Abstract
The main challenge for guided wave inspection is exact defect characterization and sizing. EMAT generated Lamb waves usually have low signal-to-noise ratio which reduces the defect detection, characterization and sizing capabilities. That's why in most cases the method is used only as a screening tool. The Synthetic Aperture Focusing Technique is a process that increases the signal-to-noise ratio by numerically focusing the acoustic fields. In this paper the application of SAFT is tested over EMAT generated Lamb waves. The improvement of lateral resolution and signal-to-noise ratio is evaluated. Results are presented as a comparison between standard B-scan and SAFT processed data.
Highlights
Application of ultrasonic guided waves in non-destructive testing is growing rapidly for a variety of reasons
The results show the ability of Synthetic Aperture Focusing Technique (SAFT) to increase the inspection range and respectively the sensitivity of meander coil EMAT equipment
The proposed algorithm for post-processing of ultrasonic signals received from EMAT generated Lamb waves is based on SAFT
Summary
Application of ultrasonic guided waves in non-destructive testing is growing rapidly for a variety of reasons. The most common and simplest configurations for generation of guided waves in plates and pipes are the so-called meander coil EMAT. The equipment usually includes a hand-held scanner which provides axial and circumferential scanning for inspection of pipes and plates using guided waves. This allows real time images (B-scans) to be generated [3]. The SAFT analysis is an imaging process that increases the signal-to-noise ratio and improves lateral resolution by numerically focusing the acoustic fields This imaging technique has been applied to imaging defects in plates using guided waves generated using piezoelectric transducers [5,6]. In this paper an offline post-processing SAFT technique is described which uses the complete B-scan data recorded from hand-held scanning of steel plates using EMAT generated Lamb waves
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