Exploiting Non-Linear Chirp and Sparse Deconvolution to Enhance the performance of Pulse-Compression Ultrasonic NDT

A pulse-compression procedure based on Non-Linear Chirp for Ultrasonic Non Destructive Testing is presented. Non-Linear Chirp signals can be tailored to reproduce any desired continuous spectrum. Here, such capability is exploited to take into account the features of the specific hardware set-up in use, and particularly to adapt the excitation signal to the probes. An application of the proposed procedure to Air-Coupled Ultrasound Imaging is also presented. In order to enhance the imaging resolution, L1-norm Total Variation deconvolution is exploited and compared with standard L2-norm Wiener deconvolution. Although the usage of Air-Coupled probes entails a high attenuation of the ultrasonic signals due to transmission in air and reflections at the airsample interface, the experimental results show that the combination of Pulse Compression technique and of advanced signal processing guarantees the effectiveness of the inspection.