A high-sensitivity and small-size pressure sensor based on dual fiber Bragg grating (FBG), a diaphragm and hinge-lever structure is proposed. Its measurement principle is described and simulation analysis is conducted. We compensate for temperature cross-sensitivity by using an additional FBG to accurately measure the ambient temperature. Sensing experiments indicate that the pressure sensitivity is 5.227 pm/kPa within the range of 0–1.0 MPa, which is three times greater than that of a single-diaphragm pressure sensor without a flexible hinge lever. The sensor is suitable for accurate and stable pressure measurement in oil and gas pipelines and similar environments.

Underwater pipelines are exposed to harsh environments, including high salinity, multi-modal vortex corrosion, and severe wave interference. Their safety is essential for the development and transportation of marine energy. Therefore, real-time safety monitoring of long-distance energy pipelines is of great strategic importance for ensuring the safety of life and property and energy security. With the rapid development of energy development, the corrosion and leakage mechanisms of natural gas pipelines, as well as their identification and early warning, have become the focus of attention. Optical fiber sensing technology has been applied to various energy safety monitoring fields. However, the mechanism of sound source fluctuations in pipeline leakage and the mutual coupling mechanism between distributed optical fiber sensing technology and leakage sound waves are not yet clear. This paper establishes a model based on sound wave propagation and leakage noise response, derives a quadratic fitting relationship between pipeline pressure fluctuations and leakage orifices and a relationship between leakage noise source standard deviation and orifices, and proposes a complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) permutation entropy underwater natural gas pipeline leakage signal recognition method based on distributed optical fiber acoustic sensing technology. The results of theoretical analysis are verified by experiments. It shows that the signal processing method of CEEMDAN permutation entropy is superior to traditional noise reduction methods, which can better preserve the features of the original signal; the radial basis function (RBF) neural network model can accurately identify four different leakage features with an accuracy of 88.15%, and its recognition stability and generalization ability are superior to convolutional neural network, backpropagation, and random forest. Therefore, the research results of this paper provide a new method for safety monitoring in the application of energy pipeline transportation engineering, and expand the potential application scenarios of distributed acoustic sensing sensor systems and RBF neural networks.

Multi-dimensional acceleration sensors are used in important applications in the aerospace, weapon equipment, and nuclear fields and have strict requirements in terms of performance, volume, and mass. Fiber Bragg grating acceleration sensors use optical wavelength signals as a medium for information transmission to effectively eliminate the influence of electromagnetic interference between multi-dimensional sensors. In this study, we designed a composite flexure hinge three-dimensional acceleration sensor. To this end, we investigated the coupling mechanism between a new integrated elastomer structure and fiber grating to determine the influence of structural parameters on the static and dynamic characteristics, volume, and mass of the sensor. By optimizing the strain distribution, amplitude, and frequency and coupling characteristics between dynamic dimensions, a design theory and a method for integrating the three-dimensional acceleration sensor were developed. The size of the optimized accelerometer is only 25 mm × 25 mm × 30 mm. Performance testing revealed that, along the three spatial dimensions, the sensor had sensitivities of 51.9, 39.5, and 20.3 pm/g, respectively, resonance frequencies of 800, 1125, and 1750 Hz, respectively, and a measurable frequency range of 0–250 Hz.

A three-dimensional (3D) FBG accelerometer was proposed by installing three FBGs in an integrated oscillator structure which consists of two pairs of flexible hinges, a thin cylinder mass block and a base. The theoretical model of the proposed 3D accelerometer was established, and the dynamic response characteristics of the 3D accelerometer with optimal structural parameters were simulated using finite element software. Lots of sensing tests were finished and the sensing data showed that the sensitivities of the proposed 3D accelerometer in X-, Y-, and Z-directions are 108.7 pm/g, 144.2 pm/g, and 27.9 pm/g respectively, the working frequency range in X- and Y- directions are 40 – 300 Hz, and the acceleration amplitude range is 1 – 10 g. The proposed 3D accelerometer has the advantages of small size (28 mm $\times38$ mm $\times38$ mm), light weight (42 g), and simultaneous measurement of multi-dimensional acceleration.

To meet the needs of vibration monitoring with special requirements for the size and quality of accelerometers, a miniaturized fiber Bragg grating accelerometer based on flexible hinges is proposed in this paper. The sensor uses a flexible hinge as an elastic body, and the suspended arc package realizes the miniaturization of the accelerometer. At the same time, the grating prepared by bending-resistant optical fiber successfully solves the problem of light loss in arc-shaped packaging. The structural model and principle of the accelerometer are introduced, and its sensing characteristics are analyzed theoretically and by simulation. The physical size of the prepared accelerometer is 17 mm × 12 mm × 10 mm, and its mass is only 4.44 g. The experimental results show that the resonant frequency of the accelerometer is about 900 Hz, the sensitivity is 26.962 pm/g in the flat range of 20-400 Hz, and the lateral interference is less than 5%. The accelerometer is suitable for medium and low frequency vibration monitoring in narrow spaces in aerospace and other fields.