Nonlinear Ultrasonic Phased Array Imaging based on Amplitude Modulation

Ultrasonic phased array is an advanced ultrasonic detection and imaging technology with powerful applicability, which is widely used in the non-destructive testing and evaluation of material defects in the field of industrial non-destructive testing. However, the requirements for the detection accuracy of damage and defects in complex industrial structures are deeply increasing nowadays. When the crack in the equipment is partially closed or smaller than half wavelength, the crack may be underestimated or missed, which often results in serious consequences. Nonlinear ultrasonic method has attracted considerable attention for its high sensitivity to early material damage and micro defects, and therefore its application in ultrasonic phased arrays has broad potential and value. On the other hand, an amplitude modulation (AM) method is proposed, which is more efficient than studying specific high-order harmonics as nonlinear component. In this work, we utilize nonlinear ultrasonic phased array imaging based on AM method to realize the detection of fatigue cracks. The fatigue cracks were made from compact tensile specimens of 7075 aluminum alloy by fatigue tensile test. The imaging result shows that compared with conventional ultrasonic phased array, the nonlinear ultrasonic phased array imaging based on the AM method can not only detect and evaluate fatigue cracks in the specimen, but also has the sensitivity and selectivity to the nonlinear response. This work provides theoretical guidance for nonlinear ultrasonic phased array imaging detection in industrial structures.