| Summary: | Acoustic detection technology has the advantages of low cost, short detection period, online detection and low power consumption. However, the complex circuits and procedures are needed to measure the acoustic absorption while using the conventional method. In order to solve the problems, a dual-frequency measurement based on echo voltage is proposed. The mechanical structure and the measurement circuits are designed. The acoustic absorption coefficients at two different frequencies are calculated and the acoustic relaxation absorption spectrum is obtained. The relaxation frequency and the acoustic absorption are measured at the concentration of 100.0%, 70.0%, 50.8% and 35.5% of carbon dioxide-nitrogen mixed gases. The relationship between the relaxation absorption and the gas concentration is obtained and is utilized to build a mathematical model. Then the unknown concentration of carbon dioxide is able to be obtained. Finally the experiments are done to verify the feasibility of the measurement.
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