• Journal of the Korean Magnetic Resonance Society
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• v.24 no.3
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• pp.66-69
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• 2020

In ultra-low field magnetic resonance imaging (ULF-MRI), the strength of a static magnetic field can be comparable to that of gradient field. On that occasion, the gradient field is accompanied by concomitant gradient field, which yields distortion and blurring artifacts on MR images. Here, we focused on the distortion artifact and derived the equations capable of correcting it. Its usefulness was confirmed through the corrections in both simulated and experimental images. This solution will be effective for acquiring more accurate images in low and/or ultra-low magnetic fields.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.72.1-72.1
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• 2014

In this study, we extrapolate a nonlinear force-free field (NLFFF) from an observed photospheric magnetic field to understand the three-dimensional (3D) coronal magnetic field producing a huge solar flare. The purpose of this study is to develop a NLFFF extrapolation code based on the so-called MHD relaxation method and check how accurately our model reconstructs a coronal field. Furthermore, we apply it to the photospheric magnetic field obtained by Helioseismic and Magnetic Imager (HMI) on board Solar Dynamics Observatory (SDO) to reconstruct a 3D magnetic structure. We first investigate factors in controlling the accuracy of our NLFFF code by using a semi-analytical solution obtained by Low & Lou (1990). To extend a work done by Inoue et al. (2014), we apply various boundary conditions at the side and top boundaries in order to make our solution close to a realistic solution. As a consequence, our solution has a good accuracy when three components of a reference field are all fixed at the boundaries. Furthermore, it is also found that our solution is well matched to the Low & Lou solution in the central area of a simulation domain when the three components of a potential field are fixed at side and top boundaries (this approach is close to a realistic solution). Finally, we present the 3D coronal magnetic field producing an X 1.5-class flare in the active region 11166 through the extrapolation from SDO/HMI.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.92.2-92
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• 2001

This paper presents the time optimal reorientation solution of three-axis spacecraft which has only three magnetic torquers. It has been very difficult problem because the magnetic torquer generates only perpendicular to Earth magnetic field vector. In this paper, minimum-time solution using only magnetic torquer is solved using collocation method and nonlinear programming solver NPSOL. IGRF Earth magnetic field model used to simulate magnetic field. The result is verified by comparing to the result of numerical integration. The solution is obtained for the various reorientation maneuver of three axes rigid spacecraft. And the results show that all three axes of rigid spacecraft are controlled effectively only by magnetic torqure.

• Smart Structures and Systems
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• v.9 no.5
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• pp.427-439
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• 2012

The present paper deals with the analytical solution of a functionally graded piezoelectric (FGP) cylinder in the magnetic field under mechanical, thermal and electrical loads. All mechanical, thermal and electrical properties except Poisson ratio can be varied continuously and gradually along the thickness direction of the cylinder based on a power function. The cylinder is assumed to be axisymmetric. Steady state heat transfer equation is solved by considering the appropriate boundary conditions. Using Maxwell electro dynamic equation and assumed magnetic field along the axis of the cylinder, Lorentz's force due to magnetic field is evaluated for non homogenous state. This force can be employed as a body force in the equilibrium equation. Equilibrium and Maxwell equations are two fundamental equations for analysis of the problem. Comprehensive solution of Maxwell equation is considered in the present paper for general states of non homogeneity. Solution of governing equations may be obtained using solution of the characteristic equation of the system. Achieved results indicate that with increasing the non homogenous index, different mechanical and electrical components present different behaviors along the thickness direction. FGP can control the distribution of the mechanical and electrical components in various structures with good precision. For intelligent properties of functionally graded piezoelectric materials, these materials can be used as an actuator, sensor or a component of piezo motor in electromechanical systems.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.4
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• pp.185-191
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• 2003

In this Paper, we propose an accurate and stable solution of the transient electromagnetic response from three-dimensional arbitrarily shaped conducting objects by using a time domain magnetic field integral equation. This method does not utilize the conventional marching-on in time (MOT) solution. Instead we solve the time domain integral equation by expressing the transient behavior of the induced current in terms of temporal expansion functions with decaying exponential functions and Laguerre·polynomials. Since these temporal expansion functions converge to zero as time progresses, the transient response of the induced current does not have a late time oscillation and converges to zero unconditionally. To show the validity of the proposed method, we solve a time domain magnetic field integral equation for three closed conducting objects and compare the results of Mie solution and the inverse discrete Fourier transform (IDFT) of the solution obtained in the frequency domain.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.7
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• pp.326-331
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• 2005

We obtain analytical expressions the magnetic field of ferrites for DC magnetron sputtering device, which has been widely used for vacuum thin film deposition, and suggested the equation on maximum radius of the magnetic field by analytic solution. Also, the analytic results are compared with some calculations using magnetization elements of right-angled hexahedron.

