Low-frequency acoustic absorption realized by ultrasparse coiling-up metasurfaces

Abstract

In this work, an ultrasparse coiling-up acoustic metasurface with deep-subwavelength scale is proposed to achieve a broadband acoustic absorption, which has been verified by analytic calculations, numerical simulations as well as experimental measurements. By adjusting the slit width of input channel and the period length between adjacent absorbers independently, acoustic absorption with high efficiency is realized in a low filling rate manner, and the results are analyzed by coupled mode theory (CMT) effectively. For a composite acoustic absorber cascaded by six coiling-up cavities with different heights, an average absorptivity of 93% is obtained in a broadband of 226 Hz-304 Hz, and the device thickness is around 1/10 of the minimum operating wavelength. Moreover, the proposed absorber is insensitive to the incident angle of the acoustic wave, and the absorptivity is still over 75% even when we adopt grazing incidence, which can be utilized to serve as an acoustic perfectly matched layer in air background.