Anti-reverberation Acoustic Communication Technology Across Metal Tanks

In order to obtain internal information of a closed metal tank,such as temperature data,data transmission across the metal wall becomes an urgent problem to be solved.Because the metal medium has shielding effect on electromagnetic（EM）waves propagation,the attenuation of EM waves is extremely high when propagating through a metal wall,which greatly reduces the channel capacity of EM wireless transmission.In addition,the method perforating holes in the metal wall to pass through the wire will destroy the integrity of the metal closed container.In some extreme environment applications,such as fuel tanks of rockets,this approach will influence the mechanical properties of metal wall,which will reduce its reliability and safety.Since vibration signals can propagate from the wall of the metal closed container to the outside of the metal closed container with low attenuation,the use of acoustic waves can realize data transmission without destroying the physical structure of the metal closed wall.However,when acoustic waves pass through the metal closed wall,there will be severe reverberation in the closed physical structure of the metal wall.The acoustic waves passing through the metal closed wall exhibit characteristics such as propagation loss,long tail and reverberation interference.From the communication point of view,these characteristics will cause inter-symbol interference（ISI）that limits the data transmission rate.Therefore,an anti-reverberation method must be introduced in of the kind of acoustic communication system to adapt to the above acoustic characteristics.For data communication across the metal closed wall,this paper studies the acoustic propagation channel model through the metal closed wall and determines the main factors that affect the data transmission rate of the acoustic communication system.Based on the method of Orthogonal Frequency Division Multiplexing（OFDM）in radio communication,the acoustic wave communication algorithm is designed,including encoding,modulation,decoding,and demodulation,etc.After being verified by the MATLAB software,the communication algorithm is transplanted to the digital signal processing（DSP）hardware platform.The performance test in the actual tank was completed.The main research contents and innovations of this paper mainly include:1.The impulse response characteristics of the acoustic propagation channel model through the metal closed wall was studied.Based on the theoretical analysis of the metal tank vibration,time-frequency analysis of the impulse response is conducted.It is concluded that there are still short-reverberation frequency points or frequency range that can be used for high-speed data transmission in the acoustic propagation channel.How to select these frequency points is shown.2.In order to improve the data rate of acoustic communication system across the metal closed wall,this paper proposes a communication method of discrete orthogonal frequency point,based on the principle of OFDM.The short-reverberation discrete frequency points can realize the multi-channel parallel communication,which can effectively improve the data rate under the acoustic propagation channel.The communication algorithm and system was modeled and verified by the MATLAB,and a portable algorithm package to DSP hardware platform is formed.3.Based on the DSP hardware platform,the transplantation of the communication algorithm and real-time testing have been completed,which realizes the acoustic real-time communication system across the metal closed wall.The communication experiment in an actual metal tank indicates that:In the propagation environment of the long-tail metal tank with T₂₀=660ms,four discrete frequency points with short reverberation（1200,4600,5300,6000 Hz）are selected,Based on the four frequency points,the data rate of the communication system is 80 bps,which is more than 50 times higher than the data rate of various traditional time-domain modulation methods under the acoustic propagation channel.This paper proposes a technical method that effectively improves the data rate of communication system across the metal closed wall by acoustic sound waves,which can fully exploit the potential transmission capacity using the acoustic characteristics of the closed metal tank.This method also provides an idea for high-speed communication of directly-buried sensors in closed metal containers,such as high-pressure gas tanks,fuel tanks,solid rocket engines,fuze warheads,etc.This method is also widely applicable to aviation,aerospace and industrial intelligent monitoring.