Dezhkunov N V, Francescutto A, Serpe L, Canaparo R, Cravotto G
BSUIR, P. Brovka St. 6, 220013 Minsk, Belarus.
Dept of Engineering & Architecture, University of Trieste, 34127 Trieste, Italy.
Ultrason Sonochem. 2018 Jan;40(Pt B):104-109. doi: 10.1016/j.ultsonch.2017.04.004. Epub 2017 Apr 6.
The way in which a cavitation zone develops in a focused pulsed ultrasound field is studied in this work. Sonoluminescence (SL), total hydrophone output and cavitation noise spectra have been recorded across a gradual, smooth increase in applied voltage. It is shown that the cavitation zone passes through a number of stages of evolution, according to increasing ultrasound intensity, decreasing pulse period and increasing ultrasound pulse duration. Sonoluminescence is absent in the first phase and the hydrophone output spectra consists of a main line with two or three harmonics whose intensity is much lower than that of the main (fundamental) line. The second stage sees the onset of SL whose intensity increases smoothly and is accompanied by the appearance of higher harmonics and subharmonics in the cavitation noise spectra. In some cases, the wide-band (WBN) component can be seen in noise spectra during the final part of the second stage. In the third stage, SL intensity increases significantly and often quite sharply, while WBN intensity increases in the same manner. This is accompanied by a synchronous increase in the absorption of ultrasound by the cavitation zone, which is manifested in a sharp decrease in the hydrophone output. In the fourth stage, both SL and WBN intensities tend to decrease despite the increased voltage applied to the transducer. Furthermore, the fundamental line tends to decrease in strength as well, despite the increasing ultrasound intensity. The obtained results clearly identify the different stages of cavitation zone development using cavitation noise spectra analyses. We then hypothesize that three of the above stages may be responsible for three known types of ultrasound action on biological cells: damping viability, reversible cell damage (sonoporation) and irreversible damage/cytotoxicity.
本研究探讨了聚焦脉冲超声场中空化区的发展方式。在施加电压逐渐平稳增加的过程中，记录了声致发光（SL）、水听器总输出和声空化噪声谱。结果表明，随着超声强度增加、脉冲周期减小和超声脉冲持续时间增加，空化区经历了多个演化阶段。第一阶段不存在声致发光，水听器输出谱由一条主线和两三个谐波组成，其强度远低于主线（基波）。第二阶段声致发光开始，其强度平稳增加，同时空化噪声谱中出现更高的谐波和次谐波。在某些情况下，在第二阶段的最后部分，噪声谱中可以看到宽带（WBN）成分。在第三阶段，声致发光强度显著增加，通常相当急剧，而WBN强度也以同样的方式增加。与此同时，空化区对超声的吸收同步增加，这表现为水听器输出急剧下降。在第四阶段，尽管施加在换能器上的电压增加，但声致发光和WBN强度都趋于下降。此外，尽管超声强度增加，但基波强度也趋于下降。通过声空化噪声谱分析，所获得的结果清楚地识别了空化区发展的不同阶段。然后我们假设上述三个阶段可能分别对应于超声对生物细胞的三种已知作用类型：抑制活力、可逆性细胞损伤（声孔效应）和不可逆损伤/细胞毒性。
