Figure 2.

Relative rf amplitude ${\mathit{\omega }}_{\mathrm{1},\mathrm{rel}}$ and phase ${\mathit{\varphi }}_{\mathrm{rel}}$ as a function of $\mathit{\vartheta }$ for $z=$ -4, 0, 2, and 4  $\mathrm{mm}$ and all $r$ values in the 3.2  $\mathrm{mm}$ MAS probe at a resonance frequency of 600  $\mathrm{MHz}$ . Under MAS, the rf amplitude and phase experienced by a crystallite will vary periodically with the rotor frequency. These time-dependent modulations of the rf field are strongest at the edges of the rotor for large $r$ and $z$ values.