Detection of Micro-scaled Flaws in the Steel Sheet using Line-focused High-Frequency Ultrasound Transducer

We implemented ultrasound non-destructive testing to detect micro-scaled flaws in the steel sheet using a cylindrically focused ultrasound transducer to save the scanning time. A few ten to hundred micrometer-sized flaws marked by laser on the steel sheets were successfully detected by 35-MHz ultrasound images and subsequent analysis based on envelope-processing and logarithmic compression. Also, our scanning system showed that the proposed transducer reduced testing time compared to a spherical transducer. For validation of detection, the positions of detected flaws in ultrasound was compared with that of optical microscope. Then, the ultrasound profiles at the position of the flaws were obtained to identify the properties of the signals reflected by the flaws. As a result, the scanning time was dramatically decreased by adopting a cylindrically focused transducer, while detection of the flaws was validated by comparing with the positions of real flaws. This work demonstrated that the cylindrically focused ultrasound transducer is a viable solution detecting micro-scaled flaws in the steel plate while reducing scanning time.