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NMR in Earth’s Magnetic Field Using High-Tc SQUID
Sept. 4, 2007 (H3) Qiu et al. recently reported the first ever NMR measurements in Earth’s magnetic field (EMF) performed on liquid samples while using a high-Tc SQUID as a detector . Prepolarizing was done by applying field pulse of 10 mT intensity. High-resolution NMR spectra of water, benzene, fluorobenzene and 2,2,2-trifluoroethanol were recorded by a YBCO rf SQUID of substrate resonator type. In trifluoroethanol, the broadband detection characteristics of the SQUID with a noise floor in EMF of about 70 fT/ enabled authors to simultaneously observe fluorine and proton spectra at 1940 and 2060 Hz Larmor frequency, reflecting their heteronuclear J coupling in the high-field limit without showing a measurable chemical shift. Two J coupling spectra are shown in Figure 1. To reduce the effect of EMF fluctuations on the spectral linewidth, the authors introduced frequency-adjusted averaging, which largely compensates the line broadening. The ability to perform high resolution NMR spectroscopy in the absence of magnetic shielding opens the door to a future new class of relatively low-cost, mobile, flexible NMR and MRI scanners based on SQUID receivers operating at 77 K.
 L. Qiu et al., Nuclear magnetic resonance in the earth’s magnetic field using a nitrogen-cooled superconducting quantum interference device, Appl. Phys. Lett. 91, 072505 (2007).
Fig. 1. Heteronuclear J coupling spectra (100-times averaged) of 2,2,2-trifluoroethanol and fluorobenzene (the inset) recorded in EMF by the high-Tc rf SQUID