Coil Axis Research Articles

Influence of piston and magnetic coils on the field-dependent damping performance of a mixed-mode magnetorheological damper

This work presents a 2D simulation study of a mixed-mode magnetorheological (MR) damper in which the influence of the geometric elements of the piston and magnetic coil on the MR damper’s performance is investigated by using the Ansoft Maxwell software tool. Four results of the simulation, which are magnetic flux density (B), MR fluid yield stress (τ0), and are used to compare the performance of the MR damper. Multiplication of the yield stress by the active operating mode length represents the variable portion of the active (on-state) damping force of the flow mode motion, while the value of represents the active damping force of the shear mode motion. The contribution of each operating mode (shear and flow) is related to the mixed-mode geometry and piston velocity. Therefore, each operating mode is evaluated separately. In this work, a total of 154 simulations are done in which 74, 20 and 60 simulations are conducted to analyse the effect of the piston radius, coil dimensions (width and length) and coil boundary lengths, respectively, on the performance of the MR damper. The simulation results show that increasing the piston radius can increase the value and reduce the value. For a given area of magnetic coil housing, a greater housing length in the axial direction of the piston can increase the achieved yield stress of the MR fluid and hence consequently the performance of the MR damper. A minimum boundary length is needed around the magnetic coil in order to attain a supreme magnetic field distribution. However, there is an optimised value for axial coil boundary lengths, which are the lengths of the upper and lower mixed-mode areas.

Optimization of magnetic resonance imaging high-order axial shim coils using boundary element method

In this paper, we present a novel nonlinear optimization algorithm for designing a shim coil system, especially a high-order axial shim coil, for a magnetic resonance imaging（MRI) system. In an MRI equipment, in order to eliminate higher-order harmonic components of the magnetic field within the volume of interest（VOI), passive shimming（PS) is adopted in traditional methods. However, such a method is suitable for the global shimming with low accuracy and poor target. Active shimming（AS) makes up for the shortcomings from PS with a set of shim coils which are designed to generate a specific magnetic fields to improve magnetic field homogeneity within the VOI. Because the complexity of wire pattern increases with the order of AS coil increasing, conventional optimization model cannot meet the design requirements for producing the complicated magnetic field. In this paper, we propose a nonlinear optimization method of designing the axial shim coils for an open-style bi-planar MRI system, based on boundary element method. The optimization model is built in light of influence extents of the various parameters on the coil characteristics for different shim coils. In such a new method, the field error between the magnetic field produced by designed shim coil and the desired target value is selected to be an optimal value subjected to some constraints including line spacing and coil radius, which makes it possible to realize the manufacture process. Meanwhile, the more design parameters, which involve not only the stream function values at each node, but also the compensation parameters and/or the number of grid nodes, are regarded as optimized variables to control the magnetic deviation and characteristics of designed coil. By using some designed shim coils for a 0.5 T open style bi-planar superconducting MRI, including Z1, Z2, Z3 and Z4, the efficiency of such a numerical design method is displayed. Especially for high-order shim coils, more optimized parameters are involved to control the magnetic deviation of the coils, thereby providing a more flexible and straightforward method of designing the axial shim coils.

The Production of a Uniform Magnetic Field Using a System of Axial Coils for Calibrating Magnetometers

The construction of an axial 8-coil system based on Helmholtz coils is described, which enables a magnetic field with a nonuniformity of not more than 0.1% to be produced at a distance of half the radius from the center of the coil system. The results obtained are confirmed by experimental investigations.

Performance Tests of Prototype High-Field HTS Coils in Grenoble

Longitudinal and transverse quench propagation tests were performed at the Laboratoire National des Champs Magnetiques Intenses (LNCMI) high-field test facility on instrumented double pancake coils fabricated by CEA-Saclay using co-wound high-temperature superconductor (HTS) tapes. Energy deposited on an embedded heater initiated a quench and its subsequent propagations. Following the resulting thermomechanical analysis, a conductor design with stacked HTS tapes co-wound with stabilizers was conceived. A ten-turn demonstrator racetrack coil has been fabricated from the stacked HTS conductor with an aim to investigate the operation margin of an HTS coil in a background magnetic field misaligned from the coil axis as expected for the operating condition of an accelerator magnet insert. A test setup with a high current capacity up to 3 kA and angular variability that utilizes a room-temperature 376-mm-bore 10-T resistive magnet at LNCMI in Grenoble has been built. The performances and operation margin of the racetrack coil were investigated.

