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

Abstract

We present pre-polarization surface nuclear magnetic resonance (PP-SNMR) measurements performed with a Superconducting QUantum Interference Device (SQUID) magnetometer on water-filled pallet boxes. The SQUID directly detects the three components of the magnetic field (B-field) NMR response, while conventional SNMR experiments would detect its time derivative and most of the time only a single component. Each of the three vector components of the magnetic field NMR response consists of a component oscillating at Larmor frequency and of a non-oscillating component. We extend the general SNMR theory to model the measured signals. For the non-oscillating signal, another magnetic decay with a large amplitude is superimposed on the signal originating from the water-filled boxes, and we were unable to extract the desired signal. For the oscillating signal component, however, we report good agreement between the measured signal and the forward model in amplitude and phase. Measuring all three components of the B-field introduces a sensitivity to lateral inhomogeneities, which we demonstrate by repeating the experiment with one and two emptied boxes.