Analytical model and the characterization of an infrasound generator in the air

In the context of the CTBT (Comprehensive nuclear Test Ban Treaty), a global detection network of geophysical stations is established in order to provide global coverage for nuclear explosions monitoring. An approach is the measurement of the infrasonic dynamic pressure in the atmosphere with microbarometers, which are operational in the monitoring network. The CEA develops this type of sensor. These instruments must respond to minimum requirements, particularly in terms of frequency response. To characterize and validate these requirements, a dynamic pressure infrasound generator was built in 2001 by the CEA. Actually, this generator is greatly in need of an accurate characterization, as far as there are no normalized methods or references in infrasonic frequency domain. An analytical modeling of the sound pressure in the cylindrical cavity of the calibrator is presented. An experimental characterization is also performed and some comparisons are made. This work serves to highlight the influence of thermodynamic transition from isothermal to adiabatic transformation, the influence of the loudspeaker membrane viscoelastic nonlinearities, and aim to characterize the amplitude response and the phase response of the generator from 10e-4 Hz to 200 Hz.