# Design and Experimental Verification of a PZT Pump with Streamlined Flow Tubes
## 1 Introduction  
As a functional material, piezoelectric ceramics play an irreplaceable role in modern intelligent industry [1; 2; 3]. Piezolectric ceramics have been widely used in modern intelligent devices, such as pressure sensors [4], vibration energy collecting devices [5], intelligent wearable devices with human-computer interaction [6], and so on. At the same time, with the advent of MEMS (Micro-Electro-Mechanical System), the inverse piezoelectric driving technology that converts electrical energy into mechanical energy has become a research hotspot in research concerning modern micromachines [7; 8]. The actuator has not only decreased in size but also enhances conversion efficiency in ultrasonic motors [9], ultrasonic transducers [10], piezoelectric pumps [11], and so on. Among them, the piezoelectric pump is further divided into valve piezoelectric pumps and valveless piezoelectric pumps. As an emerging piezoelectric-driving-fluid technology, the valveless piezoelectric (PZT) pump has shown ever-increasing application potential in aerospace, biomedical, microfluidics and sensor fields [12; 13; 14]. It has many advantages when compared with traditional motor pumps, like its simple structure, compact size, lack of electromagnetic interference and easy integration,The absence of the movable valve can decrease the probability of crushing damage of the transported substance. Thus, the valveless PZT pump has been applied to clinical medical drug delivery and biological laboratories [15; 16; 17]. At the same time, the delivery characteristics of valveless PZT pumps are mainly determined by their flow tube structure. Different flow tube structures would change the flow field tremendously, and therefore would be used in different applications. The innovation of flow tube structure has become a new direction of valveless piezoelectric pump research [18; 19]. In 1993, [PERSON] et al. historically proposed the first cone-shaped flow tubes valveless PZT pump for fluid delivery. Since then many scholars in the field have begun to delve into further research on valveless PZT pumps with cone-shaped flow tubes [20; 21]. In 2011, [PERSON]. et al. designed a valveless PZT pump with 3D cone-shaped flow tubes to study the influence of excitation voltage and geometric parameters on the performance of piezoelectric ceramic [22]. In 2015, [PERSON] et al. systematically studied cone-shaped flow tubes with different angles, to optimize the valveless PZT pump [23; 24]. In addition to the traditional cone-shaped flow tube valveless PZT pump, other types of valveless PZT pump have also been widely studied. In 1995, [PERSON] et al. used unique structure called the \"Tesla valve\", which has been proved to be more suitable for micro particles delivery, as the fluid channel of a PZT pump [25; 26]. In 2007, [PERSON] et al. found that the Y-shaped flow tube exhibited obvious flow resistance difference during the pump chamber compression and expansion strokes. Later, they proposed the Y-shaped flow tube valveless PZT pump for functional polymer delivery which expand the applications of the valveless PZT pump in the medical and health care [27; 28]. In 2018, [PERSON] et al. developed a valveless PZT micropump with a crossed cone-shaped flow tube, to greatly improve micro-medical equipment for human health [29]. In 2019, [PERSON] et al. designed a valveless PZT pump with bluff-body in the pump chamber. The pump can reduce backflow and increase output flow rate, which has potential applications in the drug delivery field [30]. The application of valveless PZT pumps, in the field of fluid delivery, has been studied by many scholars over more than twenty years. However, the singularity of the flow trend, which would cause a stronger internal vortex and less flow stability, has not been preferably modified. In 2009, [PERSON] et al. designed a valveless PZT micropump with an acoustically featured channel structure in the pump chamber.