Key Technology Research Of Digital Ultrasound Imaging System Based On FPGA

With the advantages of non-invasive detection and high real-time performance,ultrasound imaging technology is widely used in the field of medical imaging.Compared with piezoelectric ceramic ultrasound imaging technology,MEMS digital ultrasound imaging has obvious advantages in low power consumption,miniaturization,and high resolution,which is considered as the core technology of next generation ultrasound imaging and has become a hot spot for academic research at home and abroad.In the field of digital ultrasound imaging,due to the unique structure and piezoelectric characteristics of MEMS,the traditional piezoelectric ceramic imaging digital driver and receiver system is no longer applicable,and a new system driver and receiver circuit needs to be developed for MEMS fully integrated digital ultrasound imaging technology.In view of the above problems,this thesis conducts research on the optimization design of the beamforming algorithm optimization and circuit design,envelope detection circuit design,ultrasonic high voltage drive circuit design and other key technologies for portable MEMS digital ultrasound imaging for human 80 mm superficial tissues.The main research contents and results are as follows.First,we optimize the minimum variance beamforming algorithm,which is a key technology in MEMS digital ultrasound imaging system.By diagonal loading and spatial smoothing,the problem of low imaging stability of the minimum variance beamforming algorithm and poor imaging effect in the middle and near field is solved.For the portable MEMS digital ultrasound imaging applied to 80 mm superficial tissue of human body,the circuit optimization scheme of focusing,amplitude variation tracing and dynamic aperture techniques in digital beamforming algorithm is proposed,and the structural parameters of MEMS ultrasound transducer are determined.The imaging effects of the above scheme and the optimized algorithm are verified by simulation using Field II simulation tool.The results show that the transverse imaging resolution of the optimized algorithm for minimum variance beamforming achieves 2 mm in the 80 mm probing range and meets the design expectations.Second,according to the technical parameters determined by the above imaging algorithm,the digital beamforming circuit of MEMS digital ultrasonic imaging is optimized,and the FPGA verification is realized.Specifically,the circuit includes:20ns precision dynamic focus delay,dynamic aperture and amplitude variation tracing,DDS digital synthesizer with LUT compression,and CIC low-pass filter.The verification results show that the focus delay control accuracy and envelope detection results meet the algorithm index requirements.Third,The MEMS ultrasonic high voltage driving circuit is designed and verified.The hardware circuit test platform is built and the single-array characteristics of the MEMS ultrasonic transducer are tested.The results show that the characteristic frequency of MEMS ultrasonic transducer is 129 k Hz and the maximum displacement at Vpp = 10 V is 187 nm,which is in accordance with the parameter characteristics of MEMS ultrasonic transducer.The designed MEMS ultrasonic high-voltage driving circuit is verified to be functionally correct and meet the performance requirements.In summary,this paper presents a systematic study of the digital beamforming optimization algorithm,digital beamforming circuit design,and ultrasonic high voltage drive circuit design for portable MEMS ultrasonic imaging of human 80 mm superficial tissue.The research content and results will lay a solid foundation for the subsequent development of fully integrated low-power,miniaturized MEMS digital ultrasound imaging system.