Tc)kiwadai ， Ube ， Astudy on establishing the mechanical model of stirrer driven by pjezoelectric actuator and used 丘)r dissolving thrombus is presented in this papeL A simplified state space model is established based on the analysis ofthe device ' s dynamics ， And the method ofgrey box system identification is introduced to modify some uncertain parameters ofthe mathematical model to get a more accurate modeL The accuracy ofthe mathematical model is verified experimentally ． Key PVords： Mechanical Model ， Piezoelectric Actuator， Thrombus Treatment ， System identification

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Recently medical treatment device using a complex vibration is developed, it has been designed for the improvement of the conversion efficiency. However, few reports are available on the vibration transducers as used in small blood vessel. In this paper, the new type longitudinal-torsional complex vibration transducer was designed. The principle of vibration conversion from longitudinal vibration to longitudinal-torsional complex vibration was described in detail. In order to obtain the most effective performance, the structure parameters of the vibrator involving the mode conversion were mentioned. The important parameters to achieve the highest conversion efficiency from longitudinal vibration to torsional vibration were investigated by using the finite element method analysis models. The angled-multilayered converter was designed, and the important parameters as layers offset angle and lead angle of twist structure were discovered. The most effective parameters were obtained for the offset angle was 10 degree and the lead angle was 56-59 degree. It was confirmed that the vibration conversion efficiency was improved by making a hole for the suction into the device.