• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.9
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• pp.454-461
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• 2001

Acoustic noise and vibration of a BLDC motor is a coupled phenomenon between mechanical characteristics and electromagnetic origins through the motor air-gap. When a relative misalignment of rotor in the air-gap center exists on the assemblage, it is considered to influence the motor system characteristics. In this paper, the back electro motive force(BEMF) is analyzed by Finite Element Method(FEM) and verified by experiments for the SPM and IPM type motors. For magnetic field analysis, a FEM is used to account for the magnetic saturation. Using these results, the FEM is made to determine the appropriate electromagnetic field analysis in BLDC motors with rotor eccentricity ratio. A radial magnetic imbalance force of BLDC motor with rotor eccentricity is analyzed. Results demonstrate that the imbalance force is increased according to the degree of misalignment. An IPM motor, mostly chosen to realize high-speed operation, shows a worse effect on magnetic unbalanced forces and dynamic responses compared with SPM motor due to magnetic saturation when the rotor eccentricity exists.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.119-122
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• 2003

This paper describes characteristics for insertion losses of Isolator have an effect on material parameter. One purpose of the paper is to present insertion loss on this resonator for magnetic loss, dielectric loss, magnetic field and saturation magnetization. Another is to study the effect of propeller resonator on response characteristics. In this paper, the analysis and measurement of the response characteristics were carried out for the isolator prototype. The measurement results agreed on the simulation results and acquire insertion loss $0.18\;{\sim}\;0.24dB$, return loss 27dB, isolation 27dB and bandwidth 500MHz on this condition saturation magnetization 550G, dielectric loss 0.0004, magnetic loss 20 and dielectric constant 14.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.1
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• pp.7-14
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• 2014

Aircraft variable frequency power and a new application of induction motor under the aero-power are introduced. The transient models and simulation of induction motor are reviewed. A new transient model and simulation method is presented that includes deep-bar effect and magnetic saturation. Dynamic magnetizing inductance, rotor resistance and leakage reactance are considered as varying parameters in state-space model. Base on known rotor structure and speed, these parameters can be calculated.

• Structural Engineering and Mechanics
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• v.80 no.5
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• pp.523-538
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• 2021

The mechanical behaviour and stability of coal mining engineering underground is significantly affected by ground water. In this study, nuclear magnetic resonance imaging (NMRI) technique was employed to determine the water distribution characteristics in coal specimens during saturation process, based on which the functional rule for water distribution was proposed. Then, using discrete element method (DEM), an innovative numerical modelling method was developed to simulate water-weakening effect on coal behaviour considering moisture content and water distribution. Three water distribution numerical models, namely surface-wetting model, core-wetting model and uniform-wetting model, were established to explore the water distribution influences. The feasibility and validity of the surface-wetting model were further demonstrated by comparing the simulation results with laboratory results. The investigation reveals that coal mechanical properties are affected by both water saturation coefficient and water distribution condition. For all water distribution models, micro-cracks always initiate and nucleate in the water-rich area and thus lead to distinct macro fracture characteristics. With the increase of water saturation coefficient, the failure of coal tends to be less violent with less cracks and ejected fragments. In addition, the core-wetting specimen is more sensitive to water than specimens with other water distribution models.

• Journal of Magnetics
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• v.6 no.1
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• pp.9-12
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• 2001

The dependence of the magnetoimpedance effect (MI) on magnetic properties has been investigated in mumetal thin films prepared by rf magnetron sputtering. Coercivity of thin films prepared at 400 W was about 0.4 Oe, and the magnetic anisotropy field of films deposited under a uniaxial magnetic field decreased with increasing film thickness. The saturation magnetization of mumetal films increased with rising input power and thickness and was smaller than that of permalloy films. Transverse incremental Permeability (TPR) of films of 1$\mu m$ thick increased with increasing effective permeability. The magneto impedance ratio (MIR) was proportional to TPR in films 1$\mu m$ thick but in spite of lower effective permeability at higher thicknesses, MIR increased due to skin effect. The height of the double peaks in the MIR curves decreased with decreasing anisotropy and thickness. The maximum MIR value for a 4$\mu m$ thick 75% at 36.5 MHz.

• Korean Journal of Materials Research
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• v.12 no.11
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• pp.880-882
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• 2002

We have prepared magnetic thin films of FeSiB by sputtering and examined microstructure and magnetic properties of the annealed films in order to investigate the feasibility of the films to microsensor application. Effects of vacuum annealing on the magnetic properties of $Fe_{84}$$Si_{6}$$B_{10}$ films have been examined as a function of temperature. The heating rate and the holding time were 10 K/min and 1 hour, respectively. Vacuum condition was held during cooling to prevent oxidation of the films. The coercivity did not show any noticeable change (~1500 A/m), although the grain size of the crystalline phase in the annealed films increased gradually up to about 16 nm until 673 K. However, both the grain size and the coercivity increased steeply when the annealing temperature increased over 723 K. Since the saturation magnetization is closely related to the phase evolution, the variation of the saturation magnetization of the annealed films was similar to that of the ribbon materials; the thin films were transformed from amorphous to crystalline with $\alpha$-(Fe,Si) phase by increasing annealing temperature.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.14-15
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• 2002

Iron nitride alloy films prepared in the form of laminated ${(Fe_{97}Al_3)}_{85}N_{15}/Al_2O_3$ multilayers (Ml's) due to excellent soft magnetic properties and high saturation magnetization [1, 2] are very promising materials for poles and shields in ultra high density thin film heads. The present work concerns the ferromagnetic (FM) coupling effect as a function of the thickness of $Al_2O_3$ spacers by analysis of the magnetic domain structure.

• Journal of Magnetics
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• v.19 no.1
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• pp.10-14
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• 2014

In this study, we fabricate an integrated microfluidic chip with a planar Hall effect (PHE) sensor for single magnetic bead detection. The PHE sensor was constructed with a junction size of $10{\mu}m{\times}10{\mu}m$ using a trilayer structure of Ta(3 nm)/NiFe(10 nm)/Cu(1.2 nm)/IrMn(10 nm)/Ta(3 nm). The sensitivity of the PHE sensor was 19.86 ${\mu}V/Oe$. A diameter of 8.18 ${\mu}m$ magnetic beads was used, of which the saturation magnetization was ~2.1 emu/g. The magnetic susceptibility ${\chi}$ of these magnetic beads was calculated to be ~0.14. The diluted magnetic beads solution was introduced to the microfluidic channel attributing a single bead flow and simultaneously the PHE sensor voltage was measured to be 0.35 ${\mu}V$. The integrated microchip was able to detect a magnetic moment of $1.98{\times}10^{-10}$ emu.

• Journal of Electrical Engineering and Technology
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• v.2 no.2
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• pp.241-248
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• 2007

The accuracy of all the schemes that belong to vector controlled induction machine drives is strongly affected by parameter variations. The aim of this paper is to examine iron losses and magnetic saturation effect in sensorless vector control of induction machines. At first, an approach to induction machine modelling and vector control scheme, which account for both iron loss and saturation, is presented. Then, a model reference adaptive system (MRAS) based speed estimator is developed. The speed estimation is modified in such a way that iron losses and the variation in the saturation level are compensated. Thus by substituting an artificial neural network flux estimator into the MRAS speed estimator. Experimental results are presented to verify the effectiveness of the proposed approach.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.