Application of frequency compounding to ultrasonic signals for the NDE of concrete

In ultrasonic NDT of heterogeneous materials the internal microstructure of the material produces backscattered noise that can make the detection of true defects difficult. The noise is caused by the stationary scatterers that cause constructive and destructive interference to the propagating wavefront. Morevoer, in situations where the defects are significantly larger than these random scatterers, defects detection is significantly limited due to the presence of the additive noise caused by the interfering scatterers. This interference causes the presence of speckle noise in ultrasound imaging, thereby limiting the detectability, and making images generally difficult to interpret. Speckle also limits automated computer-aided analysis, such as edge detection, and 3D display. In this study, Frequency Compounding (FC) method has been applied to the ultrasonic signals in concrete. Due to the heterogeneous nature of the material, the received echoes suffer from clutter arising from the material microstructure. In this study, it was shown in simulations that the signal-to-noise ratio (SNR) of the A-scan signals can be improved by splitting the spectrum into narrower subbands and sum. Experiments were performed to validate the simulated results. The possibility of using this type of processing in such material and merits are discussed.