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

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. Plain Language Summary: The surface nuclear magnetic resonance (NMR) signal can be difficult to isolate in the presence of a high‐amplitude noise source with an overlapping frequency, such as when a strong powerline harmonic sits atop the NMR signal. We demonstrate that the timing of surface NMR steady‐state sequences can be manipulated to alter the location of the NMR signal in the frequency domain, allowing one to separate the NMR signal from the overlapping strong noise source. Field results are given highlighting the feasibility of the technique and demonstrating that high fidelity NMR signals can be extracted even when they share a frequency with a higher amplitude powerline harmonic. Key Points: Steady‐state schemes allow users to control the nuclear magnetic resonance (NMR) signal's location in the spectraSteady‐state schemes can be exploited to increase separation between the NMR signal and nearby narrow‐band noise sourcesFrequency shifted steady‐state surface NMR data can be inverted reliably [ABSTRACT FROM AUTHOR]