Powder transportation by unidirectional ultrasound radiated from a pair of phase-shifted bending vibrators

In the present paper the mechanism of operation is studied for a new type of ultrasonic powder-transportation device proposed by the authors. The device consists of a pair of phase-shifted bending vibrators facing each other across a gap. The upper vibrator is laterally shifted relative to the lower one by a quarter-wavelength of the bending mode and the two vibrators are driven in temporal phases different from each other by 90°. In such a condition, powder is transported in one direction through the gap. It is shown that radiation pressure caused by high-intensity ultrasound radiated from the plates is the propelling power of the transportation. The transportation takes place when the bending vibration is phase-matched to ultrasound in the air and unidirectional ultrasound is radiated along the plates