Imaging And Separation Of Acoustic Sources Based On Phase Conjugation Method

With the development of military technology, noise becomes a threat to the safety of the vessel, and it remains the primary task of noise control to obtain the information of noise sound source. However, the marine environment is complex, owing to the multipath phenomenon of the ocean acoustic channel and the heterogeneous medium, and the current sound source localization method is faced with lots of problems, resulting in low localization accuracy. The phase conjugation method does not require any prior information of the sound source, and it could do better in multipath issues and be more superior to identify sound source in complex environment, so the phase conjugate method can well deal with the identification and imaging of complex noise source. Nowadays, the application of phase conjugation method is mainly limited in the imaging and identification of single sound source, this paper addresses a detailed study of numerical analysis for the identification and separation of multiple noise sources based on the phase conjugation method. The major contribution is as follows:The different forms of phase conjugation array for the identification of single sound source were studied numerically. The results show that the higher identification accuracy could be obtained when using PCD method, and could break the diffraction limit(0.5λ)in the near field; the higher accuracy could be obtained using propeller array, the spatial resolution could be near to 0.28λ.Based on phase conjugation theory, the phase conjugation sound field of two point sources was studied numerically by using different array forms consisting of discrete elements, and the radiation sound field of two point sources was reconstructed with different strength ration and with different frequency. The numerical results show that higher identification accuracy could be obtained when using PCD method; the higher resolution could be obtained by the planar array for the two point sources; the closer between sources and array, the larger distance between two sources, the better identification accuracy was obtained; the two sources could be distinguished obviously without the distraction of pseudo source when d=λ, z=0.1λ, and could not be separated when z≥1.52λ; the identification distance was restricted to 0.8λ when z=0.1λ; for two point sources at different frequencies, the location accuracy for high frequency sound source was better.The acoustical contribution analysis towards complex sound field was studied numerically. The acoustical contribution coefficient of two point sound sources and a vibrating plate towards the target location were analyzed. The results show that the contribution weights of each source towards the target point could be obtained by acoustical contribution analysis, the whole radiation sound field value at the target point be reduced if the positive parts were well controlled, which can be helpful for guidance of noise control.