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Based on the modification of the radial pulsation equation
of an individual bubble, an effective medium method (EMM) is presented for
studying propagation of linear and nonlinear longitudinal acoustic waves
in viscoelastic medium permeated with air bubbles. A classical theory
developed previously by Gaunaurd (Gaunaurd GC and \"{U}berall H, {\em J.
Acoust. Soc. Am}., 1978; 63: 1699--1711) is employed to verify the EMM under linear approximation
by comparing the dynamic (i.e. frequency-dependent) effective parameters,
and an excellent agreement is obtained. The propagation of longitudinal
waves is hereby studied in detail. The results illustrate that the nonlinear
pulsation of bubbles serves as the source of second harmonic wave and the
sound energy has the tendency to be transferred to second harmonic wave.
Therefore the sound attenuation and acoustic nonlinearity of the
viscoelastic matrix are remarkably enhanced due to the system's resonance
induced by the existence of bubbles. 相似文献
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许多Lamb波传感应用中,板周围环境的微小变化即待检测的外部微小变化,可看作是对于薄板中Lamb波的自由边界条件的微扰。本文选择合适的微扰边界条件,推导了适用于多种薄膜负载的各向同性板中弹性波传播的一般特征方程,应用此一般特征方程讨论了传感应用中常见的液体薄膜负载、各向同性固体薄膜负载对薄板Lamb波传播的影响,并与精确理论进行了比较,同时本文还用此方法分析了传感中常见而且精确理论计算较为复杂的粘滞液层负载和固体复合层负载的情况。最后我们对负载液层薄膜时的情况进行了初步实验研究,验证了我们的微扰近似理论。 相似文献
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The propagation of longitudinal acoustic waves in weakly compressible elastic media permeated with air bubbles is investigated on the basis of the radial pulsation equation of a single bubble. The multiple scattering of waves in such media is rigorously described by using a self-consistent approach. Theoretical results show that there exists strong acoustic localization in a range of frequency slightly above the bubble resonance frequency, even for a very small volume fraction of bubbles. Further study reveals that the localization is in fact attributed to collection behaviour of bubbles, allowing for an efficient cancellation of propagating waves. This is essentially consistent with the known conclusions recently drawn for bubbly liquid by Kou et al. [2003 Appl. Phys. Left. 83 4247] 相似文献
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