Tunable sound-absorbing metasurface using asymmetric adjustable apertures

We propose a tunable acoustic metasurface that achieves low-frequency broadband absorption using mechanically adjustable apertures. The metasurface consists of sub-wavelength Helmholtz resonators with adjustable apertures integrated into their neck. By breaking symmetry in aperture closure between adjacent resonators, the metasurface induces hybrid resonance that enables perfect absorption of sound at desired frequencies. A metasurface sample incorporating iris-diaphragm-inspired apertures is fabricated via 3-D printing, and its absorption performance at any desired frequency within a tunable range from 400 to 540 Hz is experimentally validated using impedance tube measurements. Moreover, by combining unit cells with individually adjusted apertures, the metasurface achieves over 90% absorption over a one-third octave range (390–485 Hz) while preserving tunability.