Application of SAGE algorithm to estimate thin layer material´s thickness in ultrasonic NDE

Accurate thickness measurement of thin layer material is usually difficult in ultrasonic nondestructive evaluation (NDE), because the reflected ultrasonic echoes often overlapped which makes it difficult to separate these echoes and get the arrival times accurately. This paper used improved space alternating generalized expectation maximization (SAGE) algorithm to separate the reflected echoes and estimate the echoes´ parameters for the purpose of acquiring the accurate arrival time of the echoes. With the accurate arrival time estimated, the thin layer material´s thickness can be evaluated. Two experiments were carried out on a thin steel sheet with 20 MHz and 5MHz transducers using the improved SAGE algorithm, and the results validate the method´s accuracy.