High-speed gas concentration measurement using ultrasound

This paper describes a detection method with a millisecond temporal resolution using ultrasound to determine the gas concentration. Although gas chromatography has long been employed to detect the concentration of a gas, it cannot be used to detect quick changes in the concentration of a gas. Hence, we examined alternate methods, and found that a change in the concentration of a gas causes a shift in the amplitude pattern of an ultrasound signal, which is regulated by the gap between an ultrasonic transmitter and receiver. Using this principle, we fabricated a high-speed gas concentration monitoring device. Then we tried to detect the exchange between nitrogen and air to confirm that this sensor can trace rapid gas changes. In addition, we found that this device can measure the change from pure nitrogen to a mixture of 5% oxygen and 95% nitrogen with a 45 dB signal-to-noise ratio.