NOISE SUPPRESSION AND FLAW DETECTION OF ULTRASONIC SIGNALS USING EMPIRICAL MODE DECOMPOSITION
In ultrasonic non-destructive testing, the precise detection of flaw echoes buried in backscattering noise caused by highly scattering materials is a problem of great importance. In this paper, a new signal decomposition method for analyzing non-stationary or nonlinear data called empirical mode decomposition, is proposed to deal with ultrasonic signals. A new de-noising technique that combines empirical mode decomposition and filtering simultaneously in time domain and frequency domain is designed to suppress noise and enhance flaw signals. Sythetic and experimental signals are de-noised using this EMD-based filtering technique. Simulated results are presented and analyzed, showing that the proposed technique has an excellent performance even when the signal-to-noise ratio is very low (-23 dB). The improvement in flaw detection was experimentally verified on a pipeline sample with artificial flaws.