As a core component of aircraft thermal management systems, the plate-fin heat exchanger (PFHE) plays a decisive role in determining the system’s thermal safety limits. Local temperature non-uniformity within PFHEs is a key factor that degrades heat transfer efficiency. To overcome limitations of traditional performance evaluation models and localized thermal monitoring techniques, this study develops a comprehensive evaluation model incorporating non-uniformity parameters and implements a localized temperature monitoring system using fiber Bragg grating (FBG) sensing arrays. Twenty-four compact, vibration-resistant FBG sensors with fast response characteristics were embedded inside the flow channels, facilitating real-time temperature field mapping. Experiments conducted on a customized aviation thermal simulation platform detected significant temperature non-uniformity on both fluid sides, yielding coefficients of variation of 0.130 (cold side) and 0.041 (hot side). The comprehensive model quantitatively demonstrates the degradation mechanism: temperature gradients cause substantial thermal efficiency reductions of 45% and 43% on the cold and hot sides, respectively. This integrated evaluation framework and monitoring methodology offer crucial insights for guiding PFHE geometric optimization and advancing aerospace thermal management strategies.

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 issue of localizing and reconstructing the impact force through double-inverse approaches is widely recognized as an ill-posed and computationally demanding problem. Such a challenge has emerged as a prominent research topic of interest and great concern in the field of structural health monitoring. This study proposes a novel and efficient hierarchical methodology that is adept at ascertaining both the location and time history of an impact force through data obtained from a single accelerometer. The proposed methodology entails an efficient retrieval of uncorrected modal constants with a ratio function referred to as generalized transmissibility. The generalized transmissibility symbolizes the ratio of responses from identical accelerometer subjected to two distinct impacting scenarios, one excited at a yet-to-be-identified location and the other at a pre-determined reference location. The theoretical disclosure of the correlation between the generalized transmissibility at pole frequencies and retrieved uncorrected modal constants is demonstrated in details herein. These modal constants are then served as a signature to identify the impact location. Following localization, the force reconstruction problem is tackled by fitting a parametric model, wherein a gaussian basis function is employed to effectively approximate the time history of impact force. Experimental demonstrations on a metallic plate and a composite wing were carried out to validate the efficient and accurate localization as well as the rapid reconstruction capabilities in response to an impact force applied anywhere on a 2D structure.

The packaging technology of fiber Bragg grating (FBG) sensors is the key to determining their operational performance. A method for encapsulating FBG temperature sensors using ultrasonic-assisted soldering technology has been proposed and attempted. This packaging method is based on the successful connection between SiO2 quartz glass and Invar alloy. Implementing this soldering connection depends on the active components in the solder, which are dispersed into SiO2 and metal alloys to form more stable substances. The FBG with the removed coating is reliably connected to the metal capillary through ultrasonic soldering. The fragile FBG is adequately protected in the capillary. Sn-based solder with a melting point of 297 ℃ has been selected. The soldering temperature of 330 ℃ avoids significant residual stress caused by the difference in the thermal expansion coefficient of the material at the joint. Excellent bonding strength between optical fibers, solder, and capillaries is necessary for encapsulating sensors. Compared to adhesive, solder packaging is no longer affected by the creep of the sealant. The results show that the working range of FBG temperature sensors encapsulated in epoxy resin is -25 ℃ -115 ℃, while temperature sensors encapsulated by welding can operate stably at -50 ℃ -280 ℃. Sensors packaged using ultrasonic-assisted soldering technology have the potential to be embedded in metal substrates, creating favorable conditions for the development of intelligent electromechanical components.

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.

The fast response is a significant index for measuring the performance of temperature sensors. In this pa-per, a copper capillary temperature sensor is developed utilizing fiber Bragg grating (FBG) as the sensing element and nano-copper suspension as the filler. Nano-copper suspension with high thermal conductiv-ity is meaningful to improve the response speed of this sensor. The relationship between the preparation parameters of nano-copper suspension and the thermal conductivity is accurately established to obtain the optimum response time of the temperature sensor. The suspension with small particle size and high concentration significantly improves the sensor's response speed, which is close to the bare FBG. In ad-dition, the temperature sensor encapsulated with a copper capillary tube has high sensitivity, which is three times that of the bare FBG. This temperature sensor and bare FBG are simultaneously applied to the motor with a winding inter-turn short circuit as the initial fault. Both this sensor and the bare FBG capture the coincident temperature field, which implies that the sensor has no apparent response lag compared with the bare FBG in practical applications. Results demonstrated here may afford some valu-able references for obtaining temperature filed in small electromechanical components.(c) 2023 Elsevier Ltd. All rights reserved.

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 field of mechanical manufacturing is becoming more and more demanding on machining accuracy. It is essential to monitor and compensate the deformation of structural parts of a heavy-duty machine tool. The deformation of the base of a heavy-duty machine tool is an important factor that affects machining accuracy. The base is statically indeterminate and complex in load. It is difficult to reconstruct deformation by traditional methods. A reconstruction algorithm for determining bending deformation of the base of a heavy-duty machine tool using inverse Finite Element Method (iFEM) is presented. The base is equivalent to a multi-span beam which is divided into beam elements with support points as nodes. The deflection polynomial order of each element is analysed. According to the boundary conditions, the deformation compatibility conditions and the strain data measured by Fiber Bragg Grating (FBG), the deflection polynomial coefficients of a beam element are determined. Using the coordinate transformation, the deflection equation of the base is obtained. Both numerical verification and experiment were carried out. The deflection obtained by the reconstruction algorithm using iFEM and the actual deflection measured by laser displacement sensors were compared. The accuracy of the reconstruction algorithm is verified.

