Ultrasonic correlation analysis in quefrency domain for structural imaging

An ultrasonic quefrency (Fourier transformation of frequency) analysis was utilized to image the internal structure of materials. The imaging method comprises four processes: (l) calculation of spectrum, (2) division by the power spectrum of a pulse or other component, (3) Fourier transformation into the quefrency domain, and (4) analysis and imaging in the quefrency domain. In this study, we applied this method to image the defects in carbon-fiber-reinforced plastics (CFRP). Compared with the conventional ultrasonic images, this method was proven to provide greatly improved images, suggesting that this method is a powerful tool for nondestructive inspection of composite materials including CFRP.