Cascaded Weak Reflector Coaxial Cable Structure for Point and Distributed Large-Strain Sensing

In this paper, we present a truly distributed sensing modality based on a cascaded weak reflector coaxial cable structure (CWR-CCS) for large strain measurements. Compared to an optical fiber, a coaxial cable is much more robust and has a larger strain capability to survive harsh conditions, which may enable important applications in structural health monitoring. By drilling serial shallow holes into a commercial flexible coaxial cable perturbing the local impedance along its axial direction, CWRs along the coaxial cable are introduced due to impedance mismatch, forming the CWR-CCS. Gating a certain number of sequential reflectors in the time-domain reflection signal of the CWR-CCS followed by Fourier transform, a localized multi-beam interferometer is revealed, which serves as a point sensor. By monitoring the spectral shift of the multi-beam interferometer, localized disturbances can be determined. By sliding the time gate along the entire coaxial cable, distributed sensing is realized. Large strain measurements (up to 18000 με) are conducted to verify the utility of the proposed CWR-CCS as a sensing modality. The proposed distributed sensing configuration has the advantages of ease of fabrication, robustness, large strain survivability, and ease of signal interrogation.