Hefner BT, Marston PL
Department of Physics, Washington State University, Pullman 99164-2814, USA.
J Acoust Soc Am. 2000 Apr;107(4):1930-6. doi: 10.1121/1.428475.
Unlike most common solids, "plastic" polymer solids typically have shear and Rayleigh wave phase velocities less than the speed of sound in water. Subsonic Rayleigh waves on smooth objects in water are not classified as leakey waves and it is necessary to reexamine backscattering mechanisms. Also the intrinsic material dissipation of the Rayleigh wave can be significant. Backscattering by acrylic or polymethlmethacrylate (PMMA) spheres in water is analyzed and measured in the region ka = 1.5-7 and it is found that prominent low-lying resonance peaks of the form function f exist. The peaks can be modeled with quantitative ray theory as the result of coupling of subsonic Rayleigh waves with sound through acoustic tunneling. The most prominent maximum of f=5.63 occurs at ka = 1.73 and is associated with the quadrupole (or n=2) partial wave. In addition to explaining the scattering, the target strength is found to be sufficiently large that such spheres may be useful for passive low frequency targets.
与大多数常见固体不同，“塑料”聚合物固体的剪切波和瑞利波相速度通常小于水中的声速。水中光滑物体上的亚声速瑞利波不属于泄漏波，因此有必要重新审视反向散射机制。此外，瑞利波的固有材料耗散可能很显著。对水中丙烯酸或聚甲基丙烯酸甲酯（PMMA）球体的反向散射进行了分析，并在ka = 1.5 - 7的区域进行了测量，发现形式函数f存在明显的低位共振峰。这些峰可以用定量射线理论建模，作为亚声速瑞利波通过声隧道效应与声音耦合的结果。f = 5.63的最显著最大值出现在ka = 1.73处，与四极子（或n = 2）分波相关。除了解释散射外，还发现目标强度足够大，以至于这种球体可能对被动低频目标有用。
