Brillouin sensing cable: Design and experimental validation

We report on the design and experimental validation of a distributed Brillouin-based optical fiber sensor embedded into concrete structures for temperature and strain measurement. A composite-made wave-like coating designed by finite-element analysis ensures the sensor is transferring optimally temperature and strain fields from the concrete to the optical fiber, where Brillouin scattering takes place. During all experiments, sensors have been interrogated with a commercially available Brillouin optical time-domain reflectometer unit. First, temperature sensitivity of the Brillouin frequency shift were evaluated in PANDA and SMF28 optical fibers, before wrapping them into the specific sheath for embedment into a 3 m-long reinforced concrete beam. Temperature measurements during concrete beam casting agreed with reference measurements, and showed the significant sensor coating influence. A month later, strain measurements performed during a four-point bending experiment showed promising results: linearity and reliability of measurements were demonstrated, under tensile as well as compressive loadings.