Radio wave propagation of three types of birdcage transmit/receive radio-frequency (RF) coils (lowpass filter, highpass filter, and bandpass filter configurations) was analysed for mouse body ...magnetic resonance imaging at main magnetic fields of 1.5, 3.0, 4.7, 7.0, 9.4, and 11.7 T (Larmor frequencies of 63.87, 127.74, 200, 300, 400, and 500 MHz) in terms of magnetic (|B1|) field sensitivity and homogeneity. The observed radio wave propagation in the central axial |B1| field, as influenced by the biological subject, was calculated numerically in the finite-difference time-domain method and compared with assessment criteria using the mean value and standard deviation. The results for different Larmor frequencies RF shielding cage configurations, and biological subject loading versus unloading were compared and are discussed in detail.
This article presents a novel coil design method for cubic wireless charging space frames to achieve even magnetic flux density distribution inside. The method is demonstrated in two hardware ...designs. The new coil design (i.e., Design-2) is upgraded from an elementary design (i.e., Design-1), which is inherited from the conventional Helmholtz coil to fit the cubic structure, by folding the terminal wires to the neighboring edges to form "L" shapes. Consequently, the magnetic flux density inside the space frame in Design-2 becomes stronger and more evenly distributed than that of Design-1. This important feature of the proposed design methodology is validated by theoretical calculations based on Biot-Savart law, simulation results based on finite-element method (FEM), and practical measurements based on a three-dimensional (3-D) printed prototype. The proposed coil design method could be potentially applied to cubic space frames for many 3-D wireless charging applications ranging from portable devices to underwater unmanned vehicles. The structure can form a 3-D wireless charging chamber that can in principle be scaled up to different sizes.
At present, increasing the torque density is one of the main directions in the design of special motors. The application of soft magnetic materials with high saturation magnetic flux density can ...further improve the torque performance of the motor. The continuous casting slab (CCS) explored in this manuscript belongs to silicon steel, which is an alloy sample extracted from the slab before the rolling of silicon steel. CCS has the characteristics of high saturated magnetic flux density, although its iron loss characteristics are similar to the DT4C, but it avoids the expensive cost of silicon steel processing. In summary, its magnetic and mechanical characteristic are tested to explore the torque impact of its application in the design of high torque density motors, aiming to provide design references for the development and application of new materials for iron cores.
•Proposes a novel method merging CAD with magnetic flux simulation for point generation and magnetic flux measurement.•Specifically magnetic objects from additive manufacturing, selecting measurement ...points with high flux variation.•Utilizes RBF equations within an automated magnetic measurement system to reconstruct flux density.•Attains notable enhancement in measurement speed and accuracy.
This study proposes a method that combines computer-aided design (CAD) of magnetic objects with magnetic flux simulation data to generate measurement points. The researchers of this study employed radial basis function (RBF) equations, which were applied within an existing automated magnetic measurement system platform, to reconstruct the magnetic flux density distribution of the tested object. This study specifically concentrates on using magnetized objects produced through additive manufacturing as the measurement subjects. Specifically, the NdFeB magnet examined in our study was fabricated using the pallet deposition modeling (PDM) method and was later magnetized using an electromagnet. These objects were integrated into existing simulation software, and measurement points with high magnetic flux variation were selected based on the magnetic characteristics. The data acquired from these points serves as control points for RBF interpolation, facilitating the reconstruction of magnetic flux distribution. Through this approach, a notable improvement in measurement speed and accuracy was effectively achieved.
•Forming abrupt magnetic flux density change for electromagnetic energy harvesters.•Studying how the formation affects the power density of the harvesters.•Revealing that the cubic-magnet ...configuration leads to the best yields.•Proving that alternating polarities enhance power outputs by up to over 20 times.
