-like pattern, and the contrast between low and high values increased with an increase in applied stress.

Research on vibration energy harvesting technology of power equipment based on alternating magnet array

AbstractVibration with a frequency of 100 Hz is widely distributed in the power equipment, and it can provide a new way to supply energy for sensors by vibration energy harvesting. The vibration energy harvesting method based on electromagnetic induction principle was studied through the arrayed structure of magnets and coils. Static magnetic field models were established for four magnet array structures and it was found that the alternating magnet array has the largest magnetic flux and magnetic flux gradient. Based on the alternating magnet array, prototypes of energy harvester with vertical and parallel movement mode were proposed. Through structural parameter optimisation analysis, two different energy harvesters were fabricated and it was found that the energy harvester with a parallel movement mode has better output performances. The energy harvester could provide output voltage/current and power of 8.35 V/17.39 mA and 15.13 mW (matched resistance is 200 Ω) at an acceleration of 5 m·s−2. The 100 mF capacitor could be charged to 2.72 V within 300 s, and the final voltage of the capacitor is greater than 3 V, which could sustainably drive commercial wireless temperature/humidity sensors.

A Suitable Magnetic Field Source Composed of an HTS Coil and HTS Bulks for Magnetic Drug Delivery System

To realize Magnetic Drug Delivery System (MDDS), it is necessary to reduce the frictional force on the inner surface of the blood vessel and increase the magnetic force in the longitudinal direction of the blood vessel acting on magnetic drugs deep inside the body. In other words, where the magnetic drugs are concentrated, the magnetic flux density gradient in the longitudinal direction of the blood vessel must be large and the magnetic flux density gradient perpendicular to the blood vessel surface must be small. However, creating such a magnetic field distribution with a single magnetic field source is difficult. Therefore, we investigated a magnetic field source configuration method that can increase the magnetic flux density gradient in the longitudinal direction of the blood vessel and decrease the magnetic flux density gradient perpendicular to the blood vessel surface by configuring the magnetic field source with an HTS coil and zero-field-cooled HTS bulks and using the antimagnetic effect of the HTS bulks. We examined the effect of the number of cylindrical HTS bulks on the magnetic force acting on the magnetic drugs. The shielding current field of the HTS bulk had the effect of reducing the magnetic flux density gradient perpendicular to the blood vessel surface and the relative position of the area where the magnetic drugs are concentrated and the shielding current region within the HTS bulk greatly affected the magnetic flux density gradient perpendicular to the blood vessel surface. Based on these results, we examined the effect of the distance between two cylindrical HTS bulks placed inside an HTS coil on the magnetic force acting on the magnetic drugs. The magnetic force in the longitudinal direction of the blood vessel was able to be increased by placing the HTS bulks so that the boundary of the HTS bulk (shielding current region) is near the area directly below the area where the magnetic drugs are concentrated. The distance between the square-column HTS bulks that maximized the magnetic force was longer than that of the cylindrical HTS bulks.

Particle-in-Cell Simulations for the Improvement of the Target Erosion Uniformity by the Permanent Magnet Configuration of DC Magnetron Sputtering Systems

Improving the target erosion uniformity in a commercial direct current (DC) magnetron sputtering system is a crucial issue in terms of process management as well as enhancing the properties of the deposited film. Especially, nonuniform target erosion was reported when the magnetic flux density gradient existed. A two-dimensional (2D) and a three-dimensional (3D) parallelized particle-in-cell (PIC) simulation were performed to investigate relationships between magnetic fields and the target erosion profile. The 2D PIC simulation presents the correlation between the heating mechanism and the spatial density profiles under various magnet conditions. In addition, the 3D PIC simulation shows the different plasma characteristics depending on the azimuthal asymmetry of the magnets and the mechanism of the mutual competition of the E × B drift and the grad-B drift for the change in the electron density uniformity.

Thermomagnetic instabilities in 3D network of superconducting lead nanofilaments in porous glass

Thermomagnetic instabilities in the lead-porous glass (Pb-PG) nanocomposite in superconducting state were studied, and a model was proposed that relates magnetization jumps and heat release spikes with average critical current density. The samples were created by filling porous glass (characteristic pore size d = 7 nm) with lead from a melt under pressure, which created a 3D multiply connected system of lead filaments. The critical temperature of superconducting transition in Pb-PG T c = 7.2 K is the same as for bulk lead and the critical magnetic field H c (0) ≈ 40 kOe is much higher than H c bulk (0) ≈ 800 Oe for bulk lead. Hysteresis and magnetic flux jumps were observed in the magnetization curves m(H) of the Pb-PG nanocomposite, which are connected with the formation of magnetic flux gradients in a system of interconnected contours. Magnetic flux jumps are thermomagnetic processes accompanied by heat release which was directly observed by measuring adiabatic temperature change in the sample during magnetic field sweep. The flux jumps in the magnetization and heat release events were almost periodic in the magnetic field. The period dependences on the magnetic field are similar to the calculated average critical current density dependence j c (H).

