Levitation Coil Research Articles

Experimental observation of the vertical displacement between heating and levitation regions in an electromagnetic levitation coil

Scientific progress in the relevant fields of science and technology requires the production of crystals with quality beyond the current state of the art. Electro-magnetic levitation (EML) is a prospective method for the growth of high-purity crystals, allowing for avoidance of any contact between the crystal-melt and the crucible. Contactless crystal growth reduces the number of crystal defects commonly abundant in conventional crystal growth methods. The EML method also allows crystal growth of materials with very high melting points. In this article, we report detailed measurements of the EML method. The induction coil used in this study has three turns and one counterturn. We subject different metal material (Al, Cu, Sn, and Ni) samples to the induction coil’s electromagnetic field. For each sample, we measure the induced lift force, Joule heating, and components of magnetic induction as a function of position inside the coil. The results show that the maximum heating in an EML coil is emitted in the area below the levitation zone, a discrepancy not reported earlier. Our findings suggest that this shift should be considered in coil design to avoid instability of the levitated material. We hope this study will serve as a stepping stone for developing EML techniques. The experimental results we provide will be used to evaluate the accuracy of current and future theoretical models of EML coils. This, in turn, will facilitate progress in the application of EML to the growth of larger crystals of higher quality.

Development of SQUID detection technology for a superconducting gravimeter.

In this paper, we present research on the development of SQUID (Superconducting QUantum Interference Device) detection technology for a superconducting gravimeter (SG), aiming to achieve precise real-time measurements of gravity. We provide an introduction to the composition and internal details of the SQUID-based superconducting gravimeter (SSG). The internal components of the SSG are designed based on theoretical calculations to optimize the system and enhance its sensitivity. With the current in the levitation coil set to persistent mode, a unique proof mass is levitated through electromagnetic force. We demonstrate the equilibrium position of the levitated proof mass by assessing the change in the coil inductance. Furthermore, we present preliminary experimental results of earth tidal measurements using the developed SQUID detection technology and compare these outcomes with measurements from an absolute gravimeter (FG5X) and with theoretical calculations. These comparisons confirm the potential of the proposed new gravity measurement technology.

A novel magnetic circuit and structure for magnetic levitation ruler

The single axis linear displacement measurement system of CMM is composed of grating ruler, servo motor and linear motion mechanism. Although the measuring accuracy of grating ruler is high, the accuracy of servo motor and linear motion mechanism is low. Therefore, the complex structure limits the measurement accuracy of the linear displacement measurement system. This paper introduces a novel linear displacement measurement system named magnetic levitation ruler. According to the working principle of grating ruler and the characteristics of magnetic levitation technology, the magnetic circuit design and structural design of magnetic levitation ruler are completed in this paper. The mover core of the magnetic levitation ruler is in the stable working magnetic field provided by the stator yoke. The horizontal control coil wound on the mover core can obtain more stable ampere force to improve the control accuracy of the mover core displacement. Therefore, the mover core can be moved in step mode, and the length of each step is fixed. Each step is the minimum scale of the magnetic levitation ruler. Therefore, the mover core can implement displacement measurement while moving in a linear motion. This paper analyzes the working principle of levitation, horizontal motion, and displacement measurement of magnetic levitation ruler, and determines the structural materials and parameters of magnetic levitation ruler with the help of finite element analysis software. The simulation results show that the levitation force of the magnetic levitation ruler is proportional to the current passing through the levitation coils, and the thrust of the horizontal control coil is less disturbed by the magnetic field. Compared with the linear displacement measurement system with rotational servo motor or permanent magnet synchronous linear motor as the core, the magnetic levitation ruler has stable magnetic field, strong controllability, high integration, and is easier to achieve high-precision control.

<b>Evaluation of Vibration Resistance of Levitation and Guidance Ground Coils by Electromagnetic Excitation Tests Using a Superconducting Magnet</b>

During superconducting Maglev vehicles running, ground coils vibrate due to the reaction force of levitation force and guidance force. In electromagnetic excitation tests, a ground coil is vibrated under the strong magnetic field of a superconducting magnet. This paper describes an examination of test conditions based on numerical analysis, a processing method for energizing only the unit coil to be evaluated, and the electromagnetic excitation test results of the levitation and guidance coil. The vibration resistance of levitation and guidance ground coils were evaluated by electromagnetic excitation tests.

