Non-uniform Magnetic Field Distribution Research Articles

Calculation method of electromagnetic losses and hot-spots temperature of giant magnetostrictive transducer

Due to the complex energy conversion processes and limited avenues for heat dissipation in the giant magnetostrictive transducer (GMT). Large losses and elevated internal temperature rise are inevitable, this would bring into serious reliability problem for GMT. Accurately analyzing its electromagnetic losses and hot-spots temperature are crucial for designing and optimizing the transducer. High-power GMT typically use permanent magnet (PM) to provide a bias magnetic field for enhanced power density. Although, this structure could significantly reduce the volume of driving part, it also caused issues such as non-uniform magnetic field distribution and bias magnetic field, which have great influence on the magnetic energy loss and hot-spots temperature rise. The previous researches seldomly investigate these influences on total loss at GMT system level. Additionally, the differential excitation coil loss caused by AC resistance among multi-layers can’t be neglected, which can lead to variations in coil loss and temperature rise. Therefore, this paper proposed a detailed electromagnetic losses and hot-spots temperature rise calculation model from material level to GMT system level. This method can obtain the distribution of electromagnetic losses within multiple factors, and the hot-spots temperature rise considering the temperature non-uniform distribution. Firstly, we have developed a precise loss calculation model, which takes the influence caused by PM bias and non-uniform magnetic field on magnetic energy loss into account. Additionally, the proposed model could conclude the impact of inter-coil resistance variations on the eddy current loss in excitation coil. Secondly, based on of the non-uniform distribution of losses in driving part, using the divisional thermal modeling approach and a 2-D T-shaped equivalent thermal network, we further constructed a transient temperature calculation model for GMT. This approach can effectively improve the energy conversion efficiency of GMT, so as to enhance the thermal reliability of the transducer. Finally, a testing system for the loss-thermal of GMT was established to validate the effectiveness of proposed model. Results indicate that the average error between our loss calculation model and experimental results is 2.93%, while the corresponding error for without considering the above factors is 15.97%. This confirms the necessity of conducting a detailed electromagnetic losses calculation model. In addition, the average error of the temperature rise calculation model is less than 5%, while the error for without considering the losses distribution and heat dissipation paths difference is exceed 10%. In conclusion, our proposed method accords well with the measured results, and can provide significant fundamental for design and optimization of GMT.

Design of a volumetric cylindrical coil-tuned at 298 MHz for 7 T imaging

The concept of a 2D cylindrical High Pass Ladder (2D c-HPL) is used in the development of this ultra-high radio frequency (UHRF) volumetric head coil for 7 T tuned at the Larmor frequency of 298 MHz. The architecture of the 2D c-HPL helps to overcome the challenges associated with non-uniform magnetic field distribution. The prototype consists of an individual resonating array of inductance-capacitance (LC) elements and each component is tuned to the precise fo frequency. The tuning of the (i) inductance, (ii) capacitance, (iii) mesh size, and (iv) coupling coefficient play critical roles to attain the desired Larmor frequency. For this proof-of-concept, the prototype of a volumetric head coil consists of a cylindrical array size of 4 × 6, with individual LC components of inductance magnitude, 98 nH and four fixed value capacitors and one tunable capacitor that allowed to achieve the desired precession frequency, fr = 298 MHz. The model was tested for three different fo values of 269, 275, and 286 MHz. The mutual coupling and the eigenfrequencies were compared through bench testing and dispersion equation. The experimental data were in good agreement (<5%) with the theoretical eigenfrequencies from the dispersion relation. The theoretical eigenfrequencies and the experimental eigenfrequencies are in good agreement for eigenmodes (1,2), (1,3), (2,2), (2,3), and (4,3).

Thermal Analysis and In-Field Critical Current Estimation of Conduction-Cooled REBCO Magnet Considering Nonuniform Temperature Distribution

Due to the high upper critical field and transition temperature, REBCO coated conductor show great promise for conduction-cooled magnet applications. The normal zone of high temperature conductor (HTS) spreads slowly, and the conversion of a weak spot into a hot spot is localized and quite fast. Hence, in-field critical current weak spot evaluation under the nonuniform temperature gradient is important for conduction-cooled magnet stability estimation. Cooling path design needs to take the weak spot into account. In this study, a temperature-field-angle dependent critical current estimation neural network was first trained based on a public database of HTS critical current. The equivalent thermal conductivity was applied for the interface contact between the turns. Thermal contact conditions were given to the interface between the coil and bobbin considering actual production situations, such as thermal grease. Combing the non-uniform magnetic field and thermal distribution, the critical current distribution was evaluated to track the weak part. The results of this study will be employed in the design analysis of high magnetic field conduction cooling magnets in the future.

