Frequency Shifting Steady‐State Surface NMR Signals to Avoid Problematic Narrowband‐Noise Sources

Abstract

Recent developments in surface nuclear magnetic resonance (NMR) based on steady‐state sequences show great enhancements in signal quality and mapping speeds. We demonstrate how manipulating the timing and phase of these sequences can shift the NMR signal away from problematic narrow‐band noise sources, for example, co‐frequency powerline harmonics, or shift narrowband noise sources away from the NMR signal. The spectral separation of the NMR signal from co‐frequency noise sources enables production of high‐quality data under one of the most challenging noise scenarios in surface NMR. We demonstrate the feasibility with surface NMR measurements at a site where the Larmor frequency coincides with a powerline harmonic. We separate the NMR signal and powerline noise by up to 5 Hz and obtain high‐quality data, which are readily inverted. The approach is straightforward to implement, well suited for field processing, and shows great potential to expand the range of conditions allowing surface NMR measurements.