As the basic application of fiber optic sensing technology, strain measurement accuracy as a key index needs to be further calibrated and analyzed. In this paper, accuracy calibration experiments and the related analyses of two fiber-optic sensing technologies, the fiber-optic grating (FBG) and optical frequency domain reflectometry (OFDR), are carried out using a standard beam of equal strength and a mature resistive strain gauge (ESG). The fiber-optic single-point strain data for loading and unloading changes of the beams of equal strength show good continuity and linearity, with good cyclic stability, and the error in the strain test data is less than 2% after repeated loading. At the same time, using finite element theory to analyze the data and using the measured data error within 5%, a good strain test curve linearity is achieved and R2 is better than 0.998. After repeated loading and unloading tests, it is verified that the fiber grating and the distributed optical fiber in the strain test have good stability in repeatability accuracy. The calibration experiments and data analysis in this paper further illustrate the three sensing technologies in determining the strain test accuracy and the advantages and disadvantages of the indicators, and the development of the fiber optic sensing technology application provides basic technical support.

Defects occurring during the welding process of metal structural components directly affect their overall strength, which is crucial to the load-bearing capacity and durability of the components. This signifies the importance of accurate measurement and assessment of weld strength. However, traditional non-destructive testing methods such as ultrasonic and non-contact camera inspection have certain technical limitations. In response to these issues, this paper analyzes the detection principle of weld strength, revealing that weld defects reduce the effective area of the structural bearing section and cause stress concentration around them. Through repeated experimental data analysis of samples, strain distribution data along the one-dimensional direction caused by defects such as slag inclusion and porosity were obtained. Experimental results show that this method can identify defect types in welds, including slag inclusion, porosity, and unevenness, and accurately measure the location and size of defects with a precision of 0.64 mm, achieving qualitative analysis of weld defects. Additionally, by deploying distributed optical fiber sensors (DOFS) at different vertical distances along the weld direction, the propagation law of stress induced by different types of weld defects on samples was thoroughly analyzed. This further validates the advantages of this method in weld strength detection, including high spatial resolution, high sensitivity, and non-destructive measurement.

The precise evaluation of micro-crack sizes and locations is crucial for the safe operation of structures. Traditional detection techniques, however, suffer from low spatial resolution, making it difficult to accurately locate micrometer-scale cracks. A method and experimental study were proposed in this paper for identifying and locating micro-cracks using optical fiber strain sensing based on OFDR to address this issue. The feasibility of this method for micro-crack detection was verified by the combination of a polyimide-coated sensing optical fiber (PISOF) and tight sheath sensing optical fiber (TSSOF). A calculation method for micro-crack widths based on distributed optical fiber strain curves was established, and the test results of different optical fibers were compared. Through multiple verification experiments, it was found that the strain peak curves of both fiber types could accurately locate micro-cracks with a precision of 1 mm. Additionally, the crack widths could be obtained by processing the distributed strain curves using a computational model, enabling the accurate capture of micro-crack characteristics at the 10 μm level. A strong linear relationship was observed between the optical fiber stretching length and the crack width. Notably, the relative error in calculating the crack width from the strain curve of PI fiber was very small, while a linear relationship existed between the maximum strain value of the TSSOF and the crack width, allowing for the calculation of the crack width based on the maximum strain value. This further validated the feasibility of the method designed in this paper for the analysis of micro-crack characteristic parameters.

The generalized Radon–Fourier transform (GRFT) is a well-established coherent accumulation technique for high-speed and high-mobility target detection. However, this method tends to suffer from the difficulty of identifying the main lobe from multiple blind speed sidelobes (BSSLs) and the computational complexity is generally high. To address these challenges, we propose a new method, namely the BSSL Traction Particle Swarm Optimization (BTPSO), to robustly and accurately extract the main lobe. In the method, the relationship between the main lobe and the BSSLs is used to attract particles to potential positions of the main lobe in the group when trapped in local optimal, and a new termination criterion in which multiple particles should converge to the same optimal value is proposed to avoid local convergence. Simulation examples show that the proposed method can improve the probability of converging to the main lobe peak while reducing cost time, and its good adaptability to low signal-to-noise ratio (SNR) cases is well verified.

The equivalent circuit is a commonly used tool for performance analysis during CMUT design and optimization. In this study, the immersion equivalent circuit model of square CMUT array is established for the first time. Using this model, the vibration, electrical, and acoustic characteristics of square CMUTs can be rapidly analyzed. Consequently, it can replace the time-consuming finite element model for design and optimization. For comparison with the equivalent circuit model presented in this paper, the finite element model of the square CMUT array was established by COMSOL 6.0a. The theoretical calculation results of the equivalent circuit model are highly consistent with the FEM results. Finally, a 28×28 CMUT array composed of square cells was fabricated using the wafer bonding process, and its vibration and impedance characteristics were tested using a Laser Doppler Vibrometer and an impedance analyzer. All experimental results well verified the accuracy of the proposed equivalent circuit models.

Laser-screen targets suffer from prolonged response time, and printed-circuit-board (PCB) targets induce substantial kinetic energy loss of fragments upon penetration. To mitigate these technical limitations, this study develops a novel screen-printed velocity measurement film (VMF) characterized by a fast response time and low kinetic energy loss. The proposed VMF consists of silver conductive grids and a polyethylene terephthalate (PET) substrate, with an ultra-thin overall thickness of 0.175 mm and identical width and spacing of 0.8 mm for all silver strips. This work comprehensively elaborates the film fabrication procedure and validates its practical engineering performance through live-fire fragment penetration experiments. Experimental results demonstrate that the VMF achieves an average response time of 0.14 μs under metallic fragment impact, with average fragment kinetic energy losses of 1.32 J and 2.09 J when penetrating the first and second VMF layers, respectively. Owing to its rapid transient response and minimal interference with fragment flight trajectories, the designed VMF effectively improves the precision of fragment velocity measurement, possessing great application potential for field blast-testing scenarios.