Research Of Underwater Acoustic Communication Technology Based On Parametric Acoustic Array

Acoustic communication technology is one of the most important researches in underwater acoustic domain. This technology can utilize a relatively small transmitting transducer to generate a low frequency sound with great directivity. It can not only solve the big problem that the size of transducer in underwater remote communication is relatively large, but can also be utilized in data transmission in vertical channel.Parametric acoustic array is a result of nonlinear function of water. The paper not only introduces the principle of parametric acoustic array producing, but also deduces nonlinear acoustic wave equation. In order to fully understand the basics of parametric acoustic array and prepare for data analysis, the author experiments in a basin to measure sound pressure of difference frequency sound in various underwater site. The distribution of sound pressure of difference frequency sound in the experiment indicates that the energy of parametric acoustic array is concentrated and has a good pointing.Parametric acoustic array has its remarkable characteristics. This paper mainly studies the directivity of parametric acoustic array and the energy conversion efficiency of difference frequency sound. In order to measure the directivity of parametric acoustic array,the author experiments in sink. Firstly the paper makes theoretical analysis, derives the directivity of parametric acoustic array function, and carries out numerical simulation. Secondly the author experiments in sink and get exact numerical value which is compared with simulation result.At last, the paper analyzes causes which lead to high directivity of parametric acoustic array.In the study of energy conversion efficiency of parametric acoustic array,firstly the paper analyzes the result of sink experiment, discusses the energy variation regular of difference frequency sound on central axis of transducer, derives formula of energy conversion efficiency, analyzes effects of various factors and puts forward methods of improving conversion efficiency.The main part of this paper is underwater acoustic experiment based on parametric acoustic array. Firstly it makes theoretical simulation to identify the method of data modulation and demodulation in the experiment. The author chooses Frequency Shift Keying(FSK) as modulation method due to its relatively higher reliability. After comparing degree of noise resistant and multiplicity resistance, the author chooses demodulation method with the best result. After identifying methods of data modulation and demodulation, the author does experiments in sink. After demodulating the sound wave received by hydrophone, the author gets the same experiment result. It turns out that underwater data communication based on parametric acoustic array is feasible. That is to say this technology of parametric acoustic array can utilize a relatively small transmitting transducer to generate a low frequency sound with great directivity.