Fig. 4: Acoustic response performance of the WS.

a Schematic diagram of experimental setup for testing the WS. Inset is the laser beam focused on the WS’s hub diaphragm. b Velocity response of the WS at 500 Hz for different acoustic pressure. c Time response and the corresponding frequency spectrum of the WS for the 500 Hz acoustic wave at 0.05 Pa. d Frequency response of the WS with various sound pressure levels. e Velocity versus acoustic pressures at various frequencies. f Time response and the corresponding frequency response spectrum of the WS to dual frequency acoustic signals at 500.00 Hz and 500.05 Hz. g Time response and the corresponding frequency response spectrum of the WS to acoustic signals at 499.95 Hz, 500.00 Hz and 500.05 Hz. h Schematic diagram of directionality measurements. i Time response of the WS to the incident acoustic wave at 500 Hz in different directions. j Theoretical and measured directionality of the WS at 500 Hz, the blue curve is the theoretical results and the red dots are the measured results. All measurements are performed in the hub diaphragm of the WS. Error bands (d) and bars (e) represent the s.d. of the results of at least three replicates