| In 2021,the total volume of passengers of China’s subway reaches 23.602 billion,and the daily average number of passengers in 43 cities exceeds 64 million.As the main transportation means in modern cities,subway has the advantages of environmental protection,low carbon and high capacity.Subway stations are the main hubs of urban transportation,maximizing passenger travel demand and playing the role of rail transit delivery and interchange.With the rapid development of communication technology and the trend of subway intelligence,the type and number of exposure sources of the subway wireless communication system have increased dramatically,forming a complex electromagnetic environment on the subway platform.The thermal effects of radiofrequency（RF）electromagnetic exposure on human tissue and neurological damage have caused widespread concern,and the World Health Organization has defined RF electromagnetic fields as a possible human carcinogen.Most of the existing researches focus on the electromagnetic compatibility of the subway wireless communication system,and fewer researches report on human health effects caused by the RF exposure sources on the subway platform.Therefore,this dissertation presents the safety assessment of RF electromagnetic exposure for occupational personnel and passengers on the subway platform and has important significance in this area.This dissertation uses numerical electromagnetic dosimetry and experimental measurement methods to assess the safety of the station attendant,the adult and child passengers in the RF electromagnetic environment on the subway platform.RF exposure source models of the subway platform and numerical models of the adult and the child are constructed.The electromagnetic dose distribution of the adult and child models in the RF electromagnetic environment of the subway platform is quantified and analyzed.The numerical calculation results are compared with the electromagnetic exposure limits established by the International Commission on Non-Ionizing Radiation Protection（ICNIRP）guidelines.The safety of occupational exposure and public exposure in RF electromagnetic environment of the subway platform is assessed.The electromagnetic environment of subway platforms is measured experimentally to determine the spatial electric field intensity distribution,and further assess the safety of RF electromagnetic exposure of subway platforms.This dissertation studies the safety assessment of RF electromagnetic exposure on subway platforms.The main research is as follows:（1）Safety assessment of RF electromagnetic exposure to the ceiling mounted antenna on the subway platform.In the finite element high frequency structure simulator（HFSS）,a subway platform ceiling mounted antenna model and numerical models of the adult and the child are constructed,and the distributions of the induced electric field strength,the magnetic field strength and specific absorption rate（SAR）of the adult and child models exposed to the ceiling mounted antenna are calculated.The SAR distributions in human tissues at different positions and working frequencies are compared and analyzed,and the numerical calculation results are compared with the electromagnetic exposure safety standards.At different positions,the maximum SAR value of the adult model under electromagnetic exposure of the ceiling mounted antenna is 2.6382×10-6 W/kg,which is 6.5955×10-6 times the occupational exposure limit（0.4 W/kg）and 3.2978×10-5 times the public exposure limit（0.08 W/kg）of the ICNIRP guidelines.The maximum SAR value of the child model is 1.4089×10-6 W/kg,which is 1.7611×10-5 times the public exposure limit of the ICNIRP guidelines.The above results show that the electromagnetic environment of the ceiling mounted antenna on the subway platform has low safety risk on the occupational exposure of the attendant and the public exposure of the passengers.（2）Safety assessment of RF electromagnetic exposure by the leaky coaxial cable on the subway platform.The leaky coaxial cable model and numerical models of the adult and the child are established in HFSS software.The SAR distributions of adult and child models emitted by the RF exposure of the leaky coaxial cable are calculated,and the calculated results are compared with electromagnetic exposure safety standards.The maximum SAR value of the adult model is 1.5859×10-7 W/kg at different positions on the subway platform,which is 3.9648×10-7 times the occupational exposure limit and 1.9824×10-6 times the public exposure limit of the ICNIRP guidelines.The maximum SAR value of the child model is1.0854×10-7 W/kg,which is 1.3568×10-6 times the public exposure limit of the ICNIRP guidelines.At the nearest position to the leaky coaxial cable,the maximum SAR value of child’s brain tissue is 4.98 times that of adult brain tissue,indicating that the child’s brain tissue has a greater risk of RF electromagnetic exposure.The above results show that the electromagnetic environment of the leaky coaxial cable on the subway platform has low safety risk on the occupational exposure of the attendant and the public exposure of the passengers.（3）Measurements of the electromagnetic environment on subway stations.The method and equipment for measuring the electromagnetic environment of subway platforms are introduced,and field measurements of the electromagnetic environment are implemented for three typical subway platforms,including subway elevated platform,subway underground island and side platform.The measurement results are compared with the numerical calculation results for verification,and finally the measurement results are compared with the electromagnetic exposure safety standard.The maximum value of the electric field intensity on the subway elevated platform is 0.098 V/m,which is 0.075%of the ICNIRP occupational exposure limit and 0.163%of the public exposure limit.The maximum value of the electric field intensity on the subway underground platform is 0.09 V/m,which is 0.1%times the ICNIRP occupational exposure limit and 0.22%times the public exposure limit.The above results show that the electromagnetic exposure levels of the subway elevated platform,subway underground island and side platforms are within the ICNIRP limits.The systematic research results of this dissertation indicate that the occupational exposure of the subway attendant and the public exposure of the adult and child passengers in the RF electromagnetic environment of different types of subway platforms are within the limits for international and national electromagnetic exposure safety standards.The results of this dissertation have important reference values for the development of electromagnetic exposure safety standards for urban rail transit,and provide a data base for the safety protection of subway platform staff and subway platform passengers.Meanwhile,the dissertation is helpful to eliminate the concerns of subway occupational staff about the health effects of the working environment,and public concerns about the safety of subway electromagnetic exposure. |
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