Metal-packaged Fiber Bragg Grating Research Articles

Half-size metal-packaged fiber Bragg grating for simultaneous measurement of strain and temperature

The cross-sensitivity of fiber Bragg grating (FBG) corresponding to strain and temperature is common in practical applications. In order to achieve accurate and simultaneous measurement of temperature and strain, half size of apodized FBG is packaged on the equal strength beam by tin alloy, and the other half is in a free state. The independent temperature and strain can be obtained through a decoupling matrix using the sensitivity difference of the two parts. The experimental results show that the strain sensitivity of the metal-packaged part FBG is 1.04 pm / μe, with a correlation coefficient of higher than 0.999. When temperature varies from −10 ° C to 80°C, the temperature sensitivity of the metal-packaged part and the free part of FBG are 35.5 and 11.2 pm / ° C, respectively. This method of using a single FBG to decouple temperature and strain has potential applications in optical fiber sensing.

Research on the Durability of Metal-Packaged Fiber Bragg Grating Sensors

Compared to conventional adhesive packaging for fiber Bragg grating (FBG) sensors, metal packaging is considered a new and robust method with excellent advantages such as stability and resistance to high and low temperatures. Current research mainly focuses on metal coating methods, the enhancement of temperature sensing characteristics, and the method of welding onto the substrate. However, the durability of the metal packaging, which determines the measurement accuracy and lifetime of a metal-coated FBG sensor, has been ignored. This letter introduces our long-term investigation of the durability of three metal-packaged FBG sensors over the past four years. The metal packaging process for the bare FBGs and sensor substrates, the experimental design, and the test methods are presented. The research results show that the central wavelength of a prestretched metallized FBG decreases due to natural aging after 10 months and that its sensing capabilities, such as its negative strain detection capacity, sensitivity, linearity, and repeatability, significantly degrade after 48 months, revealing a deficiency in our current understanding.

Real-time monitoring of bolt clamping force at high temperatures using metal-packaged regenerated fiber Bragg grating sensors

Inappropriate clamping force in bolted flange joints operated at high temperatures has been regarded as the main issue that endangers the reliability and safety of a plant. In order to accurately and reliably measure the bolt clamping force, an innovative technique is proposed using metal-packaged fiber Bragg grating (RFBG) sensors. A metal-packaged RFBG sensor is developed by a combination of magnetron sputtering and electroplating followed by spot-welding on a bolt, and calibrated by uniaxial tensile and thermal tests. The clamping force in a bolted steel-steel joint is monitored by the metal-packaged RFBG sensor spot-welded on the bolt and analyzed by a finite element model. The sensor exhibits good linear response to axial loads applied to the bolt when exposed to constant high temperatures up to 500 °C, as well as good stability and repeatability. Its thermal response is non-linear and can be expressed as a cubic-polynomial function of temperature. The variation of the clamping force in the bolted joint subjected to thermal loading is then monitored by the sensor, which is further verified by a comparison of the experimental results and the numerical predictions showing a satisfactory agreement. The results demonstrate that this technique provides a new possibility for real-time monitoring of bolt clamping force and structural health monitoring of bolt joint structures operating in high-temperature environments.

Fabrication and characterization of metal-packaged fiber Bragg grating sensor by one-step ultrasonic welding

A metallic packaging technique of fiber Bragg grating (FBG) sensors is developed for measurement of strain and temperature, and it can be simply achieved via one-step ultrasonic welding. The average strain transfer rate of the metal-packaged sensor is theoretically evaluated by a proposed model aiming at surface-bonded metallic packaging FBG. According to analytical results, the metallic packaging shows higher average strain transfer rate compared with traditional adhesive packaging under the same packaging conditions. Strain tests are performed on an elaborate uniform strength beam for both tensile and compressive strains; strain sensitivities of approximately 1.16 and 1.30 pm/μϵ are obtained for the tensile and compressive situations, respectively. Temperature rising and cooling tests are also executed from 50°C to 200°C, and the sensitivity of temperature is 36.59 pm/°C. All the measurements of strain and temperature exhibit good linearity and stability. These results demonstrate that the metal-packaged sensors can be successfully fabricated by one-step welding technique and provide great promise for long-term and high-precision structural health monitoring.