Vibration characteristics in magnetic levitation type seismic isolation device composed of multiple HTS bulks and permanent magnets

An HTS bulk field-cooled by a permanent magnet can levitate stably without any other control systems. The stable levitation can be realized by a specific characteristic of the HTS bulk that the HTS bulk returns to its original position by restoring force against horizontal displacement. We devised a magnetic levitation type seismic isolation device taking advantage of the specific characteristic of the HTS bulk. This device is quite different from conventional one composed of bearing and damper, because this device can completely remove horizontal vibration. We made a model device composed of YBCO bulks and permanent magnets to verify the seismic isolation effect of our device. Levitation force and vibration stability strongly depend on magnetic stiffness between HTS bulk and permanent magnet. Therefore, we prepared an YBCO bulk and a permanent magnet unit arranged on a row and investigated the characteristics of levitation force and horizontal vibration as functions of vibration amplitude, vibration frequency, and initial air gap between the bulk and the permanent magnet unit. Large initial air gap is desirable for levitation force, while small air gap under operation is effective for securing vibration stability.