Vibration transmission characteristics against vertical vibration in magnetic levitation type HTS seismic/vibration isolation device

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.