Synthetic Aperture Ultrasonic Imaging Algorithm Based On Adaptive Beamforming

The beamforming is the core position in the ultrasonic imaging system,which directly determines the quality of the imaging.The width of the main lobe and the side lobe amplitude are two important indicators in measuring the quality of the beamforming.The narrower the main lobe,the higher the imaging resolution;the lower the side lobe level,the higher the image contrast.Traditional beamforming is the representation of a delay and sum beamforming which has the characteristics of simple design and fast imaging.But it can not achieve dual dynamic focusing,so its beamforming has the higher side lobe and the wider main lobe,and the imaging quality is not high.Usually,the fixed window function is used to apodize the beamforming results and reduce the sidelobe.However,this will increase the width of the main lobe further,which is not conducive to increase imaging resolution and contrast at same time.This paper will focus on those two problems and carry out some studies including beam control,adaptive beamforming,signal reconstruction and imaging combine with robust adaptive beamforming,compression perception algorithm and synthetic aperture beamforming.The main contributions are as follows:1.Through the study of traditional beamforming,it is found that it can not achieve dual dynamic focusing and dynamic apodizing,which will introduces adaptive beamforming.Adaptive beamforming can be divided into two algorithms:closed-loop and opened-loop.The closed-loop algorithm is relatively simple,but the requirement of the system's stability limits its convergence rate and the opened-loop algorithm can provide faster response,but the accuracy of calculating covariance limits its application.In contrast,opened-loop algorithm is more promising.2.In order to lower the main lobe width,side lobe level of SAF's beams and to improve robustness of algorithm,resolution and contrast in images,a robust Capon beamforming algorithm based on eigenspace is presented.Under the principle of minimum variance,this algorithm firstly uses the Toeplitz to realize the reconstruction of the interference noise covariance matrix and to make it keep nonsingular.Secondly,the vector error is constrained by the signal subspace and the circular constraint set.Finally,the optimal weight vectors under constraint conditions are obtained through Lagrange number multiplication and dichotomy.Furthermore,the ES-RCB algorithm has a strong robustness and ultrasonic image using the proposed method not only performs better in anti-interference,resolution and contrast but also improves the quality of ultrasonic images effectively.3.For the disadvantages of large amount of data,high system complexity and hard real-time imaging in the calculation process of ES-RCB.A synthetic aperture ultrasonic imaging algorithm based on compressed sensing and robust Capon beamforming in eigenspace is presented(CS-ES-RCB-SAF).Under the premise of obtaining the original signal,the algorithm firstly makes the measurement matrix in the compressed sensing theory combine with the channel weight in the SAF beamforming,which will realize the non-uniform sampling in the receiving process.Secondly,the measurement signal is imported into the ES-RCB algorithm to obtain the weight vector and completing the apodization of the measurement signal.Finally,the sparse matrix and the measurement matrix are calculated by the original signal and the measured signal and the reconstruction algorithm is used to reconstruct the data matrix for subsequent imaging processing.Simulation results show that CS-ES-RCB-SAF can performs effectively in reducing the mount of data,complexity of system and restore the images better at the same time.