The Super Resolution Imaging Of Ultrasonic Synthetic Aperature Based On Time Reversal

With the advancement of science and technology and the development of society,the technologies updates rapidly in the industrial field,such as aviation,aerospace,railways,nuclear power plants,and new materials.On the one hand,they have promoted the development of non-destructive testing technologies,and on the other hand have placed higher requirements on non-destructive testing.The advantages of ultrasound are significant,the strong penetrating power and the good direction of propagation made ultrasonic testing become a major branch of non-destructive testing.Ultrasound phased array imaging technology is one of the most promising detection methods.It integrates phased array technology and ultrasonic imaging technology,so it has a wide detection range,high speed,high data utilization,large detection depth,and good noise resistance.With the advantages of adaptability and reliability,the imaging speed is also faster than others.However,the imaging resolution is limited by acoustic diffraction,and the detection depth and the lateral resolution are inconsistent.In order to improve the imaging resolution,it is necessary to use a higher frequency ultrasonic wave.However,the higher frequency always means greater attenuation in the propagation process will be.In order to improve the ultrasound imaging resolution,in the premise of unchanged ultrasonic operating frequency,this thesis studies the super-resolution imaging method based on the time-reversal acoustic theory,which improves the imaging resolution and the image quality.The main work and innovation of this thesis are as follows:1.According to the different resolution limit under Rayleigh criterion at different depth,one-point,double-point models are established.The thesis chooses the full-matrix capture method for data acquisition which can cover most extensive data.All elements in the array are selected as the transmit element and receive element,and acoustic signals are transmitted and received to construct ultrasonic data array.Therefore,for an N-dimensional linear array,the ultrasound array data collected by the full-matrix capture has a total of N~2 time-domain signals that carry the maximum amount of information related to the measured object.After all A-scan signals are obtained,the signals are windowed to remove unwanted parts outside the imaging area to optimize the A-scan signal.2.Perform center frequency time reversal multi signal classification imaging on the full-matrix captured data above,and also perform total focusing imaging on the data.Comparing the two results.The simulation results show that under the condition of the different resolution limit decided by Rayleigh criterion,ordinary ultrasonic imaging cannot identify the defect points,but TR-MUSIC can identify all the defect points.3.Add noise to the basic simulation model to study the change of TR-MUSIC imaging results.The results show that this method is robust to noise,and the SNR higher than1 dB does not have much impact on the simulation results.The defect point location information can still be accurately identified.4.Experimental verification of double-point test block.The results show that this method accurately identifies the defects in the test block.The results show that the TR-MUSIC method has a strong ability to distinguish small defects and has strong robustness to noise.Super-resolution ultrasound imaging can be achieved.