A novel regional strain homogenized diaphragm based fiber Bragg grating (FBG) high pressure sensor has been proposed in this paper. The optimization model of regional strain homogenized rectangular diaphragm is established to avoid chirp of FBG caused by nonuniform strain. The modal simulation analysis of optimization result is carried out. The analysis shows that this structure with a 4 mm length homogenized region of X axial strain under external load can realize stable transformation of pressure and strain. The experimental prototype is designed with pre-stretched FBG attached to the axis of the rectangular diaphragm bottom. The characteristics of the sensor have been measured by pressure and temperature experiments. The results match the model well that the pressure sensitivity of the sensor reaches 30.8714 pm/MPa with linearity error of 0.9996. The spectrum remains stable without chirping and the full width at half maxima (FWHM) fluctuation is 0.01 nm, indicating that the strain in the adhesive area of FBG is homogenized. Meanwhile, pressure measurement range of the sensor is 0-30 MPa. The resolution of the sensor is 0.0324 MPa. The pressure sensor with sensitive diaphragm of 8 x 15 x 1.5 mm3 can optimize installation space, determine FBG sensing homogenized strain and realize the distributed measurement with high sensitivity in a small space, which is suitable for collecting pressure infor-mation of deep oil and gas wells along pipelines.

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.

The flow maldistribution inside plate-fin heat exchangers is a decisive factor leading to the deterioration of heat transfer performance. This article proposes the configurations of flat and curved baffles with different holes to optimize flow distribution. The invasive method using fiber Bragg grating (FBG) sensors for monitoring the local flow velocity in heat exchangers is first proposed. Multiple FBG sensors are embedded in the plate-fin core to measure the flow velocity of each channel. The effectiveness in balancing the flow velocity of flat and curved baffle configurations is compared against a header configuration without a baffle. The results indicate that adding a baffle, whether it is flat or curved, is profitable to facilitate the flow field inside the plate-fin core. Compared with no baffle configuration, the flat and curved baffle configurations achieve a decrease rate of 61% and 66% in the sum flow nonuniformity of heat exchangers. The standard deviation has been reduced by 60% and 80%, respectively. The energy loss caused by the curved plate configuration is relatively low. The embedded FBG sensors address real-time monitoring of local flow velocity in the plate-fin heat exchanger. The ameliorative baffle structure in the header and FBG sensing technology provide ideas for optimizing and monitoring the internal flow field inside plate-fin heat exchangers.

在汽车电子控制系统中,变速箱档位的位置信号是调节整车运行的重要参数.随着电子技术的发展,变速箱档位传感器在满足精度要求的前提下应尽量减小传感器体积.运用Flux和Matlab对永磁体周围空间的磁场强度分布进行仿真计算,综合分析单磁铁方案、双磁铁方案、正弦充磁磁铁方案三种设计方案在磁场强度、线性度、精度的表现,提出一种采用正弦充磁方式的变速箱档位传感器,分析实际装配中磁铁的尺寸及磁铁与霍尔芯片间隙对传感器测量角精度的影响,基于仿真结果优化设计了具有小体积高精度特点的正弦充磁变速箱档位传感器.

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.

The stress concentration appears in the form of a quadratic or higher-order strain distribution, which affects the measurement accuracy of fiber Bragg grating (FBG). The FBG spectrum presents asymmetric deterioration when the stress concentration exceeds a specific limit, making the symmetric Gaussian fitting algorithm no longer suitable for seeking its peak wavelength. In this paper, the degree of stress concentration is defined by the quadratic coefficient of the strain field. The bearing capacity of different length FBGs to the Gaussian fitting algorithm is investigated under the quadratic strain distribution. The experimental results show that the FBG with shorter length had a higher tolerance to the Gaussian peak-seeking algorithm. The Extreme fitting algorithm based on a single peak has been proposed to adapt to the asymmetric changes of FBGs spectra. The exceptional adaptability of the Extreme peak-seeking algorithm compared with Gaussian fitting has been proved, which provides a reliable reference for the accurate peak seeking of FBG reflect spectrum in a nonuniform strain field.

在低温环境中,光纤光栅(Fiber Bragg Grating,FBG)材料的热膨胀系数和热光系数会发生改变,从而影响其温度传感特性.文章通过实验研究了裸光纤光栅传感器和黄铜管封装的光纤光栅传感器在低温下的温度传感特性.结果表明,在80-300 K温度范围,裸FBG温度传感器的灵敏度为6.43 pm/K,线性度为0.974,在80-230 K温度范围,温度与光纤光栅的中心波长呈现非线性关系;黄铜管封装的FBG温度传感器,在整个温度范围内灵敏度可达26 pm/K,线性度为0.996,较裸FBG温度传感器均有较大提升.对比实验表明,对光纤光栅进行封装,可以提高其温度灵敏度和线性度,改善温度传感特性.

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.