Measurement of Helmholtz Coil

Based on the basic principles of electromagnetism, the application of Shanghai Fudan-day Welcomes UNESCO Instruments Ltd. THQHC-1 type Helmholtz coil magnetic field measuring instrument for measuring coil uniform magnetic field generates a magnetic field on the carrier to get round the coil axis, online circle center at (coordinate origin) at the maximum magnetic field strength. Starting from the coordinate origin, to the sides, the magnetic field lines accelerate the decline, when the distance exceeds the coil radius, the decelerating decline. Conclusions for the understanding of a uniform magnetic field reference.

A chaotic vibration energy harvester using magnetic material

This paper presents a new wideband electromagnetic vibration energy harvester (VEH) composed of a magnetic core embedded into the coil axis. The magnetic core generates a nonlinear magnetic force, which gives rise to the nonlinearity in the behavior of the VEH. Moreover, the magnetic core increases the flux linkage with the coil. These features improve the operational bandwidth and output power of the VEH. Numerical analysis and experimental measurements reveal that the operational bandwidth of the proposed VEH is over 30 Hz in which the output power is kept about 0.1 mW. Moreover, the proposed VEH operates by complicated oscillation due to nonlinear forces acting on the oscillator. Evaluation of the Lyapunov exponent for the measured oscillation suggests that the proposed VEH produces chaotic oscillation.

Top-Level System Designs for Hybrid Low-Field MRI–CT with Potential of Pulmonary Imaging

We previously discussed “omni-tomography”, but intrinsic conflicts between the magnetic fields of the MRI and the X-ray tube within the CT are inherent. We propose that by using low-field MRI with a negligible fringe field at the site of the CT source, it is possible to create a CT–MRI system with minimal interference. Low field MRI is particularly useful for lung imaging, where hyperpolarized gas can enhance the signal. Three major designs were considered and simulated, with modifications in coil design and axis allowing for further variation. The first uses Halbach arrays to minimize magnetic fields outside, the second uses solenoids pairs with active shielding, and the third uses a rotating compact MRI–CT. Each system is low field, which may allow the implementation of a standard rotating CT. Both structural and functional information can be acquired simultaneously for a true hybrid image with matching temporal and spatial image acquisition.

An Automated Indoor Scalar Calibration Method for Three-Axis Vector Magnetometers

In this paper, we propose a new indoor magnetometer calibration system using the 3-D Helmholtz coil. In this method, in order to the use two-step calibration algorithm instead of rotating the sensor in a constant magnetic field vector, the vector rotates around the magnetometer. In other words, a three-axis magnetometer can be calibrated by a zero degrees of freedom system while a shielded Helmholtz coil provides and rotates a constant magnetic field vector. The results of this calibration method will be compared with the classical calibration method in the earth's magnetic field as well. We also present evidence that the magnetometer does not need to align with the Helmholtz coil axis; instead, it can be calibrated with any arbitrary direction of the Helmholtz coil. It is shown that this method can be performed easily and fast in order to calibrate the three-axis magnetometer in an indoor environment. Meanwhile, it can provide almost the same calibration parameters and thermal model for the magnetometer, compared with the classical one.

Research of Drives of Power Amplifiers of Magnetic Levitation Servo Spindle Applied to Micro EDM Based on FPGA

The drives of power amplifiers of magnetic levitation servo spindle applied to micro EDM (Electron discharge machining) based on FPGA (Field programmable gate array) are developed. The drive module that produces the PWM (Pulse width modulation) waves that conform to the requirements of spindle power amplifiers involving three-level half bridge switch power amplifier, three-level full bridge switch power amplifier and motor power amplifier, according to input of action values from magnetic levitation servo spindle controller DSP (Digital signal processor) is designed. Multi-PWM producing algorithm by single timer with multi comparing nodes is proposed. After being applied to control system of magnetic levitation servo spindle, the drives accomplish conversion from DSP action values to PWM waves. The PWMs that drive radial coil current power amplifier have phase difference of 180°. The PWMs that drive axial coil current power amplifier have dead zone time and their wave shapes are complementary. The PWMs that drive the motor power amplifier conform to requirements of power amplifier chip LMD18200. Using FPGA to realize the drive function of spindle power amplifier makes the drive design more flexible, resource distribution of DSP more optimized, the task of algorithms running more centralized, and the drives module gets simpler and more reliable because the phase shift circuit and dead zone circuit are cancelled but the function of phase shift and dead zone is reserved.

