Circular Magnetization Research Articles

Simpler optimized stellarators using permanent magnets

A first-of-a-kind optimized stellarator for confining plasma has been designed and is being constructed with planar circular coils and permanent magnets composed of identical elements. The equilibrium is optimized to be quasi-axisymmetric for good particle confinement. The combination of permanent magnets and planar coils is significantly simpler to construct than fabricating three-dimensionally shaped coils, yet they are able to produce lower helical magnetic ripple than existing devices by two orders of magnitude in , a characteristic neoclassical transport metric.

A High‐Performance Rotational Energy Harvester Integrated with Artificial Intelligence‐Powered Triboelectric Sensors for Wireless Environmental Monitoring System

The prevailing energy harvester utilizes a convectional magnet that limits the output power due to the imperfect coupling of the flux linkage and the leakage of the magnetic fluxes away from the coil. Herein, a circular Halbach array magnet comprising the arc magnets is proposed as a high‐performance rotational energy harvester for preventing flux leakage by concentrating the magnetic flux in a particular path. The Halbach magnet is made up of eight individual arc magnet segments that are kept apart by 1 mm to induce a fourfold increase in magnetic flux density over a conventional magnet. The proposed rotational energy harvester can deliver an exceptional 603.2 W m−3 power density, which is attributed to a three times increase in the power density. The harvested power is utilized to charge a 30 mAh battery for driving a complete IoT system for the development of self‐powered wireless environmental monitoring systems. Furthermore, an intelligent system is designed using cutting‐edge artificial intelligence (AI) technology which accounts for Mxene/P(VDF‐TRFE)‐based triboelectric sensor output data and considers different weather parameters to accord a high accuracy of 99% in wind speed prediction.

Design and research of hybrid piezoelectric-electromagnetic energy harvester based on magnetic couple suction-repulsion motion and centrifugal action

In this paper, a hybrid piezoelectric-electromagnetic energy harvester (HEH) based on magnetic couple suction-repulsion motion and centrifugal action is proposed. Using a control variable approach, the effect of two variables on the output performance was investigated under different parameter conditions in order to maximize the output power. At a mounting angle of 60 degrees for the piezoelectric cantilever beam and a mass of 3.2 g for the rectangular magnet, the entire piezoelectric-electromagnetic harvester can produce 13.32 mW of power, which can successfully power low-power electronic devices such as light-emitting diodes (LEDs). The power generated by mixing piezoelectricity and electromagnetism is 1.16 times greater than the power generated by the piezoelectric generation unit alone and 70.1 times greater than the power generated by the electromagnetic generation unit alone. The composite piezoelectric-electromagnetic hybrid mechanism greatly increases the power output of the entire structure compared to the single generation mode. The suction-repulsion process is accomplished using magnetic coupling. This makes the piezoelectric cantilever beam deformed by the magnetic force and has power output. At the same time, the magnetic suction-repulsion makes the circular magnet complete cutting magnetic induction line motion at the same time, which cleverly combines piezoelectricity and electromagnetism. The form of reciprocating motion of the magnet in the coil frame using suction-repulsion is also proposed for the first time. In addition, compared with those structures that strike the piezoelectric cantilever to generate electricity, this paper uses magnetic coupling, which makes the piezoelectric cantilever beam more durable and longer in use. In summary, this structure has good prospects for application in the direction of powering wireless networks or low-power electronic devices.

A 3-D Force Sensor Based on Combination of Magnetic and Piezoresistive Transduction

Tactile sensors have been playing a crucial role in the operation of robot hands, especially in the analysis of grasping stability. However, the current three–dimensional (3-D) force sensors generally adopt the single sensing transduction(such as the capacitive 3-D force sensor only includes capacitance as a sensing transduction) and output the coupled signals, lacking accurate force decoupling. Here, we present a 3-D force sensor with self-decoupling by combining magnetic and piezoresistive transduction. Based on the characteristics of axially magnetized circular magnet, we explain the sensing principle of shear force which is using four Hall elements mounted with the cross-type to measure the shear force by detecting the sliding distance and direction of the magnet (can only move horizontally), and utilize a piezoresistive element to measure the normal force. In addition, we use a neural network to model the sensor response to improve the detection accuracy of shear force. The sensor resolutions for normal force and shear force are 0.3N and 0.2N, respectively, and the measurement ranges are more than 20N and 6N, respectively. By mounting our sensor at the gripper, we further show the performance of sensor for detecting 3-D force in the process of grasping object. The proposed 3-D force sensor could be beneficial for the adaptive grasping of robot hands.

