Bloch–Siegert Effect for Surface Nuclear Magnetic Resonance Sounding Experiments in the Unsaturated Zone

authored by: Tobias Splith, Thomas Hiller, Mike Müller-Petke
Abstract: The Bloch–Siegert effect is relevant for NMR experiments where components of the excitation pulse other than the circularly polarized component have an influence on the evolution of the magnetization of the spin system under consideration. For linearly polarized excitation fields this happens at amplitudes higher than roughly one tenth of the magnitude of the static magnetic field. Since surface nuclear magnetic resonance (SNMR) experiments, also called magnetic-resonance-soundings (MRS), are conducted in the relatively low local field of the earth, the Bloch–Siegert effect can quickly become relevant. This is especially the case for SNMR experiments in the unsaturated zone, where due to short relaxation times fast pulses of high intensity must be used. To describe the Bloch–Siegert effect, we use the average Hamiltonian approximation obtained by the Magnus expansion of up to fifth order, as well as the solution of the Bloch equations. The results of these approximations are tested against the Bloch simulations and it is shown that they are only valid for limited ranges of the excitation field amplitude. The influence of the Bloch–Siegert effect on sensitivity kernels is described and verified with experimental data obtained with a small scale SNMR sensor on water containers.
External Organisation(s): Federal Institute for Geosciences and Natural Resources (BGR)
Leibniz Institute for Applied Geophysics (LIAG)
Type: Article
Journal: Applied magnetic resonance
Volume: 55
Pages: 357-373
No. of pages: 17
ISSN: 0937-9347
Publication date: 04.2024
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic version(s): https://doi.org/10.1007/s00723-023-01582-3 (Access: Open)

BibTeX

@article{dfafb94cda224a049fe470d45ee1fa7c,
title = "Bloch–Siegert Effect for Surface Nuclear Magnetic Resonance Sounding Experiments in the Unsaturated Zone",
abstract = "The Bloch–Siegert effect is relevant for NMR experiments where components of the excitation pulse other than the circularly polarized component have an influence on the evolution of the magnetization of the spin system under consideration. For linearly polarized excitation fields this happens at amplitudes higher than roughly one tenth of the magnitude of the static magnetic field. Since surface nuclear magnetic resonance (SNMR) experiments, also called magnetic-resonance-soundings (MRS), are conducted in the relatively low local field of the earth, the Bloch–Siegert effect can quickly become relevant. This is especially the case for SNMR experiments in the unsaturated zone, where due to short relaxation times fast pulses of high intensity must be used. To describe the Bloch–Siegert effect, we use the average Hamiltonian approximation obtained by the Magnus expansion of up to fifth order, as well as the solution of the Bloch equations. The results of these approximations are tested against the Bloch simulations and it is shown that they are only valid for limited ranges of the excitation field amplitude. The influence of the Bloch–Siegert effect on sensitivity kernels is described and verified with experimental data obtained with a small scale SNMR sensor on water containers.",
author = "Tobias Splith and Thomas Hiller and Mike M{\"u}ller-Petke",
note = "Funding Information: Open Access funding enabled and organized by Projekt DEAL. This research was funded by the German Research Foundation (Deutsche Forschungsgemeinschaft-DFG) under grant MU 3318/8-1. ",
year = "2024",
month = apr,
doi = "10.1007/s00723-023-01582-3",
language = "English",
volume = "55",
pages = "357--373",
journal = "Applied magnetic resonance",
issn = "0937-9347",
publisher = "Springer-Verlag Wien",
number = "4",
}