Research On FPGA-based Steerable Parametric Array Beam Forming Algorithm And System

Parametric array is a new type of speaker that can transmit audio signals in a specified direction.It is a research hotspot in recent years and has broad application prospects in the fields of broadcasting and communication.The acoustic parametric array modulates the audio signal onto the ultrasonic carrier through amplitude modulation,and then through the nonlinear effect of air,the audio signal will self-demodulate along the signal propagation direction,thereby forming a highly directional sound beam.This thesis studies the basic theory of acoustic parametric array,and briefly explains the Westervelt direction,Berktay far-field solution and KZK equation.In order to optimize the synthesis beam of the acoustic parametric array,this thesis combines the acoustic parametric array with the phased array technology.Through the beam synthesis algorithm,improving the resonance frequency of the ultrasonic transducer array element and the hardware control accuracy,the flexible control of the difference frequency acoustic beam is realized.The main work content is as follows:(1)For the directivity of parametric array beams,a combination of phase weighting and acoustic focusing is proposed for improvement.By deriving the beam focusing algorithm of the one-dimensional linear array,simulation analysis proves the influence of different focal lengths on the beam.Simultaneously,the Chebyshev weighting method and the phase-weighted acoustic focusing algorithm are analyzed and compared.The results show that the acoustic focusing beam synthesis algorithm can effectively improve the beam directivity.(2)For the inconsistency of the resonance frequency of the parametric array transducer,an equivalent electrical parameter matching method is proposed for transducer selection.The effect of the inconsistent resonant frequency of the transducer on the beam of the parametric array array is analyzed.The screened transducer is combined into a transducer array for experimental verification.Experimental results show that the transducers with the same parameters can improve the intensity of the parametric array beam.(3)Aiming at the problem of phase control accuracy of phased array signals,a composite delay method combining system delay and phase delay is proposed.The effectiveness of the delay method is verified by simulation and experiment,and high-precision delay control with an error of less than Ins is realized.(4)Design and build a phased parametric array system,and experiment with the proposed beam synthesis algorithm.The experiment verifies and analyzes two different beam synthesis algorithms.At the same test distance,the actual sound field test was performed on the Chebyshev weighting method based on amplitude weighting and the acoustic focusing beam synthesis method based on phase weighting,respectively.By studying the directivity of the phased parametric array,the effectiveness of the amplitude-weighted phased array beam control algorithm and the phase-weighted focused parametric array acoustic beam control algorithm are verified respectively.At the same time,filter the consistent transducers and form a transducer array and conduct experiments,which proves that the method can improve the directivity of the parametric array beam.These research results have important guiding significance for the application and development of phased parametric array beam synthesis technology.