S. Sasaki

Tohoku University, Japan

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Publications (5)5.51 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We have devised a magnetic levitation type superconducting seismic isolation device using pinning effect of HTS bulk and investigated the characteristics of vibration transmission and damping in a model device with two types of permanent magnet (PM) systems with copper plates; the one was for stable stationary levitation named “PM-PM system” and the other was for improving damping effect named “vibration absorbing system (VAS)”. To clarify the electromagnetic behaviors of these systems, we calculated the distributions of eddy current and magnetic force within the copper plates during a horizontal vibration using a numerical simulation code based on the three-dimensional finite element method (3D-FEM) analysis. As the results, the vibration transmission was reduced due to the Lorenz force generated in the copper plate.
    IEEE Transactions on Applied Superconductivity 01/2012; 22(3):3600804-3600804. · 1.20 Impact Factor
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    ABSTRACT: We have investigated the basic properties of levitation force and vibration transmission in a magnetic levitation type su- perconducting seismic isolation device. Since it is very difficult in a realdeviceofaseismicisolationdevicetokeepthestationarylevita- tion against any horizontal disturbances, we havedevised a perma- nent magnet-permanent magnet (PM-PM) system with a copper plate and verified that the stable stationary levitation of the seismic isolation object could be achieved by using the PM-PM system with the copper plate. In addition, to improve the damping ef- fect, we adopted vibration absorbing system composed of a copper plate and a permanent magnet. We investigated the basic prop- erties of vibration transmission and damping effect in the model device having the PM-PM system with the copper plate and vi- bration absorbingsystem. Thevibration transmissionwasreduced and the damping effect was greatly improved by the magnetic in- teraction between the copper plate and the permanent magnet in the PM-PM system with the copper plate and vibration absorbing system. We investigated the relationship between the magnetic in- teraction between the copper plate and the permanent magnet and obtained a suitable thickness of the copper plate in the PM-PM system and a suitable structure of vibration absorbing system for reducing the vibration transmission and improving the damping ratio effectively.
    IEEE Transactions on Applied Superconductivity 01/2011; 21(3):2233-2236. · 1.20 Impact Factor
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    ABSTRACT: We have investigated levitation force characteristics of a magnetic levitation type superconducting seismic isolation device composed of HTS bulks and permanent magnets. Large levitation force at a small gap of less than 3 mm has been already obtained, while only small levitation force at a large gap of more than 5 mm. In a practical use of the superconducting device, the HTS bulks should be cooled by not LN<sub>2</sub> but a cryocooler. This means that large levitation force at a large gap of more than 5 mm is required due to a vacuum layer thickness in a cryostat. Therefore, we investigated the suitable size and arrangement method of the permanent magnet and the HTS bulk to improve the levitation force at a large gap of more than 5 mm effectively. By adopting a permanent magnet arrangement of "Halbach array", we could greatly improve the levitation force at a large gap of more than 5 mm. Based on the experimental and computed results of levitation force and magnetic field distribution, we could achieve further improvement of the levitation force by optimizing the size of the permanent magnet and the HTS bulk. The suitable width and thickness of the permanent magnet were 10 mm against a disk-shaped HTS bulk 32 mm in diameter and the suitable thickness of the HTS bulk was less than 2 mm at a gap of more than 5 mm.
    IEEE Transactions on Applied Superconductivity 07/2010; · 1.20 Impact Factor
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    ABSTRACT: We have devised a magnetic levitation type superconducting seismic isolation device taking advantage of the specific characteristic of HTS bulk that the HTS bulk returns to its original position by restoring force against a horizontal displacement. The superconducting seismic isolation device is composed of HTS bulks and permanent magnets (PM rails). The PMs are fixed on an iron plate to realize the same polarities in the longitudinal direction and the different polarities in the transverse direction. The superconducting seismic isolation device can theoretically remove any horizontal vibrations completely. Therefore, the vibration transmissibility in the longitudinal direction of the PM rail becomes zero in theory. The zero vibration transmissibility and the stationary levitation, however, cannot be achieved in the real device because a uniform magnetic field distribution in the longitudinal direction of PM rail cannot be realized due to the individual difference of the PMs. Therefore, to achieve stationary levitation in the real device we adopted a PM–PM system that the different polarities are faced each other. The stationary levitation could be achieved by the magnetic interaction between the PMs in the PM–PM system, while the vibration transmitted to the seismic isolation object due to the magnetic interaction. We adopted a copper plate between the PMs to reduce the vibration transmissibility. The PM–PM system with the copper plate is very useful for realizing the stationary levitation and reducing the vibration transmissibility.
    Physica C Superconductivity 01/2010; 470(20):1791-1794. · 0.72 Impact Factor
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    ABSTRACT: Using a model levitation system composed of an HTS bulk and permanent magnet rows, we investigated the dynamic characteristics of vibration transmission against a vertical vibration as functions of the weight of a levitating object, vibration amplitude, initial and actual gaps between the bulk and the permanent magnet rows. The bulk vibrated in substantially synchronism with the permanent magnet rows and the waveform of relative displacement between the bulk and the permanent magnet rows was sinusoidal. The vibration transmissibility measured in the frequency range below 5 Hz was between 1.00 and 1.08. Using the experimental results of spring and damping constants, we theoretically evaluated the natural frequency and vibration transmissibility of the model system in the frequency range of 0 Hz to 100 Hz. The natural frequency decreased with the weight of the levitating object at a constant actual gap. This means that the vibration removal performance is improved by increasing the initial gap. The larger actual gap at a constant weight of the levitating object was effective for improving the vibration transmissibility in the vibration frequency range above the natural frequency, while the smaller actual gap was effective for improving the damping effect. Therefore, it is important to choose the most suitable field-cooling condition of the bulk by considering the trade-off relationship between the vibration transmissibility and the damping effect according to the weight of the levitating object.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor