• Journal of Magnetics
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• v.18 no.3
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• pp.276-282
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• 2013

In this paper, magnetic flux distributions of several permanent magnet arrays, including Halbach array, are analyzed and compared. Also, braking force characteristics on a moving solid conductor in the eddy current brake systems with such magnet arrays are analyzed. Then, a new performance index taking into account the maximum braking force and the volume of the magnet is introduced for the comparison and case study of permanent magnet arrays. By changing the lengths, magnetization directions and the height of the permanent magnet arrays, a higher braking force per volume of the magnet can be achieved.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.11
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• pp.533-539
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• 2005

In the previous work, we performed the analysis of a tubular type moving-magnet linear oscillatory actuator (LOA) with cylindrical Halbach array by using 2-d analytical formulas and confirmed validity of analytical results by comparison of those with both finite element (FE) computation and experimental results. This paper deals with the dynamic characteristic analysis of the moving-magnet LOA with cylindrical Halbach array. Control parameters such as the thrust constant, the back-emf constant, resistance and inductance are obtained from both analytical and experimental results. And then, the dynamic simulation algorithm is established by the state and output equation obtained from voltage and motion equation. Finally, for various values of frequency, the dynamic simulation and experimental results for the characteristics of the voltage, current and displacement of moving-magnet LOA are presented. The simulation results are validated extensively by experiments. The experimental and simulation results for the variation of stroke according to control voltage are also presented for various values of frequency.

• Investigative Magnetic Resonance Imaging
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• v.23 no.3
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• pp.179-201
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• 2019

Portable low-cost magnetic resonance imaging (MRI) systems have the potential to enable "point-of-care" and timely MRI diagnosis, and to make this imaging modality available to routine scans and to people in underdeveloped countries and areas. With simplicity, no maintenance, no power consumption, and low cost, permanent magnets/magnet arrays/magnet assemblies are attractive to be used as a source of static magnetic field to realize the portability and to lower the cost for an MRI scanner. However, when taking the canonical Fourier imaging approach and using linear gradient fields, homogeneous fields are required in a scanner, resulting in the facts that either a bulky magnet/magnet array is needed, or the imaging volume is too small to image an organ if the magnet/magnet array is scaled down to a portable size. Recently, with the progress on image reconstruction based on non-linear gradient field, static field patterns without spatial linearity can be used as spatial encoding magnetic fields (SEMs) to encode MRI signals for imaging. As a result, the requirements for the homogeneity of the static field can be relaxed, which allows permanent magnets/magnet arrays with reduced sizes, reduced weight to image a bigger volume covering organs such as a head. It offers opportunities of constructing a truly portable low-cost MRI scanner. For this exciting potential application, permanent magnets/magnet arrays have attracted increased attention recently. A magnet/magnet array is strongly associated with the imaging volume of an MRI scanner, image reconstruction methods, and RF excitation and RF coils, etc. through field patterns and field homogeneity. This paper offers a review of permanent magnets and magnet arrays of different kinds, especially those that can be used for spatial encoding towards the development of a portable and low-cost MRI system. It is aimed to familiarize the readers with relevant knowledge, literature, and the latest updates of the development on permanent magnets and magnet arrays for MRI. Perspectives on and challenges of using a permanent magnet/magnet array to supply a patterned static magnetic field, which does not have spatial linearity nor high field homogeneity, for image reconstruction in a portable setup are discussed.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.3
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• pp.266-272
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• 2012

This paper has aims to share fundamental knowledge for magnetic abrasive polishing and to mainly introduce recent research results. In order to enhance a magnetic flux density for nonferrous materials, advanced magnetic abrasive polishing system which is called 2nd generation system was established by electro-magnet array table, and the effectiveness of the electromagnet array table was evaluated in real polishing experiments. To increase adhesiveness of the abrasives in high speed polishing, a silicone gel agent was proposed and carbon nanotube particles as new magnetic abrasives were applied in the magnetic abrasive polishing. In addition, a strategy for optimal step-over determination by heuristic algorithm was introduced for applying large size workpiece. Curved surfaces having a uniform radius were simulated and tested with installed electro-magnet array table.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.841-842
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• 2006

In this paper, a synchronous permanent magnet planar motor (SPMPM) with Halbach array is proposed for its performance improvement. The magnetization and flux density distribution are obtained by magnet scalar potential; the characteristics such as back-EMF and thrust are evaluated. It can be concluded that the analysis of SPMPM with Halbach magnet array is credible and feasible.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.24-26
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• 1997

A new permanent magnet has been suggested the novel permanent magnet array using advanced analytical approaches in 1979 by Klaus Halbach. In this paper, the Halbach array is utilized to compose the field system. The ferro-magnetic materials of the electric machines cause the fatal energy loses in high frequency. But Halbach any enables to make the various field distribution without ferro-magnetic materials. This paper presents the magnetic characteristics are analyzed by the analytical method and FEM in case that the field system is composed of the Halbach array.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.615-616
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.137-138
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• 2013

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.127-129
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• 2006

In this paper, a synchronous permanent magnet planar motor (SPMPM) with Halbach array is proposed for its high energy density. The magnetization and flux density distribution are obtainedby magnet scalar potential the characteristics such as inductance, back-EMF and thrust are evaluated. It can be concluded that the analysis of SPMPM with Halbach magnet array is credible and feasible.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.24-29
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• 2022

One of the recent proposals with nuclear magnetic resonance (NMR) is a multi-bore NMR which consists of array of magnets which could present possibilities to quickly cope with pandemic virus by multiple inspection of virus samples. Low temperature superconductor (LTS) can be a candidate for mass production of the magnet due to its low price in fabrication as well as operation by applying the helium zero boil-off technology. However, training feature of LTS magnet still hinders the low cost operation due to multiple boil-offs during premature quenches. Thus in this paper, LTS magnet with low mechanical stress is designed targeting the "training-free" LTS magnet for mass production of magnet array for multi-bore NMR. A thorough process of an LTS magnet design is conducted, including the analyses as the followings: electromagnetics, mechanical stress, cryogenics, stability, and protection. The magnet specification was set to 4.7 T in a winding bore of 85 mm, corresponding to the MR frequency of 200 MHz. The stress level is tolerable with respect to the wire yield strength and epoxy crack where mechanical disturbance is less than the minimum quench energy.