when sound wave frequency is higher than 20KHz and spreads in the continuous medium(such as water),it will give rise to the movement of medium particles on its wave-front surface,and make the medium particles obtain great acceleration and kinetic energy.Generally,it can be up to 2000 times the acceleration due to gravity.In this condition,the caffeine escapes quickly and drifts in the water.In this way, coupled by the action of super-critical fluid,the removal effect of caffeine from tea is enhanced.