Fiber Optic Acoustic Vibration Sensors for Ultrasound Measurement in Low-Pressure CO₂ Environment

The detection of acoustic signals in the Martian environment is significant to understand the issues such as the evolution of the universe, structure of matter, origin of life, and future migration of humans. We proposed a method for testing ultrasonic wave by using fiber-optic Fabry-Perot vibration sensors in a low-pressure CO
₂
environment. We conducted high-precision sound wave amplitude and speed measurement tests with different center frequencies at 21, 25, 34, and 40 kHz under different gas compositions, pressures, and distances. Results showed that under the conditions of 15 °C and gas pressure in the range of 600 Pa to 1 MPa, the measured average sound velocity of ultrasonic signals at each frequency was 268.79 m/s in the CO
₂
environment, which was lower than the velocity of 336.18 m/s measured in the air environment. The results in this study can be applied to theoretical and experimental studies of future Mars probes pertaining to ultrasonic positioning and detection.