Progress in Superconductivity
- Volume 9 Issue 1
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- Pages.23-28
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- 2007
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- 1229-4764(pISSN)
First-order Wire-wound SQUID Gradiometer System Having Compact Superconductive Connection Structure between SQUID and Pickup Coil
SQUID와 검출코일의 초전도 결합방식이 개선된 1차 권선형 미분계 시스템
- Lee, Y.H. (Bio-signal Research Center, Korea Research Institute of Standards and Science) ;
- Yu, K.K. (Bio-signal Research Center, Korea Research Institute of Standards and Science) ;
- Kim, J.M. (Bio-signal Research Center, Korea Research Institute of Standards and Science) ;
- Kwon, H. (Bio-signal Research Center, Korea Research Institute of Standards and Science) ;
- Kim, K. (Bio-signal Research Center, Korea Research Institute of Standards and Science) ;
- Park, Y.K. (Bio-signal Research Center, Korea Research Institute of Standards and Science)
- Published : 2007.10.31
Abstract
In order to have a superconductive connection between the wire-wound pickup coil and input coil, typically Nb terminal blocks with screw holes are used. Since this connection structure occupies large volume, large stray pickup area can be generated which can pickup external noise fields. Thus, SQUID and connection block are shielded inside a superconducting tube, and this SQUID module is located at some distance from the distal coil of the gradiometer to minimize the distortion or imbalance of uniform background field due to the superconducting module. To operate this conventional SQUID module, we need a higher liquid He level, resulting in shorter refill interval. To make the fabrication of gradiometers simpler and refill interval longer, we developed a novel method of connecting the pickup coil into the input coil. Gradiometer coil wound of 0.125-mm diameter NbTi wires were glued close to the input coil pads of SQUID. The superconductive connection was made using an ultrasonic bonding of annealed 0.025-mm diameter Nb wires, bonded directly on the surface of NbTi wires where insulation layer was stripped out. The reliability of the superconductive bonding was good enough to sustain several thermal cycling. The stray pickup area due to this connection structure is about