Urban sensor networking using thick slots in manhole covers

Conversion of a manhole cover into a slot antenna is an environmentally-robust method of retrofitting sewage systems for environmental monitoring networks. Challenges in this design include the fact that the environment is harsh and not static, the radiation source is at ground level, and the antenna can not protrude from the ground. In this paper, we demonstrate successful sensor network retrofitting of common sewage systems through radiation from manhole tunnels to above-ground nodes, forming a wireless sensor network used to combat combined sewer overflows. Underground sensor-to-above-ground wireless links are established by manhole covers modified to have slits with appropriately spaced coaxial connections that create efficient slot antennas. The antenna was modeled and simulated using a full-wave simulator accounting for all features of the metallic shape of the cover. The antenna is shown to perform as expected as verified by outdoor measurements, but more importantly as implemented in a real life sensor network test bed