An Improved One-Cycle Control Algorithm for a Five-Phase Six-Leg Switching Power Amplifier in Active Magnetic Bearings

To achieve levitation in active magnetic bearing (AMB) systems, levitation coils must be driven by a switch power amplifier (SPA). Therefore, SPA performance is important to stable levitation. In previous studies, five-phase six-leg (5P6L) SPA topology was proposed to reduce hardware costs. However, current tracking performance degrades due to the coupling problem of the five-phase current and freewheeling loss. Then, the rotor may deviate markedly from the balance position, affecting rotor stability. The keys to solving these problems lie in the duty cycle control of the common leg and the compensation of freewheeling loss. This article proposes an improved one-cycle control (OCC) algorithm in which the duty cycle of the common leg is optimized by finite control set model predictive control (FCS-MPC), and the freewheeling loss is compensated for by a high-precision mathematical model. In addition, the parameter uncertainty of the FCS-MPC model is analyzed, and the convergence of the optimization algorithm is investigated. Simulations and experiments show that the proposed algorithm is effective, and the high dynamic response and low steady-state error performance of SPA are achieved.

Liquid dripping dynamics and levitation stability control of molten Ti–Al–Nb alloy within electromagnetic fields

The dripping dynamics of the electromagnetically levitated (EML) liquid Ti–Al–Nb alloy under high temperatures was investigated by both numerical simulation based on the Arbitrary Lagrangian–Eulerian method and corresponding EML experiments. A dripping formation parameter εD was defined to describe the critical shape of alloy droplet. According to the simulated results, the high-temperature dripping phenomenon took place when εD < 0.68, which was in good agreement with experimental data. When dripping event occurred, the Lorentz force applied on alloy droplet decreased by approximately 11.7% within 0.07 s. Three typical methods were accordingly proposed to avoid the dripping failure of a bulk liquid Ti–Al–Nb alloy, which was implemented by enhancing electric current, adjusting levitation coil diameter, or increasing coil winding number. To control the droplet shape, the deformation pattern and the flow behavior of the liquid alloy were studied in a wide current range from 700 to 1400 A. With the increase in excitation current, the cone-shaped alloy melt transformed to a rhombus, and the flow behavior transformed from a typical four toroidal flow vortexes up to a complex eight toroidal flow vortexes. Moreover, the centroid position of liquid alloy rose up significantly at first and then slowly approached to levitation ceiling.

Equivalent inductance model for the design analysis of electrodynamic suspension coils for hyperloop

Hyperloop is a new concept of ground transportation. In Hyperloop, travelling occurs in near-vacuum tubes under 0.001 atm at a subsonic speed of up to 1200 km/h. During acceleration to and driving at a subsonic speed, magnetic levitation is employed. Thus far, various levitation technologies in existing high-speed maglev trains have been considered. Among those technologies, superconducting (SC) electrodynamic suspension (EDS) is a highly effective levitation system for Hyperloop owing to its advantages of a large levitation gap, levitation stability, and control being unnecessary. However, analyzing an EDS system requires the electromagnetic transient analysis of complex three-dimensional (3D) features, and its computational load generally limits the use of numerical methods, such as the 3D finite element method (FEM) or dynamic circuit theory. In this study, a novel model that can rapidly and accurately calculate the frequency-dependent equivalent inductance was developed. The developed model was then applied to design an EDS system using the decoupled resistance-inductance equations of levitation coils. Next, levitation coils of SC-EDS were designed and analyzed for use in Hyperloop. The obtained results were compared with the FEM results to validate the developed model. In addition, the model was experimentally validated by measuring currents induced by moving pods.

Capsule Vehicle Dynamics Based on Levitation Coil Design Using Equivalent Model of a Sidewall Electrodynamic Suspension System

