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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.

A tunable C-band multi-wavelength ring cavity erbium-doped fiber laser based on a Sagnac loop and tunable filter was developed and experimentally demonstrated. In this fiber laser, a Sagnac loop fabricated using a 3 × 3 coupler and polarization-maintaining fiber is employed as the comb filter. A 4-m-long C-band and 0.8-m-long L-band erbium-doped fiber serve as the gain medium, and a tunable filter connected to the 3 × 3 coupler is used for laser wavelength adjustment. In the experiment described herein, switchable single-wavelength lasing was realized from 1528.6 nm to 1562.5 nm in 4.9-nm intervals, and the peak power variation was less than 1.12 dB during 10 min of scanning at 26 °C. In addition, switchable double- and triple-wavelength lasing were realized, for which the tunable wavelength scope was 28.6 nm and 19.9 nm, and the power fluctuation was less than 1.14 dB and 1.39 dB, respectively.

An optical fiber microdisplacement sensor based on symmetric Mach-Zehnder interferometer (MZI) with a seven-core fiber and two single-mode fiber balls is proposed. The rationality and manufacturing process of the MZI sensing structure are analyzed. The fabrication mechanism of the Mach-Zehnder sensor by CO2 laser is described in detail. Experimental results show that temperature sensitivities of the two dips are 98.65 pm/°C and 89.72 pm/°C, respectively. The microdisplacement sensitivities are 2017.71 pm/mm and 2457.92 pm/mm, respectively. The simultaneous measurement of temperature and microdisplacement is demonstrated based on the sensitive matrix. The proposed Mach-Zehnder interference sensor exhibits the advantages of compact structure, simple manufacturing process, and high reliability.

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.

The smart structures and skins have wide application prospects in future morphing aircrafts and spacecrafts and have attracted much attention in recent years. This paper proposes a stretchable sensing skin with S-shape multicore optical fiber implantation. Different from previous approaches, the multicore fiber with FBG sensor array is embedded into a super elastic substrate in S-shape to form a stretchable sensing skin. This S-shape configuration makes the optical fiber stretchable enough to deform with the skin, and using the multi-core configuration, various types of fiber sensors can be inscribed on different fiber cores to measure the skin shapes and external loads. The sensing characteristics of the skin and the shape sensing of a morphing wing prototype is demonstrated, and the nonlinear characteristics and relaxation of the sensing responses are analyzed. The 3D shapes of a morphing wing prototype are measured at four airfoil profiles using the stretchable sensing skin, the results are verified by visual measurements. The proposed stretchable sensing skin should have broad application prospects in future morphing flight vehicles.

An in-line optical fiber Mach–Zehnder interferometric (MZI) sensor is proposed and experimentally demonstrated for magnetic field measurement. The fabrication mechanism of the optical fiber microstructures by CO2 laser is described in detail. The sensor with symmetrical structure is fabricated by splicing a 7-mm length of seven-core fiber and two fiber peanuts, which is encapsulated with magnetic fluid in the capillary. The transmission spectrum of the MZI is modulated by the refractive index of the magnetic fluid, which is affected by the magnetic field. The experimental results indicate that the mode interference is sensitive to the magnetic field and different dips of the interference spectrum have different sensitivities. Hence, simultaneous measurement of the temperature and magnetic field can be achieved by simultaneously monitoring two different dips. The sensitivities of the magnetic field and temperature can reach up to 0.062 nm / Gs and 0.081 nm / ° C, respectively. The proposed Mach–Zehnder interference sensor has a more compact structure, simple manufacturing process, and high reliability, which would find potential applications in weak magnetic sensing fields.