Research On Improvement Of Acoustic Source Identification Performance Of Equivalent Source Method Based Near-field Acoustic Holography

Near-field acoustic holography(NAH)is a valid sound source identification and spatial sound field visualization technology.The equivalent source method based near-field acoustic holography(ESM based NAH)is not limited to the shape of the sound source.With the simple establishment of the mathematical model and the simple construction of its transfer matrix,it has been widely used in recent years.Since the evanescent wave decays exponentially with the increase of the hologram distance,the classical ESM based NAH is suitable for near-field measurement,and the average distance of the microphones limits the upper limit frequency.Given this,this paper proposes a new regularization parameter determination method and a compressive equivalent source method(C-ESM)based NAH with moving equivalent source grid model,aiming to improve the sound field reconstruction performance of ESM based NAH at large hologram distances and a wide frequency range.First of all,the basic theory of classical ESM based NAH using Tikhonov regularization is introduced.Taking combo array as an example,the reconstruction performance of the three regularization parameter determination methods: GCV,Hald empirical formula and Bayesian are compared in different hologram distance,signal-to-noise ratio(SNR)and sound source frequency.Among them,the GCV method involves high-dimensional matrix operations,which is the most time-consuming;the Hald empirical formula method requires a priori knowledge of SNR;the Bayesian approach has the best general performance.Secondly,in order to overcome the limitations of the above regularization parameter determination methods at large hologram distances,this paper proposes a new regularization parameter determination approach.The hologram distance is explicitly introduced into the determination of regularization parameters,which meets the needs of the solution norm compensation penalty caused by the large hologram distance and the actual microphone frequency response mismatch and the measurement background noise interference,and obtains a robust reconstruction result.Comparing this method with the fixed method and the Bayesian method,both simulation and experiment show the superiority of the new regularization determination approach under large hologram distance and noise interference.Finally,to further improve the performance of the recently proposed compressive equivalent source(C-ESM)near-field acoustic holography,this paper proposes a moving equivalent source grid model of C-ESM near-field acoustic holography.The influence of the sound source positioning deviation caused by the misalignment of the sound source and the equivalent source grid points is reduced.Compare with the C-ESM based on fixed equivalent source grid in the face of sound source localization performance and sound field reconstruction.The results show that the moving equivalent source grid model of C-ESM near-field acoustic holography has better sound source localization accuracy and sound field reconstruction performance.