Non Contact Pick-Up of Drop of Liquid from Micro-Well with Megahertz Ultrasound
In recent years, considerable attention has been paid to the noncontact transport of small objects and droplets as an important technology in pharmacy industries, and new material science/engineering. Our aim in this report is to develop a noncontact pipette, and we focused on the method to pick-up a single droplet from micro-well plate without contact. A focused immersion transducer is placed below a micro-well plate. By emitting burst waves at 1.5 MHz, a droplet is ejected from the well and caught by the pressure nodal plane in the standing wave field. First, by observing the deformation of the ejected droplet and the surface of liquid in the micro-well plate with a high-speed video camera, we discussed the principle of droplet pick-up. Next, in order to pick-up any type liquid, we investigated the effect of surface tension and viscosity on the noncontact ejection of droplet for water, ethanol, and silicone oil. In this experiment, we found a linear relationship between the ejected droplet volume and the surface tension. In addition, we discuss the ratio of Ohnesorge number to Reynolds number in association with the stability of drop-on-demand inkjet printing operations, and determine the condition for droplet jetting.