In the industry, there are many structures made from composite materials that cannot be inspected by contact or immersion.
Air-coupled ultrasound testing (ACUT) is one of the most emerging NDE approaches for application in the inspection of structures when contact or immersion is not desirable.

In ACUT, the main techniques used are
a) Through-transmission compressional wave
b) Through-transmission shear wave
c) Pseudo pulse-echo
d) Through-transmission Lamb Waves
e) Pitch-Catch Lamb wave.

All of them suffer from a low signal-to-noise ratio (SNR) due to the enormous differences in acoustic impedances that are manifested in the system, between the transductors and the air and between the pieces and the air, to this must also be added the attenuation of the UT inside of materials used in the industry such as honeycomb, CFRP or GFRP structures.

To implement this type of application it is necessary to have transducers that can overcome this acoustic impedance difference and ultrasonic devices with cutting-edge capabilities in terms of signal sensitivity, digitalization, pulsing capabilities, and frequency range.
In addition, it is necessary to establish strategies that allow for improving SNR.

The matching filtering approach applies a correlation between an exciting signal into an object and the signal transmitted through the part, therefore the signal-to-noise ratio (SNR) is increased and the resolution is enhanced. The complexity required in electronics to generate an exciting signal for matching filtering techniques and the implementation problems have hindered its use in the field of practical NDT applications. But they are viable now with the new generation of UT devices that include AWG capabilities.

In this contribution, we present a comparative study on the benefits of applying matching filtering based in AWG to main ACUT techniques for the inspection of Honeycomb and CFRP parts.

We also discuss the effect of matching filtering on improving the Signal-to-Noise Ratio (SNR) in the main ACUT techniques in comparison with the use of average of signal and the implications that this carries out into the productivity of the inspection.