Fig. 5: Experimental demonstration of the tunable acoustic vortex characteristics.
From: Tunable acoustic vortex generation by a compact rotating disk
a Summary of phase (first line), and acoustic amplitude (second line) distributions at z = 40 mm for Ω/2π, 2Ω/2π, and 3Ω/2π Hz. b Normalized experimental amplitude–frequency spectrum of the plain disk, and experimental phase and amplitude distributions at 4Ω/2π Hz. The experimental spectrum was tested at locations consistent with the simulation (z = 40 mm and R = 40 mm). c The bars depict the average of phase difference data. The phase value of each measurement for the stationary microphone 1 (Micro 1) is denoted by φ0. At 36 evenly spaced measurement points along the r = 30 mm circle, the phase value for the moving microphone 2 (Micro 2) is denoted as φi (i = 1, 2, 3…36), as shown in the insets. The relative phase value at the ith measurement point is expressed as ∆φi = (φ0 - φi). ∆δi = ∆φi+1 − ∆φi represents the difference in the relative phase between adjacent measuring points i and i + 1. \(\overline{\varDelta {{\phi }}_{i}}={\sum }_{i=1}^{36}\varDelta {\delta }_{i}/36\) represents the average of ∆δi. The value of \(\overline{\varDelta {{\phi }}_{i}}\) under the experiment is shown by the blue bars. The black line represents the variance of ∆δi (i = 1, 2, 3…36). The reference value (red bar) represents the value \(\overline{\varDelta {{\phi }}_{i}}\) under the ideal acoustic vortex phase distribution and is used for comparison with the experimentally generated acoustic vortex.
