A novel noninvasive real-time monitoring heat flux measurement with only one measuring point based on tapered metallized fiber Bragg grating (T-MFBG) has been proposed in this article. The preparation of T-MFBG involves magnetron sputtering of the first metal layer Ti and electroplating of the second metal layer Ni. The axially increased diameter of T-MFBG broadens the spectrum with the increase of heat flux. The heat flux sensing theoretical model and working principle of T-MFBG are established to analyze the sensing characteristics of T-MFBG. Numerical analysis and theoretical calculation show that the full-width at half-maximum (FWHM) of T-MFBG with a length of 10 mm and a diameter of 500- 550 mu m increases linearly with the heat flux, and the stable transformation of heat flux and FWHM can be realized. A heat flux calibration platform was built and its feasibility was verified by simulation. The outlet pipe section heat flux of the piston pump in the hydraulic system was quantitatively measured by the T-MFBG heat flux measurement method. When monitoring the heat flux of stainless steel, the sensitivity of T-MFBG is 0.0025 pm/(W/m(2)). The measurement range is 0-6795 W/m(2). The heat flux measurement method based on T-MFBG with a length of 1 cm and a maximum diameter of 1 mm has the advantages of heat flux-FWHM linear conversion, single-point, real-time, small installation space, and noninvasive. It can provide theoretical guidance for the design of fiber grating heat flux sensors and facilitate the design of a series of sensors for specific measurement requirements.

A non-invasive, real-time monitoring, spectral analysis heat flux sensor with single measuring point based on chirp fiber Bragg grating (CFBG) has been proposed in this paper. When CFBG senses heat flux, the linear increase of axial thermal expansion leads to spectral broadening. The measurement of heat flux can be realized by the measurement of the full width at half maximum (FWHM). The theoretical model and working principle of CFBG heat flux sensor are established to determine the heat flux sensing characteristics of CFBG. The numerical analysis and theoretical calculation show that CFBG heat flux sensor can realize stable transformation of heat flux and FWHM. A heat flux calibration platform was built and its feasibility was verified by simulation. The sensitivity of CFBG sensor to monitor heat flux in a wide temperature range is 1.078 pm/(W/m2). The heat flux of the pipe wall at the outlet of the axial variable piston pump in the hydraulic system was quantitatively measured by the CFBG heat flux sensor. The sensor has a spatial resolution of 1 cm, a length of 10 mm, a diameter of 0.125 mm, and a sensitivity of 1.078 pm/(W/m2). It has the advantages of high spatial resolution, single measurement point, real-time measurement, small installation space, and non-invasiveness. The theoretical model can provide theoretical guidance for the design of fiber grating heat flux sensor, and it is convenient to design a series of sensors for specific measurement requirements.

This article proposed an integrated temperature/pressure dual -parameter sensor in small hydraulic pipelines, and a set of small hydraulic pipeline experimental system is specially built to verify the dynamic measuring performance of it. A fiber Bragg grating (FBG) integrated sensing structure was designed and fabricated to achieve simultaneous monitoring of temperature and pressure. Specifically, the temperature measurement structure was encapsulated by an Invar capillary and a stainless -steel protective tube with asymmetric holes on both sides. The protective tube blocked the impact of the fluid on the temperature sensing element. Asymmetric holes ensured that the hydraulic oil filled the protective tube, allowing a uniform temperature field to surround the temperature sensing element. The secret to achieving large-scale temperature measurement was the Invar capillary's low thermal expansion coefficient. The pressure measurement structure was made of beryllium bronze diaphragm and FBG. The strain captured by FBG was converted from fluid pressure by a beryllium bronze diaphragm. High sensitivity and simplicity were significant advantages of this pressure measurement structure. The close installation position of the two modules effectively ensured the temperature compensation effect of the pressure measuring module. The results indicated that the integrated dual -parameter sensing structure worked efficiently in the temperature range of 30-80 degrees C and the pressure range of 0-1 MPa, which was widely adopted in small hydraulic pipelines. The temperature and pressure sensitivities were 12.055 pm/degrees C and 3.643 pm/kPa, respectively. The FBG temperature/pressure dual -parameter integrated sensor proposed in this article achieved effective monitoring of temperature/pressure parameters in small hydraulic pipelines.

In this paper, a novel integrated sensing structure based on double quartz tubes stepped fiber grating is proposed, which can effectively solve the measurement inaccuracy problem caused by the traditional fiber Bragg grating (FBG) sealing process. Based on thermoelasticity theory, a mathematical model of the temperature sensing performance of the proposed integrated stepped FBG sensing structure is established, and the structural and material influencing parameters of its sensing performance are investigated by combining with Comsol 6.0 simulation; meanwhile, a sample of the proposed integrated stepped FBG sensing structure is prepared, and the temperature sensing performance is tested by temperature sensing experiments, the temperature sensitivity can reach 35.84pm/ degrees C, and the temperature resolution is 0.030 degrees C/pm, which is better than that of the metallized FBG (15.91pm/ degrees C), and verifies the validity of the theoretical model of the temperature sensing performance of the proposed integrated stepped FBG sensing structure. Finally, the temperature cycling response experiment verifies that the sensing structure based on double quartz tubes stepped fiber grating proposed in this paper can effectively improve the temperature sensing performance of FBG based on effectively solving the problems of the traditional adhesive sealing process.

