SPLIT-SPECTRUM PROCESSING WITH FINITE IMPULSE-RESPONSE FILTERS OF CONSTANT FREQUENCY-TO-BANDWIDTH RATIO

A limitation to the ultrasonic non-destructive evaluation of materials with coarse structure is the poor signal-to-noise ratio caused by backscattering noise. Split spectrum signal processing, based on the decomposition of the ultrasonic signal by multiple narrow-band filtering, has been proved efficient for the suppresion of such noise. Its application, however, has been limited by the long processing time of the filtering process which uses discrete Fourier transforms. Here a new decomposition method is presented, based on finite impulse response filters of constant frequency-to-bandwidth ratio. This method is more efficient for split-spectrum processing of ultrasonic signals having wide frequency bandwidths or long time duration, and could be implemented in real-time with tapped delay lines. The choice of the optimal processing parameters is discussed theoretically and experimentally verified on ultrasonic data obtained from austenitic steel and graphite-epoxy samples. © 1990.