Search, Identification and Positioning of the Underground Manhole with RFID Ground Tag

Road formation is the basic requirement of modern country. Manholes on the road are the main objects result in uneven surfaces. They are not only the killer of public safety, but also the main cause of national compensation; therefore, it is necessary to implement the underground manhole. However, it is not easy to search for the manhole from underground. Thus, it is essential to develop a set of searching, authentication, and precision positioning technologies. We analyze the pros and cons of metal detection, GPS location and RFID authentication approaches as well as their restrictions, of which the first two can only be used as navigational aids to arrive at the scene. While RFID can help to identify manholes, putting the manhole cover 20 cm below the asphalt concrete (AC) pavement creates more complications. Not only the reading distance is way too long for normal operation, but also the filling through the aquifer, and to avoid metal interference comes from the manholes, traditional RFID reader cannot achieve such purpose. Therefore special design is inevitable. In this paper, we analyze the RFID spectrum as well as the characteristics of binding RFID tags and metal. We then utilize the environmental characteristics of underground manhole, and design a special-purpose RFID tag - Ground Tag, in order to propose an integrated solution for searching, authentication and precision positioning of the underground manhole.