A novel method for ultrasonic non-destructive testing: Using system identification approach

One of the challenges in non-destructive testing using the ultrasound pulse-echo technique is to identify defects whose sizes are less than or equal the resolution caused by the ultrasound pulse. Existing methods require a reference specimen of the same defective material, which may not be available in some cases. In this paper a new method for detecting and identifying such defects is presented. In the proposed approach, each layer of the test specimen is modelled as a LTI filter, and therefore, each defect is characterized by its transfer function. A combination of time gating and system identification is used which do not require a reference specimen. To demonstrate the performance of the proposed approach, it has been simulated in various circumstances. Results show that the proposed method can detect such defects, does not depend on the test set-up parameters (including the ultrasound transducer), does not require a reference specimen, and is capable of detecting and identifying several defects situated in different depth on top of each other.