This paper investigates a two-dimensional ultrasonic manipulation technique for small objects in air. The ultrasonic levitation system consists of a rectangular vibrating plate with four ultrasonic transducers and a reflector. The configuration of the vibrator, the resonant frequency, and the positions of the four transducers with step horns were determined from finite element analysis such that an intense acoustic standing-wave field could be generated between the plates. A lattice flexural vibration mode with a wavelength of 28.3 mm was excited on the prototype plate at 24.6 kHz. Small objects could get trapped in air along the horizontal nodal plane of the standing wave. By controlling the driving phase difference between the transducers, trapped objects could be transported without contact in a two-dimensional plane. When the phase difference was changed from 0° to 720°, the distance moved by a small particle in the orthogonal direction was approximately 29 mm, which corresponds with the wavelength of the flexural vibration on the vibrating plate.

A junction for noncontact ultrasonic transportation paths in which small objects can be manipulated is proposed. The junction consists of a vibrating disc and a reflector. The reflector is installed parallel to the vibrator to generate an acoustic standing wave in the cavity between the vibrating disc and the reflector. The resonance modes of the acoustic field in the disc cavity between the two plates are calculated theoretically. The distributions of the sound pressure amplitude and the acoustic radiation force in air are calculated using finite element analysis. The flexural vibration modes with one nodal circle and four nodal lines at 45.4 kHz and two nodal circles and three nodal lines at 58.1 kHz are used to trap and eject small objects, respectively. The transportation velocity and the thrust force in the radial direction for a polystyrene particle with a diameter of 2 mm and a weight of 0.3 mg are 812 mm/s and 24 μN, respectively. The ejection direction of the trapped object can be controlled by the driving condition of the vibrating disc.

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