• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권2호
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• pp.61-67
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• 2003

This paper describes a development of magnetic tomography system using two poles perpendicular magnetic field. In the system, the relative permeabilities of the object are detected by Hall sensors located along with tube circumference. The signals according to the size and position of the object could be separated in case the relative permeability of the object are over 10. Moreover, the size and location of the object could be determined in real time.

• Investigative Magnetic Resonance Imaging
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• 제22권3호
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• pp.141-149
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• 2018

Purpose: The purpose of this study is to develop a simple method to measure magnetic susceptibility of arbitrarily shaped materials through MR imaging and numerical modeling. Materials and Methods: Our 3D printed phantom consists of a lower compartment filled with a gel (gel part) and an upper compartment for placing a susceptibility object (object part). The $B_0$ maps of the gel with and without the object were reconstructed from phase images obtained in a 3T MRI scanner. Then, their difference was compared with a numerically modeled $B_0$ map based on the geometry of the object, obtained by a separate MRI scan of the object possibly immersed in an MR-visible liquid. The susceptibility of the object was determined by a least-squares fit. Results: A total of 18 solid and liquid samples were tested, with measured susceptibility values in the range of -12.6 to 28.28 ppm. To confirm accuracy of the method, independently obtained reference values were compared with measured susceptibility when possible. The comparison revealed that our method can determine susceptibility within approximately 5%, likely limited by the object shape modeling error. Conclusion: The proposed gel-phantom-based susceptibility measurement may be used to effectively measure magnetic susceptibility of MR-compatible samples with an arbitrary shape, and can enable development of various MR engineering parts as well as test biological tissue specimens.

• Advances in Computational Design
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• 제7권1호
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• pp.57-68
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• 2022

A simulation study of the distribution of magnetic flux induced by a U-shaped electromagnet into a two-layer massive object with variations in the depth and properties of the surface layer has been carried out. It has been established that the hardened surface layer "pushes" the magnetic flux into the bulk of the magnetized object and the magnetic flux penetration depth monotonically increases with increasing thickness of the hardened layer. A change in the thickness and magnetic properties of the surface layer leads to a redistribution of magnetic fluxes passing between the poles of the electromagnet along with the layer and the bulk of the steel object. In this case, the change in the layer thickness significantly affects the magnitude of the tangential component of the field on the surface of the object in the interpolar space, and the change in the properties of the layer affects the magnitude of the magnetic flux in the magnetic "transducer-object" circuit. This difference in magnetic parameters can be used for selective testing of the surface hardening quality. It has been shown that the hardened layer pushes the magnetic flux into the depth of the magnetized object. The nominal depth of penetration of the flow monotonically increases with an increase in the thickness of the hardened layer.

• 새물리
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• 제68권11호
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• pp.1249-1261
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• 2018

원형 막대자석이 강자성 원형 막대 물체에 작용하는 자기력에 대한 정량적인 표현이 자기화 이론, 자기에 대한 Gilbert 모형, Ampere 모형을 바탕으로 유도되었다. 이 연구에서 유도된 자기력은 원형 막대자석의 잔류 자기화 자기장과 단면적, 강자성 원형 막대 물체의 포화자기장과 단면적에 비례하며, 그리고 이들 사이의 거리에 관계되는 양의 제곱에 반비례한다. 반지름 0.4 cm이고 길이 7 cm인 알니코V 원형 막대자석과 페라이트 원형 막대자석이 반지름 이상 거리에 있는 강자성 물체에 작용하는 자기력은 각각 3.6711 N과 0.1857 N 이하로 계산되었다.

• 대한의용생체공학회:의공학회지
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• 제25권3호
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• pp.183-188
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• 2004

Magnetic resonance current density imaging (MRCDI) is a useful method for measuring electrical current density distribution inside an object. To avoid object rotations during the conventional MRCDI scans, we have reconstructed current density component images by applying a spatial filter to the magnetic field data measured both inside and outside the object. To measure the magnetic field outside the object with MRI, we immersed the object in a water tank. To evaluate accuracy of the current density imaging, we have made a conductivity phantom with a corresponding finite element method model. We have compared the experimentally obtained current density images with the ones calculated by the finite element method. The average errors of the reconstructed current density images were 6.6 ∼ 45.4 ％ when the injected currents were 1 ∼ 24 mA. We expect that the current density component imaging technique can be used in diverse biomedical applications such as electrical therapy system developments and biological electrical safety analysis.