A levitation system based on sidewall electrodynamic suspension (EDS) is considered for a capsule vehicle, which is a next-generation high-speed transportation system currently being studied. This levitation system does not require controlling of the gap between the guideway and the vehicle on which the superconducting electromagnet is mounted. However, when the vehicle is operated in a levitated state, the ride comfort is worse than that of the levitation system based on electromagnetic suspension (EMS), making it necessary to develop methods that can ensure good riding comfort. In addition, because the EDS system is complex and nonlinear with a combination of electromagnetics and mechanical dynamics, it is complicated to analyze the dynamic characteristics of the capsule vehicle, and the corresponding numerical analysis is time-consuming. Therefore, to easily understand the running dynamics of a capsule vehicle in the sidewall EMS system, the magnetic suspension characteristics corresponding to the primary suspension are simply modeled by considering the levitation stiffness in the vertical direction and the guidance stiffness in the lateral direction, similar to that in the case of the mechanical suspension. In this study, mathematical models of the levitation and guidance stiffnesses with respect to the speed and position of a vehicle body running at high speeds in a levitated state in the sidewall EDS system were derived for three design proposals of the levitation coil. The dynamic behavior of the vehicle based on the three design proposals was investigated by simulating a capsule vehicle model with 15 degrees of freedom.

Numerical Investigation on Low-temperature Superconducting Negative Spring in Magnetic Levitation

A new terrestrial gravitational wave detector, Superconducting Omni-directional Gravitational Radiation Observatory (SOGRO), has been proposed in 2016 and seen as a competitive candidate of middle-frequency gravitational wave detector. In this detector, there are three pairs of 5-ton low-temperature superconducting test masses separated by 30–50 m and magnetically levitated by superconducting coils carrying persistent currents. To get a sensitivity of 10− 19 − 10− 20Hz− 1/2, the levitation frequency of the test masses need to be as low as 0.01 Hz. Because of the machining and assembling errors, the levitation coil will tilt with respect to gravity and deviate from the center of the levitation coil. Alignment coils can cancel the tilt but bring extra stiffness to the test mass that enlarges the frequency. We numerically have studied a downscaled prototype of the superconducting magnetic levitation of SOGRO and find a possible design of the superconducting levitation system, which can reduce the levitation frequency to less than 0.01 Hz without increasing any hardware and complexity of the system. This study will benefit the development of SOGRO and other superconducting levitation devices.

Design Model of Null-Flux Coil Electrodynamic Suspension for the Hyperloop

The Hyperloop has been developed using various technologies to reach a maximum speed of 1200 km/h. Such technologies include magnetic levitation technologies that are suitable for subsonic driving. In the Hyperloop, the null-flux electrodynamic suspension (EDS) system and superconducting magnets (SCMs) can perform stable levitation without control during high-speed driving. Although an EDS device can be accurately analyzed using numerical analysis methods, such as the 3D finite element method (FEM) or dynamic circuitry theory, its 3D configurations make it difficult to use in various design analyses. This paper presents a new design model that fast analyzes and compares many designs of null-flux EDS devices for the Hyperloop system. For a fast and effective evaluation of various levitation coil shapes and arrangements, the computational process of the induced electromotive force and the coupling effect were simplified using a 2D rectangular coil loop, and the induced current and force equations were written as closed-form solutions using the Fourier analysis. Also, levitation coils were designed, and their characteristics were analyzed and compared with each other. To validate the proposed model, the analyzed force responses for various driving conditions and the changed performance trend by design variables were compared with analyzed FEM results.

Magnetic levitation and compression of compact tori

The magnetic compression experiment at General Fusion was a repetitive non-destructive test to study plasma physics to magnetic target fusion compression. A compact torus (CT) is formed with a co-axial gun into a containment region with an hour-glass shaped inner flux conserver and an insulating outer wall. External coil currents maintain the CT off the outer wall (radial levitation) and then rapidly compress it inward. The optimal external coil configuration greatly improved both the levitated CT lifetime and the rate of shots with good flux conservation during compression. As confirmed by spectrometer data, the improved levitation field profile reduced plasma impurity levels by suppressing the interaction between plasma and the insulating outer wall during the formation process. Significant increases in the magnetic field, density, and ion temperature were routinely observed at magnetic compression despite the prevalence of an instability, thought be an external kink, at compression. Matching the decay rate of the levitation coil currents to that of the internal CT currents resulted in a reduced level of MHD activity associated with unintentional compression by the levitation field and a higher probability of long-lived CTs. An axisymmetric finite element MHD code that conserves system energy, particle count, angular momentum, and toroidal flux was developed to study CT formation into a levitation field and magnetic compression. An overview of the principal experimental observations and comparisons between simulated and experimental diagnostics are presented.

