Hoff L, Sontum PC, Hovem JM
Norwegian University of Sciene and Technology, Department of Telecommunications, Trondheim.
J Acoust Soc Am. 2000 Apr;107(4):2272-80. doi: 10.1121/1.428557.
A model for the oscillation of gas bubbles encapsulated in a thin shell has been developed. The model depends on viscous and elastic properties of the shell, described by thickness, shear modulus, and shear viscosity. This theory was used to describe an experimental ultrasound contrast agent from Nycomed, composed of air bubbles encapsulated in a polymer shell. Theoretical calculations were compared with measurements of acoustic attenuation at amplitudes where bubble oscillations are linear. A good fit between measured and calculated results was obtained. The results were used to estimate the viscoelastic properties of the shell material. The shell shear modulus was estimated to between 10.6 and 12.9 MPa, the shell viscosity was estimated to between 0.39 and 0.49 Pas. The shell thickness was 5% of the particle radius. These results imply that the particles are around 20 times more rigid than free air bubbles, and that the oscillations are heavily damped, corresponding to Q-values around 1. We conclude that the shell strongly alters the acoustic behavior of the bubbles: The stiffness and viscosity of the particles are mainly determined by the encapsulating shell, not by the air inside.
已开发出一种用于描述包裹在薄壳中的气泡振荡的模型。该模型取决于壳的粘性和弹性特性，这些特性由厚度、剪切模量和剪切粘度来描述。该理论被用于描述奈科明公司的一种实验性超声造影剂，它由包裹在聚合物壳中的气泡组成。在气泡振荡呈线性的振幅下，将理论计算结果与声衰减测量结果进行了比较。测量结果与计算结果拟合良好。这些结果被用于估计壳材料的粘弹性特性。估计壳的剪切模量在10.6至12.9兆帕之间，壳的粘度在0.39至0.49帕斯卡秒之间。壳的厚度为颗粒半径的5%。这些结果表明，颗粒的刚性比自由气泡大约强20倍，并且振荡受到严重阻尼，对应于约为1的品质因数。我们得出结论，壳强烈改变了气泡的声学行为：颗粒的刚度和粘度主要由包裹壳决定，而非由内部的空气决定。
