TY - JOUR

T1 - First Measurements of Surface Nuclear Magnetic Resonance Signals Without an Oscillating Excitation Pulse – Exploiting Non-Adiabatic Prepolarization Switch-Off

AU - Hiller, Thomas

AU - Costabel, Stephan

AU - Dlugosch, Raphael

AU - Müller-Petke, Mike

N1 - Funding Information: We like to thank two anonymous reviewers for their valuable comments. Furthermore, we like to thank Kai Holtappels from the German Federal Institute for Materials Research and Testing for providing the necessary logistics to conduct our field experiments. This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft ‐ DFG) under grant MU 3318/4‐1. We used the NMR MIDI of Radic Research. Open access funding enabled and organized by Projekt DEAL.

PY - 2021/11/15

Y1 - 2021/11/15

N2 - Recently, small-scale surface nuclear magnetic resonance (SNMR) measurements with a footprint of about a few square meters have gained interest in the soil geophysics community as they directly provide water content and pore geometry information. Here, the application of strong prepolarization (PP) fields enables the detection of water in the vadose zone. Introducing PP into SNMR shifts the reference for the decay of the SNMR signal from the excitation pulse to the end of the PP, effectively increasing the instrumental dead time, which is already too long to measure short signals associated with unsaturated fine-grained soil. In an approach to overcome this limitation, we present the first measurements of SNMR signals from a water reservoir without an oscillating excitation pulse. Instead, we use the non-adiabatic, that is, imperfect, switch-off of the PP-field as an effective excitation mechanism. We complement our field experiments with numerical simulations of the corresponding SNMR spin dynamics.

AB - Recently, small-scale surface nuclear magnetic resonance (SNMR) measurements with a footprint of about a few square meters have gained interest in the soil geophysics community as they directly provide water content and pore geometry information. Here, the application of strong prepolarization (PP) fields enables the detection of water in the vadose zone. Introducing PP into SNMR shifts the reference for the decay of the SNMR signal from the excitation pulse to the end of the PP, effectively increasing the instrumental dead time, which is already too long to measure short signals associated with unsaturated fine-grained soil. In an approach to overcome this limitation, we present the first measurements of SNMR signals from a water reservoir without an oscillating excitation pulse. Instead, we use the non-adiabatic, that is, imperfect, switch-off of the PP-field as an effective excitation mechanism. We complement our field experiments with numerical simulations of the corresponding SNMR spin dynamics.

KW - non-adiabatic switch-off

KW - prepolarization

KW - surface nuclear magnetic resonance

UR - http://www.scopus.com/inward/record.url?scp=85120812404&partnerID=8YFLogxK

U2 - 10.1029/2021GL095371

DO - 10.1029/2021GL095371

M3 - Article

AN - SCOPUS:85120812404

VL - 48

JO - Geophysical research letters

JF - Geophysical research letters

SN - 0094-8276

IS - 23

M1 - e2021GL095371

ER -