Three types of one-sided actuating piezoelectric micropumps are studied in this paper. In the first type, one-sided actuating micropump with two check valves can enhance the flow rate and prevent the back flow in suction mode to keep the flow in one direction. Furthermore, the frequency modulator is applied in the micropump to adjust and promote the maximum flow rate higher than 5.0？mL/s. In the second type, valveless micropump with secondary chamber shows that the secondary chamber plays a key role in the application of the valveless micropump. It not only keeps the flow in one direction but also makes the flow rate of the pump reach 0.989？mL/s. In addition, when a nozzle/diffuser element is used in valveless micropump, the flow rate can be further improved to 1.183？mL/s at a frequency of 150？Hz. In the third type, piezoelectric actuating pump is regarded as an air pump in the application of a microfuel cell system, which can increase more air inlet to improve the fuel/air reaction and further increase the performance of fuel cell. 1. Introduction In recent years, micropump plays a significant role in many fields, specifically in chemical, medical, and thermal managements. Since there are distinct requirements in each field, several types of micropumps have been designed to meet those requirements. Micropumps, which have the advantage of small size and configurable dimension, are gradually becoming one of the solutions for electronic heat dissipation. There are several types of actuation approaches in developing, such as electromagnetic [1, 2], piezoelectric [3, 4], shape memory alloy , electrostatic , and thermopneumatic  devices. Most of actuations are complicated in structure and have great energy consumption. However, piezoelectric actuation has the notable advantages that are a relatively simple component and energy consumption. Micropumps can be categorized into two major types: displacement pumps [8–10] and dynamic pumps [11, 12]. Displacement pumps use the moving mechanical part to change the volume of the chamber, such as the one-sided actuating diaphragm pumps. Dynamic pumps usually utilize the interactions of the fluid with an electric or magnetic field, which continuously applies force on working fluid. Electrohydrodynamic  and magnetohydrodynamic  are the examples of dynamic pump. Considering flow direction elements, micropumps can be classified as with or without valves. The first prototype of a valveless pump consisting of a circular cylindrical volume where the top had a thin brass diaphragm to which a piezoelectric
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