光外差超声无损探伤系统的实验设计和信号处理

Nondestructive Evaluation System Employing Optical Heterodyne and Ultrasonic Techniques

对光外差超声无损探伤实验系统的结构、原理进行了说明。分析了系统参数设计中信号光与本振光的光程差、探测器的相对位置和聚焦透镜的焦距这三个要素对外差效率的重要影响, 根据理论计算所设计的光外差超声无损探伤系统,外差效率可达0．965。该系统用于由脉冲激励超声工件的内部探伤,观察到距离1555 mm处钢管微小裂缝的超声反射信号。对零差信号利用三角函数拟合和最小二乘法进行数学处理,可测得裂缝处相对探测点的距离,相对误差为 0．19％,可以达到对金属管道远程无损探伤的要求。

The configuration and the principle of a nondestructive evaluation system employing optical heterodyne technique and ultrasonic technique are explained. The key factors including optical path difference, relative position of detector and fo cal length, which have effects all heterodyne effeciency are analyzed. The heterodyne efficiency of the nondestructive evaluation system designed according to the theoretical calculations can be up to 0. 965. The system is employed for interiorly non destructive evaluation of work pieces in which ultrasonic is motivated by pulse. A ultrasonic signal reflected by a mini split within a steel pipe at a distance of 1555mm is received with this heterodyne system. The distance between the starting point of ultrasonic signal and reflected ultrasonic signal by a mini gap is obtained in the methods of trigonometric function fitting and least squares technique. The percentage error of the result is 0. 19% so that the nondestructive evaluation of long dislance metal conduit pipe can be realized.