Abstract
This paper describes augmentation of capacity for a sound source (20kHz) with a rectangular vibration plate in the stripes mode for airborne ultrasonics by using reflection plates. When two reflection plates are placed parallel to both sides of a vibration plate which radiates plane waves in the air, the radiation resistance on the vibration plate is cyclically changed by varying a distance between the vibration plate and two reflection plates. Compared with the free field, the maximum value of the radiation resistance is large and the minimum value is small. In a case where two more reflection plates are inseted perpendicular to the vibration plate at a suitable distance from the center of the vibration plate, the maximum value of the radiation resistance is sharply increased compared with the free field. Making use of this relation, electric power supplied to the ltrasonic source at a constant vibration amplitude is also increased correspondingly the change in radiation resistance, so that the acoustic output power is increased about four or six times more than that in the case in free field. Moreover, using this ultrasonic source, a high intensity ultrasonic field (164 dB) is easily produced in a rectangular vessel.
