1.School of Information and Communication Engineering, North University of China, Taiyuan 030051,China 2.School of Physics and Information Engineering, Shanxi Normal University, Linfen 041000, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 11604304), the Shanxi Province Science and Technology Tackling Key Project, China (Grant No. 201603D121006-1), the Natural Science Foundation of Shanxi Province, China (Grant Nos. 201701D221127, 201801D121150), the Shanxi Provincial Foundation for Returned Scholars, China (Grant No. 2016-084), and the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi, China (Grant No. 201657).
Received Date:23 November 2018
Accepted Date:13 January 2019
Available Online:01 April 2019
Published Online:20 April 2019
Abstract:Ultrasonic non-destructive testing, which is one of the most important and rapidly developed non-destructive testing technologies, is widely used in industrial production and other areas. Signal de-noising and feature extraction, whose performance directly affects the evaluation of non-destructive testing results, are the key technologies of ultrasonic non-destructive testing data processing, and also the core elements of ultrasonic non-destructive testing. Therefore, the research on them has important academic significance and practical value. In order to solve the problem of parameter estimation and noise reduction of ultrasonic echo in strong noise background, a novel ultrasonic echo processing method is proposed in this paper. The principle of the proposed method in this paper is as follows. The ultrasonic echo, which is generated by modulating the ultrasonic transducer, has a specific structure, but the noise in practical engineering is usually a Gauss random process, therefore the noise is independent of the ultrasonic signal structure. In this paper, the problem of parameter estimation and noise reduction of ultrasonic echo signal are converted into a function optimization problem by establishing the model of ultrasonic signal, determining the objective function, optimizing the objective function, estimating the parameters, and reconstructing the ultrasonic signal. Firstly, a dual gaussian attenuation mathematical model of ultrasonic signal is established based on practical engineering experience. Secondly, the cosine similarity function, an effective measure of data sequence similarity, is selected as an objective function according to the observed echo and the established ultrasonic signal model. Thirdly, the artificial bee colony algorithm is selected to optimize the objective function to obtain the optimal estimation parameters of the ultrasonic signal from the noisy ultrasonic echo. Fourthly, the estimation of de-noising ultrasonic signal is reconstructed by the optimal parameters based on the established ultrasonic signal mathematical model. The processing results of simulated ultrasonic echoes and measured ultrasonic echoes show that the proposed method can accurately estimate the parameters of ultrasonic signal from strong background noise whose signal-to-noise ratio is lowest, as low as –10 dB. In addition, compared with the adaptive threshold based wavelet method and empirical mode decomposition method, the proposed method in this paper shows the good de-noising performance. Furthermore, compared with the commonly used exponential model and Gaussian model in numerical and simulation analysis, the proposed dual gaussian attenuation mathematical model of ultrasonic signal in this paper can well simulate the measured ultrasonic signal, with a mean square error of 9.4 × 10–5 and normalized correlation coefficient of 0.98. Keywords:ultrasonic signal model/ signal denoising/ parameter estimation/ artificial bee colony
为了验证本文方法的降噪能力, 将本文方法和当前超声信号处理中常用的小波阈值降噪方法、经验模态分解(empirical mode decomposition, EMD)方法进行对比. 为方便研究, 不失一般性地选择图3(a)中的第二个回波作为研究对象对其加入噪声, 当信噪比SNR = –10 dB时, 本文方法、小波阈值降噪方法以及EMD方法的降噪结果如图4所示. 图 4 不同方法降噪结果对比 (a)黑色实线为含噪回波, 红色虚线为原始信号; (b)本文方法处理结果; (c)小波方法处理结果; (d) EMD方法处理结果 Figure4. Comparison of de-noising by different methods: (a) Noisy echo plotted in a black solid line, original signal plotted in a red dotted line; (b) signal de-noised by our proposed method; (c) signal de-noised by wavelet method; (d) signal de-noised by EMD method