In this paper, we originally investigate how formulation of abrupt magnetic flux density change influences the electric outputs, e.g. open-circuit voltage, power density and charging rates, of electromagnetic energy harvesters. Electromagnetic energy harvesters are comprised of one magnet array and two sets of coil arrays. In a certain volume, the dimension and number of magnets evidently determines the number of abrupt magnetic flux density change (denoted as β, β=0,1,2,3,5,7) and further the output voltage. To study how this correlation affects the performance of the harvester, a configuration is first proposed and by conducting simulation, we infer that the highest voltage is induced by the case where β=3, namely when the length, height and width of the magnet are the same. This hypothesis is further validated by three series of experimental results: the open-circuit voltage first increases, reaches its peak where β=3, and falls off sharply as β increases from 0 to 7; the cubic-magnet array configuration yields the highest power and power density, more than 20 times higher than that of the case without abrupt magnetic flux density change. The instantaneous power reaches as high as 284 mW under resonance at 1 g excitation acceleration with an overall dimension of 4.8cm × 3.9cm × 2.5cm; The charging-capacitor experimental results confirms this as the cubic magnet case yields the largest charging rate and highest saturation voltage. We mainly attribute this phenomenon to the collective relation of the flux change and magnet volume as β grows from 0 to 7. This finding reveals the best configuration of magnet arrays that leads to the most desirable performance from electromagnetic energy harvesters.
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This article presents the methods to design and model an eddy-current (EC) probe composed of one or more electromagnets (EMs) and a magnetic flux density (MFD) sensor for detecting defects near the ...edge of a conductive workpiece (WP). Both cavity and crack defects are considered; the former characterized by a conductivity field and the latter modeled as two overlapping boundaries, and their perturbed effects on the EC-generated MFD field are analyzed using a distributed current source (DCS) computing method. Two approaches, defect-free subdomain formulation and dimension-reduction for analyzing defect-perturbation, are presented to shorten the time to compute the DCS solutions to the defect-detection problem. The accuracy and computational efficiency of these proposed approaches have been numerically evaluated, which demonstrate significantly improved performance with greatly reduced computation when compared with finite-element analysis (FEA) and can further shorten the time to compute the matrix inversion. The effectiveness of the magnetic field-based method has been experimentally verified with two prototype EC probes designed to overcome limitations associated with impedance-based EC probes commonly designed using a lumped-parameter approach.
Application method of static-field magnetization to magnetically levitated mover system with high critical temperature ( T c ) superconductors is discussed. The system is composed of a levitated ...mover, magnetic rails, a linear induction motor (LIM) and some power supplies. In the paper, static-field magnetization is applied to superconductors in the levitated system from bottom superconductor surfaces. Then, magnetizations in superconductors are tried to control using static-field on superconductor surfaces. That is, magnetic flux density distributions are successfully forced to change to initial flux density distributions.
Flux pinning in high-temperature superconducting (HTS) bulk is essential for power applications. Since HTS bulk integrated in the motor/generator requires pulse field magnetization (PFM) before ...operation, evaluating the time evolution of the trapped magnetic flux density distribution is important in the development of power applications. In general, scanning the Hall element over the HTS bulk surface provides a detailed measurement of the magnetic flux density distribution. However, the mechanical scanning speed is too slow relative to the elapsed time of PFM, to obtain information about the transient behavior of the penetration magnetic field. Therefore, we have placed Hall elements at several locations with characteristic crystal structures on the HTS bulk surface and measured the magnetic flux density in a short period of time. In this study, we have constructed a system that can measure the magnetic flux density distribution every approximately 1 ms, which we name a two-dimensional magnetic field sensor (2DMFS) and measured the distribution of the magnetic flux density that enters the bulk during PFM on the HTS bulk surface. The sample is a GdBCO bulk of 45 mm diameter and 19 mm thick, which we used in our axial-gap type HTS rotating machine. In this paper, we'll show the transient magnetic flux density distribution that penetrated the sample during PFM and contrast it with the conventional measurement method.
Wind turbine drive trains consist of mechanical components, such as the gearbox, the bearings, and the rotating shaft, and an electrical component, such as the electric generator. These components ...are electromagnetically and electromechanically coupled with each other and have continuously rotating parts, making them more susceptible to faults. Unfortunately, these components are individually modeled while performing finite element analysis (FEA), and the coupling effects are neglected, yielding approximations that are not acceptable for, e.g., modal analysis. This article addresses the issue and presents an FEA model of the complete wind turbine drive train subsystem. Here, a unique co-simulation platform was developed to integrate and analyze the mechanical and electrical components of the drive train. The case studies performed here report the existence of electromagnetic coupling among the components of the drive train by simulating various faults, such as broken gearbox tooth and demagnetization of permanent magnets and studying their influence on the magnetic flux of the electric generator. This article offers new insights on motivation, applications, and the importance of FEA modeling of the entire wind turbine drive train, and how it could be critical to non-destructive evaluations and fault detections on the wind turbines.
