Potential applications of tandem shock waves in cancers therapy

Interaction of two successive shock waves focused to a common focal point - tandem shocks, has been investigated. The time interval between the two shocks can be varied. We have demonstrated that acoustical inhomogeniety created in water by the first wave strongly modifies propagation of the second wave. In short time intervals between the waves (5–20μs), the second wave, rather surprisingly, arrived the focus as a rarefaction wave producing a large number of cavitations. Amplitude of the second wave gradually decreases with the increasing time delay between the waves. Schlieren photos show very complex pressure field at the focal region for such time delay. For a longer time delay (50–500 μs) the second wave is almost totally damped at the focus. Propagation of the second wave as a pressure wave is renewed only for very long time delays (0,7 - 2 ms) when cavitations produced by the first wave are quenched.