Application Of Wavelet Analysis In Nondestructive Testing Of Quality Of Material For Steel And Iron

Electromagnetic nondestructive testing on the quality of steel has been studied for many years and acquired a great deal of achievements. However there are many problems in the testing of hardness and cracks, and mess problem of work pieces. Especially the unlinear relation between the degree of hardness of aluminium and initial magnetic permeability, these all affected the testing of the metal hardness seriously. To settle the above problems, base on the above, by comparing the different methods of signal analyzing, wavelet transform is selected as the main studying tool for the project.Signal and information processing is one of the most rapidly developed subject in the field of information science in recent twenty years. The signal processing mainly included signal denoising, character abstracting and border abstracting. Signal denoising is to be the most common in the signal processing, the classical signal denoising method such as the pure time domain method, the pure frequency region method, fourier transform method, the window fourier transform method. But these methods all have limitation in the real application. The wavelet transform is a new development unite time domain with frequency region analysis method in 1980's. And it all has well localization characteristic property in time domain and frequency region. The wavelet transform has got broad application in signal denoising. The study made a introduction of wavelet analysis in detecting the quality of iron and steel, full use of its preponderance to deal with the non-stationary signals to get the signals which can not obtain from the traditional Fourier transform.All kinds of disturbance should be eliminated because there have been multifarious influences in the process of testing, and there is always a real-time and flexible requirement for signal processing. However, possibly do not have filtering system at present in testing systems or do not be only the simple filtering circuit, request in two aspects very difficult to satisfy all above. Along with the development of PLD device and EDA technology, using FPGA to implement wavelet filter, as it not only meet the real-time requirement, but also has some flexibility. The main work is as the following:1. In the text, the basic theory of wavelets transform is introduced. The respective characteristic of wavelets transform is analyzed and the basic theory of the multi-resolution analysis and two scales equation besides mallat algorithm based on the orthogonal wavelet transform are elaborated. In addition, some wavelet functions commonly used in the actual project question are introduced and wavelet analyzing is in the practical application of signal processing.2. In above theory of wavelet foundation, from the method of low pass filter signal denoising based on Fourier transform, the method of threshold value signal denoising based on wavelets transform is discussed. in this paper in analyzing the classic method of the soft threshold value signal denoising and hard threshold value signal denoising deficiency foundation, the choice of threshold value and thresholding function in threshold value signal denoising based on wavelets transform is discussed, puts forward improved thresholding function of wavelet by step, the numerical value experiment in the new thresholding functions by computer simulation are carried out. Finally, the actual signal is applied Matlab to simiulate.3. According to the theory of wavelet filter, this article makes deep researches on Biorthogonal wavelet theory, on this basis, completes the design of wavelet filter, through analysis of the design philosophy of FPGA in pipeline. At last, we have added this wavelet filter module in testing system, proved that this system is real-time, veracity, agile.