Analytical Design Methodology for Wind Power Permanent Magnet Synchronous Generators

In this paper a novel analytical design methodology for wind power permanent magnet synchronous generators is presented. This kind of electric generator plays a major role in small-scale wind energy conversion systems up to 10 kW. The proposed diameter-cubed sizing equation is based both on the generator requirements, imposed by the application, and the design parameters that rely on the designer criteria. The magnetic field waveforms of both the permanent magnets field and the armature field are considered from the first moment through the winding factors, as well as the slots effects given by the Carter factor. The analytical model of the permanent magnet synchronous generator is validated with the finite element method, showing good agreement, both with no load and under load. As the generator is unsaturated, the main source of divergence between the analytical and the finite element model are the iron losses, due to the nonuniform magnetic field distribution.

Design of anti-misalignment PCB coil for wireless power transfer

This paper focuses on the problem of the non-uniform magnetic field distribution in short-distance magnetic coupled wireless power transfer (MC-WPT) systems, which causes the transfer power and power transfer efficiency to decrease when the transmitter and receiver coils are offset. At first, the distribution law of the magnetic field generated by the printed circuit board (PCB) coil is studied. A new method is proposed to design the transmitter coil, which combines a genetic algorithm (GA) with a partial element equivalent circuit (PEEC). The appropriate turn radii are first obtained by the GA, and the quality factor is further evaluated by the PEEC to select the optimal coil turns. Finally, the PCB coils with uneven pitches are fabricated, and experiments are carried out on an MC-WPT system. The effective power transfer area is expanded noticeably and the high efficiency of the system remains stable, which is very useful to provide a wider working space and steady wireless energy supply for mobile objects.

Influence of magnetic field of a radial focusing external magnetically insulated diode on emission behavior of intense pulsed ion beam

We investigated the effect of magnetic field in the anode and cathode gap (A-C gap) of a radial focusing (Br) external magnetically insulated diode on the emission behavior of IPIB. The magnetic field distribution between the A-C gap was analyzed by finite element method. The non-uniform magnetic field distribution induced the stronger ion emission at the outer ring area of the anode. It revealed the reason for the more serious depletion of the anode outer ring. Within the magnetic induction intensity less than 1.37 Bcrit, it was found experimentally that the diode voltage and ion beam density reached a higher value with the increase of magnetic field. A smoother surface of Al2O3 ceramic was observed after the irradiation of IPIB generated by the Br diode. The study provides guidance for optimizing ion emission uniformity and efficiency of Br diode, promoting the effective application of IPIB technology in materials science.

Magnetorheological fluids subjected to non-uniform magnetic fields: experimental characterization

Magnetorheological (MR) fluids are suspensions of fine, low-coercivity, high-magnetizable particles in a continuous liquid phase. When subjected to magnetic field, the material exhibits a rapid change in the apparent viscosity of several orders of magnitude. This unique capability has been successfully exploited in automotive semi-active suspensions systems or systems for manufacturing high quality optics. In a majority of the existing systems, the rheology of MR fluids is controlled by an external uniform field oriented perpendicularly to the fluid flow direction. In general, it is an inherent feature of MR systems operating in flow, shear or squeeze modes, respectively. There is an experimental evidence that the behavior of MR fluids in the so-called pinch-mode (in which the fluid is subjected to non-uniform magnetic field distributions) clearly stands out against the remaining three operating modes. With the predecessors, the flow through the channel occurs once a pressure across it exceeds the field-dependent threshold pressure. For comparison, in pinch mode valves the magnetic flux energizes mostly the layers of the materials near the channel walls. The outcome is a change in the channel’s effective diameter achieved solely via material means without changing its geometry. To study the fluid’s unique behaviour in the pinch mode, the authors designed a prototype valve assembly and examined several fluid formulations of various particle concentration levels across a wide range of external (velocity, magnetic field density) stimuli in an organized effort to further comprehend the phenomenon. The obtained data indicate that the magnitude of the particular effect does not only depend on the magnitudes of the magnetic stimuli but also on the particle concentration; the smaller the concentration of particles the more pronounced the pinch mode like behavior is. In general, the authors believe that the study may provide guidelines as to the selection of fluid formulations for developing novel valveless actuators utilizing MR fluids operating in pinch mode.

