Acoustical Porous Absorber with Embedded Local Resonance

Traditional sound absorbers are inefficient in low frequencies. To obtain high absorption in low frequencies, a high thickness of these materials should be used; due to the constraints in construction and lack of space, the use of traditional absorbers is not affordable for absorbing the low frequency sounds. One of the methods available for high absorption in low frequencies to get lower thickness of absorber is use of acoustical metamaterial. Acoustical metamaterials are known due to special sound characteristics such as transmission, absorption and orientation that are not available in natural materials. These features are created by the repetitive structure and the various configurations of the metamaterial. In this study, in order to overcome the problem of absorption at low frequencies and thickness of the absorber, the characteristics of absorption of foam-based porous structures by using local resonance blocks have been analyzed. Elements embedded in absorber materials have been considered with different shapes and properties by finite element method (by Comsol software) to improve the absorption of sound, specially in low frequency. The results showed that applied cylinders filled with air with high diameter and low thickness inside porous absorber improved the absorption at low frequencies.