阻抗边界附近粘弹性球壳的动态声辐射力

Dynamic Acoustic Radiation Force on a Viscoelastic Spherical Shell near an Impedance Boundary

当入射声波包含多个不同的频率分量时,物体受到的声辐射力会含有随时间变化的动态分量,称为动态声辐射力.动态声辐射力在医学成像、物质参数反演等领域得到了越发广泛的应用.利用镜像原理,从理论上推导了双频率声波作用在阻抗边界附近的粘弹性球壳上时产生的动态声辐射力,并以合成树脂球壳为例进行计算.结果显示:与稳态声辐射力相比,动态声辐射力在峰值处会出现劈裂现象,且劈裂后两峰的间距恰好等于两个无量纲频率之差,因而当两频率十分相近时可以将其近似为稳态声辐射力;增加边界声压反射系数可以明显提升动态声辐射力的峰值,而球壳与边界距离的变化则会使动态声辐射力出现周期性变化,且其变化周期刚好为半波长.当球壳相对较薄时,由于空气的声阻抗远小于水,充气球壳的动态声辐射力会远强于充水球壳.本文的计算结果预期可以为边界附近利用动态声辐射力进行声操控提供理论基础.

When the incident acoustic wave contains many different frequency components,the acoustic radiation force on the objects will have a dynamic component that changes with time,which is called the dynamic acoustic radiation force.Dynamic acoustic radiation has been widely used in medical imaging,parameter inversion and other relevant fields.Based on the image theory,the expression of the dynamic acoustic radiation force acting on a viscoelastic spherical shell near an impedance boundary for a dual-frequency wave is theoretically deduced.Numerical calculations for a viscoelastic lucite shell are provided as an example.The results show the splitting of the resonant peaks for the dynamic acoustic force,which produces two peaks that are separated by a dimensionless frequency shift equal to the modulation dimensionless frequency.Therefore,when the two frequencies are very close,the dynamic radiation force can be approximated as the steady radiation force.The increase of the boundary reflecting coefficient leads to the enhancement of the peak value of the dynamic acoustic radiation force.Moreover,the dynamic acoustic radiation force changes periodically along the variation of shell-boundary distance.When the spherical shell is relatively thin,the dynamic acoustic radiation force for the air-filled spherical shell is much stronger than that for the water-filled one bacause air has a much lower impedance than water.These results are expected to provide a theoretical basis for the acoustic manipulation near the boundary using the dynamic acoustic radiation force.