Characteristic Analysis, Simulation, and Experimental Comparison of Two Kinds of Circular Magnet Array in Energy Harvesting

The circular Halbach array is of great application value in electromagnetic energy conversion. The Halbach array can be formed with multiple magnets according to a specific method. The magnetic flux intensity of the magnet array is concentrated and enhanced in a certain area. The concentrated magnetic flux intensity could lead to a higher rate of change in the magnetic flux when the magnet and the coil move relatively. The spatial arrangement, structural dimensions, and residual flux density of the Halbach array are the main factors affecting its performance. Some areas with almost no magnetic induction in the Halbach array affect the performance of electromagnetic energy conversion. This paper conducted a comparative study of the Halbach array and the two-directional magnet array in terms of energy conversion. The root mean square (RMS) value and phase of the induced voltage in the coil were analyzed by a finite element method. Simulation shows that the RMS value of the induced voltage in the coil is equal when the gap is 1.55 mm and the REMEH adopts either of the two magnet arrays. The two-directional array has advantages in the energy harvesting performance when the gap is less than 1.55 mm, while the Halbach array has advantages in the energy harvesting performance when the gap is greater than 1.55 mm. The experimental verification of the designed prototype was implemented in this study. The experimental voltage is in good agreement with the simulation voltage. The threshold value of the gap in the experiment is about 2 mm, which is slightly higher than the simulation value. This characteristic has a certain reference value for the application of the Halbach array in the electromagnetic field.

Competition of localized thermal buoyancy and Lorentz forces in an electrolyte enclosed in a cavity

We study the flow of an electrolyte inside a slender square cavity produced by two competing localized forces, the thermal buoyancy force produced by the heating of a central part of the horizontal bottom wall and a vertical downward Lorentz force. This force is produced by a constant horizontal electric current between the slender vertical walls and a couple of circular magnets with opposing polarization placed on the center of both square vertical walls. The flow inside the cavity is considered two dimensional and simulated using the lattice Boltzmann equation method. We find the map of the flow patterns and their transitions for a Grashof number Gr in the range 0≤Gr≤4×103 and a Chandrasekhar number Ch in 0≤Ch≤1×107. For Gr≤2×103, the plane Gr-Ch can be divided in three regions with sharp changes in the flow patterns and the average Nusselt number on the top wall and the average asymmetry. One region is dominated by the buoyancy force, another by the Lorentz force, and there is an intermediate one, where neither of these forces dominates. For larger Gr, there are no sharp transitions.

Magnon transport in Y3Fe5O12/Pt nanostructures with reduced effective magnetization

For applications making use of magnonic spin currents damping effects, which decrease the spin conductivity, have to be minimized. We here investigate the magnon transport in an yttrium iron garnet thin film with strongly reduced effective magnetization. We show that in a three-terminal device the effective magnon conductivity can be increased by a factor of up to six by a current applied to a modulator electrode, which generates damping compensation above a threshold current. Moreover, we find a linear dependence of this threshold current on the applied magnetic field. We can explain this behavior by the reduced effective magnetization and the associated nearly circular magnetization precession.

Towards self-powered technique in underwater robots via a high-efficiency electromagnetic transducer with circularly abrupt magnetic flux density change

In this article, we present a high-efficiency electromagnetic transducer harvesting kinetic energy from the ocean current for self-powered technique in underwater robots to tackle the electric energy replenishment problem. A circular magnet array with alternating magnet arrangement was employed for providing a sudden change in magnetic flux density. A gear train was introduced into the compact design to greatly increase the rotation speed of the rotor. The finite element method is used to simulate and compare the magnetic flux density distributions and the induced voltages in the coil under different magnet arrays (conventional Halbach magnet array and proposed alternating one) with different magnet dimensions and numbers. The finite element method analysis shows that the alternating array displays a much larger changing magnetic flux density rate resulting in high induced electromotive forces. The experimental results based on a fabricated prototype indicate that the transducer yields maximum average output power of about 0.51 W with an energy conversion efficiency of 30.91% under the water flow speed of 0.64 m/s with a load resistance of 1 kΩ. We also investigated the capability of the transducer for self-powered applications in underwater robots. The transducer charged a 20 mF capacitor from 0 V to 29 V in 50 s. Also, the prototype charged a lithium battery embedded inside an underwater robot by 75% within 400 s. This study, with a broad application prospect, can advance the future development of self-powered underwater robotic systems.

