Temperature Self-Compensated High-Temperature and Vibration Sensor Based on Step-Coated FBG Twin Reflection Spectrum

In response to the need for vibration monitoring in high-temperature harsh environments, this paper proposes a miniaturized temperature self-compensated high-temperature and vibration sensor based on step-coated metallized fiber Bragg grating (FBG) twin reflection spectrum. By nickel-plating the half-length region of a single FBG, the reflection spectrum is induced to split into twin peaks. The wavelength difference between the metallized and non-metallized regions is exploited to decouple temperature and vibration signals, eliminating the need for an additional reference FBG. The sensor employs laser welding to fix the step-coated FBG onto a 310S stainless steel flexible hinge elastomer, replacing the traditional adhesive encapsulation, thereby improving its high-temperature resistance up to 600°C. The theoretical models for the nickel plating thickness, temperature-vibration decoupling, and installation stiffness influence are derived and validated. Sensor performance is verified through numerical simulations and experimental tests. The results indicate that, under threaded mounting conditions, the sensor operates within a frequency range of 100–1000 Hz, with a maximum vibration sensitivity of 8.38 pm/g and a natural frequency of 2142 Hz. The lateral interference error is less than 6.54%, and the sensor can withstand shock loads exceeding 80 g. In high-temperature environments, the temperature sensitivities of the metallized and non-metallized FBGs are 24.55 pm/°C and 13.25 pm/°C, respectively, with linear fitting coefficients greater than 0.996. The overall sensor size is Φ22 mm × 15 mm, with a compact structure, making it suitable for health monitoring in high-temperature harsh environments, such as those in gas turbines.