Numerical Investigation of the Position and Asymmetric Deformation of a Molten Droplet in the Electromagnetic Levitation System

In this study, a numerical model was developed of the electromagnetic levitation system based on the actual structure and size of the levitation coil. The model was then used to investigate the effects of the induced magnetic field, the electric field, and the magnetic force on the lateral drift and irregular deformation of different sized copper droplets. In addition, several tests were conducted in order to verify the conclusions obtained from the numerical simulation analysis.

Low Noise ZVS Switch Sharing Multichannel Switching Amplifier for Magnetic Bearing Applications

In a magnetic bearing system, the levitation coils or electromagnets must be driven by an amplifier in order to control their currents for levitation stability. This amplifier typically drives every coil individually with hard-switching H-bridges. However, the inherent high dv/dt of hard-switching in conjunction with the large parasitic capacitance of magnetic bearing coils typically results in high current spikes and severe ringing in the switching process, which may interfere with position sensors and system communication. Furthermore, driving each coil individually requires a large number of switches. In this brief, a switch sharing zero-voltage-switching (ZVS) multichannel switching amplifier topology is proposed, which not only reduces the number of switches needed when driving multiple coils, but also eliminates current spikes and reduces the switching loss of the magnetic bearing amplifier. The proposed topology is experimentally tested to validate expected benefits.

Simulation analysis and experimental study of the temperature characteristics of electromagnetic levitation

This paper aims to realize the electromagnetic levitation of experimental samples with low conductivity and high density at relatively low temperatures. The relationships among the temperature characteristics of an electromagnetic levitation device and the structural size of the induction coil, the size of the experimental sample, the levitation position, respectively, which were studied using Maxwell and ANSYS through simulation analysis. Simulation results show that the maximum temperature produced by the induction coil decreases with an increase in winding turns of a stable coil and increases in the half-taper angles of levitation and stable coils; increases with the levitation position, that is, the temperature of the levitation device is higher at the bottom than in other areas; and increases initially and then decreases with an increase in the radius of the levitation sample. Other parameters, such as the first winding radius of the levitation coil, the planar space between the levitation and stable coils, the winding spacing of coils, and the winding turns of the levitation coil, slightly influence the maximum temperature that the induction coil can provide. Furthermore, constructing an experimental platform allowed for the discovery of the relationships between the parameters of the induction coil and its temperature characteristics; these relationships are consistent with the simulation results. The spherical levitation sample with a radius of 5.1 mm reaches its maximum temperature of 853 °C after 55.65 s, thereby achieving the objective of melting when the first winding radius of the levitation coil is 17 mm, the planar space between the levitation and stable coils is 16 mm, the winding spacing of coils is 8 mm, the winding turns of the levitation coil are 3, the winding turns of the stable coil are 2, the half-taper angles of the levitation and stable coils are 15°, and the levitation position is 17 mm.

5-DOF Real-Time Control of Active Electrodynamic MAGLEV

This paper presents the five degree-of-freedom (5-DOF) control of an electrodynamic MAGLEV suspension with active control of the levitation coils. A sled with built-in permanent magnets moves past an array of fixed coils to generate Lorentz forces that provide lift and guidance. When active control of the levitation coil currents is implemented, multi-DOF trajectory control can be achieved, leading to stable electrodynamic levitation that can actively reject disturbances independently of sled speed. This paper shows successful control of the multi-DOF trajectory of a passive sled by active control of the coil currents, using both a sliding mode controller with nonlinear input mapping from coil currents to levitation forces, and a multi-DOF nonlinear observer. The paper also compares the use of look up tables versus analytical models of the magnetic field density used to estimate the magnetic forces and torques acting on the sled. The performance of the proposed approaches is demonstrated experimentally.

Highly Efficient Liquid Hydrogen Storage System by Magnetic Levitation Using HTS Coils

Highly efficient liquid hydrogen storage system is studied with magnetic levitation using high-temperature superconducting (HTS) coils. The system also has high safety in case of emergency, such as an earthquake, with a seismic isolation to absorb vibrations provided by HTS levitation coils setup on the ground side. In such an emergency case, it is considered that a large amount of ac losses are generated in HTS coils, and the winding temperature may rise to lead to a coil quench. In this study, the self-oscillation-type heat pipe (OHP), whose thermal transport property is much greater than that of solid thermal conduction, is used to cool the coil windings. As a result, an HTS coil equipped with an OHP cooling system can be realized, supporting both low heat loads in the usual operation and high heat loads in an emergency.

