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    Project Abstract

    Many communities and cities in the U.S. are struggling from combined sewer overflow (CSO) and sanitary sewer overflow (SSO). These communities use a single sewer system to handle both storm sewer (from rainfall) and sanitary sewer (from buildings and homes). During a heavy rainstorm the water treatment plant can be overwhelmed causing a CSO or SSO, in this case untreated must be diverted directly into nearby waterways. The CSO and SSO can contaminate waterways and impacting human health and the environment. In our project, more than 150 wireless sensor nodes are being deployed to monitor the sewer flow in South Bend, IN - a mid-size city in the U.S. as shown in Fig. 1. These sensors nodes monitor the sewer in real time and control valve actuators in the sewer system to intelligently contain excess sewage greatly reducing or eliminating the amount that must be directed untreated into waterways.

    street view
    Figure 1. A wireless sewer sensor network

    One of the major challenges in this project is transmitting information from sensors below ground in the sewer system to a street level network which then relays information to a central node to make decisions and take action. To address this unique transmission challenge, we create a "manhole antenna" using a structurally strong, yet relatively low dielectric constant composite made of fiberglass and high strength foam as shown in Fig. 2. This sandwich structure can withstand the extreme structural loads and corrosive environment of a roadbed. Previously, a conventional cast-iron manhole cover was studied and converted to a thick slot antenna [1]. The slot is implemented by milling the thick cast-iron manhole cover. However, the antenna was not fully protected from the loads and harsh environment of the active road bed and the feeding wire corroded.  Therefore, the newest antenna design provides isolation from the external physical environment while efficiently radiating electromagnetic waves. The robust composite manhole cover is attached to a thin slot antenna to communicate with above-ground nodes in the sensor network [2].
    (a) Prototype
    (b) Antenna sandwich structure without a ring

    Figure 2. Prototype of the composite manhole cover

    In ground antenna
    Figure 3. Fabricated composite manhole cover slot antenna with sandwich structure and test setup.
    A smart manhole cover antenna is being designed to investigate the effect of antenna adaptability in this network. We project that an adaptable antenna will be a great advantage in the dynamic environment of a road as weather and traffic patterns can significantly affect the radiation patterns. Since the antenna is truncated by the surrounding earth ground, the ground effect is also studied as shown in Fig. 4.
    Tunable Antenna

      (a) In free space                                        (b) In a manhole tunnel
    Fig. 4. Ground effect on a composite manhole antenna

    1. J. F. Mastarone, W. J. Chappell, “Urban sensor networking using thick slots in manhole covers,” IEEE Antennas and Propagation Society International Symposium, Page:779-782, 2006.
    2. S. Jeong, C. Yang, J.R. Courter, S. Kim, B.R. Pipes, and W.J. Chappell, “Multilayer Composite for Below Ground Embedded Sensor Networking,” IEEE Int. Conference of Antennas and Propagation, page: 1-4, Jul. 2008.

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