Fig. 6: Acoustic vortex characteristics at different rotation rates.
From: Tunable acoustic vortex generation by a compact rotating disk
a The sonogram of the amplitude–frequency spectrum at different rates. At rotation rates of 139.3, 208.9, and 417.8 rad/s, corresponding topological charges of 3, 2, and 1 were observed at 66.5 Hz. b The mode purity distribution of generated l-order acoustic vortices (l = ±1, ±2, ±3) at different rotation rates.
