Droplet ejector using surface acoustic waves

Abstract

The present study aims to investigate droplet ejection using Surface Acoustic Waves (SAW). The interests in droplet ejection microsystems have dramatically grown in recent years due to inkjet printhead demand (Drop-On-Demand). Among several actuating methods (thermal, piezoelectric, etc.), the thermally driven inkjet printhead is the most successful (low cost, easy fabrication and high printing quality). Almost all of the current ink jet printers eject ink droplets through nozzles, with a direction of ejection always perpendicular to the nozzle surface. Surface acoustic waves devices are widely used for frequency filtering and are mainly devoted to cellular phones and telecommunication handset. Nowadays, recently published works have demonstrated the interest of SAW for guiding and positioning small liquid droplet atop a flat surface. This paper describes a new way to eject droplets (water, ink, etc...) using SAW. The surface acoustic waves devices used to eject droplets are carried out on lithium niobate substrates (LiNbO3 cut Y+128°, X propagation). The Rayleigh waves are excited using classical inter-digital transducers (IDT). The design of IDT has been simulated with finite element analysis and boundary element methods. The computations on the design of the IDT have been compared with measurements. The vibration amplitude of the wave necessary to droplet ejection is measured using a heterodyne laser probe. The range of the droplets volume ejected is between 100nl and 1μl. The influence of the supply voltage on the ejection is described.