Study On Key Algorithms Of Ultrasonic Phased Array Imaging

With advantages of ultrasound indirection, penetration, energy, et al,and the deflection and focusing properties of beam, ultrasonic phased array imaging technology has played a vital role in nuclear, medical, construction, metallurgy and other fields. Along with the maturity of hardware technology, the enhancement of detection performance to ultrasound imaging equipment mainly depends on the improvement and innovation of imaging algorithms.Based on ultrasonic transmitter, receiver and post processing, this dissertation are focus on classic ultrasound phased array imaging algorithm, post-processing imaging and full matrix- full focus imaging algorithms to simplify the imaging system and improve resolutions. Firstly, analyses generation mechanism of side lobes and grating lobe to get optimization standards of probe parameter. Secondly, researches on beam focusing and scanning mode improve the linear scanning mode, and come up with a single scanning imaging algorithm. Thirdly, a simulation model based on matlab + field II has been established by combination of these ultrasonic phased array imaging technology. Simulation and experiments show that the imaging resolution sequentially increases through single point focus, segment focus and dynamic aperture focusing. It's easily proved that dynamic aperture focusing can maintain the same vertical resolution at different depthsFurther improvement for the system imaging resolution has been studied through post-processing imaging, including relevant delay compensation method, coherent technology and time-gain control technology. It can be concluded that relevant delay compensation method can correct systems-channel time error and phased delay calculation errors, and enhance the magnitude of the acoustic synthesis beam without reference to the phased launch delay. Based on noise filter of acoustic phase and beam synthesis, coherent technology is used to improve signal to noise ratio. Similarly, time gain control will reduce the undetected probability of defects in accordance with the image threshold and acoustic attenuation rule.In the study of full matrix- full focus algorithm, two elements(echoes) of the whole matrix get equal amplitude to each other in the corresponding time, which comes out the virtual focus imaging with parts of the matrix. Precisely because of this, static 1/2 matrix and dynamic matrix synthesis method have been introduced to reduce about 50% amount of the processing data,which has improved the efficiency of the system to a certain extent.