Study of environmental conditions effects on the mechanical-acoustic properties of microphones

International audienceMore and more applications, such as noise control in hostile environments, acoustic thermometry, gas metrology or optimization of thermoacoustic engines, require performing acoustic measurements with microphones in ?extreme? atmospheric conditions or even non atmospheric ones. Being able to predict and characterize the sensitivity and frequency response of microphones in these conditions of use is then of fundamental purpose. However, regarding the variety of potential applications, it is not realistic to perform microphones calibrations for all environmental conditions of possible interest. The main global properties of microphones should then be predicted by a reliable modelling procedure that enables to take into account the effects of environmental conditions on its mechanical-acoustic properties. Basically, the sensitivity and frequency response of a microphone are determined almost by its geometrical structure and dimensions, and by the mechanical properties of its membrane, which are both related to the temperature of the cartridge. On the other hand, the acoustic behaviour of a microphone strongly depends on the physical properties of the gas in the cartridge, which are function of the nature, static pressure and temperature of the gas and can easily be calculated. For the sake of the present work, an analytical model available in the literature is used to describe the behaviour of a 1/4?? microphone. This global modelling is associated to a mechanical study for predicting the temperature effects on the properties of the constituting materials. A comparison is presented with experimental results obtained for the resonance properties of the membrane in vacuum and for the frequency response under helium atmosphere of a 1/4?? microphone in order to check the validity of the theoretical approach suggested here