Single Droplet Jetting Mechanism Based on Parallel Travelling Rayleigh Surface Acoustic Waves

Single droplet jetting is investigated in this paper. Jetting was induced by parallel travelling surface acoustic wave (PTRSAW) devices with straight inter-digital transducers (SIDTs), which were fabricated on a double-sided polished, 0.5 mm-thick, 128° Y-X single-crystal LiNbO3 substrate. The PTRSAW device was mainly composed of two sets of symmetrically distributed SIDTs connected in parallel, which induced two columns of 29.1 MHz PTRSAWs simultaneously. A single droplet jetting phenomenon with $0.8\ \mu\mathrm{L}$ of deionised water was captured by a microscope with a high-speed camera. The experimental results show that this method has the advantages of strong driving ability, simple device structure, instant reaction and high ejection efficiency. A complete mathematical model of droplet jetting based on RSAW technology is established and realised by COMSOL finite element simulation software with a multi-physics interface of laminar two-phase flow and level set. The droplet jetting mechanism was analysed from the liquid volume fraction distribution, pressure and velocity evolution during the jetting process. The characteristics of the jetting droplets is strongly dependent on the SAW streaming force, which is well supported the experimental results.