Experimental Studies on Laser Induced Underwater Converging Shock Waves Based Generated by Pseudo Phase Conjugate Method

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Underwater shock waves are utilized for the medical treatment of kidney stones, extracorporeal shock wave lithotripsy (ESWL). In ESWL, spherical converging shock waves are generated outside the human body, and propagate into the human body toward the kidney stones. The shock waves break the kidney stones into many smaller fragments, and then the fragments are excreted with urine. The treatment by ESWL is said to be a method with smaller physical strain, however it is also said that the effective fragmentation of kidney stones has not been realized yet.The speed of sound is not uniform in a human body, thus, different parts of a shock wave arrive at the kidney stone at different times. As the result, the impact force applied to the kidney stone is smaller than the impact force that is applied to the kidney stone when all the parts of a shock wave arrive at the kidney stone simultaneously. This is the reason why the effective fragmentation of kidney stones has not been realized yet by ES … More WL.In order to solve the above mentioned problem, the present study carried out the experiments on laser induced underwater shock waves, and obtained the following results.(1) The method of pulsed laser induced shock waves can generate the pseudo phase conjugate shock waves in the field of non-uniform speed of sound which consists of water and PMMA.(2) The pseudo phase conjugate shock wave focuses on a point even in the field of non-uniform speed of sound.(3) It is possible to change the pressure waveform of the shock wave at the focal point by changing the shape of the wave front of the shock wave. The result suggests that it may be possible to reduce the negative pressure that appears just behind the shock wave with positive pressure and that is thought to give damage to organs in a human body.(4) The numerical results given by the method of Green's function is qualitatively in agreement with the experimental ones. The present study is based on the idea that applies the phenomena of crack bifurcation to the treatment of kidney stones by ESWL. Accordingly, the following studies on crack bifurcation is also published.(5) When a solid material breaks under strong impact force, fast propagating cracks appears. A fast propagating crack bifurcates into two cracks or more when the crack speed is high enough, and the energy release rate is continuous across the bifurcation. Less