• Advances in concrete construction
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• v.11 no.4
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• pp.315-321
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• 2021

In this article, an analytical solution of the dynamical behavior in an orthotropic non-homogeneity elastic material using for elastodynamics equations is investigated. The effects of the magnetic field, the initial stress, and the non-homogeneity on the radial displacement and the corresponding stresses in an orthotropic material are investigated. The analytical solution for the elastodynamic equations has solved regarding displacements. The variation of the stresses, the displacement, and the perturbation magnetic field have shown graphically. Comparisons are made with the previous results in the absence of the magnetic field, the initial stress, and the non-homogeneity. The present study has engineering applications in the fields of geophysical physics, structural elements, plasma physics, and the corresponding measurement techniques of magneto-elasticity.

• Progress in Superconductivity and Cryogenics
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• v.18 no.2
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• pp.30-36
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• 2016

For the magnetic field analysis or design, it is important to know the behavior of the magnetic field in an interesting space. Magnetic field mapping becomes a useful tool for the study of magnetic field. In this paper, a numerical way for mapping the magnetic field within the cylindrical center volume of magnet is presented, based on the solution of the Laplace's equation in the cylindrical coordinate system. The expression of the magnetic field can be obtained by the magnetic flux density, which measured in the mapped volume. According to the form of the expression, the measurement points are arranged with the parallel cylindrical line (PCL) method. As example, the magnetic flux density generated by an electron cyclotron resonance ion source (ECRIS) magnet and a quadrupole magnet were mapped using the PCL method, respectively. The mapping results show the PCL arrangement method is feasible and convenience to map the magnetic field within a cylindrical center volume generated by the general magnet.

• Current Optics and Photonics
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• v.7 no.2
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• pp.119-126
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• 2023

The vibratory and rotational levels of many biological macromolecules lie in the terahertz (THz) band, which means that THz techniques can be used to identify and detect them. Moreover, since the biological activity of most biomolecules only becomes apparent in aqueous solution, we use microfluidic technology to study the biological properties of these biomolecules. THz time-domain spectroscopy was used to study the THz absorption characteristics of graphene oxide (GO) aqueous solution at different concentrations and different exposure times in fixed electric or magnetic fields. The results show that the spectral characteristics of the GO solution varied with the concentration: as the concentration increased, the THz absorption decreased. The results also show that after placing the solution in an external electric field, the absorption of THz first increased and then decreased. When the solution was placed in a magnetic field, the THz absorption increased with the increase in standing time. In this paper, these results are explained based on considerations of what is occurring at the molecular scale. The results of this study provide technical support for the further study of GO and will assist with its improved application in various fields.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.3
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• pp.141-145
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• 2006

The line current problem(2-dimensional space : point source) is not easy to analyze the magnetic field using the standard finite element method(FEM), such as overhead trolley line or transmission line. To supplement such a defect this paper is proposed the coupling scheme of analytical solution and FEM. In analysis of the magnetic field using the standard FEM. If the current region is a relatively small compared to the whole region. Therefore the current region must be finely divided using a large number of elements. And the large number of elements increase the number of unknown variables and the use of computer memories. In this paper, an analytical solution is suggested to supplement this weak points. When source is line current and the part of interest is far from line current, the analytical solution can be coupling with FEM at the boundary. Analytical solution can be described by the multiplication of two functions. One is power function of radius, the other is a trigonometric function of angle in the cylindrical coordinate system. There are integral constants of two types which can be established by fourier series expansion. Also fourier series is represented as the factor to apply the continuity of the magnetic vector potential and magnetic field intensity with tangential component at the boundary. To verify the proposed algorithm, we chose simplified model existing magnetic material in FE region. The results are compared with standard FE solution. And it is good agreed by increasing harmonic order.