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

水下冲击波用于肾结石的医疗治疗，体外冲击波碎石术（ESWL）。在ESWL中，球形会聚冲击波在人体外产生，并且朝向肾结石传播到人体内。冲击波将肾结石破碎成许多更小的碎片，然后这些碎片随尿液排出体外。据说ESWL治疗是一种物理负荷较小的方法，但也有人说，肾结石的有效破碎尚未实现。声音在人体内的速度是不均匀的，因此冲击波的不同部分在不同的时间到达肾结石。结果，施加到肾结石的冲击力小于当冲击波的所有部分同时到达肾结石时施加到肾结石的冲击力。这也是ES至今未能有效粉碎肾结石的原因 ...更多信息 为了解决上述问题，本文开展了激光水下冲击波的实验研究，得到了以下结果。(1)利用脉冲激光诱导激波的方法，可以在水和有机玻璃组成的非均匀声速场中产生赝相位共轭激波。(2)即使在非均匀声速场中，赝相位共轭激波也能聚焦于一点。(3)可以通过改变冲击波的波前形状来改变冲击波在焦点处的压力波形。该结果表明，可以通过正压来减少冲击波后面出现的负压，该负压被认为会对人体器官造成损害。(4)用绿色函数法计算的结果与实验结果定性地一致。本研究是基于将裂纹分叉现象应用于ESWL治疗肾结石的思路。相应地，还发表了以下关于裂纹分叉的研究。(5)当固体材料在强冲击力下断裂时，会出现快速扩展的裂纹。当裂纹速度足够大时，快速扩展裂纹分叉为两条或多条裂纹，且能量释放率在分叉处是连续的。少

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