Abstract
The phase sensitivity of the condenser type acoustic transducers at low frequencies is crucial for locating large-scale natural and manmade activities, but is now commonly calibrated based on comparison methods. Although the primary method, which traces its sensitivity back to the international standard unit is few studied. Recently, the explicit sensitivity models of the condenser type acoustic transducers based on the laser-pistonphone technique are built, and can be used to study the phase responses of acoustic transducers at infrasonic frequencies. So that, in this paper, the phase sensitivities of acoustic transducers when its rear vent connected to the calibrating sound field or outside atmosphere are studied in detail. Secondly, time domain analysis of generated sound pressures by displacement excitation are derived to reveal the mechanism of phase variation. Calculations show two distinct sensitivities with 90° phase lead and −10° phase lag limits for vent in field and vent out field calibrations, which are dominated by the pressure leakage and heat conduction effects at infrasonic frequencies.
Highlights
Infrasounds are commonly produced by large-scale natural and manmade activities, earthquakes, volcanic eruptions, landslides, nuclear explosions, spacecraft launch and landing, etc., and have caused wide concern in recent years
The phase response of acoustic transducers are commonly calibrated using in-situ or calibrator methods to get their phase consistency,[13,14,15,16] while the primary calibration,[17,18,19] by which the acoustic transducer is calibrated with reference to non-acoustic standards and with the highest possible precision, is few studied
For vent out field calibrations, it can be seen that the amplitude sensitivity will be increased to a certain extent under the influence of pressure leakage and heat conduction effect of the acoustic transducer, but will not show attenuation as the diaphragm deformation response does
Summary
Infrasounds are commonly produced by large-scale natural and manmade activities, earthquakes, volcanic eruptions, landslides, nuclear explosions, spacecraft launch and landing, etc., and have caused wide concern in recent years. In-depth analysis has showed that the primary calibration of the acoustic transducer at low frequencies contains two coupling mechanisms Sound pressures both in the pistonphone and acoustic transducer will decrease due to the coupled pressure leakage and heat conduction effect.[25,26] Secondly, these sound pressures couple with the diaphragm elasticity, and determine the diaphragm deformation.[27,28,29] Based on these, explicit sensitivity models characterizing the relationship between the diaphragm deformation and structures of acoustic transducer and pistonphone were derived.[27]. That in this paper, the phase sensitivities of acoustic transducer at infrasonic frequencies, when its rear vent connected to the calibrating sound field or outside atmosphere are studied in detail. Divide the diaphragm deformation with the calibrating sound pressure, equation (1), explicit sensitivity models of acoustic transducer for both vent in field and vent out field calibrations are obtained as
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