Speckle reduction by energy time-frequency filtering

Structural noise is a very important limitation to the visibility of flaw echoes in ultrasonic testing and evaluation of highly scattering materials. In order to enhance the signal-to-noise ratio, different algorithms have been developed. One of these techniques is based on filtering the spectrum low band of the received echo to obtain a significant improvement of the defect visibility. Based on this idea, in this work a new time–frequency technique is presented. In this method, block-processing autoregressive techniques are used to estimate the instantaneous center frequency of the traveling wave. From this information, a time–frequency filter is designed tuned at half the estimated instantaneous center frequency. Experimental results and the comparison with the non-time–frequency filtering technique are also included, showing that the proposed method has an excellent performance on SNR enhancement.