探测泡状介质中声速和衰减的压力依赖性：实验观测、理论模型和数值计算
Probing the pressure dependence of sound speed and attenuation in bubbly media: Experimental observations, a theoretical model and numerical calculations
摘要：
泡状介质的衰减和声速的问题仍然部分未解决。关于泡沫介质的衰减和声速的压力依赖性变化的全面数据是不可用的。我们对这个问题的理论理解仅限于线性或半线性理论模型，这在大振幅气泡振荡的情况下是不准确的。在这里，通过控制脂质涂层气泡的大小（平均直径约5.4 μ m），我们报告的第一次观察和表征的同时，在气泡水中的声速和衰减的压力依赖性低于，在和高于MBs共振（频率范围在1- 3 MHz之间）。随着声压的增加（12.5- 100 kPa），衰减和声速峰值的频率降低，而声速的最大和最小振幅增加。我们提出了一个非线性模型的压力依赖的声速和衰减的估计与实验吻合得很好。通过与线性和半线性模型预测值的比较，验证了模型计算的有效性。先前开发的模型的主要挑战之一是在较高空隙率（例如0.005）下气泡共振处的衰减的显著高估。我们解决了这个问题，将气泡的相互作用和比较的结果与实验。气泡-气泡相互作用的影响随着压力的增加而增加。在检查的曝光参数，我们用数字表明，即使对于低空隙率（例如5.1*10-6），随着压力的增加，声速可能会成为4倍以上的非气泡介质中的声速。
英文摘要：
The problem of attenuation and sound speed of bubbly media has remained partially unsolved. Comprehensive data regarding pressure-dependent changes of the attenuation and sound speed of a bubbly medium are not available. Our theoretical understanding of the problem is limited to linear or semi-linear theoretical models, which are not accurate in the regime of large amplitude bubble oscillations. Here, by controlling the size of the lipid coated bubbles (mean diameter of ~5.4um), we report the first time observation and characterization of the simultaneous pressure dependence of sound speed and attenuation in bubbly water below, at and above MBs resonance (frequency range between 1-3MHz). With increasing acoustic pressure (between 12.5-100kPa), the frequency of the attenuation and sound speed peaks decreases while maximum and minimum amplitudes of the sound speed increase. We propose a nonlinear model for the estimation of the pressure dependent sound speed and attenuation with good agreement with the experiments. The model calculations are validated by comparing with the linear and semi-linear models predictions. One of the major challenges of the previously developed models is the significant overestimation of the attenuation at the bubble resonance at higher void fractions (e.g. 0.005). We addressed this problem by incorporating bubble-bubble interactions and comparing the results to experiments. Influence of the bubble-bubble interactions increases with increasing pressure. Within the examined exposure parameters, we numerically show that, even for low void fractions (e.g. 5.1*10-6) with increasing pressure the sound speed may become 4 times higher than the sound speed in the non-bubbly medium.
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