This work proposes a semianalytical technique based on the boundary element method (BEM) to predict the signals due to flaws (cracks) that are typically encountered in eddy current (ECT) ...nondestructive testing (NDT). Two case studies, for two different narrow opening notches in a finite thickness aluminium plate, were performed by experimental measurements to corroborate the theoretical model. The signal which has been modelled is the perturbation in the magnetic flux density (MFD) components B x , B y , and B z due to narrow opening flaws. The proposed analytical model uses the magnetic vector potential (MVP), arising from electric dipole sources, to determine the voltage induced in a hypothetical small circular loop located around the evaluation point. Based on the linear relationship between the voltage induced and the magnetic flux in the surface enclosed by the hypothetical loop, a linearity constant that transforms the induced voltage to the MFD component has been computed. Appropriate vector potential Green's functions have been used to transform the electric dipole sources to the magnetic vector potential components to determine the voltage induced in the hypothetical loop.
•The unbalanced magnetic pull (UMP) model of axial-varying eccentric rotor was established with Maxwell stress tensor method.•With the signal demodulation techniques, the frequency modulation of ...various signals from simulation and experiment was extracted.•Based on the modulation features, the relevance among magnetic flux density, UMP, and vibration acceleration was established.
In the presence of non-uniform loads, rotor misalignment emerges as a prevalent fault in permanent magnet synchronous motors (PMSMs), leading to the manifestation of an axial-varying eccentric air–gap. Considering the three-dimensional (3D) nature of magnetic flux under axial-varying eccentric fault, 3D finite element (FE) analysis method was used in this paper. Then, the electromagnetism simulations were conducted to calculate the magnetic flux density and unbalanced magnetic pull (UMP). With the signal demodulation algorithm based on principal component analysis (DPCA), the frequency modulation of various signals from simulation and experiment was extracted. Furthermore, based on the modulation features, the relevance among magnetic flux density, UMP, and vibration acceleration was established with shaft frequency as the link. The coupling of magnetic field and vibration level shown in results was analysis, which provide important theoretical and engineering references for the safe operation of PMSM system and the exact identification of rotor tilting faults.
To improve the power transfer efficiency in wireless power transfer systems, a novel configuration of a magnetic resonant structure is proposed in this paper. According to the analytical expression ...of mutual inductance, the magnetic field can be improved by weakening the demagnetizing factor for coils with a ferrite core. In this paper, the demagnetizing factors of a cylindrical ferrite core and a novel ferrite core are investigated. Compared with the cylindrical ferrite core, the proposed ferrite core has a smaller demagnetizing factor and an increased mutual inductance. In addition, the magnetic field through the receiving coil is enhanced due to the thin ferrite axis where the magnetic field is concentrated. The proposed ferrite core is designed and analyzed. Moreover, the effects of pitch and lateral misalignment, as well as the number of turns of the receiving coil, the core loss, and the load, are studied. Experimental prototypes are established to validate the performance of the wireless power transfer system with different types of receiving structures. The results indicate that the proposed structure is superior to others and that it shows better performance in power transfer efficiency and transfer distance, which is in good agreement with the theoretical and simulation analysis.
The paper investigates the magnetic properties and design of energy harvester system including the magnetic spring and vibration generator. The magnetic flux density measurements were conducted by ...means of Hall-Effect magnetic sensors mounted on the magnetic spring. The amplitude of variable component of the magnetic flux density in the magnetic spring depends on the vibrations frequency resembled by vibration generator. In the magnetic spring, two resonant frequencies at 86 Hz and 110 Hz are identified and the reached maximum amplitude value of magnetic flux density is ∼1mT. To confirm the usefulness of the manufactured magnetic spring, the calculation of the magnetic flux density in 2D axis-symmetric model of vibration generator and magnetic spring has been carried out using the Ansys Maxwell. The results of the simulation are in accordance with the measurements. Through simulation analysis and laboratory measurement tests, a better understanding of the properties of magnetic springs prototype has been achieved.
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•Magnetic flux density measured by Hall-Effect sensors in magnetic spring.•2D Magnetostatic Finite Element Simulation.•Analysis of the magnetic flux density at different frequencies.
Fe soft magnetic composites (SMCs) with low core loss were fabricated via surface oxidation of the Fe powders by H2O and O2 at elevated temperatures. Surface oxidation prevents magnetic dilution due ...to the formation of the ferromagnetic iron oxide coating layer, giving rise to high magnetic flux density and effective permeability of the SMCs compared with those fabricated with traditional phosphate coating. Mechanism of the oxidation process has been investigated where Fe3O4 forms by reactions of Fe with H2O and O2. The Fe3O4 coating layer tends to convert into γ-Fe2O3 with increased oxidation temperature and time. By controlling composition of the coating layer, low core loss of 688.9mW/cm3 (measured at 50mT and 100kHz) and higher effective permeability of 88.3 can be achieved for the Fe SMCs.
