The gas identification technology has huge potential applications in medical diagnoses, food industries, early warning of poisonous gas leakage, fire prevention, antiterrorism, military, etc. Although electronic noses may be used to identify different gases, it has been a big challenge to identify gases by a single sensor. In this work, we demonstrate a novel gas identification strategy based on a single metaloxide-semiconductor (MOS) sensor assisted by an ultrasound. The identification is based on different ultrasonic effects on the steady sensing responses of an ultrasonically radiated MOS gas sensor to different target gases. It does not need a complicated feature extraction computation. Our experiments show that the success rate of identification can be up to 100% if strong enough ultrasound is employed. The identification process can also give the concentration of the gas to be identified. The identification result is immune to the interference of impurity gases to some extent. The anti-interference capability may be strengthened by increasing the vibration velocity and choosing proper sensing materials.
The bulk acoustic wave (BAW) assisted gas sensor utilizes the BAW to raise the sensitivity of a gas sensor, which provides a new and universal physical strategy to greatly improve the sensitivity of gas sensors. However, the physical principle of this type of gas sensor has not been clarified yet. In this work, the physical principle of the BAW assisted gas sensor is investigated experimentally and theoretically, and the effects of sound pressure and acoustic streaming on the sensing process are directly verified. It indicates that the transfer of target gas molecules onto the sensing surface can be enhanced by sound pressure on the sensing surface, which results in a significant increase of both the sensing response and sensitivity. Also, it is found that the sensing surface can be cooled down by acoustic streaming, which causes a sensing response change opposite to the change direction caused by the sound pressure, and little change of the sensitivity. It is predicted and experimentally verified that when both acoustic streaming and sound pressure exist on the sensing surface, the sensing characteristics should be between those of the two extreme working modes in which there is only sound pressure or acoustic streaming on the sensing surface.
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