NMR MEASUREMENT BY CONTROLLING THE EFFECTIVE MAGNETIC FIELD

摘要

A radio frequency (Rf) pulse is applied to a coil (6). A sample is placed on support (3) and an antenna coil (6a) detects Rf signals from the nuclei. The effective magnetic field (B) applied to the sample is a vector sum of the resonant offset of the nuclear spins ( DELTA H) and the Rf field of a spin-lock pulse (B1). This effective field B is controlled to enhance NMR measurement. Several methods of control are described, those being: (a) performing an adiabatic passage on DELTA H; (b) controlling the Rf pulse such that B1 and DELTA H vary sinusoidally in time; (c) inverting B after on half of the Rf pulse.