Phase offset mechanism on far-field radiation from multi-piston line sources and near-field acoustic energy density flux

Considering the relationship between the far-field radiation and the outflow of acoustic energy over the radiation surface, phase offset mechanism (POM) is proposed and analyzed in this paper. POM aims at controlling acoustic radiation through adjusting vibration phases of partial areas on the radiation surface without changing total energy of vibrating sources. Multi-piston line sources are selected to verify the effect of POM patterns on decreasing radiated power by changing the initial vibration phases of constituent sources. The theoretical model is built to calculate the radiation efficiency and the acoustic directivity in the far field. The results indicate that POM makes acoustic radiation power redistribute among different frequency ranges. Radiation efficiency has been decreased dramatically in lower frequency range by applying POM patterns to the multi-piston line sources. Meanwhile, the acoustic pressure has been reduced greatly within the area where the original focusing acoustic pressure is relatively large. The acoustic energy density flux near the sources is further simulated by finite element method. As can be found from the swerve of the density flux directions, phase difference of the sources in POM patterns blocks acoustic energy out at lower frequencies, leading to radiation cancellation in the far field. This research could possibly provide guidance on the design of sound control measures. (C) 2019 Elsevier Ltd. All rights reserved.