Spectral Distance Amplitude Control for Ultrasonic Inspection of Composite Components

Abstract

Ultrasonic inspection of sound-attenuating material like Fibre Composites requires correction for the loss of echo amplitude. Conventional Distance Amplitude Control (DAC) is not always sufficient, because it does not count for the spectral shift towards low frequencies after long sound paths. Therefore the detection of small flaws is limited, because they require high frequency ultrasonic signal. Consequently, small and deep defects are underestimated in conventional ultrasonic testing. In this paper, a method called SDAC (“spectral distance amplitude correction”) is presented. SDAC is based on digital signal processing algorithms and consists of a signal analysis module and a signal processing module. Analysis provides the typical sound attenuation characteristics of a specific material. Based on these characteristics, the compensation algorithm in the signal processing module recovers the lost spectral signal components in each A-scan. Processed A-scans look like if there was no sound attenuation. Then flaw echoes can be directly compared with each other, widely independent of the flaw’s depth and size.