Research On Synthetic Aperture Focusing Technology For Ultrasonic Imaging

Synthetic aperture focusing algorithm for ultrasonic imaging is an image reconstruction technology. It has advantage of composite sub-apertures into full aperture. The resolution of the reconstruction image does not change with the depth and position with synthetic focusing. The synthetic aperture focusing technology can achive higher resolution under the condition that using the same conducter contrast with other image methods. The defect can be measured more precisely with this imaging method.The principle of synthetic aperture focusing technology has been researched and the factors which influence the image resoulution have been analized. This thesis also presents methods and algorithm which can promote image resolution. And the attempation has been tried out to apply the synthetic aperture focusing technology in ultrasonic phased array systems.The dissertation mainly covers the following aspects:1. The effectiveness of synthetic aperture focusing algorithm is verified through simulation. The results show that the delay accuracy is the key effector which influences the image quality on condition that the transducer factors are determined.2. Experiments have been executed through Multi2000 system. The raw B scan data has been collected through scaning the defects using single element. And the synthetic aperture focusing algorithm has been used to process the data. The results show that the resolution can be promoted 17% at least with synthetic aperture focusing algorithm according to the -6dB theorem.3. The model of synthetic aperture focusing algorithm is derived based on the acoustic radiation principle. And the parameters which influence the image quality have been analized. The prarmenters selection principle is defined.4. A new synthetic aperture focusing algorithm has been presented. The algorithm uses coefficients calculated at different scales based on the wavelet transformation. It resolves the problem that the delay time can not predicted precisely between different scan positions. This algorithm has higher resolution compared with the tranditional delay and sum method.5. The synthetic focusing algorithm has been applied in ultrasonic phased array systems. The resolution in the far field where the focusing effectiveness is not obvious with phased array can be promoted. 6. A portable ultrasonic imaging system is presented using synthetic aperture focusing technology. It lays foundation for the practical application of SAFT in ultrasonic inspecton field.