Distribution Characteristics Of Difference-frequency Sound Field Of The Parametric Acoustic Array

Parametric acoustic array is the application of the two-wave nonlinear interaction theory.And it has drawn wide attention in underwater acoustic field, because it can obtain the low-frequency sound wave of high-directivity in a small size. Difference-frequency sound wave generated by the parametric acoustic array is the core of the parametric array technology.So the in-depth study of the distribution characteristics of the difference-frequency sound field is the foundation for the development of parametric array technology and acoustic wave interaction theory.The parametric acoustic array theory of Lighthill and Westervelt are introduced in this paper. And the sound pressure and directivity formulas of parametric array are obtained. Then the effects on the pressure and directivity of difference-frequency sound field are analyzed when changing the amplitudes, directivities and frequencies of primary frequency waves. And the effects on sound pressure and directivity of low-frequency sound field which is generated by three-wave interaction are investigated through numerical calculation by Matlab, when changing the amplitudes and phases of the high-frequency, mid-frequency and low-frequency sound waves. Based on the above theory and simulation analyze, an experimental method for describing the distribution characteristics of difference-frequency sound field is proposed from axial sound pressure, phase distribution and directivity. Especially the phase distribution of difference-frequency sound field can be obtained by this method, which is always ignored.The experimental measurement system of parametric acoustic field is designed and built.The effects on the distributions of sound pressure and phase of the difference-frequency sound field are studied, when changing the amplitude, initial phase and frequency of the original frequency sound wave. And the results are consistent with the laws of simulation, so the measurement method can be proved to be feasibility. It can be concluded that the source levels of the primary sound wave can only influence the sound pressure amplitude. And the phase distribution of difference-frequency sound field has a linear relationship with the initial phase of the primary sound wave. The directivity of difference-frequency sound wave is with reference to the primary sound wave frequency, difference-frequency. The distribution characters of difference-frequency sound fields generated by two transmitting transducers of the different frequency bands are measured, and the results were analyzed.