Noncontact ultrasonic transportation of droplet using an acoustic waveguide

Abstract

In the next generation of the pharmaceutical industry, noncontact transportation technology of liquid is highly required for higher purity production process. In this paper, we focused on transporting liquid without contact using ultrasonic levitation. An acoustic waveguide was developed to excite a highly confined travelling wave using a plate vibrator and a semicylindrical reflector. We used an aluminum plate as a vibrator and an acrylic semi-cylindrical tube as a reflector to excite travelling waves of bending vibration at 37 kHz on the vibration plate. In the waveguide between the vibration plate and the reflector, a droplet could be trapped at the position of horizontal nodal line, and experienced the horizontal thrust force due to the travelling wave. Then, the droplet would be transported without contact. We designed the waveguide using a finite element analysis to find an appropriate propagating mode for trapping droplet. We also confirmed that the vibration distributions on the plate and the sound pressure field inside the waveguide were travelling waves by using a laser Doppler vibrometer and a probe microphone. Noncontact transportation of liquid with an ethanol droplet has been demonstrated. The movement was observed with a highspeed video camera. A droplet of around 1.5 mm in diameter was successfully transported without contact between two horizontal antinodal lines of the sound pressure distribution. The transportation distance and the maximum velocity have reached 65 mm and 2.3 m/s, respectively.