Characterising the stress ratio effect for fatigue crack propagation parameters of SAE 1045 steel based on magnetic flux leakage

The aim of this study was to determine the relationship between fatigue crack length, a, the number of cycles, N, the magnetic flux gradient intensity, dH/dx and the stress ratio, R. Fatigue crack growth tests were performed using a constant tensile load amplitude on SAE 1045 steel in the form of single-edge cracks. Stress ratio values of 0, 0.1, 0.2, 0.3 and 0.4 were used to study the characteristics of the magnetic flux gradient. A crack opening displacement device was used to detect the parameters of the stress intensity factor range, ΔK, fatigue crack growth rate, da/dN, and N. Meanwhile, a metal magnetic memory sensor device was used to detect the H value at the stress concentration zone when a 1 mm-increase in the crack occurred. The experimental results showed that as the fatigue cycle and crack length increased for each R, dH/dx also increased exponentially. The governing equations were derived based on the magnetic flux gradient for the fatigue crack length equation and the fatigue cycle equation, with the stress ratio. Based on a statistical analysis of the magnetic flux leakage signals, it was found that all the data were within a range based on a 90 % confidence level. Thus, the magnetic flux leakage parameters could be used to construct fatigue crack growth behaviour models for ferromagnetic materials and potentially as an alternative method for predicting the fatigue life.

A Non-Uniform Planar Coil in Electromagnetic Vibration Energy Harvesting for Enhanced Output Power

Planar electromagnetic vibration energy harvester (EVEH) is a promising technology for compact, low form factor self-powered wireless devices. However, planar EVEH has the limitation of non-fully utilized magnetic flux gradient and low output power due to its structure constraint and weak magnetic flux gradient capturing capability. Planar coil is the key component in harvesting magnetic flux gradient and determining the output electromotive force (EMF) voltage and output power. A novel non-uniform distributed planar (NUDP) coil is proposed to break the current limitation of output power for the planar coil. The boost in output power is realized with tight inner windings and loose outer windings. The breakpoint is determined based on power increasing rate for each winding. The optimal winding radius for both inner and outer coils is investigated using discrete non-linear constraint heuristic optimization method. The designed NUDP coil-based EVEH achieves peak-to-peak output voltage of 305 mV and output power of 1.163 mW at 64.3 Hz resonant frequency and 0.05 g acceleration. It realizes 16.3% higher output power and 19.4% higher output voltage than uniform distributed planar (UDP) coil under the same spring and magnet. The power density of the proposed prototype reaches 9.616 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> g <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is 15.025 times higher than the state-of-the-art EVEHs with the planar coil.

Detection of Uniaxial Fatigue Stress under Magnetic Flux Leakage Signals using Morlet Wavelet

This paper demonstrates the application of continuous wavelet transform technique for magnetic flux leakage signal generated during a uniaxial fatigue test. This is a consideration as the magnetic signal is weak and susceptible to being influenced by an external magnetic field. The magnetic flux leakage signal response of API steel grade X65 is determined using Metal Magnetic Memory under cyclic load conditions ranging from 50% to 85% of the UTS. To facilitate further signal analysis, the magnetic flux gradient, the dH(y)/dx signal were converted from a length base into time series in this study. Magnetic flux leakage readings indicated a maximum UTS load of 56.5 (A/m)/mm at 85%, where a higher load resulted in a higher reading and the signal contained Morlet wavelet coefficient energy of 1.02×106 µe2/Hz. As increasing percentages of UTS loads were applied, the signal analysis revealed an increasing linear trend in the dH(y)/dx and wavelet coefficient energy. The analysis revealed a strong correlation between the wavelet coefficient energy and the dH(y)/dx amplitude, as indicated by the coefficient of determination (R2) value of 0.8572. Hence, this technique can provide critical information about magnetic flux leakage signals that can be used to detect high stress concentration zones.

Optimization of a vibrating MEMS electromagnetic energy harvester using simulations

Nowadays, wireless sensor networks (WSN) are becoming essential in our daily life. However, a major constraint concerns the energy power supply. Indeed, batteries need to be recharged or replaced often which implies a limited lifetime for WSN nodes. One alternative consists in harvesting mechanical energy from surrounding vibrations of the environment. Using finite element simulations, we report here a complete guideline to optimize a MEMS electromagnetic energy harvester consisting of an in-plane vibrating silicon frame supporting an array of micromagnets that faces a static 2D micro-coil. The dimensioning of the magnet array and the specific design of the coil are addressed, considering patterned 50 \(\upmu \)m thick NdFeB films with out of plane magnetization. The optimization of the electromechanical coupling which allows to efficiently convert the energy results from a trade-off between the high magnetic flux gradients produced by the micromagnets and the maximum number of turns of the facing coil.

