| The continuous development of the level of production in the modern society puts forward higher requirements for product quality control.As a non-destructive testing technology that has been widely used in product design,production,and use,the improvement of ultrasonic detection accuracy greatly contributes to the control of product quality.Ultrasonic detection is a nondestructive detection method that can effectively detect the internal characteristics of an object.By examining the delay and amplitude of the received wave,the position,size,shape,and properties of the internal defect of the sample can be obtained.In order to obtain better detection accuracy,we usually use linear frequency modulation signals instead of traditional narrow pulses as the transmitted wave signals.However,due to the large time width of the LFM signal,the direct wave aliasing interference problem is often introduced.In this paper,the received signal in ultrasonic detection is analyzed,and the influence of the direct wave signal on the ultrasonic detection result is studied.Based on the characteristics of ultrasonic detection channel,a combined adaptive filtering algorithm is proposed to eliminate the direct wave.The main work of this article is summarized as follows:1.Based on the high correlation of the direct wave components between two equally spaced receiving channels,a dual-combined adaptive filter structure is designed: the received signal of each channel is used as the input signal of its own filter,and it is also used as another filter.The reference signal;select two filtered error values as the output,as the corresponding channel eliminates the direct wave interference results.And the above structure is extended to a multi-receiver channel scenario.2.Based on the least-mean-square criterion,the performance cost function of the above-mentioned dual-combination and multi-combination adaptive filter structure is given,and the Wiener solution and the filter coefficient iteration formula based on the LMS algorithm are deduced.And through the simulation,the feasibility of the algorithm is verified.3.Participated in the development of ultrasonic testing platform for the rail flaw detection in the laboratory,and used the combined adaptive filter proposed in this paper to perform the direct wave cancellation experiment in the actual scene and achieved good results. |
