基于激光多普勒测量粒子振速的声压复现方法研究

The precise unit realization is the precondition of sensor calibration. Current sound pressure reference depends on the reciprocity of electro-acoustic transducer and it is an indirect unit realization. It is not suitable for the primary calibration of the new type sensors such as MEMS microphones. To achieve the sound pressure unit realization directly, the project focuses on the precise measurement of particle acoustic velocity in sound field by laser Doppler technology. The analysis of two beam interference fringes distortion model and the following behavior of tracer particles in the sound field will be carried out. The impact mechanism of Gauss beam model with beam waist position, cross angle and the sound frequency and intensity on the fringe distortion will be analyzed. And the simulation speed is set up to make the actual measurement of interference fringes in different regions and then the distortion model of fringes can be verified. At the same time, the optimization of the plane traveling wave, the direct measurement of the characteristic impedance and its reverse solution are taken to ensure the strict functions of the particle velocity and the sound pressure. Through the spectrum analysis and autocorrelation of the Doppler signal of the scatting particles, the accurate tracing particle velocity will be obtained. The equations of particles motion in multi-field and the relationship of physical characteristics of particles with the following character by the dimensional theory are discussed. The following characteristics of different tracer particles at different frequency and different intensity of the acoustic field and the velocity correction of the tracing particle to the real particle acoustic velocity can be obtained. Finally the unit realization of sound pressure by laser Doppler and the new primary calibration method of microphone can be realized accurately.

物理量值的准确复现是实现传感器校准的前提，现有声压基准依托换能器互易性实现声压量值的间接复现，已不适用于MEMS等新型声学传感器的原级校准。项目拟通过声场中双光束干涉条纹的畸变模型和示踪粒子的跟随性等因素的影响机制研究，探讨基于激光多普勒技术实现声压量值的直接复现。通过分析高斯光束模型下束腰位置、交叉角度及声场频率和强度对条纹畸变的影响机制，建立干涉条纹畸变模型，建立模拟速度源对干涉条纹不同区域进行实测，与畸变模型相佐证；同时，优化平面行波声场，通过特征声阻抗的测量和逆向求解，确立粒子振速与声压间的严格数学模型，采用多普勒信号的频谱分析和自相关处理，得到示踪粒子振速；建立粒子在多物理场作用下的运动方程，通过量纲分析建立粒子物理特性与跟随性的函数，获得粒子在不同频率和强度声场中的跟随特性及其速度修正。最终根据粒子振速与声压的函数关系，实现基于激光多普勒粒子振速测量的声压量值的准确复现。

物理量值的准确复现是实现传感器校准的前提，现有声压基准依托换能器互易性实现声压量值的间接复现，已不适用于MEMS等新型声学传感器的原级校准。项目基于激光多普勒测速原理和散射光子的自相关解调法研究空气声声压量值的直接复现，针对声压复现中的主要影响因素开展机理研究和量化评估：.（1）根据高斯光束的传输模型和双光束干涉原理，仿真分析了测量体内干涉条纹的畸变条件，采用CCD成像法和转盘法实现了干涉条纹畸变的测量及其对声压复现影响的量化评估；.（2）示踪粒子的大小是影响其跟随性和散射效率的主要因素，采用粒径测量仪得到粒径大小，根据BBO方程分析粒子的跟随性，为示踪粒子的选型提供依据；.（3）实现时域加窗的光子自相关解调法抑制介质平均流速的干扰，提高自相关曲线特征时间点的提取精度，提高声压复现的准确度；.（4）结合经验公式和密度测量仪等关键参数的测量仪器，实现介质声阻抗的测量，并评估其对声压复现测量贡献的测量不确定度分量。.基于上述研究成果，项目建立了行波管、驻波管和自由场中激光多普勒测速法的声压复现装置，其中：行波管和驻波管测量系统中，1 kHz声压测量的不确定度为0.10 dB （k=2），与互易法的偏差小于0.10 dB；自由场测量系统中，测量频率范围为500 Hz~20 kHz，1 kHz声压测量的不确定度为0.34 dB（k=2），500 Hz~10 kHz频段的测量结果与互易法偏差小于0.50 dB。项目研究成果有助于提高激光多普勒测速法空气声声压复现的技术水平，在声质点振动速度传感器、MEMS传感器及传声器高温校准等方面具有广阔的应用前景。