Study Of S-band Microwave Attenuation Characteristics In Fire Smoke And Flame

S-band microwave, with the advantages of huge capacity, strong penetrability and good real-time performance, has been widely applied into communication, radar, remote sensing and positioning, and other fields of technology. And this band of microwave has also been adopted in fire rescue including wireless communication systems, indoor positioning and life detecting radar. However, microwave signal propagation faces many issues like interference, time delay and interruption in fire scene result from scattering and absorption caused by flame and smoke. Hence, it is of great significance to deeply investigate the influence of fire smoke and flame on microwave communication and develop a theoretical techniques and applications of communication and detection in fire scene.To study the effects of smoke and flame in fire scene on S-band microwave propagation, through experiments and theoretical analysis this work built the related microwave propagation models and revealed the influence laws of characteristics of fire smoke and flame on microwave attenuation, which provide the theoretical guidance and technical support for solving how to propagate microwave in fire scene. The main research contributions are as follows:From the perspective of physical property of smoke and basic theory of electromagnetic wave, microwave attenuation mechanism in fire smoke was discussed. Considering the wavelength of microwave much larger than smoke particle size, Rayleigh scattering approximation theory was adopted to compute the cross section of scattering and absorption and to analyze the main reason of microwave attenuation by smoke particle. Meanwhile, microwave propagation models in fire smoke environment were also built.The experimental study of attenuation characteristics of S-band microwave caused by fire smoke. We designed an experimental platform for microwave propagation in scene of fire and measured the related characteristic parameters such as attenuation and smoke density in four types fire smoke including cotton smoldering, polyurethane flame, N-heptane flame and diesel flame. The results showed that fire smoke obviously attenuates the propagation of microwave and the attenuation grows as the increase of the smoke concentration. And the effects on microwave propagation characteristics varies from different types of fire smoke. To be specific, the microwave attenuation caused by N-heptane and diesel flame is greater and produces a more significant attenuation effect. Besides, the attenuation coefficients of different concentration of smoke are calibrated and the formulae of microwave propagation and attenuation under a given special condition are also proposed.The experimental study of attenuation characteristics of S-band microwave caused by flame. According to the attenuation mechanism, we analyzed the influence laws of ethanol flame on S-band microwave experimentally. Research showed that the microwave attenuation in flame depends on the frequency of microwave and the electromagnetic characteristics of flame. Specifically, the microwave attenuation will raise with the increase of the frequency of microwave if the frequency is smaller than the collision frequency of electron-neutral particle. And the microwave attenuation grows monotonically with electron density increase. In addition, while with the increasing of electron-neutral collision frequency, the microwave attenuation increases at first, reach the peak with the best collision frequency and then decreases gradually.