A fiber Bragg grating (FBG) sensing based triaxial vibration sensor has been presented in this paper. The optical fiber is directly employed as elastomer, and the triaxial vibration of a measured body can be obtained by two pairs of FBGs. A model of a triaxial vibration sensor as well as decoupling principles of triaxial vibration and experimental analyses are proposed. Experimental results show that: sensitivities of 86.9 pm/g, 971.8 pm/g and 154.7 pm/g for each orthogonal sensitive direction with linearity are separately 3.64%, 1.50% and 3.01%. The flat frequency ranges reside in 20–200 Hz, 3–20 Hz and 4–50 Hz, respectively; in addition, the resonant frequencies are separately 700 Hz, 40 Hz and 110 Hz in the x/y/z direction. When the sensor is excited in a single direction vibration, the outputs of sensor in the other two directions are consistent with the outputs in the non-working state. Therefore, it is effectively demonstrated that it can be used for three-dimensional vibration measurement.

We proposed a miniature one-dimensional vibration sensor based on a small-diameter fiber Bragg grating in this paper. The working principle and theoretical model of the FBG vibration sensor were deduced and established theoretically. A genetic algorithm has been used to globally optimize the nonlinear programming problem of sensor size and sensitivity. The modal analysis of the vibration sensor was carried out by using finite element software to verify the feasibility of the optimization results. Then metal 3D printing was utilized to realize the integrated processing and miniaturization of the sensor. The experimental results show that the natural frequency of the sensor packaged with the small-diameter FBG is 1949.5Hz, and the sensor has a good working state in the frequency range of 5-1300Hz. The sensitivity and the linearity of the optimized sensor are 65.42 pm/g and 99.997% at the frequency of 100Hz, respectively. Through the comparative experiments, it can be found that the small-diameter FBG presents an obvious sensitization effect compared to the ordinary FBG with a 118.3% sensitivity improvement. This optimization theory is promising in multi-dimension, high performance, and microminiaturization optical vibration sensor design and fabrication.

To detect hydrogen gas leakage rapidly, many types of hydrogen sensors containing palladium alloy film have been proposed and fabricated to date. However, the mechanisms and factors that determine the response rate of such hydrogen sensor have not been established theoretically. The manners in which response time is forecasted and sensitive film is designed are key issues in developing hydrogen sensors with nanometer film. In this paper, a unilateral diffusion model of hydrogen atoms in Pd alloy based on Fick’s second law is proposed to describe the Pd–H reaction process. Model simulation shows that the hydrogen sensor response time with Pd alloy film is dominated by two factors (film thickness and hydrogen diffusion coefficient). Finally, a series of response rate experiments with varying thicknesses of Pd–Y (yttrium) alloy film are implemented to verify model validity. Our proposed model can help researchers in the precise optimization of film thickness to realize a simultaneously speedy and sensitive hydrogen sensor. This study also aids in evaluating the influence of manufacturing errors on performances and comparing the performances of sensors with different thicknesses.

A miniature FBG vibration sensor with high performance and low angle dependence has been proposed and applied in the two-dimensional vibration measurement of a vibration isolation platform in this paper. Considering the bonding points with maxim replacement, the sensitivity and resonant frequency theoretical model of the elastomer and packaged small-diameter FBG were established. The genetic algorithm was utilized to achieve the globally optimized structure sizes under multiple constraints, while the modal simulation analysis was carried out to verify the result. A novel ‘figure of merit’ defined as the product of the resonant frequency, the sensitivity, and the inverse of package volume was proposed for the performance evaluation of the sensor in the unit space of its package. The first-order and second-order frequencies of its X/Y direction of 1105.4 Hz/1266.1 Hz, while the sensitivity is 127.861 pm/g and 116.668 pm/g, correspondingly. The cross-interference in the X/Y directions of the sensor is less than 2%. Moreover, the test results of the angle dependence of the sensitivity show that the sensor possesses consistent sensitivity in all directions of the 2-d plane, while the fitted sin functions in the X/Y direction have a high R ² of 0.99851 and 0.99831, respectively. Finally, the 2-D vector vibration measurement capacity of this sensor was demonstrated on a rubber spring vibration isolation platform. The results show that this miniature 2-D vibration sensor is suitable for medium-high frequencies vibration vector measurement and has a bright application prospect for the monitoring of machines.

Surface temperature is an important parameter in clinical diagnosis, equipment state control, and environmental monitoring fields. The Fiber Bragg Grating (FBG) temperature sensor possesses numerous significant advantages over conventional electrical sensors, thus it is an ideal choice to achieve high-accuracy surface temperature measurements. However, the effects of the ambient temperature and installation types on the measurement of surface temperature are often overlooked. A theoretical analysis is implemented and a thermal transfer model of a surface FBG sensor is established. The theoretical and simulated analysis shows that both substrate strain and the temperature difference between the fiber core and hot surface are the most important factors which affect measurement accuracy. A surface-type temperature standard setup is proposed to study the measurement error of the FBG temperature sensor. Experimental results show that there are two effects influencing measurement results. One is the “gradient effect”. This results in a positive linear error with increasing surface temperature. Another is the “substrate effect”. This results in a negative non-linear error with increasing surface temperature. The measurement error of the FBG sensor with single-ended fixation are determined by the gradient effect and is a linear error. It is not influenced by substrate expansion. Thus, it can be compensated easily. The measurement errors of the FBG sensor with double-ended fixation are determined by the two effects and the substrate effect is dominant. The measurement error change trend of the FBG sensor with fully-adhered fixation is similar to that with double-ended fixation. The adhesive layer can reduce the two effects and measurement error. The fully-adhered fixation has lower error, however, it is easily affected by substrate strain. Due to its linear error and strain-resistant characteristics, the single-ended fixation will play an important role in the FBG sensor encapsulation design field in the near future.

This paper presents a high sensitivity gas pressure sensor with benzyl-dimethylketal (BDK)-doped polymer optical fiber Bragg grating (POFBG), whose sensitivity is up to 8.12 pm/kPa and 12.12 pm/kPa in positive and negative pressure atmosphere, respectively. The high sensitivity can be explained by its porous chemical structure. The stability and response behavior under air pressure atmosphere has also been investigated. The new understanding of the air pressure response principle and sensitivity difference for the presented sensor can be a worthy reference.