Guianvarc'h Cécile, Gavioso Roberto M, Benedetto Giuliana, Pitre Laurent, Bruneau Michel
Laboratoire Commun de Métrologie LNE/Cnam, 61 rue du Landy, 93210 La Plaine Saint Denis, France.
Rev Sci Instrum. 2009 Jul;80(7):074901. doi: 10.1063/1.3160295.
Condenser microphones are more commonly used and have been extensively modeled and characterized in air at ambient temperature and static pressure. However, several applications of interest for metrology and physical acoustics require to use these transducers in significantly different environmental conditions. Particularly, the extremely accurate determination of the speed of sound in monoatomic gases, which is pursued for a determination of the Boltzmann constant k by an acoustic method, entails the use of condenser microphones mounted within a spherical cavity, over a wide range of static pressures, at the temperature of the triple point of water (273.16 K). To further increase the accuracy achievable in this application, the microphone frequency response and its acoustic input impedance need to be precisely determined over the same static pressure and temperature range. Few previous works examined the influence of static pressure, temperature, and gas composition on the microphone's sensitivity. In this work, the results of relative calibrations of 1/4 in. condenser microphones obtained using an electrostatic actuator technique are presented. The calibrations are performed in pure helium and argon gas at temperatures near 273 K and in the pressure range between 10 and 600 kPa. These experimental results are compared with the predictions of a realistic model available in the literature, finding a remarkable good agreement. The model provides an estimate of the acoustic impedance of 1/4 in. condenser microphones as a function of frequency and static pressure and is used to calculate the corresponding frequency perturbations induced on the normal modes of a spherical cavity when this is filled with helium or argon gas.
电容式麦克风更为常用，并且已经在环境温度和静压条件下的空气中进行了广泛的建模和特性研究。然而，计量学和物理声学的一些感兴趣的应用需要在显著不同的环境条件下使用这些换能器。特别是，通过声学方法测定玻尔兹曼常数k时，需要在水的三相点温度（273.16K）下，在很宽的静压范围内，使用安装在球形腔内的电容式麦克风极其精确地测定单原子气体中的声速。为了进一步提高该应用中可实现的精度，需要在相同的静压和温度范围内精确确定麦克风的频率响应及其声输入阻抗。以前很少有工作研究静压、温度和气体成分对麦克风灵敏度的影响。在这项工作中，展示了使用静电致动器技术获得的1/4英寸电容式麦克风的相对校准结果。校准是在温度接近273K、压力范围为10至600kPa的纯氦气和氩气中进行的。将这些实验结果与文献中可用的一个实际模型的预测进行了比较，发现吻合度非常好。该模型提供了1/4英寸电容式麦克风的声阻抗作为频率和静压函数的估计，并用于计算当球形腔充满氦气或氩气时，在其简正模式上引起的相应频率扰动。
