Project Overview:
Following the increased 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 above ground.
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).
Problem:
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. 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).
Solution:
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 aluminum plate (see image below) and passed the load-bearing test EN 124 C250.
Results:
Over five years, Fibrelite’s standard GRP covers have been installed by the municipality of Cadiz, 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 following a successful 6-month trial.
Read more in Fibrelite’s whitepaper here.
Fibrelite FL60RF attenuation compared to a 2mm thick aluminum plate