Abstract
An approach to measuring flow velocities using a probe with a spatially varying radio-frequency (RF) field and without using other magnetic field gradients is introduced. The velocities of the spins are measured as a modulation of the NMR signal from the translation of a spatial magnetization grating through a detection coil with a spatially periodic field profile. Since the same coil can be employed to create the initial magnetization grating, the overall measurement is as simple as recording the signal modulation frequency following a single excitation pulse. The design principles for a probe that has a spatially periodic field constructed from a series of lumped element circuits are discussed. Spatial modulation of the amplitude or the phase of the RF field can easily be achieved and either of these may be used to characterize a flow field. Examples of measurements of pipe flow using a probe with an amplitude modulated RF field are shown.
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