强超声在空化液体中的反常衰减

采用自动控制系统,逐点测量了长方形水槽内液体中不同位置的声压。研究发现,随着驱动声压的增大,近场声压持续增大,但衰减速度也加快,而远场声压会经历一个先上升后下降的反常过程。通过对容器中不同位置声压进行频谱分析,得到声波不同频率分量随传播距离的变化规律。结合频谱的分析表明,上述反常过程的原因是高驱动声压下气泡的非线性振动将更多声能量转移至衰减较快的高次谐波,从而导致远场的声压反而低于较低驱动时对应的声压。 

Abnormal attenuation of powerful ultrasound propagating in cavitating liquids

The remote automatic control system is used to measure the sound pressure in a rectangular container filled with liquids. Research shows that with the increasing of driving sound pressure, sound pressure of near field rises continuously but attenuates faster, whereas sound pressure of far field increases firstly and then abnormally decreases. The change regulation of different frequency components of waves during propagating could be obtained by analyzing the frequency spectra of sound pressure at different positions. Analysis combining with the spectra shows that the abnormal process should be attributed to that the nonlinear oscillation of cavitating bubbles transfers more acoustic energy to harmonics which attenuate faster under higher driving pressure, which results in the pressure of far field being lower than that of lower driving pressure.