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• Aiming at the demand of pressure monitoring of flammable and explosive gases in industrial production, a diaphragm-type FBG high-pressure gas sensor is designed to realize long-term high accuracy pressure measurement in the range of 0–50 MPa, with good static characteristics under experimental conditions, which verifies the feasibility of the pressure sensing model. • The use of glass welding encapsulation instead of the traditional adhesive encapsulation to produce FBG pressure sensors improves the durability and long-term stability of FBG pressure sensors, and provides the necessary data support and reference for the subsequent use of glass welding encapsulation of FBG sensors. • The use of glass welding encapsulation helps to maintain the long-term high accuracy measurement of the FBG pressure sensor. Large quantities of flammable and explosive gases are often used in various production processes in the chemical and energy industries. these gases, if leaked or improperly operated, can cause serious production accidents. Therefore, in order to meet the requirement for miniaturized, highly accurate, long-term stable and large-range high pressure sensors for flammable and explosive gases in industrial production, a highly accurate diaphragm fiber Bragg grating (FBG) high pressure gas sensor is designed in this paper. In this work, the working principle of the sensor is first analyzed theoretically, the circular elastic metal diaphragm of the sensor will strain under the action of pressure load, and then the strain will be transmitted to FBG. The wavelength drift of FBG is measured to achieve the measurement of the pressure load. Then finite element simulation was carried out for the diaphragm strain of the sensor to verify the feasibility of the sensor design scheme. The traditional adhesive encapsulation is then replaced with a glass welded encapsulation to improve the durability and long-term stability of the sensor. Finally, calibration experiments was conducted on the sensor, and the experimental results were compatible with the theoretical simulation analysis. The results show that the sensor realizes long-term highly accurate measurement of pressure in a large range of 0–50 MPa, and has good static characteristics under experimental conditions. [ABSTRACT FROM AUTHOR]

• The FBG sensitivity is amplified by a special spring-moving mass mechanism. The maximum tilt sensitivity is 427.3 pm/°. • Special mechanism avoids temperature strain sensitivity of FBG. • The proposed sensor has low hysteresis and extremely good linearity and repeatability. This paper presents a temperature self-compensating, high-sensitivity fiber Bragg grating (FBG) inclination sensor. A sliding mass block and a spring are selected as the inclination-force conversion components to induce strain in the substrate where the FBGs are located, resulting in a change in the center wavelength. Both sides of the sliding mass block are arranged with one FBG on each side to play the role of temperature self-compensating. By calculating the variation of the center wavelength of the two FBGs, the variation of the inclination angle can be obtained. The detailed mechanical construction and sensing mechanism of the sensor are introduced, and the theoretical sensitivity factor formula of the sensor is given. The calibration test and static characteristics analysis of the sensor are carried out with the inclination angle change as the parameter. The experimental results show that there is a good linear relationship between the inclination angle and the FBG central wavelength, and the sensor possesses good repeatability and creep resistance. The maximum angular sensitivity is 427.3 pm/°, avoiding the cross-sensitivity between temperature and strain of the FBG. The sensitivity of the sensor can be easily adjusted by replacing the sliding mass block and the spring. [ABSTRACT FROM AUTHOR]

• This paper proposes a FBG acceleration sensor based on the double-mass block structure. • The resonance frequency of the sensor is 1000 Hz, and the sensitivity of the sensor is 26.7 pm/g at 250 Hz. • The sensor has a simple structure, low cost and easy to fabricate. A double-mass block acceleration sensor based on Fiber Bragg Grating (FBG) is proposed to meet the needs of acceleration sensors in vibration monitoring. The proposed sensor is composed of FBG, beam and double mass block, and the FBG is fixed in the middle of the upper surface of the dual mass block by epoxy glue. Through theoretical analysis and experimental verification, the resonant frequency, sensitivity and lateral anti-interference ability of the sensor have been investigated. The experimental results show that the natural frequency of the sensor is 1000 Hz, the sensitivity is 26.7 pm/g when the frequency is 250 Hz, and the lateral anti-interference degree is less than 6%. And the sensor structure in this paper is simple and easy to fabricate. Therefore, it has a great application prospect in the vibration monitoring of bridges, roads and buildings. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Both directions outside the main vibration direction have excellent anti-interference ability. • Extending the base to reduce the effective length of the fiber plays a role in improving the sensitivity. • In the beam type FBG accelerometer, the accelerometer in this paper has the characteristics of small volume and easy processing. A Fiber Bragg Grating (FBG) accelerometer with cantilever beam is presented and experimentally demonstrated. The effective length of the optical fiber is reduced by changing the base of the accelerometer, so as to increase the sensitivity. The resonant frequency and the sensitivity of the accelerometer are deduced theoretically. The structural parameters were optimized by numerical simulations and the characteristics of the accelerometer were simulated by finite element simulations. The experimental results show that the resonant frequency of the accelerometer is 119 Hz, the sensitivity (the main direction z) is 134.29 pm/g within 2–60 Hz flat region. It also designed with good immunity to interference, the cross sensitivity in the x and the y directions are 3.86 % and 2.97 %, respectively. In addition, the accelerometer has the characteristics of small volume and easy processing. In general, this accelerometer has a research significance in the field of oil and gas exploration. [ABSTRACT FROM AUTHOR]

• The parallel theoretical model is proposed. • The theoretical design idea of expanding the frequency band and maintaining higher sensitivity based on adjusting the fiber length is clearly proposed. • The thought of simplifying boundary conditions is proposed. • The figure of merit is higher. A double-diaphragm acceleration geophone based on Fiber Bragg Grating (FBG) is proposed and demonstrated experimentally in this paper. The proposed geophone is mainly composed of a FBG, double diaphragms, and an inertial mass. Through theoretical analysis and experimental verification, the FBG acceleration geophone has good comprehensive response characteristics. The experimental results obtained indicate that the flat region sensitivity range is from 651.0 to 850.5 pm/G, the corresponding fluctuation is less than 2.20 dB within 1–70 Hz, the cross sensitivity is less than −16.4 dB, and the quality factor is better than 89.1 nm·Hz/G. Compared with the traditional geophones, the proposed geophone has a higher quality factor. Therefore, this type FBG geophone is very good candidate for low-frequency oil and gas exploration. [ABSTRACT FROM AUTHOR]