Multilayer composite for below ground embedded sensor networking

Sewage systems are being retrofit with sensor networks to reduce their deleterious effects on human health and the environment. To implement the sensor networks a conventional cast-iron manhole cover is replaced with a robust composite manhole cover antenna. The difficulties in designing the antenna in a manhole cover are that the antenna must radiate in a harsh environment, at ground level, and maintain low-profile. The cover must maintain structural loads as large as 2,000 pounds, due to the presence of traffic, while simultaneously being relatively ‘transparent’ for RF radiation from below ground sensors. To verify a prototype, a simple composite sandwich structure is designed, fabricated, and integrated with an aluminum slot antenna. This composite manhole cover antenna is analyzed with full-wave simulations and measured in an anechoic chamber. The simulated results show a good agreement with measured results. The magnetically center-fed slot antenna shows 2.13 dB of measured gain within the fiberglass sandwich structure.