Research On Multi-element Synthetic Aperture Ultrasonic Phased Array Beamforming Technology

Beamforming as an important technology in array signal processing has always been the focus and difficulty of research.The traditional conventional beamforming technology(CBF)uses a delay accumulation algorithm to increase the signal in the desired direction of space.The beam quality formed by the CBF is limited by the aperture of the array,and the increase of the aperture can improve the beam quality.CBF only focuses on forming the beam main lobe in the desired signal direction,neglecting the ability to suppress interference signals.In this paper,a minimum variance adaptive beamforming algorithm based on Multi-element synthetic aperture and spatial smoothing(MSAF-FBMV)is proposed.The ultrasonic phased array beamforming experiment platform is designed and the effectiveness of the algorithm is verified.This paper introduces the basic theory of beamforming firstly,from the mathematical model of the array signal,the beamforming principle to the spatial matched filter,points out the shortcomings of the CBF technology,the beam quality is limited by the array aperture,and there is no special ability to suppress the interference signal.Then for the problem that the beam quality of the CBF technology is limited by the aperture of the array,the synthetic aperture technique is introduced to achieve the effect of large-aperture beamforming with a combination of smaller apertures and special data processing methods.On the basis of this,in order to overcome the disadvantage of CBF technology that there is no special ability to suppress interfering signals,adaptive beamforming technology is introduced and the three best criteria are analyzed.The minimum variance distortionless response(MVDR)adaptive beamforming algorithm is introduced.The forward-backward spatial smoothing(FBSS)technique is used to solve the problem of signal coherence;a minimum variance adaptive beamforming algorithm based on Multi-element synthetic aperture and spatial smoothing(MSAF-FBMV)is proposed,and the detailed steps and implementation of the algorithm are given.To verify the feasibility of the algorithm,an ultrasonic phased array beamforming experiment platform was designed,and the specific design of the transmitter circuit,the receiver circuit,the FPGA core control circuit,and the data transmission circuit were introduced.Theoverall experimental flow is: transmitting three ultrasonic signals in different directions and frequencies at a specific frequency.After D/A conversion,low-pass filtering,and power amplification,the medium is propagated through the aluminum plate.The receiving module performs signal conditioning and A/D conversion on the received signals.Through the FPGA cascade transmission to the MCU,using MSAF-FBMV algorithm to complete the work of data processing in the PC side.The experimental results show that the modules of the ultrasonic phased array beamforming experiment platform are operating normally,which verifies that the minimum variance adaptive beamforming algorithm based on Multi-element synthetic aperture and spatial smoothing(MSAF-FBMV)can improve the quality of the beam,suppress the interference signal and preliminary coherence properties in the environment of coherent interference.