Broadband ultra-thin acoustic metasurface absorber with coiled structure

We theoretically and experimentally propose two designs of broadband low-frequency acoustic metasurface coiled absorbers (Sample I/Sample II) for the frequency ranges of 460 Hz-972 Hz and 232 Hz-494 Hz (larger than 1 octave), with absorption larger than 0.8 (average is 0.87), and having the ultra-thin thickness of 4.5 cm and 9 cm respectively (lambda/17 for the lowest working frequency and lambda/8 for the highest frequency). The designed supercell consists of 16 different unit cells corresponding to 16 eigen frequencies for resonant absorptions. The coupling between multiple resonances leads to broadband absorption effect in the full range of the targeted frequency spectrum. In addition, the coiling structure lead to the ultra-thin thickness of the metasurface absorbers. Our conceived ultra-thin low-frequency broadband absorbers may lead to pragmatic implementations and applications in noise control field. (C) 2019 The Japan Society of Applied Physics