Low power piezoelectric devices for fluid transportation
Date of Issue2016
School of Materials Science and Engineering
Piezoelectric diaphragm pumps are a special type of micropumps for fluid transportation, which are widely used in various fields. Piezoelectric diaphragm pumps have advantage of lower consumption, simple structure, good reliability, precise control, and small size. There have been many studies focusing on the piezoelectric diaphragm pumps, but most of them are on the pump themselves. In this thesis, we studied both pump and fluid transportation as a whole system. The aim of the thesis is to investigate the working behavior of pump system, in order to improve its performance by modifying the elements that have influences to the system. A piezoelectric diaphragm pump system is first investigated. Its working principle and vibration behavior are studied. Experiments are designed to discover the relation between the parameters of pump and tubes and system performance. Boundary conditions, as well as transducers in pump, are found to contribute to performance and vibration properties of the system. According to this observation, buffers are added to the system to modify the boundary conditions. The buffer boundary system consists of pump, in-tube, out-tube and the buffer. A soft-hard peak theory is proposed, which is proved by experiments. In a general case, there exists a soft peak at higher frequency and a hard peak at a lower frequency in the frequency response of the system. The frequency of the hard peak is mainly determined by the total length of in-tube and out-tube, while the frequency of the soft peak is mainly determined by the length of the in-tube. Influence of tubes, transducer, buffer dimensions o the resonant properties of the system are subsequently studied, results of which led to results that are consistent with the soft-hard peak theory. Buffer boundary system is also proved to be effective in vibration suppression. The principle of vibration suppression with the buffer boundary system is proposed and proved. Active and passive approach are studied in the thesis additionally, both of which are proved to be very effective. Constant flow and resonant frequency are achieved in pump system with optimized buffer boundary conditions. The buffer boundary system, instead of the inlet and outlet of pump, comprises interface to the external system. As a result, the output and resonant frequency of the pump system keeps stable even though the connection tubes are of different materials or lengths. Buffers with different dimensions are examined to investigate the influence on output properties. More importantly, the buffers could be used as energy harvesters. Energy harvested from vibration could be collected by the piezoelectric transducers of the harvester. The harvesters are studied both theoretically (by ANSYS simulation) and experimentally. An ANSYS model is built and proved to be reliable to predict the output of the energy harvester. Harvesters with different dimensions are also tested to achieve the optimized dimension for energy harvesting.