Study On Underwater Weak Signal Amplification Of Variable Parameter Effect Of Seawater Active Medium

As an important part of naval confrontation,underwater target detection has an important military strategic position.However,due to the continuous development of submarine stealth technology,underwater detection faces the problem of low signal-to-noise ratio.The mostly used array to improve the signal-to-noise ratio is also unable to meet the demand due to the limitation of platform installation space.Some studies have found that there will be amplitude amplification in acoustic propagation in active media using external excitation to excite the change of acoustic parameters,which provides a new idea for underwater weak signal amplification and signal-to-noise ratio improvement.Based on the characteristics of acoustic propagation amplification in active medium,this paper focuses on the theoretical simulation analysis method of active medium,strong acoustic excitation of seawater active medium,alternating magnetic field excitation of active medium and acoustic propagation characteristics in active medium,which solves the problems of unclear acoustic signal amplification mechanism of seawater active medium,unclear excitation means of seawater active medium and unknown amplification effect of acoustic signal.Aiming at the underwater weak signal amplification of the variable parameter effect of seawater active medium,this paper first considers the sound velocity-varying active medium,and establishes the sound propagation model of the sound velocity-varying medium.According to the analysis,the multi-scale method is selected to directly solve the theoretical solution of sound propagation,and the sound propagation simulation is carried out by the finite difference time domain method.The simulation is consistent with the theoretical results.It is obtained that when the sound velocity modulation frequency of the medium is twice the sound wave frequency,the sound wave amplification phenomenon will occur,and the amplification effect will be more obvious with the increase of the size of the active medium and the intensity of the sound velocity modulation.Then,based on the influence of temperature on the sound velocity of the medium,a method of modulating the equivalent sound velocity of the medium by strong acoustic excitation is proposed.The acoustic-thermal coupling model of the medium under strong acoustic excitation is established,and the control relationship between the sound velocity of the medium and the vibration velocity of the excited strong acoustic particle is obtained by the step-by-step approximation method.The acoustic propagation theory and simulation analysis show that the seawater active medium under strong acoustic excitation can amplify the acoustic wave,but the amplification effect is not good due to the slow change of temperature rise,and the method of using strong acoustic excitation to amplify the acoustic signal is not applicable.Finally,considering the Lorentz force in the process of sound propagation under magnetic field excitation,this paper proposes a method of exciting seawater active medium by alternating magnetic field.Through the electro-mechanical-acoustic analogy analysis,the equivalent viscosity of the medium under magnetic field excitation will change,and the control relationship between the equivalent viscosity of the medium and the magnetic field strength is derived.It is concluded that the viscosity modulation effect increases with the increase of magnetic field strength and medium conductivity.Considering the impedance matching and high conductivity of hydrogel and seawater medium,a method of adding hydrogel in seawater medium to improve the excitation effect of magnetic field is proposed.By carrying out the simulation of acoustic propagation amplification of active medium under alternating magnetic field excitation,it is found that the acoustic wave propagation process will be attenuated by viscous excitation.When the modulation frequency of the equivalent viscosity coefficient of the medium is twice the frequency of the acoustic signal,the acoustic wave has a good amplitude amplification phenomenon at the incident active medium,which verifies the feasibility of using the alternating magnetic field to excite the active medium to amplify the weak signal.In summary,this paper proposes to use the variable parameter effect of seawater active medium to amplify the underwater weak signal and improve the signal-to-noise ratio.Two excitation methods of strong acoustic excitation and alternating magnetic field excitation are proposed.The acoustic propagation model of seawater active medium is established and the acoustic propagation simulation is carried out.The simulation results are basically consistent with the theoretical results.It provides a new technical way to improve the signal-to-noise ratio of underwater weak signal and underwater detection ability.