Research On Least Mean Square Ultrasonic Phased Array Beamforming Technology

Phased array ultrasonic beamforming technology as a practical engineering application technology for array signal processing has been a research hotspot in ultrasonic inspection applications,and it is also a difficult point.In the traditional phased array ultrasonic beam synthesis,the received ultrasonic signal is subjected to the equal amplitude delay superposition to obtain the signal in the desired direction,without considering the interference noise in the received signal.Based on the principle of hollow-time equivalence in array signal processing,this paper designs an adaptive beamforming algorithm,which performs beam synthesis to obtain the desired direction signal by applying complex gain to the signals received by each element,and suppresses the interference in the signal.noise.In order to verify the feasibility of the algorithm,a phased array ultrasound experiment platform was designed.The main research work is as follows:The basic principle of the sound field radiation of the array transducer ultrasonic transducer is studied.Thus,the mathematical model of the array signal processing has been studied.Based on the traditional delay superposition algorithm,the spatial filter is introduced,and the key parameters affecting the airspace filter are analyzed.The space-time equivalence of spatial filter and delay superposition algorithm is studied.For the problem that the weights in the spatial filter and delay superposition algorithm are fixed,the noise can't be removed and the interference signal can't be removed,the adaptive beamforming technology is introduced.The common criteria of adaptive beamforming and generalized sidelobe canceller algorithm based on minimum mean square error.arestudied.The algorithm,it is difficult to find the covariance matrix and cross-correlation vector,and the coherent signal cannot be processed in the ultrasonic environment.The improvement of the generalized sidelobe canceller is introduced,and the iterative algorithm of least mean square under auxiliary transformation is introduced.The algorithm was simulated and analyzed.To verify the feasibility of the algorithm,the design of the phased array ultrasonic beam synthesis system platform was completed.The overall design of the system was introduced,and then the specific implementation of the transmit and receive circuits was analyzed.Next,the core components of the entire system,the FPGA and the MCU control system,were introduced.Analyze data communication processing in the system.The overall system work as flow: Generate a sine wave signal of a specific frequency through the transmitter section,perform D/A conversion,signal filtering,power amplification,then excite the ultrasonic signal to propagate in the aluminum plate,and perform A/D on the received ultrasonic signal.After processing,it enters the MCU through the FPGA cascade transmission and uploads it to the PC for data processing.In suppressing the interference signal,compared with the CBF algorithm,the FLMS algorithm will not be affected by the external signal-to-noise ratio,and the algorithm still has the feature of forming null traps above-80 dB in the direction of interference and suppressing interference.In terms of decohering signals,compared with the MVDR algorithm,the FLMS algorithm can suppress coherence in addition to the MVDR algorithm when the signal-to-noise ratio is-20 dB and the noise-to-noise ratio is 20 dB under the condition of low SNR.The interference direction signal,MVDR algorithm has not been able to receive the desired signal at this time;Under high signal-to-noise ratio,the signal-to-noise ratio is 20 dB,the FLMS algorithm can still maintain a good beamforming ability when the dry noise ratio is-20 dB.When the MVDR algorithm can't suppress the interference,it forms a null in the interference direction,and the FLMS algorithm does not need to solve the covariance matrix and cross-correlation vector of the received signal,which simplifies the complexity of the adaptive beam calculation.Ultrasonic signals are transmitted/received through a phased array ultrasound test platform,and the received data is processed by algorithms to verify the reliability of the experimental platform,and further to verify that the minimum mean square iteration algorithm in the transform domain is used to process ultrasonic beam synthesis decoherence and suppression of interference signal superiority.