Broadband noise attenuation in the flow duct using metamaterial-based acoustic liners

An acoustic liner design based on metamaterial is proposed for broadband duct noise reduction. The material is constructed by four periodically arranged partitions-embedded units covered by a perforated plate, forming a linear reflected phase-shifting within 0 to 2π in a wide target frequency range. The sound absorption performance under normal incident waves is firstly examined by both numerical simulation and impedance tube measurement, leading to close agreement to the target design. Then, the meta-liner is installed in a flow tube to assess its capability of reducing broadband noise in a duct with aerodynamic flows. The experiments investigations are performed in an advanced grazing flow tube developed at the Hong Kong University of Science and Technology. The effect of sound levels (ranging from 120dB to 140dB), flow speeds with the Mach number up to 0.3, and the position of sound source (at upstream and downstream sides of meta-liner) are investigated. Results show that a nearly flat transmission loss is achieved in the target frequency range by the metamaterial-based acoustic liner in various conditions, showing its potential for practical industrial applications.