用于空气旋涡流场激光声光偏转的超声换能器研究进展

Development of Air Ultrasonic Transducer for Measuring Laser Acousto-Optic Deflection Effect in Vortex Field

描述了新近发展的带有振动片的变幅杆夹心式超声换能器的结构、使用中的各种匹配，以及成功地应用于空气中激光声光偏特效应的研究。声光偏转信号被一个位移灵敏接收器接收，可作为时间的标志信息而被应用于复杂空气流场参数的测量。

China's experimental aerodynamics research, particularlly vortex field nreasurement,now needs nondestructlve and noncontactive measuring technique. Laser-ultrasonic technique is particularly effecive in such measurements. We present in this paper our dewlopment of high-power high-frequency air ultrasonic transducer and its use in measuring airacoustiC denection effect. clear observation of acousto-optic deflection requires hash power. From our previous experlnce in measuring water acousto-optic deflection effectllJ, weestimate a power of 300W is needed for observing air acoustic denection effect' After mucheffort, we belle the power to 100W. We reduce the power required from an estimated 300Wto below 100W by adopting two technlcat measures: (1) through using custom-made acoustic coupler, we succeed in reducing diverging angle within a range of ±10°; (2) we employ acuStom - made displacement sensitivity detector to increase sensitvity of signal detectiongreatly. We come to realize that the fOllowing three points should be constantly borne inmind in order to reap full benefits of our experimental capability: (1) the distance betweenradiation surface of the transducer and laser beam should be within the range of 30mm 1300mm. The smaller this distance, the stronger is the optical denection slgnall (Fig.5);but when it is less then 300mm, signals are too sensitive to change in the distance, causingobserved air acouto-optic deflection to be not so satisfsctry; (2) the laSer beam and the center of ultrasonic radiation should be so carefully adjusted as to make their centers coincide;(3) the frequency of air ultrasonic radiation should be higher than 60kHz so as to eboinatethe serious unfavorable effect of inherent noise of now field.