A beamforming strategy to improve the ultrasonic phased array inspection below concave surfaces

Parts with concave surfaces are especially difficult to inspect using ultrasound. This interface distorts the ultrasonic beam leading to image artefacts and poor ultrasound penetration. In this context, the present work demonstrates how to enhance the transmission of ultrasonic waves through concave surfaces.The proposed method consists of a beamforming strategy that compensates the refraction by using subapertures to focus on points on the specimen's surface. An aluminum specimen with a sinusoidal concave top surface was analyzed using a 64-element phased array in an immersion tank. On average, the beam computation showed a gain of 12 dB per transmission when the strategy proposed was compared to the Full Matrix Capture (FMC). Also, the Total Focusing Method (TFM) image quality of the proposed emission strategy was verified. The imaging of a side drilled hole (SDH) of 1 mm in diameter presented an improvement of approximately 11 dB in signal-to-noise ratio. Finally, fewer transmission events than the FMC were necessary to achieve a better TFM quality. (author)