Finite element modeling of metamaterial made of acoustic black hole profiles for achieving broadband sound absorption.

To achieve broadband sound absorption, acoustic metamaterial composed of periodically arranged thin annular cavities, separated by rings and connected through a main central pore is studied using finite element method. The geometry of the main pore is varied by applying different decreasing hole profile functions. Each annular cavity has a thickness of 1 mm, and the radius of the rings decreases progressively from the inlet, following linear, exponential, quadratic and sinusoidal decay functions. Considering up to 40 annular cavities, each main pore profile results in a broad frequency band of sound absorption coefficient. The exponential pore profile exhibits five absorption peaks below 1200 Hz and an average absorption coefficient of about 0.9 above 2000 Hz. In contrast, the other pore profiles achieve an average sound absorption coefficient of about 0.98 above 1500 Hz. As the radius of the inlet ring decreases, the sound absorption coefficient and the frequency band decrease. The studied metamaterial is suitable for various applications aimed at reducing broadband noise.