LAUSR

Abstract Finite size of unit cell (thickness 50 mm , area 100mm × 100mm ) presents significant challenge in achieving an absorption coefficient higher than 0.8 under the 220 Hz–500 Hz frequency. The main difficulty lies in the improvement of the absorption in 220 Hz–300 Hz due to the weak coherent coupling between elementary resonators (ERs) in such frequency range. In this article, we explored the prerequisite for strong coherent coupling and further proposed two methods for improving the coupling while maintaining the size of the unit cell. The methods for designing the novel structures are quite simple and the structures are easy to build, therefore, they provide a basis for development of meta-structures to reduce low frequency noise over a wide range.