Research Of Transmission Properties Of Terahertz Waves In The Coal Medium

With water damage of Mine getting worse, changing the traditional monitoringmethods to make the measurement results more accurate and promptly to protect livesand property of the people, and the using of terahertz to monitor the water disaster andgas which are security applications implemented is urgently needed. But before thatwe need to research the propagation rule of terahertz in the coal medium, to make thedesign and implementation of the entire system be smoothly.This paper study of generating of terahertz firstly, compared the three mainstreamgenerating method, and chose one of the solid-state electronics method which is morestable, high-emission power, and easier to implement. The design of system has beenfinished, the system has been set up, A stable generation system of THz has beenobtained, whose transmit power is greater than200mW, and the foundation for themeasurement of transmission characteristics has been laid.In this paper, the terahertz propagation in coal is divided into three issues toresearch: firstly, detected the THz attenuation characteristics in the coal samples,obtained the relationship of attenuation coefficient with the humidity of sample, thearea of sample (component of the sample), and the frequency of the incident wave.Found the value of attenuation coefficient is proportional to the humidity of sample,the humidity increased, the attenuation coefficient became larger; Obtained thatattenuation coefficient is dependent on the components of sample, and mustconsidering the composition of the sample; Got that attenuation coefficient in the75-750GHz, THz band exhibits an increasing tendency when the frequency increased.Secondly, detected the reflective properties of THz in coal samples, measured that thereflectance of coal sample is10.33%, at the same frequency110GHz, and measuredthat the reflectance of water is7.90%, inferred that THz is able to detect the water inthe coal, and proved the feasibility of measurement the water disaster with THz. Finally, chose the free space method to measured the dielectric constant which is thecharacterization of the relationship between the coal and the terahertz wave, alsofound the dielectric constant of the sample is connected with the humidity,temperature of the sample, area (component) of the sample, the incident wavefrequency dependent; obtained from the measurement, the dielectric constantincreases with the humidity of the sample, the temperature of the sample indirecteffects of the dielectric constant of coal by affect the humidity; the dielectric constantof coals samples in different regions exhibit different values, because the dielectricconstant is connected with the main mineral composition of coal, especially with thepyrite; and when the incident wave frequency increased, the dielectric constant of thesample showed a decreasing trend.