Trapped magnetic field distribution above a superconducting linear Halbach array

In applications requiring a large magnetic force, permanent magnets with non-parallel magnetization directions can be assembled in a Halbach array to generate a large gradient of magnetic flux density. The saturation magnetization of permanent magnets, however, brings a fundamental limit on the performance of this configuration. In the present work, we investigate experimentally the assembly of cuboid bulk, large grain melt-textured YBa2Cu3O superconductors ( mm3) with orthogonal c-axes so as to form a basic unit of Halbach array. The experiments are carried out at 77 K. The experimental distribution of the magnetic flux density above the array of trapped-field superconductors is compared to a similar array made of permanent magnets. A simple analytical model is developed and is shown to accurately reproduce the main experimental observations. The results suggest that a redistribution occurs in the current flowing in the central sample when the distance between the superconductors is reduced, whereas the neighbouring superconductors are unaffected. It is shown that this current redistribution yields a reduced contribution of the central sample to the magnetic flux density above the centre of the array and a new negative contribution associated with stray fields to the magnetic flux density at this location. This interpretation is confirmed by modelling of the distribution of transport currents in the superconductor using a 3D finite element model.

Energy Harvester Based on an Eccentric Pendulum and Wiegand Wires.

This study proposed an energy harvester that combines an eccentric pendulum with Wiegand wires to harvest the kinetic energy of a rotating plate. The energy harvester converts the kinetic energy into electrical energy to power sensors mounted on the rotating plate or wheel. The kinetic model is derived from the Euler–Lagrange equation. The eccentric pendulum generates a swing motion from the direction variation of the centrifugal force and the gravitational force. The magnetic circuit is designed such that, during the swing motion, an alternating magnetic field is formed to induce the output voltage of the Wiegand wire. COMSOL software was used to simulate magnetic flux density and optimize the geometric parameters of magnets. Response surface methodology was used to formulate the output voltage model. Magnetic flux density affects output voltage dramatically. However, the output voltage is not sensitive to the gradient of magnetic flux density. The experimental results indicate that when the Wiegand wire is 14.2 mm from the magnet, the generation power is 0.118–1.15 mW, in a speed range of 240–540 rpm. When the Wiegand wire is 7.0 mm from the magnet, the generation power is 0.741–1.06 mW, in a speed range of 480–660 rpm.

Transcranial stimulation analysis using the smoothed finite element method

This paper presents a series of smoothed finite element methods (SFEM) for transcranial stimulation simulations. The problem domain is first discretized into a set of four-node tetrahedral elements, and linear shape functions are employed to interpolate the field variables. Then, the smoothing domains are further formed in conjunction with the nodes, edges or faces of elements. In order to improve the accuracy of low-order interpolation, the magnetic flux density and gradient of electric potential are smoothed using the gradient smoothing technique (GST) over each smoothing domain. Based on the generalized smoothed Galerkin weakform, the discretized system equations are finally obtained. Numerical examples, including transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) problems, demonstrate that the SFEM possesses the following important properties: (1) better accuracy; (2) faster convergence; (3) higher computational efficiency; (4) more robust in transcranial stimulation simulations.

Selection field generation using permanent magnets and electromagnets for a magnetic particle imaging scanner

This paper presents a comprehensive study on modeling and implementation of the selection field using NdFeB permanent magnets, electromagnetic coils, and a hybrid system for magnetic particle imaging (MPI). Selection fields were designed for 71 mm internal workspace and their size was based on an 11.25% enhanced ratio of Maxwell configuration. The magnetic particle imaging technique uses a gradient field to define a field of view (FOV) and generate a field-free point (FFP) which is applied to localize superparamagnetic nanoparticles (SPIONs). This study aims to develop a selection field for a new 3D magnetic particle imaging scanner at (−2.15, −2.15, 4.3) T/m gradient field in (x, y, z) directions, respectively. Three different topologies for gradient fields were numerically modeled in COMSOL and analytically calculated in MATLAB for magnetic flux density (mT) and gradient field strength (T/m). A selection field with NdFeB permanent magnets was practically implemented and its result was compared with the outcomes of a numerical simulation model. Experimental results of permanent magnets selection field topology agreed well with the numerical results from COMSOL. Numerical and analytical results of other selection field topologies were in good agreement. Spatial homogeneity of the selection field topologies was investigated over a range of 40 mm symmetric across the FFP and cost-effective analysis was performed to choose an optimum topology. A hybrid system resulted in better homogeneity over the permanent magnet and electromagnetic topologies with 96.8% spatial homogeneity, and 0.30% relative gradient field strength error. High spatial homogeneity of the gradient field minimizes the image artifacts of the MPI.