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| A flaw echo detection method based on S-transformation and time-frequency spectrum spatial filtering |
| ZENG Xiang, WU Xuelei2,ZHOU Xiao-jun, YANG Chen-long,CHEN Yue-chao |
| The State Key Laboratory of Fluid Power Transmission and Control, Zhejiang University, Hangzhou 310027,China |
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Abstract Flaw echoes detection is an important task in ultrasonic testing. In order to eliminate the effects of noise and detect echoes correctly, a signal processing method based on S-transformation(ST) and time-frequency spectrum(TFS) spatial filtering is proposed．Based on the Gaussian echo model, the relationships between time of arrival(TOA) together with center frequency(CF) and ST TFS are discussed, and the reasonableness of method using the extremum of ST TFS amplitude matrix for TOA and CF extraction are illustrated. To detect the echoes, firstly the ST is performed on the original signal．Then the dual-threshold are determined by Maximum Entropy Thresholding method adaptively, and the spatial filtering is performed on ST TFS for denoising. The TOA and CF could be extracted from the denoised region. Finally, the inverse ST is performed on the denoised TFS and the signal with clear flaw echoes are gained. Simulation results show that using ST and TFS spatial filtering can remove noise and detect echoes effectively. And the experimental results of bar specimen also show the effectiveness of this method in flaw detection.
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Received: 29 March 2016
Published: 15 November 2017
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