Two-dimensional noncontact transportation of small objects in air using flexural vibration of a plate

Noncontact transportation techniques are required in the production process of medicine such as tablets and capsules to solve the problem that the surface of these small objects is polluted and cracked. Our group has been investigating the noncontact transportation technique of small objects in air over long distances using ultrasound. Ultrasound manipulation techniques enable precise positioning for small objects without contact by using high-intensity acoustic standing-wave fields. This report investigates an ultrasound transport of small objects in two dimensions. The configuration of an aluminum vibrating plate and four transducers with a step horn were determined by finite element analysis. A reflector was installed parallel to the vibrator with a distance of approximately 8 mm to generate an acoustic standing wave in air between two plates. The lattice flexural vibration mode with the wavelength of 29 mm was excited on the vibrating plate at 24.8 kHz. By controlling the phase differences of transducers, the nodal lines of the flexural vibration of the plate and the acoustic standing wave in air could be shifted to x and y directions, which enabled the manipulation of the small particles in two-dimensional plane. When the phase difference was changed from 0 to 720°, the moving distance of a polystyrene particle was approximately 28.0 mm, which corresponds with the wavelength of flexural vibration on the vibrating plate.