Noise Suppression For Lamb Wave Signals By Fractional-order Differential

Ultrasonic Lamb wave is a common form of guided wave in ultrasonic nondestructive testing. It has become an important tool for nondestructive evaluation, especially the large plate-like structure. Compared with the other conventional ultrasonic testing methods, Lamb wave method has some advantages, such as long distance spread along the structure, large detection, fast, efficient and the inspection scan is performed in a point-to-point manner. Therefore, ultrasonic Lamb wave testing can be used in all kinds of complicated environment.The received signal component is very complex in the actual detection due to the signal affected by different levels of noise interference, which impact the reliability and accuracy of detecting directly. There is thus a clear call for effective methods of noise reduction. This paper in ultrasonic lamb wave for noise removing of the main work to do the following:1、Noise reduction for ultrasonic Lamb wave signals based on the fractional-order differential:The received ultrasonic Lamb wave signals are often mixed with noise and it will affect accurately assesses their real value. In the present study, a method based on the fractional-order differential is proposed for the purpose of noise reduction. Firstly, a fractional-order differential of the amplitude spectrum of the received noisy signal is obtained with the fractional-order differentiation filter. Then, characteristic parameters of the amplitude spectrum can be extracted with parameters estimator model. The Gaussian peak is used as a model to assign the amplitude spectrum of the original signal correctly. Finally, the waveform of the ultrasonic lamb without noise can be restored by combining amplitude spectrum with phase spectrum. Experimental results show that the proposed method has effective noise reduction performance for both the simulated and experimental signals.2、Noise suppression in ultrasonic Lamb wave signals by the fractional-order differential and the Tsallis distribution:In order to reduce the influence of noise and increase the accuracy of feature extraction in ultrasonic Lamb wave signals, this paper presents a new method based on the fractional-order differential and the Tsallis distribution. Primarily, by making use of the fractional-order differentiation filter, we can receive a fractional-order differential of the amplitude spectrum of the received noisy signal. Afterwards, characteristic parameters of the amplitude spectrum can be extracted with parameters estimator model which we will establish in the paper. Then, the Tsallis distribution as a model is applied to recover the amplitude spectrum of the original signal correctly. Eventually, the ultrasonic lamb without noise can be restored by combining amplitude spectrum with phase spectrum. The results show that the proposed method can improve the performance parameters such as MSE, r, and SNR, compared with other methods. Consequently, the new algorithm based on the fractional-order differential and the Tsallis distribution has the best noise reduction performance for ultrasonic Lamb wave signals.3、Tsallis distribution-based fractional derivative method for Lamb wave signal recovery:A new fractional derivative method based on the Tsallis distribution function is developed to recover the Lamb wave signals from the noisy Lamb wave signals. After the fractional derivative of the amplitude spectrum of the noisy Lamb signal at different derivative orders, the quartic polynomial function between the peak amplitude and the derivative order as well as that between the peak frequency and the derivative order is proposed based on the Tsallis distribution function. Then, the characteristic parameters of the amplitude spectrum are deduced by using the proposed polynomial relationship. Finally, the noise-free Lamb wave signal is recovered based on the characteristic parameters. Simulated results indicate that the Lamb wave signals can be recovered in the case of the white noise, the transient noise and the sine wave signal. Experimental results confirm the validity of the method. Consequently, the developed method can recover the Lamb wave signals effectively.