Research On Ultrasonic Imaging And Enhancement For Bulk Materials

Synthetic aperture imaging is a kind of ultrasonic post-processing method based on the method of fixed -point focusing, which be used to synthesize large aperture to small aperture. And ultrasonic Fourier imaging, as a new imaging method, can obtain a image at a time by Fourier transform, which improve efficiency.In the paper, two kinds of materials of aluminum block 6061 and 43kg/m rail were tested by ultrasonic signal. Then, echo signals is acquired, and the image is processed by Fourier transform. The main contents focused on the following aspects:(1)Review the status and significance of synthetic aperture imaging and ultrasonic Fourier imaging.(2)Study some common synthetic aperture imaging theories and modeling methods, analysis ultrasonic Fourier imaging theory.(3)We give the procedure of the Wiener filter to process the ultrasound. Firstly,initial noise power spectra of no pulse phases are statistically averaged. Then the power spectra of the ultrasound phase with clutter are adaptively calculated. Last, the Wiener filter is performed to each ultrasonic phase. The experiments of the ultrasonic data filtering under different signal-noise-ratios are demonstrated that the proposed method is valid. Wiener filter has the same ability with spectral subtraction to reduce the noise superposed on the ultrasonic echo, and is more effective.(4)Introduce that three different defects are detected in the aluminum block 6061 by single array sub-aperture imaging and four array sub-aperture imaging, and compare the result with -6dB decibel drop method. Use wavelet packet feature extraction method and image threshold segmentation method based on genetic algorithm. The wavelet packet method obtains low frequency components, which improves the contrast around the defect, and the optimal threshold value is 135 by genetic algorithm and Otsu method.(5)Introduce the ultrasonic imaging system, summarize the experimental processes and experimental results, which prove the availability of defect recognition...