Research On Near-field Acoustic Holography Measurement Method Based On Equivalent Source Method In Limited Space

Near-field acoustic holography(NAH)is an important method for sound field prediction and sound source identification.Using NAH technology,the sound pressures on the surface of the sound source and the vibration velocities of the particles can be calculated by extracting sound information in the near field of the sound source,and then the entire three-dimensional sound field can be reconstructed.Traditional near-field acoustic holography technology requires all sound sources to be on the same side of the holographic surface and the other side to be a free field.Usually,the environment in which the sound source is located,however,is not a free field because of the boundary restrictions.So,the sound field data obtained by the holographic measurement surface is not only the sound waves directly radiated by the sound source,but also the multiple reflections at the interface.Therefore,the sound source cannot be identified accurately by conventional near-field acoustic holography.In this paper,proposes a near-field acoustic holography technique based on the equivalent source method in limited space has been proposed.NAH technology based on the equivalent source method in the free field is studied firstly.Then,the point source combination and structural sound source are taken as the research object,the feasibility and effectiveness of this method are analyzed numerically.And the influences of the holographic surface layout method,the distance between the measuring points of the holographic surface and the frequency of the sound source on the reconstruction accuracy have been analyzed.Aiming at the problem of sound source identification and sound field reconstruction in a limited space,the analytical solution of the Green's function cannot be given due to the limitations of the boundary properties.Therefore,this paper proposes a method to obtain the Green's function in finite space by numerical calculation,and then the three-dimensional sound field of the sound source in the free field is reconstructed by the Green's function.It is also applied to the acoustic radiation prediction and sound field reconstruction point source combination and structured sound source.The effects of sound source frequencies,holographic surface size,holographic measurement point spacing,and holographic surface position on reconstruction accuracy are analyzed.The results show that the method proposed in this paper can be used for sound field reconstruction in non-free sound fields,and has a good effect.This method solves the limitation that traditional NAH could only be applied to free-field and half-space acoustic fields.