Piezoelectric Pumps Based On Vibration Filter

Piezoelectric pump is regarded as having features of compact structure,easy miniaturization,low power consumption,high efficiency,high power density,high control precision,fast response speed and low noise.It has attracted much attention from researchers both at home and abroad,and has shown broad application prospects in biomedical treatment,chemical analysis,microelectronic devices,robots,aerospace engineering etc.However,currently the actual output power and efficiency of piezoelectric pumps are generally low,and the main reason for this situation is the low working frequency of the piezoelectric pumps,which can not bring out the high power output capability of piezoelectric materials.This dissertation studied the output characteristics of piezoelectric actuators and the working principle of a typical piezoelectric volumetric pump,and proposed that the main factor that prevents the effective working frequency of the piezoelectric pump from further improving is the dynamic load of liquid.And by introducing a type of vibration filter to cut off the rigid connection of the liquid inside and outside the pump chamber can greatly reduce the dynamic load of high-frequency vibrating liquid on the piezoelectric actuator,and thus improve the effective output and working efficiency of the piezoelectric pump at a high working frequency.In this dissertation,the dynamic load of liquid and the model of vibration filter were theoretically analyzed and experimentally verified.The vibtration filter was then applied to a resonantly driven piezoelectric pump based on a newly designed U-shaped resonantor,to develop a piezoelectric pump prototype with features of compact structure,convenient production,reliable operation and outstanding performance.The main achievements and conclusions of this dissertation are as follows:It was proposed that the dynamic load of liquid under high frequency is an important factor to hinder the further improvement of the working frequency of piezoelectric pump.Firstly,the calculation formula of the dynamic load of liquid was deduced from the model of liquid vibrating by a piezoelectric stack.The dynamic load and its equivalent stiffness are proportional to the square of the vibrating frequency and the liquid mass,which will greatly limit the output displacement and output power of the piezoelectric actuator under high frequencies.Then,considering the actual structure of a piezoelectric pump,the relationship of liquid dynamic loads between pipes with different cross-sectional areas was analyzed,which led to a conclusion that the total dynamic load on the piezoelectric actuator is proportional to the cross-sectional area of the pump chamber and the total lengths of the pipes.Meanwhile,it was pointed out that the liquid flow rate,in the working process of the piezoelectric pump,contained both DC component and AC component,in which the DC component contributed to the required pump output flow,while the unwanted AC component gave rise to the dynamic load.Using the analysis method of analog circuit diagram,the liquid mass can be analogous to the inductive component in a circuit,which will reduce the power factor of the piezoelectric actuator driving loads at high frequencies,and as a result,the drive performance of the piezoelectric actuator can not be fully utilized.Based on the fully understanding of the liquid dynamic load in the piezoelectric pump,this dissertation proposed using vibration filter to cut off the rigid connection of liquid inside and outside the pump chamber,and smooth the high frequency components in the liquid flow outside the valve,in order to reduce the high frequency liquid dynamic load in the piezoelectric pump.The mechanical model of the vibration filter was established by a spring-damper,and its effect on the attenuation of high-frequency vibration of the liquid outside the valve was analyzed theoretically.It was concluded that when the spring stiffness of the vibration filter was small enough,the dynamic load was caused mainly by liquid in the pump chamber,which can greatly reduce the dynamic load on the piezoelectric actuator,and bring out its high performance characteristic under high working frequencies.Two methods of constructing a vibration filter in a piezoelectric pump were proposed,which were constructed by means of a gas chamber or a piece of flexible film,and their elastic properties were mechanically analyzed when quivalent to springs.Using the same analysis method of analog circuit diagram,the vibration filter can be analogous to the capacitive component in a circuit,which can not only constitute a low-pass filter to attenuate high-frequency vibration,but also link to the load liquid mass(analogy to the inductive component)in parallel so that the power factor of the piezoelectric actuator driving loads can be improved dramatically.Comparative experiments were designed and carried out to test the improving effect of vibration filter on the output flow rates of piezoelectric pumps,which proved that the vibration filter can reduce the dynamic load of liquid in the piezoelectric pump and improve its effective output under high working frequencies.An experimental test platform on piezoelectric volumetric pump was designed and built,using a self-made cymbal type piezoelectric actuator based on piezoelectric stacks as the driving element.The frequency and voltage characteristics of volumetric pumps with and without the vibration filter were tested separately.The experimental results showed that the output flow rate of the volumetric pump can be improved dramatically by adding the vibration filter,which was indicated by a 10%～50%increasement of the maximum output flow rate in the non-resonant operating frequency range of 200～500 Hz.At last,the flexible thin film vibration filter was applied in a newly designed resonant piezoelectric pump based on a U-shaped piezoelectric resonator,constructing a compact and high performance piezoelectric pump system.The pump system consisted of basically two parts:a newly designed U-shaped piezoelectric resonantor and two volumetric pumps with flexible thin film vibration filters constructed inside.The U-shaped piezoelectric resonantor,designed and analysed by using finite element method,had a symmetric structure and could obtain uniform strain distribution in the surfces of piezoelectric patches,and thus had a high capacity to drive the volumetric pumps.On the other hand,by adding the previously introduced thin film vibration filter to the volumetric pumps,the driving characteristic of the U-shaped piezoelectric resonantor could be brought out to its maximum degree.A prototype pump system with the outline dimensions of 30 mm × 37 mm × 72.5 mm was fabricated,and its dynamic characteristic and main output performance were tested.Experiment results showed that the pump system could pump tap water at a flow rate of over 1660 mL/min under zero back pressure or at a backpressure of approximately 85 kPa under zero flow rate,when driven by sinusoidal voltages of 300 Vpp and resonant frequencies of 312 Hz and 345 Hz.