Non-contact long-range magnetic stimulation of mechanosensitive ion channels in freely moving animals.

Among physical stimulation modalities, magnetism has clear advantages, such as deep penetration and untethered interventions in biological subjects. However, some of the working principles and effectiveness of existing magnetic neurostimulation approaches have been challenged, leaving questions to be answered. Here we introduce m-Torquer, a magnetic toolkit that mimics magnetoreception in nature. It comprises a nanoscale magnetic torque actuator and a circular magnet array, which deliver piconewton-scale forces to cells over a working range of ~70 cm. With m-Torquer, stimulation of neurons expressing bona fide mechanosensitive ion channel Piezo1 enables consistent and reproducible neuromodulation in freely moving mice. With its long working distance and cellular targeting capability, m-Torquer provides versatility in its use, which can range from single cells to in vivo systems, with the potential application in large animals such as primates.

Reply to “Comment on ‘Magnetic circular dichroism versus orbital magnetization' ”

The relationships between orbital magnetization and some magnetic properties derived from dichroic spectroscopy are further clarified.

Giant magneto impedance effect of Co-rich amorphous fibers under magnetic interaction

The quasi-metallic fibers were selected from 1 to 40 pieces and connected in parallel in this study. The giant magneto impedance (GMI) effect of Co-based melt extract fibers in the bundle mode was investigated, and the distribution of the surface circumferential magnetic field on the fibers was also analyzed. Such distribution was induced by the driving current, which gave rise to the circular magnetization process and the GMI effect. The improved GMI effect with much higher field sensitivity was observed in these fiber bundles. Results show that the field sensitivities of the four-fiber and six-fiber bundles reach 19.5 V·m·kA−1 (at 1 MHz) and 30.8 V·m·kA−1 (at 5 MHz). The circumferential magnetic field distributed throughout the fiber’s circumferential surface is rearranged and becomes uneven due to the magnetic interaction among fibers. There are both strengthened and weakened magnetic field parts around these fibers’ surfaces. The strengthened magnetic field improves the circumferential domain magnetization of the surface, resulting in larger GMI effects. However, the weakened parts inhibit the circumferential magnetization process and, therefore, the GMI effect. This also induces greater magnetization damp because of the increased domain interactions under the strong skin effect. The co-effect between the magnetic domains and the circumferential magnetization induces the optimization of the GMI effect in the four-fiber bundles. The observed GMI effect proves that fibers in bundle form can modify the sensitivity of the GMI effect. Moreover, different fiber bundles could be tuned according to the working conditions in order to manipulate the GMI response.

Interference of a magnetic field generated by circular magnets in the retention of chromium by microbial cells and in the morphology of a mixed culture during the bio-removal of chromium from effluent

A magnetic field of 5 Hz and magnetic field intensities of 15.9 and 57.8 m T, generated by 40 circular magnets, was investigated with the objective of influencing mixed culture in the removal of chromium and total organic carbon (TOC) from an effluent contaminated with Cr(VI) and verifying the effects on mixed culture morphology and the retention of chromium by microbial cells during the treatment process. For the magnetic field time of 7 h and 48 min, the removal of Cr(VI), total Cr, and TOC corresponded to 99.97 ± 0.01, 74.2 ± 1.2, and 25.1 ± 1.5 %, respectively. This was higher than results obtained when the bioreactor was operated without a magnetic field for the evaluated time. The amount of chromium retained in the cells by the experiments with and without magnetic fields was 0.59 and 0.53 %, respectively, justifying one of the mechanisms that increase the removal. The morphology of the mixed culture did not show changes in the images from scanning electron microscopy with the presence of chromium or the magnetic field.

