Research On The Acoustic Convergence Technology Based On Time Reversal Technology

In order to achieve long distance sound convergence,the array of sound source is usually been used. However,the manoeuvring of low-frequency high-power transducer is limited by its large size and complex support system in practical application and the effect of focusing will become worse by the influence of scattering medium. In response to these problems,time reversal mirror is introduced in this paper and distributed manoeuvring is adopted. In this paper,the factors that influence the effect of focusing is discussed,and an optimization method based on genetic algorithms is put forward. At last, an experiment of time reversal focusing is designed to verify related theories in this paper. The main contents of the thesis includ:1) Based on the random process model,the relationship between SNR and duration of time-reversal window in scattering medium is discussed. In scattering field,scattered wave contains a large mount of energy and information,and time-reversal mirror use them to increase convergence gain and improve waveform. longer time-reversal window will improve effect of wave focusing,but influenced by attenuation effect during dissemination process,this increase will reach its saturation when time-reversal window is long enough.2)The theoretical result of multiple sound sources radiation field is deduced from uniform vibrating piston sound source. The research on the radiation sound field of the linear distributed sound sources shows that the directivity is better when the spacing is equal to wavelength of sound source. Moreover, a comparison between the sound field of single and multiple sound sources is made under the condition of equal radiation power, which demonstrates that mulitipule sound sources distribution only inhibits the acoustic energy in some directions.2) Keep time-reversal windows constant and study the SNR as a function of N,the imitation result show that SNR would proportionally to the square root of the number of array elements when contribution is uncorrelated,if contribution is partially correlated, SNR will reach a saturation as elements number grows. For a specific environment,besides adopting sufficient number of sound source,selecting the sites which their contribution has smaller correlation is also a good choice.3) Genetic algorithm is applied to determine the best combination of manoeuvring position in the situation which the number of sound sources is limited.4) At last,an experiment are used to testify the relationship between time-reversal window and effect of sound focusing,and the relationship between correlation and effect of sound focusing.