A high-sensitivity fiber Bragg grating strain sensor based on a rhombic hinge structure

Early-stage strain monitoring forms a crucial foundation for structural health assessment and proactive maintenance of equipment. This study presents a reusable fully encapsulated fiber Bragg grating (FBG) strain sensor that combines high sensitivity with intrinsic temperature compensation, and can be directly mounted on the surface of the object under test for strain measurement. The sensor utilizes a rhombic hinge as its elastic element. A flexible hinge model is established based on theoretical mechanics, from which a linear relationship between the central wavelength shift of the FBG and the applied strain is derived. Building on this, the key structural parameters of the sensor are optimized through numerical calculation and finite-element simulations. The final experimental tests indicate that, within a surface microstrain range of 0–400 με, the sensor exhibits a sensitivity of 5.73 pm/με (R 2 ≥ 0.999), with a repeatability error of 2.7% and a hysteresis error of 2.15%. In addition, it demonstrates good constant strain stability and effective self-temperature compensation performance. These results indicate that the sensor holds strong potential for applications in the field of structural health monitoring.