Enhanced ultrasonic imaging with split-spectrum processing and polarity thresholding

The polarity thresholding algorithm, which utilizes the frequency decorrelation principle based on the split-spectrum processing technique, is examined. Split-spectrum processing obtains an ensemble of frequency diverse signals from a wideband received signal by using a set of parallel bandpass filters with different center frequencies. Polarity thresholding acts as an on-off switch on the resulting data by setting the output to zero at time instants where the split-spectrum ensemble exhibits polarity reversal. Since the target echo exhibits significantly smaller variation with frequency compared to cluster echoes, polarity thresholding maintains the target echo while suppressing a significant portion of the clutter echos. Theoretical derivations are provided to determine the signal-to-noise ratio enhancement capabilities of the algorithm. Ultrasonic data obtained from large-grained stainless steel samples with flat-bottom holes are used to verify the theoretical results and demonstrate the grain echo suppression capability of the algorithm in imaging applications