In a piezoelectric drop generator used for generating a single droplet which is 0.5 mm in diameter, there is a piezo-actuated brass diaphragm to generate droplets (for example here or here). What is the main factor that pushes the water inside the generator in order to cause a droplet to be ejected from nozzle? (whether the main factor is diaphragm bending OR it is acoustic wave that piezo element may produce?)
Note: I use a piezo element which has a brass plate with 27 mm diameter and 0.3 mm thickness. However, when I installed in its place (Fig. 1) and fill the beneath reservoir with water (without any air bubble), I am not sure whether the brass diaphragm should bend rapidly downward to push a droplet out of the nozzle OR it should produce acoustic waves that push the water to eject a droplet. Which one is actually supposed to happen?)
Thanks
Figure 1. Schematic of a piezoelectric drop generator