Article

# Generation of Two Successive Shock Waves Focused to a Common Focal Point

Inst. of Plasma Phys., Acad. of Sci. of the Czech Republic, Prague

IEEE Transactions on Plasma Science (Impact Factor: 0.87). 09/2006; DOI: 10.1109/TPS.2006.878435 Source: IEEE Xplore

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**ABSTRACT:**A generation of focused shock waves by underwater multichannel pulsed electrical discharge on a porous-ceramic-coated electrode in saline water is studied. This work describes the effect of solution conductivity of saline water on the pressure of shock waves. It was found that the amplitude of shock waves has a nonlinear dependence on water conductivity: The amplitude increases with the increase of water conductivity up to 18-20 mS/cm and then decreases again. In this paper, we show that two effects take place. First, the electrical energy dissipated in the discharge depends on the impedance of the electrode system being affected by water conductivity. Second, the velocity of streamer growth strongly depends on energy deposition time into the discharge. The two mentioned effects result in “hill-like” shape of the curve presenting the dependence of the maximum amplitude of the shock wave on water conductivity.IEEE Transactions on Plasma Science 07/2012; 40(7):1907-1912. · 0.87 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Summary form only given. We have developed a shock wave generator where two cylindrical pressure waves are focused to a common focal region by a metallic parabolic reflector, and the waves can be switched on with a different time delay. Interaction of two successive shock waves (tandem shocks) in water focused to a common focal point was investigated. Amplitude of the of the pressure wave reaches up to 100 MPa at the focus, while the amplitude of the rarefaction wave falls down to -25 MPa (well above the cavitation threshold), producing thus numerous cavitations. Schlieren photography of the focal region demonstrated creation of a very complex pressure field with many secondary spherical short wavelength shocks that originate in collapsing cavitations. These secondary shocks can interact with cell scale structures and they are considered to play the main role in cell membranes damage when organic tissue is exposed to the shock waves. Therefore, we are interested in the waveform and the pressure amplitude of these secondary shocks with an ultimate goal in enhancement of cancer treatment efficiency by activation of sonosensitizers based on the effects of the collapsing cavitations. In this work cavitations dynamics induced by the tandem shock waves in water is investigated in more detail. It was demonstrated that the acoustical non homogeneity created in water by the first wave strongly modifies propagation of the second one. Measurements of the pressure waveforms by PVDF shock gauges at the focus demonstrated that at some time delays between shocks the second wave reaches the focus as a rarefaction wave producing thus a large number of cavitations. To determine a gas pressure in the cavitations, strong electric field in the focal area will be applied to generate electrical discharges inside the cavitations. Breakdown voltage with known diameter of the cavitations can provide information about the gas density in the fully developed cavitations. From observation of a s- peed of the cavitations collapse with the knowledge of the gas density a temperature inside collapsing cavitations and the pressure of the secondary shock waves can be determined.IEEE International Conference on Plasma Science 01/2009; -
##### Article: Biological effects of tandem shock waves on soft animal tissues – preliminary “in vivo” experiments

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**ABSTRACT:**We have investigated biological effects of two successive (tandem) shock waves focused to a common focal region on soft animal tissues, including cancer tissues "in vivo" and cancer cells "ex vivo". The tandem shock waves have been produced by our formerly developed shock wave generator where two cylindrical pressure waves are focused by a metallic parabolic reflector to a common focal region and the second shock can be switched on with a different time delay after the first one. The idea on application of the tandem shock waves is to localize the action of the shocks at a predictable region in an initially acoustically homogenous medium such as cancer tissues are. The first shock creates in the tissue some acoustical non homogeneity and cavitations, and the second shock dissipate on it, similarly as it is in the case of the lithotripsy of kidney stones. We have found that at some time interval between the shocks (10-15 Icircfrac14s) the second, originally pressure wave, reaches the focus as a rarefaction wave that produces a large number of cavitations. Collapsing cavitations create secondary, very short wavelength shocks which can interact with cell scale structures. We have demonstrated that the tumors from cancer cells exposed to the tandem shocks grow much slowly. We know that the tandem shocks locally injure a healthy tissue of a rabbit liver . In this work we will present results on synergistic effect of the tandem shocks and hematoporphyrin on the growth rate of tumors on laboratory rats. Preliminary experiments show that the combined therapy of shock waves with hematoporphyrin (i.e., sonotherapy) should be applied in the initial stage of the tumor development.IEEE International Conference on Plasma Science 01/2009;

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