20-kHz high-intensity linear-focus aerial ultrasonic sound source using a stripe-mode transverse vibration plate with thin reflectors

Abstract

This paper describes theoretical and experimental studies of a high-intensity aerial ultrasonic sound source that uses a new method to linearly focus large-capacity aerial ultrasonic sound energy (approximately 20 kHz) radiated from a stripe-mode transverse vibration plate with a rectangular shape. The sound waves are focused in the following sequence. The sound waves radiated from adjacent vibration sections in anti-phase to each other are confined by separators placed on nodal lines. These sound waves are reflected by parabolic reflectors placed between two separators and also reflected at the vibration plate surface. The reflected sound waves pass through a narrow slot located near the vertex of each parabolic reflector and are linearly focused on a region of almost the same length on the vibration plate outside the reflectors. On the other side of the vibration plate, a flat reflector of the same size as the reflection plate is located in the position where the sound waves radiated from this side are minimized. The previously reported linear-focus aerial sound source had parabolic reflectors installed for both sides of the vibration plate. Therefore, large dimensions for the reflectors were inevitable. On the other hand, the height of each reflector has been reduced successfully to as small as one fifth of the previous height by using only the radiation from one side of the stripe-mode transverse vibration plate and utilizing the reflection of sound waves at the vibration plate. This improvement has led to the achievement of an ultrasonic sound source that can produce a high-intensity linear sound field with a sound pressure of 7000 Pa (sound pressure level of about 168 dB) and a linear focal area of almost the same length as the vibration plate. © 1998 Scripta Technica, Electron Comm Jpn Pt 3, 81(12): 1–10, 1998