Under current embedded fiber optic packaging technology, when a mechanical structure is subjected to alternating loads such as temperature or force over a long period, the different thermal expansion coefficients between the fiber optic and metal can lead to loosening and sliding of the connection surface. To solve this problem, this study proposes a double quartz tube symmetrical stepped fiber structure based on the principle of mechanical connection. This structural design enables a more reliable connection between the stepped fiber optic and metal. Based on the theory of thermoelasticity, a theoretical analysis was conducted on stepped optical fibers, and a reasonable preparation process for stepped optical fibers was proposed. The controlled variable method was used to analyze experimentally the various process parameters to improve their tensile strength. A metallized stepped fiber Bragg grating (FBG) was successfully prepared, and the effectiveness of the stepped structure was verified through experimental comparison. Experimental results show that the tensile strength of the double quartz tube symmetrical stepped optical fiber is improved by processing technology and can reach 750 MPa, which is 9. 25 degrees o higher than that of the bare optical fiber obtained by mechanical removal of the coating layer (686. 5 MPa). The temperature sensitivity of the prepared metallized stepped FBG reaches 15. 59 pm/degrees C at a temperature resolution of 0. 064 degrees C/pm. The results show that metallized stepped FBG exhibits a more stable temperature sensing performance than the metallized FBG without reducing temperature sensitivity.

The FBG(fiber Bragg grating) can be embedded in metal to form smart structure, and to protect the FBG, the surface can be coated with high melting point metal such as Ni. MFBG(metalized FBG) will affect the temperature sensing performance of the FBG. In this paper, the thermal sensing performance of MFBG with single and double metal layers is investigated and the main factors affecting its temperature sensitivity and temperature response are analyzed. The thermal sensitivity of the MFBG gradually stabilizes as the thickness of the metal layer in-creases. The Ni-Ti MFBG (double-layer MFBG with Ni as the outer metal and Ti as the inner metal) was fabricated by magnetron sputtering and electroplating thickening, and a comparative thermal sensing performance experiment was conducted together with the bare FBG. Metallization of the FBG can improve the temperature sensitivity of the FBG. Samples with different metal layer thicknesses were subjected to thermal tests from 0 to 70 degrees C, the obtained data verified the soundness of the presented model. To verify the temperature sensing performance of the prepared Ni-Ti MFBG, it was embedded in a three-phase induction motor and the internal temperature of the motor was monitored. The experiments show that the prepared Ni-Ti MFBG has good tem-perature sensing performance and can accurately sense the motor temperature.

To improve the strength and performance of FBG (fiber Bragg grating), they are often encapsulated and protected or surface metallized. In this paper, based on the thermoelastic theory of J.M.C. Duhamel and F.E. Neumann, a thermal sensitivity model for bimetallic layer MFBG (metalized FBG) is established, and the thermal sensitivity performance parameters are analyzed for MFBG with single metal layers and those with Ni and Ti bimetallic layers deposited on the surface. The thermal sensitivity coefficient of the MFBG gradually stabilizes as the thickness of the metal coating increases. To verify the rationality of the theoretical model, Ni-Ti MFBG (doublelayer MFBG with Ni as the outer metal and Ti as the inner metal) were prepared by magnetron sputtering with electroplating for thickening, and the plating process and formulation were optimized. The thermal sensing performance experiments of Ni-Ti MFBG and ordinary bare FBG were conducted together. The metallization of FBG can improve the temperature sensitivity of FBG, and the relative error between the experimental data and the theoretical value is less than 5 %. When h1 (the thickness of the inner metal layer) = 1 & mu;m, h2 (the thickness of the outer metal layer) keeps increasing, the change trend of the temperature sensitivity of Ni-Ti-MFBG is consistent with the conclusion reached in the theory, which strongly proves the validity and reasonableness of the established bimetallic layer MFBG thermal sensing model, and the results of this paper have good theoretical guidance significance for the research on the connection between FBG and electromechanical components.

The corrosion, parasitic reactions, and aggravated dendrite growth severely restrict development of aqueous Zn metal batteries. Here, we report a novel strategy to break the hydrogen bond network between water molecules and construct the Zn(TFSI) 2 -sulfolane-H 2 O deep eutectic solvents. This strategy cuts off the transfer of protons/hydroxides and inhibits the activity of H 2 O, as reflected in a much lower freezing point (<−80 °C), a significantly larger electrochemical stable window (>3 V), and suppressed evaporative water from electrolytes. Stable Zn plating/stripping for over 9600 h was obtained. Based on experimental characterizations and theoretical simulations, it has been proved that sulfolane can effectively regulate solvation shell and simultaneously build the multifunctional Zn-electrolyte interface. Moreover, the multi-layer homemade modular cell and 1.32 Ah pouch cell further confirm its prospect for practical application.

