<p>Through the last decades, researchers have demonstrated that immersion phased array ultrasonic testing can identify defects under curved surfaces. However, these curved surfaces may cause imaging errors resulting in poor performances, thus compromising the reliability of the inspection. Hence, further developments are needed to allow broader use of ultrasonic phased array testing in industries that manufacture parts with complex shapes e.g., 3D printed metals, forgings, or composites. Concave surfaces are especially difficult to inspect using ultrasound. This type of interface distorts the ultrasonic beam in such a way that can lead to image artefacts and poor ultrasound penetration. In this context, the present work investigates the possibilities to enhance the transmission of ultrasonic waves through concave surfaces. A beamforming strategy is proposed to improve the transmission of the ultrasound. The idea is to use sub-apertures to focus on certain surface points, making sure the refracted beam covers the region of interest. An aluminum specimen with a sinusoidal concave top surface with an amplitude of 15 λ<sub>Al </sub>was used for the immersion inspection analysis. CIVA simulations were used to compute the beam pattern generated inside the part. As a basis for comparison, the beam of each single element transmission, as in a full matrix capture (FMC) scheme, was analyzed for a 64 element phased array centered at 5 MHz. Then, to verify the proposed method, the analysis of the beam generated by each sub-aperture of 8 elements, focusing on a specific surface point, was done. A ray-based approach was used to select the focal points on the surface that generated the desired coverage. The TFM quality of each emission strategy was verified by imaging side-drilled holes (SDH) of 1 mm in diameter. The experimental setup comprised a Verasonics Vantage 64 LE array controller and a 5L64I Olympus phased array probe. Results show that the ultrasound transmission can be greatly improved. The beam computations showed that a larger region of the part was insonified at each transmission when using the beamforming strategy. Not only the coverage was increased, but an average gain of 7 dB per transmission was also observed by using the strategy proposed, when compared to FMC. This improvement was translated into the TFM images. For example, the experimental TFM image of an SDH at a depth of 40 mm showed an improvement of approximately 10 dB in signal-to-noise ratio. Therefore, it was demonstrated that the ultrasound transmission must be adapted to the surface profile to yield a better TFM quality. It can also be noted that the proposed approach achieved a superior image quality with fewer transmissions, 55 versus the 64 required for the FMC.&nbsp;</p>

Improved Ultrasonic Phased Array Transmission Through Concave Surfaces

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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