•Surface oxidation as a new method to fabricate Fe Soft magnetic composite (SMCs).•Oxidation mechanism revealed where Fe reacts with H2O and O2 at high temperatures.•Evolution of the iron oxide coating with growth temperature and time investigated.•The iron oxide insulation coating results in improved magnetic performance.
•Fe77.7Si8B10P4Cu0.3 amorphous powder was successfully prepared by gas atomization.•High density powder compacts with amorphous can be obtained by spark plasma sintering.•Powder compacts exhibits ...high relative density (94%), saturated magnetic flux density (1.34 T), low coercivity (2.3 Oe), and high permeability (163 stable up to 20 kHz).•The effect of sintering temperature on the magnetic properties was discussed based on density and structure.
Fe77.7Si8B10P4Cu0.3 amorphous powder compacts with high relative density (ρr = 94%), high saturated magnetic induction (Bs = 1.34 T), and high permeability (μ = 163 at 20 kHz) were fabricated by spark plasma sintering. In this work, Fe77.7Si8B10P4Cu0.3 spherical amorphous powders with good amorphous forming ability were prepared by regulating the material composition and the particle size distribution by gas atomization at first. The effect of sintering temperature (Ts) on the structure and magnetic properties of powder compacts was systematically investigated. The powder compacts sintered at Ts of 696–712 K were found to remain amorphous structure and exhibit optimal structural and magnetic performance, due to the high temperature and high pressure employed in SPS with high heating rate. These results are promising for the applications of Fe-based amorphous powder alloys in soft magnetic devices requiring tens of kilo-hertz frequency.
A new Si-gradient steel (JNRFTM) with a combination of low iron loss and high magnetic flux density was developed by controlling the Si distribution in the thickness direction and the crystal ...orientation. Drone motors made of conventional Si-gradient steel (JNHFTM), new Si-gradient steel, and 3% Si steel were evaluated. As a result, the motor using the new Si-gradient steel showed both high efficiency and high torque. In conclusion, the new Si-gradient steel is a suitable core material for motors that require both high power and high efficiency, such as drone motors.
This article proposes and implements an optimized omnidirectional wireless power transfer (WPT) system using distributed transmitter coils. Under the consideration of practical WPT applications which ...involve human safety concerns, such as daily home apparatus or wireless rechargeable medical implants, the proposed system can achieve the shortest charging time within the safe limits of human exposure to radiofrequency electromagnetic energy. Based on the calculation of the magnetic intensity generated by multicoupling WPT systems, a more processable magnetic threshold model is presented and analyzed based on the common standard. A newly developed optimization model of the transmitter currents and accordant control strategy is designed and presented to realize both maximum power tracking and flux suppression at target positions. The double-resonant circuit topology with LCC compensation is adopted to reach the stable and synchronized transmitter currents. The cross-coupling problem in multiinput WPT systems will be solved as well. Full-range magnitude control is realized with a single controller and direct current (dc) power supply. The hybrid frequency pacing technique is adopted for lower switching frequency and higher system efficiency under weak coupling operations. Taking practical wireless rechargeable medical implant as the research object, both simulation and experimental results validate the feasibility and the prospect of the proposed system.
The present study investigates the wetting phenomenon of sessile ferrofluid droplets on heterogeneous substrates, exhibiting hydrophilic and hydrophobic regions. Dripping the ferrofluid on the ...interface that delimits the regions with different hydrophilicity, the relaxation dynamics of the contact angle on each side is analyzed, considering the effects associated with a non-uniform magnetic flux density. Our results show that the wetting dynamic is governed by the contact line evolution on the hydrophilic side, being strongly affected by the magnetix flux density. Due to the surface heterogeneity, it is noticed that sessile ferrofluid drops present a different shape from the typical spherical cap observed on homogeneous substrates. In addition, it is verified that the interplay of substrate heterogeneity and drop surface deformation leads to a slow dewetting on the hydrophobic surface, which depends on the field strength. The present findings may be significant for microfluidic devices exploiting magnetically controlled ferrofluid movement on heterogeneous soft materials.
•Wetting dynamics of ferrofluid droplets on heterogeneous substrates is analyzed.•Magnetowetting dynamics depends on the nature of ferrofluid-substrate interaction.•Droplet shape depends on the substrate heterogeneity and the magnetic flux density.•Interplay of substrate heterogeneity and drop deformation leads to a slow dewetting.
