Ultrasonic imaging through reverberation media

Thin layered media like thermal barrier and corrosion resistant coating layers, are important components to protect and strengthen the base materials. Nevertheless, the non-destructive testing (NDT) of base materials under thin layer media are still strongly demanded. However, surface and reverberation waves propagating in the top thin layer deteriorate the ultrasonic imaging results of base materials. Particularly, they overwhelm the reflection waves of defects, making ultrasonic NDT of base materials a challenge. These waves are determined by the structural of testing objects and called structural noises. Here, a pre-process of ultrasonic total focusing method is proposed to remove the structural noises. The pre-process utilizes the different similarity characteristics of structural noises and defect signals in diagonal matrices to suppress the noises by principal component analysis. The experimental results show that it can effectively improve the SNR about 5-8 dB and reduce array performance indicators about 30-40%.