高溫超導量子干涉元件與生物磁學

Superconducting Quantum Interference Devices and Biomagnetism

楊鴻昌(Hong-Chang Yang)

《科儀新知》 145期 (2005/04) Pp. 76-87

https://doi.org/10.29662/IT.200504.0008

摘要

超導量子干涉元件(superconducting quantum interference devices, SQUID)是最敏感的磁通感測元件。由於高溫超導體的發現，一項具挑戰性的工作就是研發在77K液氮溫度就可以工作的SQUID。目前已研發出各種不同的高溫超導約瑟芬元件技術，如自然晶界形成約瑟芬元件、階梯邊緣約瑟芬元件或斜面邊緣約瑟芬元件等。SQUID應用時要求低的雜訊，在10kHz的頻率，低溫SQUID磁通雜訊約為幾個μφ0/Hz(上标 1/2)，而高溫超導SQUID磁通雜訊則在十幾至數十μφ0/Hz(上标 1/2)的範圍，此處φ0=h/2e為磁通量子，h為普朗克常數，e為電子之電量，φ0值為2.07×10^(–7)Gauss•平方公分。低溫SQUID磁量計在1kHz的磁場敏感度約為1-5fT/Hz(上示 1/2)，而高溫超導SQUID磁量計在1kHz磁場靈敏度約為10-40fT/Hz(上标 1/2)。SQUID受到熱效應之影響會產生低頻1/f雜訊，其雜訊的物理機制是一個需要了解的問題。在應用方面，目前科學家正努力將高溫超導SQUID應用於如心磁波造影、低磁場磁共振造影、免疫撿測、DNA檢測及心臟細胞活動等先進生物醫學及其他新穎之研究。

並列摘要

Superconducting quantum interference device (SQUID) is the most sensitive detector of the magnetic flux. Since the discovery of the high-T(subscript c) superconductor substantial effort has been expended to develop SQUID devices that can be operated at temperature above the boiling temperature of the liquid nitrogen. The grain-boundary and the step-edge Josephson junctions are the promising devices for high-T(subscript c) SQUIDs. Typical levels of white flux noise are a few μφ0/Hz(superscript 1/2) for low-T(subscript c) SQUID and~10-40 μφ0/Hz(superscript 1/2) for high-T(subscript c) SQUIDs. This corresponds to a magnetic field sensitivity of 1-5fT/Hz(superscript 1/2) and~10-40fT/Hz(superscript 1/2) for low-T(subscript c) and high-T(subscript c) SQUID magnetometers respectively. The low frequency 1/f noise from thermally activated motion is a much bigger issue for high-T(subscript c) SQUID than low-T(subscript c) SQUID because the low pinning energy in high-T(subscript c) superconductors at 77K. The noise level depends strongly on the YBa2Cu3Oy (YBCO) film quality and much effort has been devoted to improve the quality of the YBCO film. There is a considerable effort to apply high-T(subscript c) SQUID in biomagnetism, for example, magnetocardiology, immunoassay, nuclear magnetic resonance imaging in low magnetic field, detection of the DNA and boimagnetic field from the heart cells, and other novel research.