Development of integrated AC-DC magnetometer using high-Tc SQUID for magnetic properties evaluation of magnetic nanoparticles in solution

We developed an integrated AC-DC magnetometer using a high critical temperature superconducting quantum interference device (high-Tc SQUID) to evaluate the static and dynamic magnetic properties of magnetic nanoparticles (MNPs) in solution. The flux-transformer method consisted of first-order planar and axial differential coils that were constructed for static and dynamic magnetization measurements, respectively. Vibrating-sample and harmonic detection techniques were used to reduce interference from excitation magnetic fields in the static and dynamic magnetization measurements, respectively. Static and dynamic magnetization measurements were performed on commercially available iron oxide nanoparticles in diluted solutions. The magnetic responses increased with the increase in concentration of the solutions in both measurement results. The magnetization curves showed that the diamagnetic signal due to the carrier liquid of the iron oxide nanoparticles existed in a dilute solution. Biasing with a proper DC magnetic field in the dynamic magnetization measurement resulted in improved signals of the second and third harmonics. Therefore, highly sensitive magnetic characterizations of MNPs utilizing the static and dynamic magnetization measurement are possible via the developed system.

Design of a Magnetic Gradient Coil with High Uniformity

Maxwell coil cannot meet the magnetic sensor calibration when the high uniformity of magnetic gradient is required and the space size is strictly limited. To solve this problem, a magnetic gradient coil with high uniformity was designed as magnetic sensor calibration device. Application of internal series method analyzed the magnetic field that a single axial symmetric coil generated, and then got the general characteristics of the magnetic gradient field distribution. On this basis, the structural parameters and the uniformity of magnetic gradient coil with high uniformity were calculated. Simulation analyses were carried out on the coil model and complete the design and production of magnetic gradient coil device. Finally, the data obtained from actual measurement and simulation proves the correctness of the design.

A Study on the Driving Torque of the Dynamic Gyro

The permanent magnetic rotator of the dynamic gyro is driven by the energized radial and axial coils through the gimbal module. Angle and angle are the significant angles to describe the moving status of the dynamic gyro. By using the magnetism and mechanism principles, the driving torque of the dynamic gyro is figured out, and some important conclusions are provided. If angle, the rotating torque and the period mean procession torque; if angle, an additional torque will be produced to the rotating torque and the procession torque will be very complex. These conclusions are quite useful for controlling the dynamic gyro.

Development of fast cooling pulsed magnets at the Wuhan National High Magnetic Field Center

Pulsed magnets with fast cooling channels have been developed at the Wuhan National High Magnetic Field Center. Between the inner and outer sections of a coil wound with a continuous length of CuNb wire, G10 rods with cross section 4 mm × 5 mm were inserted as spacers around the entire circumference, parallel to the coil axis. The free space between adjacent rods is 6 mm. The liquid nitrogen flows freely in the channels between these rods, and in the direction perpendicular to the rods through grooves provided in the rods. For a typical 60 T pulsed magnetic field with pulse duration of 40 ms, the cooling time between subsequent pulses is reduced from 160 min to 35 min. Subsequently, the same technology was applied to a 50 T magnet with 300 ms pulse duration. The cooling time of this magnet was reduced from 480 min to 65 min.

Differences between two definitions of the critical current of HTS coils

Definition of the critical current of a coil made of anisotropic high temperature superconducting conductor is rather complicated and ambiguous, since the magnetic field generated across the winding can differ considerably in relation to both its magnitude and orientation. Two definitions of the critical current of such coils are discussed. The first definition, very often used in calculations to analyze the current carrying capacity, electric field and power dissipation of individual turns, represents an operating current at which an electric field of 1 μV cm−1 appears on one turn. The second definition represents an integral approach, and is used in experiments. This definition introduces the critical current of the coil as an operating current at which an average electric field Es, usually 0.1 μV cm−1, appears on coil terminals. As an example, the distribution of the critical current and electric field of individual turns in the winding of a BSCCO model coil was analyzed. Critical currents of the coil as a function of an external magnetic field parallel with the coil axis were calculated according to both definitions. The results show that the first definition, which characterizes the winding at the local level, is suitable for HTS coils either operating in self-field or in a low external field, because the differences between the critical currents and n-indices of individual turns are considerable. The second criterion is suitable for the HTS coils operating in high fields, i.e. like high field insert coils. The self-field of a high field insert coil is negligible if the external field is high. As a result, the critical currents of all turns are almost identical, and the anisotropy in Ic(B) characteristic plays practically no role. Rather unexpected behavior of the voltage–current characteristic of the model coil is predicted if an external field is applied.

