A theoretical study is undertaken into the measurement of the flow in fluids using weak field Nuclear Magnetic Resonance (NMR). A number of methods are considered for a coil system which provides a temporary polarising magnetic field. When the polarising field is removed a coil is used to detect the subsequent Free Induction Decay. As far as we know a similar coil system has only been used previously to detect the precession signal from static fluid samples. This then is the first theoretical analysis of a fluid moving in a pipe using weak field NYIR. The signal amplitude immediately after the polarising field is removed is determined. Closed form expressions for the signal amplitude are derived for three different flow types; plug, laminar and turbulent. For a single coil system the ratio of flow to no flow amplitudes is determined as a function of fluid velocity. When a separate polarising and detecting coil system is used the fluid velocity is determined as a function of the time of maximum signal amplitude.
|Date of Award||Aug 1996|