This article has been accepted for inclusion in a future issue. IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 1
Numerical Analysis of Levitating Force Using Magnetic Shielding Effect of YBCO Plates Tomoaki Takao, Akihiro Niiro, Soichiro Suzuki, Masahiro Hashimoto, Junichiro Takeda, Toshihiro Kobayashi, and Hiroki Kamijo
Abstract—A magnetic levitation system using magnetic shielding effect of HTS bulk is studied. The system is constructed by permanent magnets, zero-ﬁeld-cooled superconducting bulks and ferromagnetic rails, and lift force stability is obtained from magnetic ﬁeld that is generated by the permanent magnet and is shaped by the superconducting bulks. In previous studies, we showed characteristics of lift force and stability about a basic model which had a small ferrite permanent magnet, three YBCO bulk superconductors and a short ferromagnetic bar. Now, improving the basic model, we found new models which have better characteristics of lift force by numerical analysis using 3D Integral Element Method (IEM). The new models are reported. Index Terms—Lift force stability, magnetic levitation, magnetic shielding effect, YBCO bulk.
Fig. 1. Schematic illustration of the basic model about the magnetic levitation system. The ferromagnetic bar is ﬁxed as a rail and the vehicle is lifted upward. It is moved in the direction.
AGNETIC levitation systems using HTS bulk have high potential and various types of levitation system have been studied –. The systems use pinning force of the HTS bulks that enables to trap or shield magnetic ﬁeld. One of the most important points about the systems is to generate stable levitation force without any active control system. This point can provide safety levitation when power failure is happened, and less power consumption is achieved for levitation. We have been focusing magnetic shielding effect of the HTS bulk, and we have been studying a magnetic levitation system using the effect –. In this study, only the stability of vertical direction has been studied among the stabilities of levitation, because this study is still basic stage. A basic model of the system consists of a permanent magnet, HTS bulks, and a ferromagnetic bar. The ferromagnetic bar as a rail is ﬁxed by structures which has to be made from nonmagnetic materials. And, the magnet and the HTS bulks are placed in a transporting vehicle. The magnetic ﬁeld generated from the permanent magnet is shaped by the HTS bulks, and the ﬁeld reaches the ferromagnetic bar. The magnetic ﬁeld nearby the HTS bulk is reduced, because the magnetic ﬁeld is shaped by the HTS bulks. The lift force increases when the vehicle goes
Fig. 2. Top view of the materials. is deﬁned as length of the magnet, and is deﬁned as width of the magnet.
Manuscript received September 19, 2005. This work was supported by the cooperative research project between Sophia University and Railway Technical Research Institute. This work was also supported by Research Foundation for the Electrotechnology of Chubu. T. Takao, A. Niiro, S. Suzuki, M. Hashimoto, J. Takeda, and T. Kobayashi are with the Department of Electrical and Electronics Engineering, Sophia University, Chiyoda-ku Tokyo 102-8554, Japan (e-mail: firstname.lastname@example.org). H. Kamijo is with Railway Technical Research Institute, Kokubunji-shi, Tokyo 185-8540, Japan. Digital Object Identiﬁer 10.1109/TASC.2006.870001
away from the rail, and the vehicle can return to the previous position. Therefore, a stable lift force without any active control system can be achieved. Another advantage of this system is to simplify the rail structure. The simple structure of rail allows reducing construction costs. We have improved the basic model of the magnetic levitation system, and we ﬁnd new models that have better characteristics of lift force than previous models. The characteristics of lift force are evaluated by numerical analysis. ELF/MAGIC...
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Fig. 10. Maximum lift force per unit weight and width of stable region. Comparison of the basic model and the new models.
stable region when the sets of HTS bulk and ferromagnetic bar are added. This shows the stable region mainly depends on the ratio of width of the HTS bulk and that of the magnet, and adding sets of HTS bulk and ferromagnetic bar does not effect the stable region when width of the magnet is wider than the sum of width of the HTS bulks. Lift force increases with adding the sets. Therefore, the improvement is very efﬁcient for increasing lift force without decreasing stable region. C. Model C The characteristics about the model C and the basic model are shown in Fig. 9. Although the model C is approximately 25% heavier than the basic model, the peak value of lift force about the model C got about 60% bigger than the basic model. The stable region of the basic model is same as the region of the model C. This is because the ferromagnetic plate on the HTS bulk helps shaping magnetic ﬁeld and provides more magnetic ﬂux to the ferromagnetic bar. This result shows that adding bent ferromagnetic material on the HTS bulk is very efﬁcient. VI. DISCUSSION On evaluating magnetic levitation system, weight of materials in the vehicle is very important factor. Fig. 10 shows lift
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