This study aims to design and develop a laser ultrasonic system and 1-3 composite line sensor that can be applied to curved structures to detect defects in structures using laser ultrasonics. The 1-3 composite line sensor applicable to curved structures was fabricated from PZTNMML ceramic disc using the dice-and-fill method. This sensor can be attached in the form of a line, and it is connected in series and applied to a large area structure. Besides, applying a deep learning technique overcomes the sensitivity of the sensor and detects defects that were indistinguishable from flaws.
The laser ultrasonic system consists of an excitation part, a receiver part, and a control part, and the excitation part has a laser generator that generates ultrasonic waves in the specimen, a beam expander that can adjust the size of the beam, and a galvanometer scanner that irradiates the pulsed laser to the desired point. The receiver part includes a sensor for receiving ultrasonic waves, a signal conditioner for impedance matching, a filter for increasing SNR by reducing noise, and a digitizer for acquiring a signal. Lastly, the control unit consists of a GUI that can be set in detail while operating the system and a control board that controls the galvanometer scanner and laser generator.
Defect detection using laser ultrasonics is a method of detecting a defect by irradiating a laser beam onto a structure and using a non-contact method by the generated ultrasonics. The pulsed laser generated by the laser generator is irradiated to the structure by a galvanometer scanner, and ultrasonic waves are generated in the structure due to the thermoelastic effect. At this time, the generated ultrasonic wave was collected by a sensor, and a signal was acquired from a data acquisition device through a signal conditioner and a filter, and it was converted into data and visualized.