The timely detection of insulator defects in transmission lines is vital for ensuring social production and people’s livelihoods. Aiming to solve the problem of the low accuracy of insulator defect detection in current detection models, this study improves the YOLO11n model and proposes an insulator defect detection model, FPFS-YOLO, that integrates FasterNet and an attention mechanism. In this study, to mitigate parameter redundancy in the backbone of the YOLO11n model, the FasterNet lightweight network was introduced, and some convolution was embedded into the shallow network to enhance its feature extraction ability. To solve problems such as insufficient attention to important features and the low detection ability of small defects in the YOLO11n model network, the ParNet attention mechanism was added, along with a small-defect detection layer, which improved the detection accuracy of the model. Finally, in order to alleviate the computational redundancy caused by these additions, the C3k2_faster module and the PSP-Head detection head were introduced. These amendments further improved the accuracy of the model network in detecting insulator defects while simultaneously reducing its computational redundancy. The experimental results show that the improved FPFS-YOLO model achieved a 91.5% mAP@50 and a 56.6% mAP@0.5-0.95, increases of 3.1% and 1.2%, respectively, while the precision and recall reached 93.2% and 86.4%, increases of 1.5% and 4.2%, respectively. The FPFS-YOLO model achieved a higher detection accuracy than the YOLO11n model and thus could be widely applied in the detection of insulator defects.

In this study, novel focusing performances of high-numerical-aperture (NA) micro-Fresnel zone plates (FZPs) with selective occlusion are identified and investigated through numerical calculations based on vectorial angular spectrum (VAS) theory, and further rigorously validated using the finite-difference time-domain (FDTD) method. The central occlusion of a standard micro-FZP can significantly extend the depth of focus while keeping the lateral size of the focusing spot essentially unchanged. When a standard micro-FZP only retains two separated transparent rings and all other rings are obstructed, it will result in multi-focus phenomena; at the same time, the number of focal points is equal to the difference in number between the two separated transparent rings. Furthermore, a focusing light needle can be generated by combining the central occlusion and wavelength shift of a standard micro-FZP. This study not only provides new ideas for the design and optimization of micro-FZPs but also provides reference for the expansion of practical applications of FZPs.