In order to achieve high-sensitivity in the detection of weak magnetic signals, the sensitive superconducting quantum interference device (SQUID) is used for NMR detector.

SQUID is a very sensitive magnetometer for extremely weak magnetic fields, based on superconducting loops containing Josephson junctions.

Most SQUID-detected low field NMR systems are set up in magnetically shielded room (MSR). But the MSR require high cost and a large space. MagQu set up a compact and sensitive High-T_c SQUID-detected NMR spectrometer using flux coupling in microtesla field without MSR.

The measuring coil, pre-polarization coil, compensation coils, and gradient coils are set up inside a miniature radio frequency shielded box (RFSB); the SQUID sensor is shielded with a superconducting vessel and installed in a liquid nitrogen cryostat that is seated in a compact magnetically shielded cylinder (MSC). The dimension of the RFSB was 1 m x 1 m x 0.6 m; the MSC is 60 cm in diameter and 70 cm in height. The NMR signals of samples are inductively coupled to the high-T_c SQUID magnetometer via magnetic flux transformer.

Reference

1. Hsin-Hsien Chen, Kai-Wen Huang*, Hong-Chang Yang, Herng-Er Horng, and Shu-Hsien Liao*” Optimization of the detection coil of high-Tc superconducting quantum interference device-based nuclear magnetic resonance for discriminating a minimum amount of liver tumor of rats in microtesla fields” , J. Appl. Phys. 114, 064701 (2013).
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3. K.W. Huang, H.H. Chen, H.C. Yang, H.E. Horng, S.H. Liao, J.J. Chieh, and S.Y. Yang, “Use of a high-Tc SQUID-based nuclear magnetic resonance spectrometer in magnetically unshielded environments to discriminate tumors in rats, by characterizing the longitudinal relaxation rate”, JINST 7, 6005 (2012).
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6. Hsin-Hsien Chen, Hong-Chang Yang, Herng-Er Horng, Shu-Hsien Liao, Shieh Yueh, and Li-Min Wang, “A compact SQUID-detected magnetic resonance imaging system under microtesla field in a magnetically unshielded environment”, J. Appl. Phys. 110, 093903 (2011).
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