Acoustic metaporous layer for sound absorption enhancement

An acoustic metaporous layer with a subwavelength thickness is designed to enhance sound absorption property of the uniform porous layer with the same thickness. Analytical and numerical studies are conducted. The proposed structure is comprised of four different slits that are arranged in a periodic manner. Each element contains a porous material with one embedded rigid partition in a horizontal direction. Through adjusting the geometric parameters of the embedded partitions, a discrete and linear phase gradient of the reflected wave is generated on the reflecting surface for wave manipulation. Within a specific range of incident angles, the high-order reflected wave carrying the highest acoustic energy can be tuned to propagate along the reflecting surface. In this case, less reflected acoustic energy radiates into the far field, and nearly perfect sound absorption can be obtained accordingly. When the period length of the metaporous layer is smaller than a half wavelength of the incident wave, all the high-order diffracted waves disappear at the arbitrary incident angles, so that the excellent sound absorption property can remain within a wide range of incident angles at the target frequency. Comparing with the uniform porous layer with the same thickness, the proposed metaporous layer also possesses the advantages of sound absorption property within a wide range of frequencies.