ABSORCIÓN PERFECTA DE BAJA FRECUENCIA POR PANELES ACÚSTICOS ULTRAFINOS BASADOS EN METAMATERIALES
Résumé
The propagation of acoustic waves inside structured materials can be extraordinary modified by using subwavelength size resonant inclusions. Those structures are named metamaterials. In this work, we study acoustic panels based on metamaterials specially designed to show perfect sound absorption by using the critical coupling of the structure to the exterior medium. We report perfect absorption produced by both, rigid backed panels and panels including ventilation and holes, where the flux of air is allowed through the structure. The structures are made by a rigid panel perforated by slits. Each slit is loaded by a set of Helmholtz resonators, producing slow-sound conditions. Thus, the slits become deep subwavelength resonators. The system is analyzed theoretically using the transfer matrix method and a modal expansion, including the thermoviscous effects. The first method allows to study the effects of the discrete number of resonators, while the second one allows to derive the effective parameters of the system. A finite element method including thermoviscous losses and experiments were used to validate the results. The designed panels show a thickness of between 40 and 88 times smaller than the wavelength in the case of monocromatic absorption (300 Hz), and 10 times smaller than the wavelength in the case of broadband absorption (10 cm for perfect absorption between 300 Hz and 1 kHz). The experimental results using 3D printed samples show perfect agreement between the analytical and numerical predictions, allowing its practical application for noise control.