Overview of low-field NMR measurements using HTS rf-SQUIDs

High-resolution low-field nuclear magnetic resonance (LF-NMR) investigations of liquid samples, recorded using a HTS radio frequency (rf) superconducting quantum interference device (SQUID) are overviewed in this paper. The measurements were performed either in a magnetically shielded room (MSR) or in the Earth's Magnetic Field (EMF). in MSR, measurements with Larmor frequencies (f(L)) ranging from 2 Hz to 40 kHz were demonstrated. The natural spectral linewidth of water and the scalar coupling spectra of 2,2,2-trifluoroethanol and of fluorobenzene were determined. An additional nitrogen-cooled resonant LC input circuit was also introduced in higher f(L) (>10 kHz) region to enhance the signal-to-noise ratio up to an order of magnitude, The influence of the speed of decay of the polarizing magnetic field (B-p) on the free-induction-decay (FID) signal was analyzed quantitatively. In EMF, NMR spectra of different liquid samples were recorded. To compensate the line broadening due to EMF fluctuations we used frequency-adjusted averaging. (C) 2009 Elsevier B.V. All rights reserved.