Generation of focused shock waves by multi-channel electrical discharges in water

A novel method for generation of focused shock waves, based on multi-channel electrical discharges in water with an increased conductivity, has been developed. The multichannel discharge is formed at a composite anode consisting of a metallic electrode covered by a thin (0.2-0.3 mm thick) porous (opened porosity 3-5%) ceramic layer. Two versions of the generators have been realized. In the first one a cylindrical pressure wave is created on a composite cylindrical anode 60 mm in diameter and 100 mm long. At the applied voltage of 30 W, the electric field on the metallic anode reaches almost the value of 1 MV/cm and a large number of short discharge channels distributed almost homogeneously on the anode surface is initiated. Each discharge channel creates a semi-spherical pressure wave, and by superposition of all of the waves a cylindrical pressure wave propagating from the anode is formed. The cylindrical pressure wave is focused by a metallic parabolic reflector (cathode) and near the focus it is transformed to a strong shock wave. In the second version a convergent spherical pressure wave is formed by the same kind of the multi-channel discharge at a composite anode in the form of a part of spherical cavity. The discharge volume with the conductive water solution was separated from the experimental space filled by distilled water by an acoustically transparent membrane. When supplying the discharges by 1 muF condenser bank charged to 30 kV, amplitude of the shock wave reached 100 MPa at the focal point for the both generators. The shock waves are sharply focused to a focal area of 3 mm in diameter transversally (full width at a half maximum) and to 40 mm longitudinally. Interaction of two shock waves generated by two subsequent discharges in the same generator has been demonstrated. Preliminary experiments on exposition of biological objects by the shock waves have been performed. Cellular damage induced by the shock waves was demonstrated on hemolysis of human erythrocytes and on damage of lymphocytes. The hemolysis grew up with the number of expositions being almost total after 150 shocks. On the contrary the viability of lymphocytes after 100 shocks was more than sixty percents compared to controls. Only one third of lymphocytes survived after 300 shocks. Nevertheless these surviving lymphocytes were totally functional and were able to respond on mitogenic stimulation. Localized damage of soft animal tissues was observed.