Study on signal intensity of low field nuclear magnetic resonance via an indirect coupling measurement

作     者：蒋凤英 王宁 金贻荣 邓辉 田野 郎佩琳 李洁 陈莺飞 郑东宁 

作者机构：School of Science Key Laboratory of Information Photonics and Optical Communications Beijing University of Posts and Telecommunications Institute of Physics Chinese Academy of Sciences 

出 版 物：《Chinese Physics B》 (中国物理B（英文版）)

年 卷 期：2013年第22卷第4期

页      面：36-39页

核心收录：

学科分类：0809[工学-电子科学与技术（可授工学、理学学位）] 07[理学] 070205[理学-凝聚态物理] 08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 080502[工学-材料学] 0702[理学-物理学] 

基　　金：Project supported by the State Key Development Program for Basic Research of China (Grant Nos. 2011CBA00106 and 2009CB929102) the National Natural Science Foundation of China (Grant Nos. 11104333, 11161130519, and 10974243) 

主　　题：indirect coupling measurement superconducting quantum interference devices low field nuclearmagnetic resonance 

摘      要：We carry out an ultra-low-field nuclear magnetic resonance （NMR） experiment based on high-T c 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 the 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 the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements 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 as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.