Gas sensors play an important role in many applications, and they have been extensively developed during the past few decades. Surface acoustic wave (SAW) sensors are widely used because of high sensitivity, small geometrical dimensions, relatively simple electronic setup, and generally low production costs.
Previous researches on SAW sensors focused mostly on the steady-state response, which means the relation between the detected gas concentration and the measured sensor output after a long stabilization time. However, the intuitionistic simulation model for sensor response in real time is still needed.
Recently, researchers from the Institute of Acoustics (IOA) of the Chinese Academy of Sciences have established a simulation model to describe the real-time response mechanism of the SAW gas sensors. The real-time model would help to visually analyze the factors affecting the sensor response and optimize the sensor parameters. The study has been published online in the Japanese Journal of Applied Physics.
This model is based on the perturbation theory, the Langmuir formula, and the fundamental transport equations. The perturbation theory is utilized to describe the relationship between the sensor’s output and the mass loading on the detector’s surface. The Langmuir formula and fundamental transport equations are quoted to depict the adsorption–desorption behavior of gases on the sensitive film. According to these theories, the mass loading curve is obtained by using the finite element method with COMSOL modeling software.
In the research, the SAW frequency response is proportional to the mass loading on the surface of a SAW device. Therefore, the frequency response curve of the SAW gas sensor in real time is simulated.
By configuring a SAW gas sensor coated with zinc oxide quantum dots, an experiment was performed to measure the frequency shifts caused by adsorbing and desorbing dimethyl methyl phosphonate. Excellent repeatability was observed in gas sensing experiments, and the simulation curve was consistent with the experimental results.
The simulation in this work and the discussions about the adsorption–desorption behavior of gas on the SAW sensitive film would benefit the realization of higher performance SAW gas sensors. In the following research, researchers will exploit this model to analyze the factors that affect the response of the SAW gas sensor and optimize the sensor.
Figure 1. The relationship between the full 3D reactor and the 2D model. (Image by IOA)
Figure 2. The comparison of the mass loading and the frequency response of the SAW gas sensor. (Image by IOA)
Funding for this research came from the National Natural Science Foundation of China (No.11574345).
QI Xiaolin, LIU Jiansheng, LIANG Yong, LI Junhong, HE Shitang. The response mechanism of surface acoustic wave gas sensors in real time. Japanese Journal of Applied Physics, 2019, 58(1): 014001. DOI: 10.7567/1347-4065/aat223.
Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China