Design and Fabrication of a Superconducting Relative Gravimeter With a Planar Spring

The relative gravimeter is in high demand to improve the performance of a navigation system. Therefore, we designed, fabricated, and tested a superconducting relative gravimeter. The proposed gravimeter features a superconducting planar spring, an electromagnetic levitation, and a superconducting quantum interference device (SQUID) sensor. The advantages of the superconductor include being able to enable the device with exceptional stability and having an extremely low noise. The coupling spring with electromagnetic levitation can also offer a low resonant frequency for better sensitivity. The device consists of a niobium mass-spring vibrometer having a planar spring, a levitation coil, and a SQUID sensor. The vibrometer was designed by conducting the mathematical analysis and the mechanical–electromagnetic finite element analysis simulation. Both the electrodischarge machining process and the high vacuum-thermal process were applied to fabricate superconducting structures. Experiments to store and discharge a persistent current in the levitation coil were carried out at 4.2 K cryogenic condition to confirm the numerical prediction. An experimental setup with a precision linear actuator was used to verify the relationship between induced inductance and displacement. The test result indicates that the gravimeter can measure the fine movement of the levitation mass by reading a SQUID output and the scale factor is $\sim 28$ mV/ $\mu {\mathrm{ m}}$ .

Measurement of Surface Tension of Cu–5Sn by an Oscillating Drop Technique

The surface tension of liquid Cu–5Sn (copper with \({5}\,{\hbox {wt} \%}\) tin) in the temperature range from \({1290}\,\hbox {K}\) to \({1560}\,\hbox {K}\) was measured by an oscillating drop technique combined with electromagnetic levitation. The levitation device uses an inhomogeneous radiofrequency electromagnetic field inside a levitation coil to position and to heat metallic material. Eddy currents are induced in a specimen to heat it to the liquid phase and to exert a Lorentz force, pushing it against gravity towards regions of lower field strength. The levitating liquid specimen takes the shape of a sphere, which is rotating and oscillating. The oscillations are recorded by a high-speed camera at \(600\,\hbox {fps}\); the temperature of the specimen is measured by a fast near-infrared pyrometer. A linear fit to the measured surface tension \(\gamma \) of Cu–5Sn as a function of temperature T in Kelvin is given by: $$\gamma (T)({\hbox {mN}\cdot \mathrm{m}^{-1}})=1195-0.052\cdot (T-1318).$$

The Influence of Eddy Effect of Coils on Flow and Temperature Fields of Molten Droplet in Electromagnetic Levitation Device

In this work, the influence of eddy effect of coils on magnetic, flow, and temperature fields in an electromagnetically levitated molten droplet was investigated by a serial of axisymmetric numerical simulations. In an electromagnetic levitation device, both metal droplet and coils are conductive materials, therefore the distributions of current density in them should be non-uniform as a result of the eddy effect. However, in previous works, the eddy effect was considered alone in metal droplet but ignored in coils usually. As the distance of coils and metal droplet is several millimetres in general, the non-uniform distribution of current density in coils actually gives important influences on calculations of magnetic, flow, and temperature fields. Here, we consider the eddy effect both in metal droplet as well as that in coils simultaneously. Lifting force, absorbed power, fluid flow, and temperature field inside a 4-mm radius molten copper droplet as a typical example are then calculated and analyzed carefully under such condition. The results show that eddy effect leads to higher magnetic force, velocity, and temperature in both levitating and melting processes than those when the eddy effect is ignored. What is more, such influence increases as the distance of droplet and coils becomes closer, which corresponds to experimental measurement. Therefore, we suggest that eddy effect of coils should be considered in numerical simulation on this topic to obtain more reliable result.

Расчет и проектирование управляемой индукционной опоры с левитационной обмоткой

The questions of theory, calculation and design-driven induction support with short-levitation coil, designed to hold the external load and smooth vertical movement of the working mechanism, have been considered. Automatically change the voltage at the terminals of the field winding smoothly adjusts the stroke levitation coil and the position of the working mechanism. On the basis of a mathematical model of the induction levitation, drawn from the equations of the magnetic, electrical, thermal and mechanical chains, derived expressions for the calculation of basic parameters and dimensions of the support are obtained. An analytical expression for calculating the characteristics of the considered control support is received. These expressions allow for restrictions on the height of the induction support. Obtained  analytical expressions of the parameters can be used to calculate the electrical devices for various purposes, containing LO.