supersonic wave creates an effect like internal explosion. it means that the expansion and compression of wave produce a lot of tiny space inside the liquid. the liquid and vapour exist in these tiny space. in the compression cycle, supersonic wave impose a positive pressure on liquid molecule, whereas a negative pressure will be created through the expansion cycle. there is a cohesion effect inside the liquid or biological tissue. inside the low-density lipocyte, the cohesive effects are comparatively weak. A negative pressure, which is relative low, can create tissue gaps easily. it is called as cavitations in physics. the explosion effects inside and outside the cells will increase the molecular movements, so as to achieve the high energy state. then lead to the lipocyte cracking.