Research On Directivity Control Theory Of Broadband Parametric Array

With the continuous development of social economy,people's requirements for the quality of life and living environment are constantly improving,and the problem of noise pollution is becoming increasingly prominent.Because the generation of noise is highly related to people's living conditions and subjective wishes,advanced technical means are essential for noise monitoring and prevention.Directional acoustic emission technology can be used in sound source devices with high directivity.Because the diffusion of acoustic waves is avoided,the generation of noise is fundamentally reduced.Parametric array is one of the representative technologies of directional acoustic emission,which can realize directional acoustic emission in a small size.Although a lot of research work is devoted to reducing the distortion level of the parametric loudspeaker array,the directional control of the parametric array has not been well developed.At present,the related work is limited to single-frequency phased parametric array.In order to solve the problem of lack of acoustics theory in the near field condition of the broadband phased parametric array,based on the classical parametric array model,the broadband expansion is carried out,and the directivity model is modified in the near field condition,and the directivity model of the broadband parametric array is established,which is suitable for the research and application of the near field characteristics of the broadband phased parametric array.Based on the acoustics theory of wideband parametric array,the beamforming algorithms of broadband phased parametric array are studied,including single beamforming algorithm,single beamsteering algorithm and multi-beamforming algorithm.Because the beamwidth of the parametric array changes with the difference frequencies,the timbre difference will be produced in the human ear,so there is a need for constant beamwidth in practical application.Algorithm is proposed by designing the carrier signal and the sideband signal control difference frequency beamforming,can carry on the constant beamwidth to the single beam design,realization of single beamsteering,make the precision higher.By extending it to the multi-beamforming algorithm,the multiple beams can point to different angles with different amplitudes and different beamwidths.According to the acoustic principle of length-limited parametric array,based on the conventional parametric array,the related acoustic theoretical model of length-limited parametric array is improved.The length-limited parametric array uses two ultrasonic carriers of different frequencies,so that the demodulated audio waves cancel each other in the far field region,and the audio waves are confined to a smaller region,thus achieving more accurate fixed-point acoustic emission.The length-limited parametric array can form an audible acoustic beam with limited beam length.It is one of the latest development directions of parametric array.The modulation method is improved to solve the problem that the nonlinear distortion of length-limited parametric array is too strong.By controlling the selection of ultrasonic frequencies and initial amplitude ratio coefficient,the beamlength control is proposed,and the control of half-amplitude beamlength is realized.An optimal beamforming model of a length-limited parametric array is established to obtain a finite length beam with a constant beamwidth at a specific distance.