Low frequency screening effect in urban areas and the engineering measurement technology

The low frequency screening effect is very good in urban districts because of a lot of underground metallic pipes. There are not only remarkable technology-economic benefits but also society benefits when considering this screening effect, which is named the city environment screening factor in practical engineering constructions. The theory of the low frequency screening effect of a multiconductor system is discussed in the paper. Then the engineering measurement technology and instruments of the screening effect are introduced in detail. Some successful application samples of the technology are presented. In general, the value of the city environment screening factor often can be 0.5 to 0.8, the lowest value may be 0.1, the highest may be 0.8 to 0.9