Sonic crystal noise barrier using locally resonant scatterers

Sonic crystal barriers have been receiving recent interest as potential noise barriers to reduce traffic noise in certain frequency bands. Sonic crystals comprise of periodic arrangements of sound scatterers for which the simplest scatterer topology is a solid cylinder. This paper investigates the acoustic performance of a sonic crystal noise barrier using vertical cylindrical shells of finite height. Locally resonant scatterers comprising of perforated or C-shaped cylindrical shells are examined. Results for the barrier insertion loss show that attenuation in a broad band gap is generated due to destructive interference between the scattered sound waves within the periodic structure. The local resonance of the scatterers creates an additional peak in insertion loss, approximately predicted by the Helmholtz resonator frequency. For the case of the perforated cylindrical shells, the location of the resonant frequency is shown to be dependent on the number and size of the holes. When the resonant frequency due to the perforations occurs within the Bragg band gap, a significant increase in insertion loss across the band gap is shown to occur. For the case of the C-shaped cylindrical shells, the size of the opening is shown to have a significant effect on both the local resonant frequency and the band gap due to Bragg scattering.