Tham khảo tài liệu 'handbook of high temperature superconductor electronics part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 8 High-Temperature SQUID Magnetometer Neeraj Khare National Physical Laboratory New Delhi India INTRODUCTION The superconducting quantum interference device SQUID is the most sensitive detector of the magnetic flux. This feature makes the SQUID an attractive device for a range of applications. The SQUIDs based on low-Tc superconductors have shown unsurpassed sensitivity for the measurement of current voltage magnetic field and magnetic field gradient 1 . Potentiality of the applications of these SQUID magnetometers in measuring the biomagnetic field 2 nondestructive testing 2 and geological prospecting 3 have been demonstrated much earlier. In spite of the commercial availability of low-Tc SQUID for several years the SQUID-based applications did not gain widespread acceptability. This has been mainly due to the inconvenience of its operation at liquid-helium temperature. The feasibility of the fabrication of high-Tc SQUID operating at 77 K was soon demonstrated after the discovery of high-Tc superconductors HTS . Since then there has been continuous progress in this area 4-6 . Several novel approaches have been conceived and applied for improving the performance of the high-Tc SQUIDs. HTS SQUID magnetometers exhibiting magnetic field sensitivity 10-50 fT Hz1 2 in the white-noise region at 77K have been demonstrated 5 . Several companies have started commercializing high-Tc SQUIDs 7 . HTS Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. SQUID magnetometers and gradiometers have been successfully used in the detection of biomagnetic signals from the heart and brain 8 9 nondestructive testing of deep buried flaws in metallic specimens 10 geophysical applications 11 and several other novel applications such as in biological immunoassays 12 sen-tinels-lymph node biopsy 13 and so forth. This chapter presents a review of the developments of high-Tc SQUID magnetometers and discusses their applications in different areas. SUPERCONDUCTING QUANTUM .
