Split Spectrum processing applications for new composite materials imaging

In this paper the performance of Split-Spectrum Processing algorithms combined with Spread Spectrum excitation for ultrasonic imaging of new composites were analyzed. Glass and carbon fiber reinforced plastic produced by Resin Transfer Molding (RTM) were the analyzed specimens. These materials are strongly affected by structural noise since air bubbles were trapped during RTM process and interlayer gaps were resent in prepreg technology. For such sort of materials, classic criterions for the parameters of Split-Spectrum algorithms are not feasible and should be revised. Furthermore, as attenuation is highly frequency dependent for these materials, Spread Spectrum and Frequency Selective Loss Compensation techniques were used in order to increase the energy and equalize the received signal. Flaw-to-Clutter Ratio Gain, Signal-to-Noise Ratio Gain and Receiver Operating Characteristics were selected as the figures of merit to make the comparisons, and resulting 3D images of the composites are given.