a novel ultrasonic non-destructive testing method using system identification techniques

one of the challenges in non-destructive testing schemes using the ultrasound pulse-echo technique is to identify those defects whose sizes are less than or equal to the detection resolution that is dependent on the width of the ultrasound pulse. existing methods also require a reference specimen of the same defective material, which may not be available in some cases. we present a new method for detecting and identifying such defects. in the proposed approach, each layer of the test specimen is modeled as a linear time invariant (lti) filter, and therefore, each defect is characterized by its corresponding impulse response. we use a combination of time gating and system identification techniques to detect and identify the defects, and as such, do not require a reference specimen. to demonstrate the performance of the proposed approach, we tested metallic blocks in which specific defects were impregnated. results show that the proposed method can detect such defects, does not depend on the test set-up (including the ultrasound transducer), does not require a reference specimen, and is capable of detecting several defects situated in different depth on top of each other