中国物理B ›› 2013, Vol. 22 ›› Issue (4): 47401-047401.doi: 10.1088/1674-1056/22/4/047401
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蒋凤英a b, 王宁b, 金贻荣b, 邓辉b, 田野b, 郎佩琳a, 李洁b, 陈莺飞b, 郑东宁b
Jiang Feng-Ying (蒋凤英)a b, Wang Ning (王宁)b, Jin Yi-Rong (金贻荣)b, Deng Hui (邓辉)b, Tian Ye (田野)b, Lang Pei-Lin (郎佩琳)a, Li Jie (李洁)b, Chen Ying-Fei (陈莺飞)b, Zheng Dong-Ning (郑东宁)b
摘要: We carry out an ultra-low-field nuclear magnetic resonance (NMR) experiment based on high-Tc superconducting quantum interference devices (SQUIDs). The measurement field is in a micro-tesla range (~ 10 μT-100 μT) and the experiment is conducted in a home-made magnetically-shielded-room (MSR). The measurements are performed by an indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using SQUID with that achieved by using the conventional low-noise-amplifier, we perform the measurements by using a commercial room temperature amplifier. The results show that in a wide frequency range (~ 1 kHz-10 kHz) the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity with measurement field increasing. This is verified by compensating the field gradient using three sets of gradient coils.
中图分类号: (Nuclear magnetic resonance)