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Here, the three-dimensional (3D) shape monitoring of polyvinyl chloride (PVC)-reinforced silicone substrate for a morphing wing is detailed, using Fiber Bragg grating (FBG) sensors. An optical fiber FBG sensor was embedded into a soft silicone substrate, which was glued onto the surface of a PVC substrate. This substrate was aligned with the morphing wing’s flexible ribs of the. Sensing experiments were carried out both with and without the PVC reinforced silicone substrate, and the sensitivity and repeatability of the two sensors were compared. The PVC-reinforced silicone substrate sensor was calibrated using standard curvature calibration blocks to obtain a relationship between wavelength shift and the bending curvature of the PVC-reinforced silicone substrate, and the wing shape was reconstructed at different deformation states. Several wing shapes were also reconstructed using a precise visual measurement system. Comparing the FBG sensing method with this visual measurement system demonstrated the effectiveness of the FBG method proposed here. Its maximum error was

Considering the complex and variability of flight environment of the morphing aircraft, usually it is difficult to solve the real-time wing shape monitoring problem when the aircraft changes its motion state or suffering the wind and waves. In this paper, with the goal of supporting real-time wing shape monitoring of morphing aircraft, three-dimensional (3D) shape monitoring of polyimide film skin for morphing wing based on the embedded Fiber Bragg Grating (FBG) sensor is designed and analyzed. Firstly, the sensitively of FBG sensors with different embedded depth in the polyimide film was analyzed, and the finding is that when the ratio value of upper/lower embedded depth is larger, the sensitively of FBG sensor is higher. Secondly, the wavelength of FBG sensors at different states were obtained, and the center wavelength shift of FBG sensors can be used to measure the bending curvatures of the wing, besides, according to the obtained bending curvatures, the 3D shape of polyimide skin of the morphing wing at different deformation states are reconstructed through interpolation and curve fitting functions. Moreover, several shape reconstruction experiments of the morphing wing were carried out with precise visual measurement, and the maximum error between FBG sensing and visual measurement is 5%. Consequently, the effectiveness of FBG sensing method for wing shape monitoring of morphing aircraft is demonstrated, as well as more potentiality and applicability for the shape monitoring in the field of soft robotics and flexible biosensor monitoring.

To meet the demands for curvature measurement in the field of biomedical intelligent equipment, soft robots and complex structures of major infrastructures, an optical fiber based soft curvature sensor is proposed. The major contribution is obtaining a soft curvature sensor with extraordinary high sensitivity and repeatability. A silicone rubber sheet is glued on the surface of polyvinyl chloride to form polyvinyl chloride (PVC) reinforced silicone rubber substrate, the fiber Bragg grating is embedded into the substrate to form the sensor. The sensor is calibrated using standard curvature calibration blocks. The characteristic of the reflected spectrum of the sensor is analyzed. The relation between the sensitivity and the fiber embedded depth is obtained. The research results prove that the real-time measurement of structure curvature can be realized by the sensor. The polyvinyl chloride reinforced silicone rubber substrate is helpful to improve the sensitivity and repeatability of the sensor. The maximum sensitivity is up to 329.2pm/m−1. The sensor has good consistency in repeated measurements, it has application presents in measuring the curvature of flexible mechanisms and complex structures.

Numerous studies have addressed various methods to interrogate fiber Bragg gratings (FBGs). However, conventional methods are ineffective for multipeak FBG demodulation. A core-and-cladding-integrated fiber Bragg grating (FBG) temperature-interrogation system, based on a modulated grating Y-branch (MG-Y) tunable laser and home-built FBG, is proposed in this study. The sensing system comprises an MG-Y tunable laser interrogation system, a 3-dB optical fiber coupler, a core-and-cladding-integrated FBG, a heating platform, and a personal computer. The core-and-cladding-integrated FBG with two reflection peaks is sampled by the designed MG-Y laser. The FBG has a period of 534 nm and a grating length of 2000 µm. It is fabricated in a single-mode fiber by femtosecond-laser writing through the fiber coating. The interrogator is suitable for temperature measurement via the core-and-cladding-integrated FBG. In tests of the temperature-interrogation system, a temperature change from 30 to 100 °C generates spectral shifts toward longer wavelengths for both the core and cladding reflection peaks. For the core and cladding, temperature sensing sensitivities of 111 and 113 pm/°C with linearities of 0.993 and 0.99, respectively, during heating and 117 and 120 pm/°C with linearity coefficients of 0.994 and 0.99, respectively, during cooling are achieved.

A double-mass block acceleration sensor based on Fiber Bragg Grating (FBG) is proposed to meet the needs of acceleration sensors in vibration monitoring. The proposed sensor is composed of FBG, beam and double mass block, and the FBG is fixed in the middle of the upper surface of the dual mass block by epoxy glue. Through theoretical analysis and experimental verification, the resonant frequency, sensitivity and lateral anti-interference ability of the sensor have been investigated. The experimental results show that the natural frequency of the sensor is 1000 Hz, the sensitivity is 26.7 pm/g when the frequency is 250 Hz, and the lateral anti-interference degree is less than 6%. And the sensor structure in this paper is simple and easy to fabricate. Therefore, it has a great application prospect in the vibration monitoring of bridges, roads and buildings.

Metallic packaging of fiber Bragg grating (FBG) sensors is developed using the ultrasonic welding method. Both polyimide-coated fiber and bare fiber could be bonded well to aluminum alloy substrate using Sn-Bi alloy. Two kinds of metal-packaged FBG sensors, coated FBG and bare FBG, are characterized for studying the thermal sensitivity, strain response, short-term creep, and temporal temperature response. Both FBG sensors showed increasing sensitivity with temperature from −40°C to 80°C. The metal-packaged coated FBG sensor displayed relative strengths in strain stability, repeatability, creep, spectra shape, and temperature response when compared with the bare one. Moreover, the boundaries between optical fiber and metal alloy are intact, and cross-sectional scanning electron microscope micrographs clearly illustrated that metal alloy coated well with the coated and bare fiber.

A Mach–Zehnder interferometer based on processed hollow-core fiber (HCF) is proposed and experimentally demonstrated for gas pressure sensing. The fiber sensor is fabricated by splicing a segment of HCF between the two coreless fibers. One end of the HCF is processed into an open cavity, which allows gas pressure of the air-core to be equivalent to that of the external environment. Gas pressure change induces refractive index change of the air-core, thus the measurement of gas pressure can be achieved by monitoring wavelength shift of the interference pattern. The proposed fiber sensor exhibits a high gas pressure sensitivity of 9.35 nm / MPa in the range from 0.1 to 0.04 MPa and a temperature sensitivity of 30 pm / ° C in the range from 30°C to 90°C. Furthermore, the fiber sensor processes the advantages of compactness, low cost, and all-fiber configuration, which makes it suitable for gas pressure measurement.

The characterization of a fiber Bragg grating in pure-silica-core and Ge-doped-core optical fiber is demonstrated under tensile strain at different temperatures. The peak wavelength of the fiber Bragg grating increases slowly under tensile strain of 1000 µe when the temperature exceeds a certain value. The wavelength response of the pure-silica-core fiber Bragg grating is less sensitive under the same high-temperature strain as compared with the Ge-doped-core one. The results show a little predominance for the pure-silica-core fiber Bragg grating in high-temperature strain sensing. The two kinds of fiber Bragg grating are capable of measuring temperatures of up to 800 °C, but it is recommended that strain measurements are conducted below 500 °C to ensure good stability and repeatability.