Research On Ultrasonic Non-destructive Testing Method Based On Fractional Fourier Transform

Fractional Fourier transform(FRFT)is a generalized form of traditional Fourier transform(FT).It has the characteristics of chirp basis decomposition,so it is very suitable for processing linear frequency modulation signal(also known as chirp signal or LFM signal).This thesis is devoted to the application of fractional Fourier transform in signal detection and the basic theory of traditional Fourier transform is deeply analyzed,which is related to the basic theory of fractional Fourier transform,the numerical methods and the relationship between them is discussed.To solve the problem in defect signal of ultrasonic nondestructive testing technology,and the thesis is organized as follows:Firstly,this thesis will expound the basic theory of Fractional Fourier transform and compare the relationship between Fractional Fourier transform and traditional Fourier transform.Further,the definition of Fractional Fourier transform and the discrete decomposition methods going to be analyzed an example about the simple square wave function will be proposed to illustrate the characteristics of Fractional order.Secondly,a separation method of defect echo signal in nondestructive testing based on fractional Fourier transform is obtained.What's more,the defect signal can be separated in fractional domain by using prior knowledge as the energy aggregation of chirp base by fractional Fourier transform.In view of the energy aggregation of chirp base by Fractional Fourier transform,the defect signal can be separated in fractional domain based on prior knowledge.Finally,we will describe the physical quantity of ultrasonic wave,according to basic principle of ultrasonic nondestructive testing pulse emission method,the influence of the system on the signal will be analyzed.The separation experiment of the given defect echo signal is carried out by numerical calculation,which shows that the fractional domain separation is more intuitive and effective than the frequency domain separation of Fourier transform.Therefore,the detection signal in ultrasonic nondestructive testing based on fractional Fourier transform is able to better detect and separate the defect signal,which is practically valuable.