Experiments for Reinforced Concrete Foundation Remote Monitoring

The design and testing of a solution to provide energy for, and communications with, sensors encased in reinforced concrete structures, without additional wiring, was investigated. The single wire transmission line technique was adapted for use on reinforcing steel (rebar) embedded in the concrete. Experiments were conducted that first validated the approach on rebar in an ambient air medium. After the validation tests were completed, testing in concrete was conducted. To interface with the rebar special directional couplers were designed that focus the energy along the rebar in one direction. To ensure the results would be transferrable to industry, the couplers were kept physically small by using a carrier frequency of 2.4 GHz. The couplers were constructed using advanced manufacturing techniques, including laser-cut copper components and computer-aided manufacturing for the plastic dielectric members. The baseline testing in air verified that the rebar functioned as a single wire transmission line and that the coupler design worked. However, when the experimentation moved to encasement of the rebar and couplers in concrete, the performance degraded significantly. The degradation in concrete was large enough to suggest that the use of 2.4 GHz may not support either communications or energy harvesting in reinforced concrete structures. A second design approach was pursued that investigated using a much lower carrier frequency of 8 kHz. Though the degradation was not as severe as with 2.4 GHz, it was still substantial enough to indicate that the rebar single wire transmission line approach faces challenges that may warrant consideration of other techniques for embedded monitoring of reinforced concrete structures. Future areas of research were identified, including transferring the research to applications for monitoring existing steel structures in air, and also consideration of the use of this research for reinforced concrete monitoring when there are concentric steel reinforcing structures present.