Simulation Study Of Ultrasonic Array Nondestructive Testing Method Based On Time Reversal Operator

In the advanced fields represented by aerospace and national defense industry,it is very important to test and evaluate the core components regularly to ensure the system works safely and reliably.Ultrasonic phased array detection has become an important detection method in the above fields due to its advantages such as flexible detection mode,large detection depth and fast detection speed.However,the imaging resolution of conventional phased array detection method cannot break the Rayleigh diffraction limit,which affects the evaluation of subsequent defects.Therefore,this paper studies the superresolution imaging algorithm based on time reversal operator.Aiming at the problem of noise sensitivity of time inversion operator estimation,the stability of super-resolution imaging algorithm is guaranteed by improving the SNR of echo signal.The main research work of this paper is as follows:The propagation characteristics of ultrasonic body wave in solid medium are analyzed.The wave equation is derived and the specific solution expression is calculated for two kinds of sound waves(cylindrical wave and plane wave)which are often used in modeling and simulation.The correlation characteristics of two common modes of sound waves in solid media(S-wave and P-wave)and the action of sound waves at discontinuous boundary surfaces are studied.Finally,the propagation attenuation characteristics of sound waves in solid media are analyzed,and an effective measurement method for attenuation coefficient of solid media is proposed to provide a theoretical basis for subsequent detection.The one-dimensional linear array is modeled.The influence of array geometric parameters and excitation signal frequency on array detection performance was analyzed by far-field sound pressure directivity function.It was proved that the detection accuracy could be improved by increasing excitation signal frequency and reducing wavelength,and the gate lobe could be effectively eliminated within the imaging range by limiting the array spacing to less than half wavelength.Beam profile modeling is used to visualize the emitted sound field of linear array,and it is verified that the side-lobe can be effectively suppressed and the width of the main lobe can be reduced by amplitude trace.Finally,point spread function modeling is used to evaluate the imaging results of phased array,and it is proved that increasing the number of array elements in a certain range can significantly improve the imaging results,and the above analysis can guide the selection of phased array in actual detection.The total focus imaging algorithm and coherent plane wave compound imaging algorithm are studied in depth.In order to solve the problem that the two algorithms above cannot realize superresolution imaging,the multi-signal classification algorithm based on time reversal operator is selected to detect the internal structure of the object under test.Aiming at the problem of noise sensitivity of time reversal operator estimation,improved TR-MUSIC algorithm based on multi-angle plane wave is proposed.Through analytical simulation,it is verified that the TR-MUSIC algorithm based on multi-angle plane wave can achieve super-resolution imaging for two point-like scatterers with radial distance of 0.6 when the SNR of echo signal is 20 d B.At the same time,simulation results show that the signal-to-noise ratio(SNR)of superresolved imaging based on multi-angle plane wave emission algorithm should be greater than 6.5d B.The improved algorithm is verified by finite element simulation.The finite element method is used to establish an accurate acoustic defect interaction model,and then the TR-MUSIC algorithm based on multi-angle plane wave is used to detect the internal structure of the tested object,verifying that the interaction between multiple defects has little influence on the final detection result.In the end,under the ultimate signal-to-noise ratio(SNR)of analytical simulation,two defects with a distance less than The Rayleigh diffraction limit were simulated,and the super resolution imaging of the two defects was realized,which verified the accuracy and stability of the improved algorithm under the condition of high noise.