PP-SNMR measurements using SQUIDs as compact three-component B-field sensors for spatial imaging

Area of Science:

• Geophysics
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Conventional surface nuclear magnetic resonance (SNMR) typically measures the time derivative of the magnetic field, often detecting only a single component.
• Direct measurement of the magnetic field (B-field) components in SNMR offers potential for enhanced sensitivity and information extraction.

Purpose of the Study:

• To present pre-polarization surface nuclear magnetic resonance (PP-SNMR) measurements using a Superconducting QUantum Interference Device (SQUID) magnetometer.
• To investigate the direct detection of three magnetic field components in PP-SNMR.
• To extend the general SNMR theory for modeling the measured B-field signals.

Main Methods:

• PP-SNMR measurements were conducted on water-filled pallet boxes using a SQUID magnetometer.
• The SQUID directly recorded the three vector components of the NMR magnetic field response.
• A forward model based on extended SNMR theory was used to analyze the oscillating and non-oscillating signal components.

Main Results:

• The SQUID successfully detected the oscillating and non-oscillating components of the B-field NMR response.
• Good agreement was observed between the measured and modeled oscillating signal components in both amplitude and phase.
• A large amplitude magnetic decay superimposed on the non-oscillating signal hindered the extraction of the desired component.
• Sensitivity to lateral inhomogeneities was demonstrated by varying the number of emptied boxes.

Conclusions:

• Directly measuring the three components of the magnetic field in PP-SNMR is feasible.
• The oscillating signal component provides reliable data consistent with theoretical models.
• PP-SNMR with SQUID detection shows promise for geophysical applications, particularly in characterizing subsurface properties.