Performance Simulation of the Active Magnetic Regenerator under a Pulsed Magnetic Field

Magnetic refrigeration is acknowledged as a potential substitute for the conventional vapor-compression refrigeration technology, owing to its high efficiency and environmental friendliness. Existing magnetic refrigeration systems are mostly based on permanent magnets, owing to the characteristics of lower magnetic field intensity, non-uniform magnetic field distribution, and lower operating frequency due to the moving parts, which results in a low cooling capacity and small temperature difference. Thus, this study proposes the application of a pulsed magnetic field, with a high intensity and frequency, to a magnetic refrigeration system to achieve a high performance. A verified numerical model is established to investigate the thermodynamic cycle and cooling performance of an active magnetic regenerator (AMR). The transient and steady-state performances of AMR under pulsed and permanent magnetic fields are compared. The results suggest that an AMR can establish a stable temperature difference under a pulsed magnetic field that is 40 times faster than that under a permanent magnetic field. The maximum steady-state cooling capacity under a pulsed magnetic field is 2.5 times that under a permanent magnetic field when the temperature difference is 20 K. Additionally, the effects of pulsed magnetic field waveforms, frequency, and intensity on the performance of AMR are investigated under various utilization factors. These results can guide the improvement of room-temperature magnetic refrigerators.

An improved eddy current loss model over broadband frequency range

To accurately predict the eddy current loss of silicon steel laminations over broadband frequency range, an improved parametric magneto dynamic model (IPMD) is proposed in this paper. According to the nonuniform distribution of magnetic field in the cross-section of the silicon steel lamination under high-frequency magnetization, the analysis area of the lamination is divided into several slices by nonlinear segmentation, wherein each slice the magnetic field distribution is regarded as uniform. Meanwhile, to accelerate the calculation speed of the IPMD model, the relationship between skin depth and slice number is deduced and verified. Furthermore, the Tellinen (TLN) hysteresis model is used when implementing the IPMD model to further increase the accuracy of eddy current loss calculation.

Effects of the non-uniform magnetic field on the shear stress and the microstructure of magnetorheological fluid

A particle-level 3D simulation was carried out to explore the difference between the shear stress and the microstructure of magnetorheological fluid in the present of different distributions of non-uniform magnetic field. The non-uniform magnetic field used in the simulation was generated by a permanent magnetic. Three types of non-uniform magnetic field distributions with the same average magnitude were obtained by locating the simulation box at different positions above a permanent magnet. The quasiequilibrated structures were first examined before the beginning of the shear simulation. Then, the typical evolution of shear stress under non-uniform magnetic field was investigated. The shear stress curve included a sharper growth region in the beginning compared to the stress curve under the vertical uniform magnetic field. At the same shear rate, the shear stresses under non-uniform magnetic fields were different from these under the vertical uniform magnetic field. The chain-like structures inside magnetorheological fluid were responsible for the difference of the shear stresses. Specially, the chain-like structures with inclination θ>90° and azimuth φ≈90° were beneficial for improving the shear stress. The volume average magnetic field was employed to quantitatively describe the characteristics of the non-uniform magnetic field. The shear stress curve of magnetorheological fluid under the volume average magnetic field matched well with the stress curve under the corresponding non-uniform magnetic field.

Equilibrium configurations in a magnetic fluid-based field mapping and gas pressure measuring system: Experiment and simulations

In this work, we present a measurement system based on the thin layer of magnetic fluid aimed at scanning either the non-uniform magnetic field distribution applicable for magnetic levitation systems (MagLev) or determining small excess gas pressure. The key idea is based on the photo registration of a transparent air-filled cavity formed in a thin magnetic fluid layer due to balancing the gas pressure and the pressure emerging due to magnetic forces. As a result, the contour of the magnetic field lines in 3D space is visible. It is shown that the theoretical analysis and numerical simulations are consistent with experimental results.

