The application of a pulse-compression procedure based on pseudorandom m-sequences to air-coupled ultrasonic nondestructive testing is presented. The signal-to-noise ratio enhancement assured by this technique is theoretically analyzed and experimentally verified, particularly focusing on the positive effect of the procedure to reduce quantization noise. The possibility of faithfully reconstructing signals whose amplitudes are lower than the quantization step of the analog-to-digital converter (ADC) board is analyzed theoretically and experimentally verified.

Pulse-compression thermography is an emerging non-destructive technique whose effectiveness strictly depends on the choice of the coded excitations used to modulate the heating stimulus. In this paper, the features of frequency-modulated coded signals, i.e., chirps, have been tested for imaging thin Teflon defects embedded within a carbon fiber composite specimen. With the aim of maximizing the heat transferred within the sample, the use of several optimized non-linear chirp signals has been also investigated and their defect detection capability compared in terms of the maximum achievable signal-to-noise ratio.

The application of a pulse-compression technique for the ultrasonic inspection of forged steel structures with high attenuation and large dimensions is presented. The performance of such a technique is theoretically analysed and validated experimentally by exploiting linear chirp signals. Based on the preliminary results, it is found that the strategy achieves a significant enhancement of the signal-to-noise ratio and then of the inspection capability. A further increase in performance can be achieved by exploiting signal processing and by developing proper hardware.