We proposed high-speed visualization of defects by guided waves using an airborne ultrasound phased array (AUPA). The AUPA can move the focal point of the acoustic wave at high-speed by electronic control. By applying this sound source to the elastic wave source scanning technique, the measurement time can be significantly reduced. This report demonstrated the proposed method to visualize thin metal plate defects. The results confirmed that the defect can be visualized by the amplitude peak distribution of the propagating guided waves. In addition, it was confirmed that applying background subtraction processing to the imaging results allows the defects to be more clearly visualized.

A scanning airborne ultrasound source technique was developed to overcome the riskiness of laser ultrasound, which uses an ultrasound source that has a fixed sound wave focusing point and thus requires mechanical motion for sound source scanning. Therefore, the measurement time becomes longer. To solve this problem, we have proposed a method of simultaneously exciting many measurement points in the target using focused ultrasound sources of different frequencies. In this paper, we investigated the visualization of defects in a thin metal plate by the scanning elastic wave source technique using an airborne ultrasound source driven at two frequencies. When the testing was performed using two frequencies, either frequency visualized the defects.

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Scanning airborne ultrasound source technique has been developed as a safe and simple non-contact non-destructive inspection method. This method enables non-contact excitation of guided waves by using high-intensity airborne ultrasonic waves. However, the airborne ultrasound source that can generate high intensity airborne ultrasounds use resonance drive, so the sound waves are emitted for a long time. As a result, the inspection results become complicated, and the inspection accuracy decreases. To solve this problem, we proposed a pulse compression using chirp signals of guided waves generated by airborne ultrasound. In this paper, we investigated the pulse compression of guided waves generated in mortar samples using an airborne ultrasound source driven by a chirp signal. As a result, it was confirmed that the visualization accuracy of defects was improved by pulse compression.