【作者】 陈敏；

【导师】 黄大贵； 徐利梅；

【作者基本信息】 电子科技大学 ， 测试计量技术及仪器， 2008， 博士

【摘要】 声频定向系统是第一种可产生高指向性可听声的新概念声源。参量声学阵的提出为利用空气中声波的非线性传播效应产生指向性声束提供了理论依据。本文探索了利用参量声学阵作为可听声源，产生指向性声频的基础理论及系统实现关键技术，以推动声频定向系统的基础性研究与实用化进程。完成的主要工作如下：根据Helmholtz的非线性声学理论及参量声学阵理论，阐明了声频定向系统的基本工作原理，并对KZK(khokhlov-zabolotskaya-kuznetsov)方程进行了初步的解析求解以获得精确的参量声学阵理论模型。提出了三维指向性图解法，以之为基础，从理论上证明了利用换能器面阵可产生三维高指向性声束，增加阵元数可抑制旁瓣、增强指向性，从而提出了一种谐振频率可调式聚偏二氟乙烯(PVDF)膜换能器及一种整体式PVDF膜换能器的设计方法。实验证实整体式PVDF膜换能器能产生高指向性的可听声。依据自解调理论，分析比较了声频定向系统的DSB法、SSB法、平方根法等信号处理方法，建立了自解调理论模型，提出了单频、宽带信号输入时声压及谐波失真的理论计算公式，明确了自解调信号声压的主要影响参数及其影响机制，提出了声频定向系统的关键技术突破方向。提出了声频定向系统信号处理方法开发的无失真包络平方条件。开发出了两种信号处理新方法：改进AM法和N阶近似平方根法。试验验证了改进AM法可有效降低DSB法的谐波失真，而N阶近似平方根法则可有效降低平方根法的谐波失真。设计制作了基于定点DSP技术的声频定向系统信号处理平台，探讨了各种信号处理方法的实时实现技术，并在该平台上实现了各种信号处理算法。在此基础上，采用MATLAB／Simulink建立了各种算法的仿真模型。应用以上理论及关键技术研究成果，成功研制出了可用于实验研究的声频定向系统样机。通过对DSB法自解调信号的测试，发现自解调理论与“Berktay远场解”的理论预测结果与实测结果有一定差异。通过对平方根法自解调信号的测试，明确了影响自解调信号测试的主要因素及相应的影响机制。更多还原

【Abstract】 The audio directional system is the first sound source that can generate an audible sound with high directivity. The parametric acoustic array theory provides the theoretical basis for utilizing the nonlinear propagation effect of the sound in the air to generate an audible sound beam with directivity. This thesis explores the basic theory and the key system implementation technologies for using the parametric acoustic array as an audible sound source to produce an audible sound with high directivity, which is significant for promoting the fundamental research and the application of the audio directional system. The main research contents and achievements are summarized as follows:The basic working principle of the audio directional system is explained according to Helmholtz’s nonlinear acoustic theory and the parametric acoustic array theory. Furthermore, the analytic solution of the KZK（khokhlov-zabolotskaya-kuznetsov） formula has been derived in this dissertation to obtain a more accurate theoretical model for the parametric acoustic array.A graphical method for three-dimensional directivity is proposed. By the method, it is verified theoretically that only the plane array of the transducer can provide the required three-dimensional directivity, and a higher directivity can be obtained by increasing the number of the array units to suppress the sidelobe level. Based on such findings, the design methods for a polyvinylidene fluoride（PVDF） film transducer with an adjustable resonant frequency and a integral type PVDF film transducer are presented. It is demonstrated by the testing result that the integral type PVDF film transducer can generate an audible sound with very high directivity.The signal processing methods, including the DSB method, the SSB method and the square rooting method, are compared according to the self-demodulation theory. The theoretical formulas for calculating their sound pressure and harmonic distortion when a single-frequency signal or a broadband signal is inputted are presented by establishing their theoretical self-demodulation models. The breakthrough points for the crucial technologies of the audio directional system are clarified by confirming the key parameters affecting the sound pressure of the self-demodulated signal and obtaining their corresponding influence mechanism.A distortionless squared envelope condition for developing the signal processing method of the audio directional system is proposed, and two new signal processing methods, the improved AM method and the N^th-order approximate square rooting method, have been developed. It is verified by experiments that the improved AM method can reduce the harmonic distortion of the DSB method effectively, and the N^th-order approximate square rooting method is useful to decrease the harmonic distortion of the square rooting method.The signal process platform for the audio directional system, which is based on the fixed-point DSB technology, has been designed and fabricated. Then, the signal processing algorithms have been carried out after the exploratory research on their real-time realizing technologies. Moreover, the simulation models of the related signal processing algorithms have been established by MATLAB/Simulink.The aforementioned theory and key technologies employed, a prototype of the audio directional system has been developed successfully. It can be applied in experimental research. It is found in the experiments for testing the self-demodulated signal of the DSB method that the theoretical results predicted by the self-demodulation theory and "Berktay’s Far-Field Solution" are inconsistent with the measured result to a certain extent. The influencing factors of the self-demodulated signal and their influence mechanism are also clarified by testing the self-demodulated signal of the square rooting method.更多还原