Dynamic tunable acoustic metasurface with continuously perfect sound absorption

Acoustic metasurfaces display significant potential for controlling sound waves by using subwavelength structures. However, serious shortcomings are evident regarding the sound absorption type, exhibiting weak reconfigurability in achieving multi-band tunable sound absorption. To overcome this challenge, an acoustic metasurface was proposed that could achieve continuously tunable sound absorption at sub-wavelength thickness. It was constructed by introducing a rotatable plate into a variable-diameter semi-cylindrical cavity ranging from 10 degrees to 175 degrees, which could independently manipulate the acoustic resistance and reactance control at the same time. This may enable the impedances of structure and air to be matched perfectly in the frequency range of 300-1500 Hz at any rotation angles. The experimental results corresponded with the simulation, showing that perfectly tunable sound absorption was achieved at a thickness of 54 mm (only 1/21 of the maximum wavelength). In addition, the acoustic metasurface produced continuously tunable sound absorption in a wide frequency range using simple, easily executable methods. It could be employed in practical engineering applications, such as engines and rotating machinery, where the noise changes in conjunction with speed.