Optimization of acoustic field for the levitation stability of droplet

For the better contactless liquid manipulation with acoustic fields, it is vital to improve the levitation stability of droplet in midair. We aim to understand the physical mechanism of the interfacial deformation and translational motion of a levitated droplet by optimizing the applied acoustic field. For this purpose, the optimization of the sound field around the levitated droplet was experimentally and numerically studied. In the present study, a water droplet was levitated by the single-axis levitator. In the numerical simulation, the sound pressure distributions with varying the reflector geometry were analyzed. With the particle in the acoustic fields, it was suggested that the reflector with a radial curvature of 27 mm (R1.5λ) and a width of 33 mm (twice of the horn's width) can be the optimal condition for the droplet levitation stability. Our numerical findings hopefully provide deeper physical insights into the levitation stability of droplets in acoustic fields for potential lab-in-a-drop applications, such as a microreactor.