Multimodal superposition modeling and acoustic field characteristics analysis of scattering sound field from spherical targets

In this paper, a multimodal superposition model of the scattered acoustic field from a spherical target is investigated and the distribution laws of the scattered acoustic field of different sizes of rigid and elastic spheres at different frequencies are analyzed. The scattering cross section is approximated as the geometric projected area under the high-frequency/large-radius condition, whereas the scattering cross section is proportional to the fourth power of the frequency under the low-frequency/small-radius condition (ka ≪ 1). The scattering characteristics of the elastic sphere are affected by both geometric and elastic scattering, and the presence of Rayleigh and whispering-gallery waves significantly affects the acoustic field in the vicinity of the elastic sphere. Numerical simulation results show that the scattered acoustic field of the rigid sphere exhibits obvious directivity and geometric shadowing effects at high frequencies, while the distribution of the acoustic field of the elastic sphere exhibits complex interference phenomena and energy attenuation due to the elastic resonance waves. This study provides a theoretical basis and quantitative evaluation method for underwater target acoustic detection and identification.