多层介质中超声相控阵声场仿真*

由于良好的声束偏转与聚焦特性,超声相控阵已经广泛应用于多层固体介质的缺陷检测。当超声束经过多层介质时,由于反射、透射以及模式转换的存在,多种声束存在于这种结构中,使得声场分析变得复杂。为了提高多层介质检测的准确性,有必要对超声声场的分布规律进行深入地了解。该文结合高斯声束等效点源模型以及射线追踪法,给出了相控阵声源在多层固体介质中激发声场的仿真方法,并且模拟计算了一维线型相控阵在楔块-铝-黄铜-钢四层固体介质中的辐射声场。通过对不同延时法则的计算,实现了声波在这种复杂介质中的偏转与聚焦,进而研究了不同焦点处聚焦声场的分布。结果表明:相控阵方法能使聚焦点处的声场幅值增大,能量集中,提高了检测分辨率;不同聚焦点处声场聚焦效果不同,实际检测时应根据检测区域结构及位置特点,合理放置相控阵换能器。与瑞利积分法的比较表明,该文的仿真方法适用于多层介质相控阵声场的计算。

Simulation of acoustic fields generated by ultrasonic phased array in multilayered medium

With the advantage of beam steering and focusing, ultrasonic phased array has been applied to the inspection of multilayered medium. When the ultrasonic beam is propagating through such medium, due to the reflection, refraction and mode conversion, several different beams exist, which may bring interferences to analysis of acoustic fields. To improve detection efficiency in multilayered medium, it is necessary to have an in-depth knowledge of the characteristics of ultrasonic fields. A systematic method combining Gaussian beam equivalent point source (GBEPS) model and ray tracing technique is given and the acoustic field emitted by ultrasonic phased array in wedge-aluminum-brass-steel four layered medium is calculated using such method. Through the calculation of time delay laws, beam steering and focusing are realized and the focused fields with different focal points are studied. Simulation result shows that, using phased array transducer, the amplitude of acoustic field at focal point can be increased, the energy can be focused, and the detection resolution can be improved. The focus effect is different at each focal point, therefore, the phased array transducer should be placed reasonably according to the structure and position of detection zones during actual inspection. In addition, compared with Rayleigh integral method, the method proposed here is capable of calculating acoustic fields emitted by ultrasonic phased array in multilayered medium.