EXPERIMENTAL STUDIES OF ACOUSTIC PROPAGATION CHARACTERISTICS IN THE LOW PRESSURE OF CO_2 AT-MOSPHERE BASED ON THE FIBER OPTICAL SENSING TECHNOLOGY

摘要

In order to meet the demand of correction for thermal model of future Mars probe and validation of performance of Mars probe in extreme environments, we need to simulate the Mars environment in the ground. The wind speed measurement is very important for the Mars environment simulation and test. The atmosphere on Mars is much different from that on earth, that the pressure ranges from 600 Pa to 1000 Pa and the dominant constituent is CO_2. In Earth, the fiber optical sensing technique has been successfully applied for the sound velocity measurement. It is interesting to study whether the fiber optical sensing technique could be used in Mars environment. The speed of sound in the low pressure of CO_2 atmosphere has been derived theoretically by assuming that the idea gas law applies to this case. We have carried out experiments to measure the speed of sound in a space environment simulator which we can fill with air or pure CO_2 respectively. The pressure in the chamber is adjusting from 10~5 Pa to 600 Pa with different intervals, the pitch-catch method using four pairs of piezoelectric actuators and sensors, with central frequencies being 21, 25, 34, and 40 kHz respectively, is applied to generate acoustic signals. We use the fiber optical sensing technology to measure the ultrasound waves speed at different pressures. The experimental results show that the fiber optical sensing technique can be applied for the sound velocity measurement in the low pressure of CO_2 atmosphere, the speed of sound rarely varies with the pressure in the range from 10~5 Pa and 600 Pa, while it depends on the composition of the gas and the temperature.