A Non-Invasive DC-10-MHz Wideband Current Sensor for Ultra-Fast Current Sensing in High-Frequency Power Electronic Converters

To enhance the performance of the converters along with improving their efficiency and miniaturization in many power electronics applications, a need for higher switching frequency is highly demanded. In high switching frequency converters, due to high common mode voltage issue, wideband, isolated, and low loss current sensor is required for the robust control design and ultra-fast protection. In this paper, we propose a non-invasive hybrid, isolated, and loss-less wideband current sensing method applicable for high-frequency power converters (dc-10 MHz). The proposed hybrid current sensing scheme combines two different isolated sensing technologies—a magnetoresistor sensor and a differential Rogowski coil sensor, which have complementary characteristics to achieve a wide sensing bandwidth. The proposed hybrid current sensor also utilizes planar magnetic field concentrators (MCON) using conductive materials to normalize the non-uniform magnetic field distributions generated by the current over a wide frequency range. We demonstrate through hardware prototypes and experiments that the proposed hybrid sensor yields to a very high sensing bandwidth of dc to 10 MHz. The performance of the proposed hybrid sensor is also evaluated in a 1-MHz dc–dc converter as well as a high-frequency H-bridge inverter module.

Theoretical modeling and experimental verification of the motor design for a 500 g micro moving-coil linear compressor operating at 90–140 Hz

This paper presents the theoretical modeling and experimental verification of the motor design for a micro moving-coil dual-opposed linear compressor operating at 90–140 Hz. A three-dimensional model is built to study the characteristics of its magnetic field and then the magnetic circuit configuration is optimized theoretically. The non-uniform distribution of magnetic field will have an important effect on the direction of the motor force, thereby decreasing the efficiency. Based on theoretical analyses, a 500 g micro linear compressor is built and then coupled with a given micro pulse tube cold finger to test the performance. Experimental results show that the developed compressor achieves an average motor efficiency of 78.6%, and a cooling power of 1.2 W at 77 K is acquired with an electric input power of 60 W. The experimental results of both linear motor and the cooler system are compared with the theoretical ones and good agreements can be observed.

Increase in Robustness against Effects of Coil Misalignment on Electrical Parameters Using Magnetic Material Layer in Planar Coils of Wireless Power Transfer Transformer

Utilization of wireless power transfer in light rail transits is seen as one solution for electrification of lines. The main advantage of this supply system is the reduction of installation; moreover, the alignment between the transmitter coil in the track and the receiver coil in the train should be perfect in order not to affect the power transfer. To reduce the effects of misalignment on the input and output electric parameters of the system, a new planar core and coil design, called hybrid intercore coil, is proposed. The proposed design uses a magnetic material layer between the windings in the inner half of the coil to create a non-uniform magnetic field distribution, which makes the system more robust against the effects of coil misalignment on the system current and voltage. Simulations with finite element method software were conducted to compare designs. The results show that the proposed design is less susceptible to the effects of misalignment and is more efficient. Prototype cores were constructed to verify the simulation results. Measurements show a smaller input overcurrent and output overvoltage when operating in resonance mode. The proposed design reduced the effects of coil misalignment on electrical parameters.

Magnetic field and operating performance analysis of conical-rotor permanent magnet synchronous motor

In order to accurately analyze the magnetic field of conical-rotor permanent magnet synchronous motor (CR-PMSM), the effectiveness of two methods was studied on handling of problems concerned with non-uniform distribution of magnetic field along axial direction in CR-PMSM, which were sectional calculation (SC) method and three-dimensional finite element (3-D FE) method. On this basis, the influence of the axial displacement and dq-axis currents on the operating characteristics of axial magnetic force and torque is analyzed by using the 3-D FE model. Analysis results show that the axial magnetic force and torque decrease with the increase of axial displacement of the rotor, and the amplitude regularity of the axial magnetic force is affected by the d-axis current. A prototype machine is fabricated and tested, in order to validate the design theory.

Comparative Study of Continuous Wave and Pulse Wave Electromagnetic Acoustic Resonance for the Measurement of Pipe Wall Thickness

This paper describes the measurement of wall thinning by continuous wave electromagnetic acoustic resonance (CW-EMAR) and pulse wave electromagnetic acoustic resonance (PW-EMAR). Simulated pipe wall thinning specimens are measured. The two methods show accurate results in the areas with a low variation of thickness, and the accuracy decreases when the thickness changes drastically. The two methods are analyzed by using the finite element method. The results show that with the increase of the bottom inclination, the accuracy of the two methods is reduced. For thin specimens, the reason for the larger error of CW-EMAR method is due to that CW-EMAR method is more easily affected by ultrasonic scattering and nonuniform distribution of static magnetic field.