• Journal of Electrical Engineering and Technology
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• 제3권4호
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• pp.584-592
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• 2008

In this paper, we propose a new model of the magnetic control force exerted on the levitation object in magnetic levitation systems. The model assumes that the magnetic force is a function of the voltage applied to an electromagnet and the position of a levitation object. The function is not explicitly expressed but represented through a 2D lookup table constructed from the experimentally measured data. Unlike the conventional model that reveals only local characteristics of the magnetic force, the proposed model shows global characteristics satisfactorily. Specially devised measurement equipment is utilized in order to gather the data required for model construction. An experimental procedure to construct the model is presented. We apply the proposed model to designing a sliding mode controller for a lab-built magnetic system. The validity of the proposed model is illustrated by comparing the performances of the controller adopting the conventional model with that of the controller adopting the proposed model.

• 한국컴퓨터정보학회논문지
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• 제6권3호
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• pp.35-43
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• 2001

지하매설물을 탐지하는 기술에는 매설물의 송신기(transmitter)를 이용하여 전자기장을 가하여 매설물을 자화시켜 땅위의 상부에서 자속을 감지하여 매설물의 위치를 찾아내는 기술로 현재 가장 널리 사용되는 방식이다. 본 논문에서는 땅속에 일정 자계를 형성하여 그 자속 변화를 감지해 매설물 유무를 판단하는 방식과 지하매설물의 탐지시스템의 제어 및 표시 장치의 설계와 구성에 대하여 제안하였다. 또한 지하매설물의 탐지시스템의 시뮬레이션을 통하여 지하매설물의 판단 유무를 측정할 수 있음을 보였다.

• 전기학회논문지
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• 제62권1호
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• pp.43-48
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• 2013

In this paper, magnetic buoyancy force on nonmagnetic solid object submerged in magnetic liquid was simulated and measured. For the evaluation of the force, a multi-physics approach of hydrostatic equilibrium considering magnetic body force as well as gravity is presented. The magnetic body force should be regarded as an additional forcing term in the momentum equation of hydrodynamics. It is also shown that the virtual air-gap based Kelvin's force formula is a useful method for the calculation of force distribution in the magnetic liquid. The experimental result which was performed by a load-cell measurement system agreed quantitatively well with the numerical one.

• 한국자기학회지
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• 제20권2호
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• pp.45-51
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• 2010

비파괴검사는 탐지물체에 물리적 손상을 가하지 않고 내부 정보를 파악할 수 있어 다양한 분야에서 이용되고 있다. 그 중 전자기를 이용한 물체의 형상추정방법의 경우 역 유한요소법을 이용하여야 하지만 이는 비선형성이 강하고 수치계산이 복잡하고 측정 센서의 개수가 미지수의 개수보다 훨씬 적어 정확한 결과를 얻는데 어려움이 있다. 본 논문에서는 탐지물체에 의한 자기장 변화 신호만을 이용하여, 물체의 시스템 내 각 센서별 위치에서 물체와 등가면적의 원의 비교를 통해 비교적 간편하게 자성물체의 부피를 판정하고 형상추정을 위한 다양한 보정과정을 거쳐 탐지물체의 형상판정이 가능한 알고리즘을 제안하고 검증하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제17권8호
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• pp.2209-2221
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• 2023

As the supply of electric vehicles increases, research on wireless charging methods for convenience has been increasing. Because the electric vehicle wireless transmission device is installed on the ground and the electric vehicle battery is installed on the floor of the vehicle, the transmission and reception antennas are approximately 15-30 cm away, and thus strong magnetic fields are exposed during wireless charging. When a metallic foreign object is placed in the magnetic field area, an eddy current is induced to the metallic foreign object, and heat is generated, creating danger of fire and burns. Therefore, this study proposes a method to detect metallic foreign objects in the magnetic field area of a wireless electric vehicle charging system. An active detection-only coil array was used, and an LC resonance circuit was constructed for the frequency of the supply power signal. When a metallic foreign object is inserted into the charging zone, the characteristics of the resonance circuit are broken, and the magnitude and phase of the voltage signal at both ends of the capacitor are changed. It was confirmed that the proposed method has about 1.5 times more change than the method of comparing the voltage magnitude at one node.