Fig. 4.

A pulse designed with three rotating frames is simulated for spin-locking of an ensemble of isolated spins-1/2. At the beginning of the simulation the magnetization is along the y-axis, and we measure the final magnetization along the y-axis, averaged over 20 values of the RF inhomogeneity, sampled uniformly between ±5% of the nominal power. We observe that magnetization is returned to near the y-axis at the end of the pulse over a large bandwidth. The pulse is repeated several times to achieve spin-locking over longer periods of time. The pulse time T is 6.38r/A, where r is the number of times the pulse is repeated (for this simulation r = 4) and A is the average RF amplitude. The pulse profile is displayed in Figure 2, its mixing performance is simulated in Figure 5, and it is tested experimentally in Figures 6 and 9