Field Modeling for Plate-Core Inductor With Significant Fringing Using Equal-Flux Contours

An inductor with winding sandwiched between two core plates is analyzed to model the nonuniform distribution of magnetic field. The winding is placed near the edge of the core to maximize the energy within the limited footprint such that the amount of energy stored outside the core volume is not negligible. The proportional-reluctance, equal-flux model is developed to build the contours with equal amount of flux by governing the reluctance of the flux path. The shapes of the flux lines are modeled by different functions that are guided by the finite-element simulation. The field calculated from the flux lines enables calculation of inductance, winding loss, and core loss. The inductance is used as a figure of merit to evaluate the modeling accuracy. Prototypes made of flexible circuit for inductors with different layouts are measured to verify the model. The measured inductances agree with the modeled result by less than 13% error.

Investigate the Humping Ferro-Damp Induced under Non-Uniform Magnetic Field Density

Under non-uniform magnetic field distribution, the humping ferro-damp used to reduce the oscillation of ferro-wave is investigated. Through experimental observation and analytic analysis, the dynamical stability at the so called “humping pool”, enclosed by both centers of permanent magnetisms, is found to be closely dependent on the oscillating frequency, field intensity &amp; the separated distance of magnetisms. Though nodal shift of pool 0.07~0.11 cm, recorded from video-camera suited on self-designed oscillating system, begins to occur as in the deployment of higher ferro-level or lower field strength 0~ 30 mT, however such the stable response of humping pool, without remarkable change of vibrating amplitude 0.03 ~0.06 cm, might be under control while oscillating frequency of 0.5~2 Hz is subjected. That could be attributed to the concentrated ferro-viscosity as well as the strongest ferro-magnetization, induced at the humps, initiates a recovering constrain for oscillating pool. Unlike above humping damp accessed, an irregular and random ferro-profile will be generated outside pool region. Such humping deployment, as a manner of shockproof, might be utilized to reduce the seismic damage and that makes damping analysis of seismic study become more practical and approach to the intended demand.

Sample Size Effect of Magnetomechanical Response for Magnetic Elastomers by Using Permanent Magnets

The size effect of magnetomechanical response of chemically cross-linked disk shaped magnetic elastomers placed on a permanent magnet has been investigated by unidirectional compression tests. A cylindrical permanent magnet with a size of 35 mm in diameter and 15 mm in height was used to create the magnetic field. The magnetic field strength was approximately 420 mT at the center of the upper surface of the magnet. The diameter of the magnetoelastic polymer disks was varied from 14 mm to 35 mm, whereas the height was kept constant (5 mm) in the undeformed state. We have studied the influence of the disk diameter on the stress-strain behavior of the magnetoelastic in the presence and in the lack of magnetic field. It was found that the smallest magnetic elastomer with 14 mm diameter did not exhibit measurable magnetomechanical response due to magnetic field. On the opposite, the magnetic elastomers with diameters larger than 30 mm contracted in the direction parallel to the mechanical stress and largely elongated in the perpendicular direction. An explanation is put forward to interpret this size-dependent behavior by taking into account the nonuniform field distribution of magnetic field produced by the permanent magnet.

Effect of non-uniform surface resistance on the quality factor of superconducting niobium cavity

The formula Rs=G/Q0is commonly used in the calculation of the surface resistance of radio frequency niobium superconducting cavities. The applying of such equation is under the assumption that surface resistance is consistent over the cavity. However, the distribution of the magnetic field varies over the cavity. The magnetic field in the equator is much higher than that in the iris. According to Thermal Feedback Theory, it leads non-uniform distribution of the density of heat flux, which results in a different temperature distribution along the cavity inter surface. The BCS surface resistance, which depends largely on the temperature, is different in each local inner surface. In this paper, the effect of surface non-uniform resistance on the quality factor has been studied, through the calculation of Q0 in the original definition of it. The results show that it is necessary to consider the non-uniform distribution of magnetic field when the accelerating field is above 20MV/m for TESLA cavities. Also, the effect of inhomogeneity of residual resistance on the quality factor is discussed. Its distribution barely affects the quality factor.