Following increasing demand for Radio Frequency (RF) friendly manhole covers, composites manufacturer Fibrelite has developed a new range of manhole access covers, designed to support data transfer between antennas underground and aboveground.
One of the primary current uses of RF/smart manhole covers is 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, floodwater and similar. Other industries adopting these include mining and telecoms (e.g. 5G signal boosters).
The Technology Explained
Traditional ductile iron and reinforced concrete manhole covers aren’t conducive to the transmission of RF signals. Metal reflects the signal, while concrete greatly weakens it (exhibits high attenuation coefficients). This means that the transmitted signal is greatly weakened, restricting range and functionality. Glass Reinforced Plastic (GRP) in contrast, absorbs far less of the signal (lower attenuation coefficient).
Recent Installations: From Cadiz To Connecticut
Over a five-year period, Fibrelite’s standard GRP covers have been installed by the municipality of Cadiz in Spain for their drinking water monitoring system (initially cast-iron covers had been installed over the system, but the signal was being blocked).
Over 100 bespoke radio frequency manhole covers (designed to fit the Sensus flow meter antenna) have been installed in Connecticut as part of an effort to automate their water meter collection services (automated water meters installed below the covers) following a successful 6-month trial.
Tried And Tested
Fibrelite’s new Radio Frequency manhole cover, the FL60RF 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.
Tested at the University of Lancaster on behalf of Fibrelite, the new FL60RF showed far lower attenuation compared to a 2mm thick aluminium plate (see image) and passed the load bearing test EN 124 C250 (now certified to C250 (25 tonne) load rating).
Image provided by Fibrelite
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