水中微小波纹圆柱体声散射低频共振调控

塑料类高分子材料甲基丙烯酸甲酯-亚克力(PMMA)圆柱中亚音速Rayleigh波低频隧穿共振可引起反向散射增强,在低频标准散射体设计等领域具有重要应用价值.提出一种微弱形变的规则波纹表面结构,可实现水中PMMA圆柱反向散射低频共振频率的无源调控.利用微扰法推导了水中微弱形变规则波纹圆柱反向散射低频共振频率偏移的近似解,讨论了波纹微扰系数、周期对规则波纹圆柱共振频率偏移的影响规律.基于Rayleigh波相位匹配方法分析了低频共振频率偏移的机理.研究表明:微弱形变规则波纹圆柱中亚音速Rayleigh波沿微弱形变波纹表面传播,与光滑圆柱体相比,传播路径的改变引起Rayleigh波传播相位变化,导致了Rayleigh波低频共振频率发生偏移.最后开展了微弱形变规则波纹圆柱体声散射特性水池实验,获取了其反向散射共振频率,明显观察到了规则波纹圆柱共振频率偏移现象,与理论预报结果吻合较好.

Manipulation of low-frequency resonance scattering from submerged slightly deformed polymer cylinders

Backscattering enhancement associated with subsonic Rayleigh wave resonance of a polymethlmethacrylate(PMMA) cylinder is observed at low frequencies in water,which suggests that the PMMA cylinders may have essential applications in the low-frequency standard scatterer design.A slightly deformed surface structure with regular corrugation is presented to manipulate the low-frequency backscattering resonance frequency of PMMA cylinder passively.Using the perturbation method,the approximate resonance frequency shift is derived for an infinite slightly deformed cylinder with regular corrugations.Based on the phase matching of Rayleigh waves,the mechanism of low-frequency resonance frequency shift is revealed.Studies show that compared with a bare cylinder,a small boundary deformation can cause the propagation path of Rayleigh waves to change,namely,the Rayleigh waves propagate along the slightly deformed surface with regular corrugations.The modified propagation path can cause the propagation phase to change,which brings about the low-frequency backscattering resonance frequency shift of a PMMA cylinder.Furthermore,how the resonance frequency shifts with the deformation coefficient and period of the corrugation is discussed in detail.The backscattering resonance frequency of the regular corrugated cylinder shifts to low frequency with the increase of ξ under the condition of the deformation coefficient ξ> 0,but shifts to high frequency with the decrease of ξ at ξ <0,and the resonance frequency shift increases with the increase of absolute value of deformation coefficient.When corrugation period m <10,the phase variation with m is too small,so the corrugation period has little effect on the resonance frequency shift.Finally,acoustic scattering experiment of the regular corrugated cylinder is conducted in the tank.The resonance frequency shift is obviously observed in the experiment,which is in good agreement with the theoretical prediction.Hence,the characteristics of backscattering enhancement associated with subsonic Rayleigh wave and the resonance frequency shifts make the PMMA deformed cylinder have potential applications such as in standard scatter design and identification using "AcoustiCode".