Static magnetic field enhanced methane production via stimulating the growth and composition of microbial community

Corn stover has a potentially valuable use as a substrate for biogas production by anaerobic fermentation. Preprocessing of corn stover, such as alkali pretreatment, is usually needed to increase substrate availability. In this study, an experimental biogas production system using a flat circular permanent magnet with a central hole to provide a static magnetic field (SMF) was devised to increase biogas production from corn stover substrate, without pretreatment, by anaerobic fermentation. The effects of varying SMF intensity on the growth of microbe populations in the activated sludge were not linear. Optimal SMF intensity was found to be 11.4 mT (±2%). At this level, the number of microbe populations increased by 85.5% compared to the control. Total gas production and CH4 content of SMF were 19.5% and 20.0% higher than those from the control NMF (no magnetic field). SMF influenced the composition of the bacterial population and significantly increased the percentage of methanogenic archaea in the overall microbe population compared to NMF. Archaea of the order methanocellales were the principal methanogenic archaea found in the decay stage. Our results indicate that SMF can potentially increase biogas production by converting agricultural waste into energy. Life cycle analysis showed that the conversion rate of chemical energy in corn stalks to CH4 was 15.2%.

A dual piezoelectric energy harvester with contact and non-contact driven by inertial wheel

In this paper, a dual piezoelectric energy harvester with contact and non-contact driven by inertial wheel is designed to explore relationship between the mass of inertia wheel and the generator performance. This harvester consists of rectangular and circular lead zirconate titanate (PZT) plates, magnet and other support structure. The model is simplified and analyzed. The supporting structure of the energy harvester is manufactured by 3D printing technology, and the standard parts such as bolts are assembled. The test system is built and the prototype is tested under different rotation speed (from 100 to 1300 r/min) and inertia wheel mass (227, 287, 348 and 407 g). This study has shown that under constant driving conditions (1000 r/min), the optimal peak-to-peak voltage and root-mean-square power are 36.07 V, 5.31 V and 5.47mW, 0.05mW across the 5kΩ resistor. Moreover, the optimal root-mean-square voltage and power are 4.87 V, 613.01 mV and 1.15mW, 21.04 μW across the 10kΩ driven through an inertial wheel. Moreover, the energy conversion efficiency of the energy harvester is 18.27% driven at the inertial wheel of 407 g. Therefore, this energy harvester can be used to collect the energy stored during the idling of the inertia wheel to supply sensor.

Improved Flow-Induced Vibration Energy Harvester by Using Magnetic Force: An Experimental Study

Vibration energy harvesting has attracted considerable attention because of its application prospects for charging or powering micro-electro-mechanical system. Abundant hydrokinetic energy of water at low velocity is contained in the fluid environment, such as rivers and oceans, which are widely existing in nature. In this paper, a flow-induced piezoelectric vibration energy harvester (PVEH) with magnetic force enhancement, which is integrated by piezoelectric beam, circular cylinder bluff body and magnets, is proposed and experimental investigated. It could transfer the hydrokinetic energy, both the vortex-induced vibration and magnetic force excitation underwater, into electricity. First, the frequency sweep experiment of the piezoelectric cantilever beam is carried out to determine the resonance frequency where the effect of magnetic force on the vibration characteristic is obtained. Furthermore, the flow-induced vibration experiment platform is setup and the energy harvesting performance of the PVEH is investigated in detail. The effects of the magnet property, flow velocity and the magnetic poles distance on the vibration frequency and the acquisition voltage are demonstrated and discussed. The results show that it could improve the harvesting performance by introducing magnetic force. It has advantages in higher output voltage for the flow-induced PVEH, especially in low velocity water flow, when the flow velocity is 0.35 m/s, the PVEH under attractive magnetic force with magnetic distance of 20 mm scavenges the higher acquisition voltage of 5.2 V, which is increased by 225% than the PVEH with non-magnetic. The results can be applied to guide further fabrication process and optimized design of the proposed flow-induced PVEH underwater with low flow velocity.

Stellarators with Permanent Magnets.

It is shown that the magnetic-field coils of a stellarator can, at least in principle, be substantially simplified by the use of permanent magnets. Such magnets cannot create toroidal magnetic flux, but they can be used to shape the plasma and thus to create poloidal flux and rotational transform, thereby easing the requirements on the magnetic-field coils. As an example, a quasiaxisymmetric stellarator configuration is constructed with only 8 circular coils (all identical) and permanent magnets.

