Study On Radio Wave Propagation Characteristics In Disaster Mine

In typical coal mine dynamic disasters such as roof collapse,coal dust explosion,and rock burst,mine roadways may collapse and block due to staggered fracture and fragmentation of rocks.Due to coal dust interference,rock shielding,and coverage,the signal from wireless devices in the disaster area is rapidly fading,making it difficult to access the rescue network.Emergency rescue in the affected mine faces great challenges.It is urgent to break through the wireless communication problem in the mine disaster area.The estimation of wireless signal propagation loss and propagation characteristics is crucial for the design,optimization,and performance evaluation of wireless emergency communication systems.This thesis aims at the wireless communication problems in non-collapsed and collapsed areas of coal mines after disasters.The wireless electromagnetic wave propagation models are established.The propagation characteristics of electromagnetic waves are studied,as well as the impact of uneven,heterogeneous,and lossy media such as coal dust,rock,and coal mines on the propagation of electromagnetic waves.At last,the parameter configuration and deployment optimization indicators of emergency rescue wireless communication systems are analyzed.For the non-collapsed region of the affected roadway,the region is approximated as a dielectric wall waveguide.Based on the multi-wavelength mode waveguide theory,the narrow-band propagation model and the tapping time delay model are established.The scattering loss of coal dust particles is derived to modify the proposed models.Using the established model,the narrowband characteristics and broadband characteristics of electromagnetic signals are discussed.The effects of the tunnel size,carrier frequency,antenna position,polarization mode,and coal dust concentration on the signal received power are analyzed.The results show that the coal dust concentration can reduce the electromagnetic wave propagation strength and the wireless coverage area,but has little effect on the time delay expansion of the wireless channel.The coal dust can also influence the frequency characteristics of electromagnetic waves significantly.If the coal dust can be neglected,the wave propagation loss decreases with the frequency.However,if the coal dust cannot be neglected,the wave propagation loss increases with the frequency.This means that there is an optimal communication band for wireless communication.This optimal band is related to the coal dust concentration.For the collapsed area of the affected tunnel,the heterogeneity of the medium in the collapsed area,the stratification properties,and the distribution location of wireless communication devices are considered.The wireless communication links are divided into three categories: air-coal,coal-coal,and coal-air communication.The reflection and transmission principles of electromagnetic waves in the stratified medium are studied.The signal transmission path parameters and attenuation of wireless transceiver devices are calculated by using the ray method.The electromagnetic wave penetration model of the collapsed tunnel after the disaster is established.The electromagnetic wave path propagation loss of these three communication links is simulated and analyzed respectively.The effects of various parameters such as rock medium,carrier frequency,and device location on the signal propagation loss are discussed.The results show that the signal propagation loss increases with the transmission distance for the air-coal link.For the coal–coal link,the path propagation loss of the signal can be divided into fast fading and slow fading regions.In the fast-fading region,the multipath effect is obvious.The larger the conductivity of the collapsed rock,the weaker the electromagnetic signal coverage ability.High gas pressure and high stress can enhance the penetration ability of the electromagnetic waves.In the coal-air link,with the increase of distance,the signal propagation loss fluctuates up and down within a certain range.For all kinds of communication links,their frequency characteristics behave the same.The lower the frequency,the better for signal transmission.This thesis contains 44 figures,4 tables,and 88 references.