Flexible Piezoelectric Drop-On-Demand Droplet Generation

[EN] The size of droplets generated by piezoelectric drop-on-demand (DOD) droplet generators can be varied to a certain degree within one order of magnitude. This variation means that the droplet size is not solely determined by the nozzle diameter, and the droplet generation process is not restricted to drops extruded through a nozzle in conventional operation. By varying the electronic driving pulse, different droplet sizes can be obtained. To investigate the interaction of piezoelectric pulse excitation and the finally produced droplets, different approaches are applied. A comparison of a modal analysis of a pure piezo based on mechanical admittance calculations proofs the usability of electrical impedance measurements. This kind of measurements are then compared to finite-element simulations of a coupled piezo system – one as actuator, the other as pressure sensor – to extend the usable methods with the result that the fluid is of minor influence on the modal frequencies. Last, two phase fluid flow simulations with consequent pressure wave evaluations of the fluid show different pressure wave frequency specta than the modal analysis.