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 air-sample interface, the experimental results show that the combination of Pulse Compression technique and of advanced signal processing guarantees the effectiveness of the inspection.