Fiber Bragg gratings (FBGs) have advantages of easy multiplexing, corrosion resistance, and anti-electromagnetic interference. FBG packaging is an important factor in optical fiber sensing, and the substrate material for packaging FBG has a great influence on sensing performance of FBG. In this paper, a FBG is packaged with an equal strength cantilever beam made of composite material. The principle of vibration sensing of the FBG sensor is theoretical analyzed. Then, experiments are performed to test the vibration sensing performance. The experimental results show that the composite material can be used to package FBG. The FBG sensor has a good response to the external vibration after package. The resonant frequency of the FBG sensor is 115Hz, and the acceleration sensitivity is almost 30pm/g in the range of 20~70Hz.
As a new type of sensing element, fiber Bragg grating (FBG) has advantages of wavelength modulation, hightemperature resistance, and anti-electromagnetic interference. In this paper, a medium-frequency FBG accelerometer based on a symmetrical double-semicircle cantilever is designed and fabricated. In the sensor, the double-semicircle cantilever acts as the elastic element. FBG is suspended and pasted on the double-semicircle cantilever by its two ends. When the sensor is subjected to the external vibration, the free end of the double-semicircle cantilever will vibrate under the action of inertial force. Correspondingly, the FBG is driven to produce axial strain. The structure and working principle of the sensor are well illustrated, the natural frequency and sensitivity of the sensor are analyzed as well. In order to verify the dynamic sensing characteristic of the sensor, some experiments are performed. Experimental results show that the natural frequency of the sensor is 410 Hz, the working frequency range is 50~300Hz, and the average acceleration sensitivity is almost 133pm/g. In the range of working frequency, FBG wavelength has a good response to the vibration acceleration, and the linearity is better than 99%. Research indicates that the proposed FBG accelerometer can be used to measure the vibration acceleration of 50 ~ 300Hz with higher sensitivity, and the sensor has the merits of small size, light mass, high sensitivity, wide working band and easy fabrication, which makes it a good candidate for acceleration measurement.
Regeneration of fiber Bragg gating (FBG) plays an important role in applications, it can make FBG resist high temperature for a long time, thus greatly improving the performance of FBG and meeting the measurement requirements. In this paper, the details of the regeneration of FBG is investigated based on high temperature annealing technology, and the temperature sensing performance of regenerated FBG(RFBG) is studied subsequently. Experimental results show that the regeneration of FBG can be realized by means of high temperature annealing with a certain temperature setting schedule. Compared with ordinary FBG, the reflected power of the central wavelength of RFBG fluctuates little with the change of temperature. During heating and cooling, the temperature sensitivity of the RFBG is 0.01295nm/°C and 0.01286nm/°C, respectively. The difference in temperature sensitivity is small, and the linearity is greater than 0.99. It shows that RFBG has good thermal stability in the range of room temperature~ 600°C.
An ambient refractive index (RI) sensor based on a microfiber coil resonator (MCR) is proposed. Using the coupling wave theory, the resonant properties of the MCR are theoretically studied. And then, using the finite difference time-domain method, the sensing characteristic of the sensor is investigated and the dependence of sensing characteristic on the MCR parameters is examined as well. Results show that the sensor is extremely sensitive to the ambient RI variation. And, the microfiber diameter determines both the sensitivity and detection limit of the sensor. Further, the rod diameter determines the free spectral range of the MCR resonance spectrum and influences the detection range of the sensor. However, the sensor sensitivity is almost constant with the rod diameter change. So, for ensuring a good performance in actual experiment, the microfiber diameter should range from 400 nm to 1 μm, and the rod diameter should range from 20 μm to 2 mm. This work provides a guideline for future research on the RI sensor based on MCR.
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