# Advances in Piezoelectric Jet and Atomization Devices
## 1 Introduction  
Atomization is defined as a process of transforming continuous liquid or solid-liquid mixtures into discrete droplets or solid particles by various approaches. The research on atomization can be traced back to [PERSON] in the 16 th century [1]. The introduction of atomization can dramatically increase the specific surface area of the fluid, and significantly improve the efficiency of fluid utilization. It is widely used in the fields of air humidification [2], agricultural irrigation [3], spray combustion [4], and many other industries. Since the piezoelectric effect was discovered in 1880, many scholars began to devote investigating to the piezoelectric driving. It was found that the piezoelectric actuator belongs to a kind of inverse piezoelectric effect based on piezoelectric ceramic material, which can produce rotation or linear motion by controlling its mechanical deformation. [PERSON] et al. [5, 6] summarized the construction, working principle, structural material, and energy recovery of piezoelectric actuators, which laid the foundation for the research on piezoelectric actuators. Due to the advantages of piezoelectric actuators, their research results have been widely applied in ultrasonic motor [7, 8, 9], piezoelectric pump [10, 11, 12], and piezoelectric atomization [13, 14, 15].  
The procedure of piezoelectric jet and atomization is the most important branch of the piezoelectric drive during such processing, where the liquid is dispersed into tiny droplets by piezoelectric drive technology, and its corresponding devices are the piezoelectric jetand atomization devices. The piezoelectric jet and atomization devices have numerous advantages such as being easy to carry, and having a high energy utilization rate, and low manufacturing cost, which have drawn public attention in various fields. In recent decades, such piezoelectric jet and atomization devices have been extensively promoted and applied in inhalation drug delivery [16], metal printing [17], biomedical [18], and other aspects. The piezoelectric micro jet device and the piezoelectric atomization device have been proposed for many years, but due to the limitations of the technical level, there is no literature to distinguish such concepts of jet and atomization, especially for what collectively refers to the two concepts of jet and atomization as the process of dispersing liquid into tiny droplets. In order to better understand and distinguish clearly, we give two different definitions for jet and atomization, respectively. When the liquid is occupied with an absolute higher proportion of ejected material than the gas, it is regard as jet; otherwise, it will be defined as atomization.  
In this paper, the work on the evolution and progress trend of the constructions of piezoelectric micro jet and atomization devices in the past three decades are reviewed and summarized. The development history of the structure of the piezoelectric micro jet and atomization device is also reviewed. The functions and applications of piezoelectric micro jet and atomization devices are classified and thoroughly analyzed, and their future development is prospected.