The pulsed field gradient nuclear magnetic resonance (PFG NMR) method has proved to be a powerful non-invasive technique to measure molecular displacement in various systems. It has been largely implemented with conventional NMR magnets where the volume for housing the flow setup is restricted. In this work we present the first approach to measure velocity distributions ex situ implementing a pulsed field gradient sequence on a single-sided NMR sensor. The open geometry of these sensors provides access to NMR measurements of a large number of applications previously excluded by the geometry of conventional closed magnets. Both, the distortions to the displacement encoding observed when implementing a PFG sequence in the presence of strongly inhomogeneous B0 and B1 fields, and the performance of the modifications proposed to eliminate these distortions are shown by means of numerical simulations. An alternating stimulated spin-echo PFG sequence implemented to remotely measure velocity distributions was combined with a multi-echo acquisition scheme to significantly increase the sensitivity of the method. The technique was implemented to measure the velocity propagator in a fluid undergoing laminar flow and good agreement with the theoretical result is observed.
Casanova, J. Perlo, B. Blümich, Velocity distributions remotely measured with a single-sided NMR sensor, J. Magn. Reson. 171 (2004) 124-130. https://doi.org/10.1016/j.jmr.2004.08.008