Comparative investigation of diagnosis media for induction machine mechanical unbalance fault

For an induction machine, we suggest a theoretical development of the mechanical unbalance effect on the analytical expressions of radial vibration and stator current. Related spectra are described and characteristic defect frequencies are determined. Moreover, the stray flux expressions are developed for both axial and radial sensor coil positions and a substitute diagnosis technique is proposed. In addition, the load torque effect on the detection efficiency of these diagnosis media is discussed and a comparative investigation is performed. The decisive factor of comparison is the fault sensitivity. Experimental results show that spectral analysis of the axial stray flux can be an alternative solution to cover effectiveness limitation of the traditional stator current technique and to substitute the classical vibration practice.

Simulation Analysis of the Sensitivity in Magnetic Induction Tomography Based on Perturbation Theory

Magnetic induction tomography (MIT) is a noninvasive and contactless imaging modality which aims at the reconstruction of the electrical conductivity in objects from alternating magnetic fields. Filtered back projection reconstruction algorithm is widely used in biomedical imaging field, and tried to use in MIT. Finite element analysis model has been established based on Scharfetter coil-coil model and perturbation theory, then simulated coaxial coil system by ANSYS software, the perturbation aroused by a target object moving on vertical coil axis. The sensitivity of a target object moves in vacuum and a salt solution were calculated respectively, the characteristics of the perturbation sensitivity in a salt solution were analyzed. The conditions of filtered back projection reconstruction algorithm in MIT were discussed.

A Broadside-Split-Ring Resonator-Based Coil for MRI at 7 T

A coil design termed as broadside-coupled loop (BCL) coil and based on the broadside-coupled split ring resonator (BC-SRR) is proposed as an alternative to a conventional loop design at 7T. The BCL coil has an inherent uniform current which assures the rotational symmetry of the radio-frequency field around the coil axis. A comparative analysis of the signal-to-noise ratio provided by BCL coils and conventional coils has been carried out by means of numerical simulations and experiments in a 7T whole body system.

Numerical Simulation on Mold Electromagnetic Eccentric Stirring and Central Segregation of Round Bloom

The paper describes multi-section round bloom casting using external MEMS, equipped with max section D600mm and min D280mm mold, the center line of D280mm mold not coincident with the axis of stirrer coils. it is exist eccentric electromagnetic stirring of mold which section less than max D600mm, a mathematical model of MEMS has been established, the index of central segregation of D280mm macrostructure had decreased less than 1.12 by optimized parameters of electromagnetic stirring and SEN immerse depth, in the end, the quality of round bloom had improved.

Motion of a slender body made of magnetizable composite in a traveling magnetic field

The motion of a slender body made of magnetizable composite in a channel, along which coils producing a heterogeneous “traveling” magnetic field are mounted, is investigated. The coil axes are vertical and lie in the same plane. A mathematical model of a slender body made of viscoelastic magnetizable material is proposed. The magnetic force is calculated from a formula used in ferrohydrodynamics of magnetic fluids with equilibrium magnetization. The problem of the motion of this body in a channel in a vertical plane under the action of the magnetic field produced in an experimental setup is numerically solved. The dependence of the body velocity on the coil switching frequency is calculated and the effect of different problem parameters on the form of this dependence is studied. The theoretical results are compared with the experimental data.

Indução eletromagnética em laboratório

Estudou-se a indução de uma força eletromotriz provocada pelo campo magnético de um solenoide em várias bobinas de prova colocadas no interior deste. Utilizou-se uma montagem experimental - disponibilizada pela infraestrutura laboratorial para o ensino do Departamento de Física da FCUP - para determinar a dependência da força eletromotriz induzida com os mais variados fatores experimentais, a saber: número de espiras da bobina de prova, área da secção transversal da bobina de prova, ângulo do eixo da bobina de prova em relação ao eixo do solenóide, frequência angular do sinal gerador e amplitude do sinal de corrente. Determinou-se, usando este mesmo método, o valor da permeabilidade magnética do vazio e comparou-se com o valor tabelado. Este trabalho teve como objetivo desenvolver uma nova abordagem pedagógica das leis da indução eletromagnética. Efetuou-se igualmente uma reflexão sobre como abordar esta experiência no ensino secundário e quais as melhores técnicas para realizar, explorar e avaliar a atividade.