Earth's field NMR flow meter: Preliminary quantitative measurements

•Earth's field NMR used with upstream pre-polarising magnet to measure fast flow.•NMR signal measured as a function of flow rate (0-1 m/s) and separation distance.•Flow model developed, parameter-free, to account for NMR signal modulation.•Successful methodology demonstration with a metallic pipe in polarising region.

In this paper we demonstrate the use of Earth's field NMR (EF NMR) combined with a pre-polarising permanent magnet for measuring fast fluid velocities. This time of flight measurement protocol has a considerable history in the literature; here we demonstrate that it is quantitative when employing the Earth's magnetic field for signal detection. NMR signal intensities are measured as a function of flow rate (0-1 m/s) and separation distance between the permanent magnet and the EF NMR signal detection. These data are quantitatively described by a flow model, ultimately featuring no free parameters, that accounts for NMR signal modulation due to residence time inside the pre-polarising magnet, between the pre-polarising magnet and the detection RF coil and inside the detection coil respectively. The methodology is subsequently demonstrated with a metallic pipe in the pre-polarising region.

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