Gas sensor

A gas sensor, including:

• a shell with a receiving cavity, the shell comprising a cover, a substrate spaced apart from the cover, and a side wall located between the cover and the substrate;
• an infrared transmitter and an acoustic sensor accommodated in the receiving cavity, and
• a flexible film connected with the side wall, wherein
• the flexible film divides the receiving cavity into a first cavity and a second cavity;
• the first cavity is formed by the joint enclosure of the flexible film, the side wall and the cover;
• the second cavity is formed by the joint enclosure of the flexible film, the side wall and the substrate;
• the infrared transmitter is located in the first cavity;
• the acoustic sensor is located in the second cavity;
• the shell comprises a vent hole communicating with an outside and the first cavity;
• and
• wherein the flexible film, the first cavity and the second cavity form a resonant system, an intrinsic frequency of the resonant system is the same as a modulation frequency of the infrared transmitter.