In this paper, we propose a damage identification method based on minimum mean square error estimation for a wind tunnel flexible plate condition monitoring system. Critical structural members of important equipment are large in size, and the measurement systems used to monitor their condition are often complex. The proposed damage identification method is based on the minimum mean squared error estimator and the generalized likelihood ratio test. It introduced activation function to generate the standard deviation of the data, which can then simulate the sensor output. A single sensor damage only affects a single dimension of the output data matrix of the measurement system. However, structural damage affects the output of multiple sensors. The damage identification method proposed in this paper can not only distinguish the sensor damage from the structure damage, but also locate the damaged sensor or structure damage location. This method can identify the measurement system output anomalies caused by structural damage and locate the approximate location of the damage. It can be applied to damage identification of important structural members such as flexible wind tunnel plates. The damage identification method proposed in this paper is of great significance for damage identification and localization of key components and sensor systems.

Combining fiber Bragg grating (FBG) sensors and finite element simulation analysis, an online monitoring method for non-invasive distributed flow velocity in pipelines has been proposed. A placement strategy has been proposed for the deployment of these FBG sensors to ensure effective sensing of strain. The cross-sensitivity problem of FBG sensors can be solved by differential FBG measurements. The principle of online monitoring of flow velocity based on the flow velocity function and finite element analysis is described and derived. Finite element analysis results show the $\boldsymbol {\varepsilon }_{1}- \boldsymbol {\varepsilon }_{2}$ at 45° of the elbow of the bend is quadratically proportional to the flow velocity. Meanwhile, the feasibility of the method is verified by experiments. The calibration results show a fitted correlation coefficient R2 = 0.9982 in the velocity range of 4.25-10.62m/s, fitted by least squares to the wavelength data. The repeatability error of the flow measurement of the proposed sensor is no more than 5.06%FS. Compared with the existing literature, the method proposed in this paper has a wider range of flow velocity measurement and applications, especially suitable for applications with strong electromagnetic interference capability and harsher environment, showing great potential for engineering applications, especially in the distributed detection of long-distance pipeline networks.

This article proposes a novel hinge-type fiber Bragg grating (FBG) accelerometer for measuring medium-frequency vertical vibrations that employ a single-notch circular flexure hinge as the elastomer of the accelerometer. The proposed elastomer allows for the simultaneous realization of high sensitivity, a compact structure, and a relatively wide working frequency range, all of which are critical for accelerometer performance. The working principle and detailed theoretical analysis of the FBG accelerometer are illustrated and conducted. Moreover, the sensitivity of the accelerometer is optimized further through a genetic algorithm in order to strike a balance between miniaturization and resonance frequency. Finite element analysis and experimental tests were carried out to validate the performance of the accelerometer. The results indicate that the proposed FBG accelerometer has a resonant frequency of 800 Hz and a working frequency range of 50–450 Hz, with a sensitivity of approximately 65 pm/g at an exciting frequency of 100 Hz between the fiber central wavelength and vibration acceleration. The results also demonstrate that the proposed accelerometer exhibits a good linear relationship with the frequency of vibration accelerations, as well as good anti-interference properties with the horizontal vibrations. It has the potential to provide a novel and simple solution for monitoring medium-frequency vibration signals in complex environments characterized by high levels of electromagnetic interference (EMI), such as in aeronautical hydraulic systems.

Effective fault detection techniques are needed to reduce the maintenance and downtime costs of induction motors. This article presents an approach for stator end-winding inter-turn short-circuit fault detection using a metal-coated fiber Bragg grating (FBG) sensor with 0.5-mm diameter and 10-mm length to monitor the temperature and magnetic field around the end winding. The sensing theory, design, manufacturing, and installation of the sensor are detailed in this article. The nickel coating on the surface of the sensor is formed by electroless plating and electroplating, which makes the sensor sensitive to both temperature and magnetic field. The feasibility of the presented approach has been supported by both simulation and experimental results. The temperature and magnetic field signals are decoupled by filtering, and the experimental data are analyzed in the time-frequency domain. The results show that the inter-turn short-circuit fault can be detected at an incipient stage with 5% shorted turns.

This paper constructs a novel curvature demodulation method for Mach-Zehnder interferometer (MZI) optical fiber sensors. The method is composed of two parts: spectral curve decomposition and support vector machine regression (SVR) of curvature. The authors fabricated the MZI fiber optic curvature sensor and carried out curvature loading experiments. The curvature demodulation method proposed in this paper includes the following steps: spectral data acquisition, data normalization, coefficient vectors calculation, and curvature calculation. The minimum root mean square errors (RMSE) of the curvature demodulation method is 0.02133 m(-1). This method has two characteristics: wide curvature demodulation range and unitive curvature regression expression. The curvature demodulation method is not only limited to the MZI sensor curvature demodulation but also applicable to the demodulation of other physical quantities with the spectral data as input. This paper provides a new idea for solving similar demodulation problems.