Focusing of pulses in axially symmetric elastic tubes with fluid filling and piezo actuator by a finite difference simulation and a method of time reversal

In this paper a novel method is presented to focus mechanical pulses in an axially symmetric elastic tube with fluid filling and a piezo actuator with the goal of contactfree dispensing of droplets in long pipetting needles of mechanical analysis systems. Focusing is achieved by superposition of different modes and by the dispersion characteristics of the modes used. Preliminary experiments turned out to be difficult due to the complexity of the system. Therefore, the whole system is simulated using the method of finite differences (FDM). The code and its evaluation are described. The focusing is performed using this FDM code and a method of time reversal. Examples for focusing are presented and the restrictions of this method are explained.