Composites manufacturer Fibrelite says that it has developed a new range of manhole access covers designed to support data transfer between antennas underground and aboveground.
The radio frequency (RF) friendly covers can be used as part of real-time remote underground monitoring systems/telematics in utilities, where transmitters under covers are used for monitoring and/or control of oil/water usage, sewer flow, and floodwater, the company said. Other industries adpting these include mining and telecoms (such as 5G signal boosters).
According to Fibrelite, traditional ductile iron and reinforced concrete manhole covers aren’t conducive to the transmission of RF signals, since metal reflects the signal, while concrete greatly weakens it and exhibits high attenuation coefficients. This means that the transmitted signal is greatly weakened, restricting range and functionality. Glass reinforced plastic (GRP), in contrast, can absorb far less of the signal (lower attenuation coefficient).
The company’s new FL60RF manhole cover draws on the low attenuation (signal absorption) properties of GRP and includes a thin structure in the middle of the cover to contain the antenna, further lowering the attenuation of the signal without compromising the strength or deflection properties of the cover, Fibrelite says.
In tests at the University of Lancaster, the new FL60RF showed far lower attenuation compared to a 2mm thick aluminium plate and passed the load bearing test EN 124 C250 (now certified to C250 (25 tonne) load rating).