Abstract: In order to overcome existing common faults of the traditional volumetric type valve-less pump, such as fluctuation, backflow and lack ability of pumping, a valve-less pump which imitates the swing of the caudal-fin is proposed. The researches on the variable-cross-section oscillating vibrator with flexible caudal-fin are carried out. Based on the study carried on the swing of the tuna which has high cruise speed, a variable cross-section vibrator with flexible caudle-fin is designed. The harmonic analysis of vibrator immerged in water is conducted with the ANSYS software. The tip amplitude of vibrator, which has different flexible caudal-fin length, is extracted when the vibrator operates in the second order bending mode. The analysis results suggest that the tip amplitude has great influence on the theoretical flow rate. Thirdly, the tip amplitude is measured utilizing a charge coupled device(CCD) laser displacement sensor. When the length of the flexible caudal-fin is 5 mm, the tip amplitude of second bending mode reaches 0.4 mm. Meanwhile, the trend of the tip amplitude, which varies with the length of the flexible caudal-fin, coincides with the result of simulation. Finally, the performance of the pump is tested experimentally：Driven by 60 V AC signals, the pressure head reaches 78 mm when the length of the flexible caudal-fin is 5 mm. This research reveals that when the other structure parameters are fixed, the length of the flexible caudal-fin determined the performance of the pump.

Key words: Bionic, Flexible caudal-fin, Piezoelectric-pump, Piezoelectric-stack, Valve-less