Brain Tumor Detection using Image Segmentation Techniques on MRI Images

A refine and absolute detection of the human disease can increase the level for the survival of well being. One of the major diseases can be determine as cancer or brain tumor. Different technique used for the tumor detection such as MRI (Medical Resonance Image), Ultrasound etc. It does not involve the X-ray so there are not side effects of MRI. Claustrophobic sensation can occur with MRI scanning because of the close machine with the suffocation and no movement while the scan can increase the time to complete the scanning process while movement can cause the errors or edge distortion. An MRI or magnetic resonance imaging is a radiology technique scan that uses radio waves and with the help of computer to produce images of different body parts. MRI scanner is a tube surrounded by a giant circular magnet. The patient is placed on a moveable bed that is inserted into the magnet. The magnet creates a strong magnetic field that aligns the protons of hydrogen atoms, which are then exposed to a beam of radio waves. A computer receives the information, which produces an image. MRI is the most accurate and safe method to detect the diseases by detecting the slight change in the body. For the best result various image segmentation techniques and the good edge detection algorithms are used for finding the edge to get the effective images for the examination purpose of medical images.

Optimisation method of magnetic levitation actuator for rotary table

This study presents a general optimisation method for determining the dimensions of the magnetic levitation (maglev) actuator for rotary tables. Combined with an improved electromagnetic numerical model of the maglev rotary tables, the optimal thickness dimensions of coils and magnets are obtained by the evolutionary optimisation algorithm. Different from the existing magnetic force model built by the harmonic analysis method, the improved numerical model involves the clearances of the neighbouring magnets in the circular magnet array and applies the numerical integration method to solve the complex Lorentz integrals. According to the evaluation function based on the numerical force model, the optimal thickness dimensions are determined via an evolutionary optimisation algorithm. By this method, the size of coils and magnets in the rotary table with the circular Halbach magnet array can be determined accurately and directly, rather than obtaining a single structure dimension by an analytical approach. In this work, the method is applied to optimise the dimensions of a maglev rotary table, and a prototype is manufactured according to the obtained optimal parameters. The experimental and simulation results verify the accuracy and validity of the proposed optimisation design method.

Improve resistance spot weld quality of advanced high strength steels using bilateral external magnetic field

Magnetically assisted resistance spot welding (MA-RSW) process has been verified capable of improving weld quality of advanced high strength steels. In the original MA-RSW process, a pair of axial mutually repulsive circular permanent magnets was adopted to produce a radial magnetic field in weld nugget region. However, the circular magnets lead to interference problems with surrounding work-pieces or fixtures in welding process, which restricts its wide use. To solve this problem, in this paper, a bilateral magnetically assisted apparatus was developed, which used a pair of axial mutually repulsive magnets with a volume of nearly 60 % smaller than that of the conventional circular one and thus could significantly avoid interference in production environment. To investigate the improvement effect of the small-sized magnetic assisted apparatus, two types of MA-RSW process, e.g. bilateral MA-RSW (BMA-RSW) process and circular MA-RSW (CMA-RSW) process were investigated on 1.6 mm thick bare dual-phase steel DP590 through comparing with the traditional RSW process. The results showed that although the stirring region in BMA-RSW process is much smaller due to its small volume, it could achieve almost the same improvement effect as the CMA-RSW process in terms of weld lobe, macro morphology, microstructure and mechanical properties, due to its stronger local stirring effect underneath the bilateral permanent magnets.

Electromagnetic design of superconducting multipole corrector magnets based on sector coils

We present here analytical formulas derived for sector coils with 2N poles, an iron screen and optional iron poles. These formulas can be used to produce optimized conceptual electromagnetic designs of superconducting cosine-theta corrector magnets with 2N poles. The main guidelines of the corresponding algorithm, i.e., design algorithm for sextupoles and higher, which has been used to produce valid conceptual electromagnetic designs of the Future Circular Collider sextupole and octupole magnets, are also presented. Generic conceptual design studies performed with DASH and DASH2in1 (for nested corrector magnets configurations) are also shown and their outcome is discussed.