The Research Of Methods Based On Frequency-hopping Ultrasonic Signal For Rail Flaw Detection

With the continuous development of railway transport, the transport capacity, load andtransport density are constantly improving, which greatly increased the burden on linefacilities, and accelerated the rail damage, then further brought hidden trouble to the safety ofthe train. The non-destructive testing（NDT） technology has been putted forward for higherrequirements, of which the ultrasonic detection technology is a kind of commonly used testingtechnique. Due to the demand of various industries, in many developed countries, theultrasonic detection technology has become an important direction of development of scienceand technology, and many advanced technology companies are also committed to thedevelopment and production of ultrasonic detection instruments. Along with the unceasingenhancement of computer operation ability as well as the improvement of signal processingtechnology and the development of integrate circuit, the better basis including software andhardware of the ultrasonic testing technology makes the instruments of modern ultrasonicnondestructive detection more accurate, more quickly, more portable, and more intelligent.The second chapter introduces the ultrasonic characteristics and common methods ofultrasonic detection. The third chapter introduces the passive detection model based on thearray signal processing, which include the algorithm of MUSIC and ESPRIT. Through theprocessing of simulation research, the influence on the performance of the algorithm causedby each parameter of the passive detection model was observed, and the simulation resultswere analyzed in theory. The fourth chapter introduces the multiple transmit multiple receive（MTMR） model and its work principle, which was represented by the ultrasonic phasedarray, and points out the shortcomings of the MTMR model, and then put forward to proposethe single transmit multiple receive（STMR）model. The fifth chapter detailedly introduces thestructure and working principle of the STMR model, and then proved the feasibility of theproposed method by simulation.In general, the main innovations of this paper lie in:1. Thinking from the perspective of bionics, the STMR model was proposed. For thismodel, all the information for positioning the defects can be obtained just through a launchand a receiver, which can avoid the operations of mulit-deflection and focusing in the MTMRmodel. As a result, the equipment load can be greatly reduced as well as the requirements oftiming control system in equipments, and the working focus was then transformed from thesignal acquisition to the signal processing. From the perspective of the information theory,that actually is increasing the use efficiency of information to reduce the quantity demand ofinformation. 2. Realizing the positioning of coherent sources, through the use of frequency-hoppingsignal. In this article, the proposed method for estimating coherent sources is different fromthe existing algorithm of DOA. Based on the characteristics of frequency-hoppingcommunication system, the new proposed method separates the coherent sources one by onefirstly, which transforms the problem into a positioning of single source, and then completethe positioning of coherent sources. One advantage of the new method is that there is no needto know the number of sources.