INFLUENCE OF CONDENSER MICROPHONES ON PHASE MEASUREMENTS IN PHOTOACOUSTICS AT LOW-PRESSURE

Condenser microphones used as photoacoustic signal detectors exhibit a phase-shift response that depends on both the nature and the pressure of the ambient filling gas. The authors develop a lumped-parameters model of the microphone damping in which the approximations are discussed. This model, after taking into account gas-slip effects on the surfaces of the condenser cartridge plates, is shown to accurately describe the response (magnitude and phase) of a commercial condenser microphone (Bruel and Kjaer 4144) for frequencies below 2. 2 kHz and ambient pressures between 1. 5 multiplied by 10**3 and 6 multiplied by 10**4 Pa.