Abstract
This paper attempts to describe the new sound sources for airborne ultrasonics with high sensitivity. They are improved sound sources of high-intensity ultrasonics which were developed previously by the authors. The structures of these sound sources consist of ultrasonic vibrators, a metalic horn, a vibration plate having flexural modes and four reflection plates. It is desired to vibrate the vibration plate of these sound sources in flexural modes as shown in Fig. 2, so called "stripes mode", in order to have efficient radiation for ultrasonics. Production of such vibration plate, however, require much experiences. But, they can be produced rather easily taking into account of the Eqs. (4) and (5), i. e. by combining the equation for bending vibration of the rectangular bars and some experimental means. The directivity of sound radiated from these plates have the beam form having four directions shown in Fig. 4 (a). These four beams can be synthesized into a single beam by the successive introduction of four reflection plates, which is shown in Fig. 7 (e). The new sound sources for airborne ultrasonics have been constructed by this way, which are capable of operating at the frequency of 19, 28, 50, 70 and 90kHz shown in Fig. 8. Fig. 9 shows the polar patterns of the sound pressure produced from the new sound sources. These patterns can be kept as far as the distance of about 10m. Fig. 11 shows the relation between the distance from the sound sources and the sound pressure level. The sound pressure level decreases monotonously as the distance increases. Table 3 shows the sound pressure produced by these sound sources compared with that of some old ones. As seen from the table, a remarkably high sensitivity was gained by the new sound sources. And, Fig. 12 shows the different waveforms of the ultrasonic pulses produced by prosound sources. It is noted that the new sound sources authors devised could be used these ducing ultrasonic pulses in general.
