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Metalens has the advantages of high design freedom, light weight and easy integration, thus provides a powerful platform for infrared detection. Here, we numerically demonstrated a broadband achromatic infrared all-dielectric metalens over a continuous 800 nm bandwidth, with strong environmental adaptability in air, water and oil. By building a database with multiple 2π phase coverage and anomalous dispersions, optimizing the corrected required phase profiles and designing the sizes and spatial distributions of silicon nanopillars, we numerically realized the design of broadband achromatic metalens. The simulation results of the designed metalens show nearly constant focal lengths and diffraction-limited focal spots over the continuous range of wavelengths from 4.0 to 4.8 μm, indicating the ability of the designed metalens to detect thermal signals over a temperature range from various fault points. Further simulation results show that the metalens maintains good focusing performance under the environment of water or oil. This work may facilitate the application of metalens in ultra-compact infrared detectors for power grid faults detection.

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In the present paper, the electromagnetic coupled heat transfer and ultrasonic propagation in a 252 kV three-phase GIS busbar chamber were numerically studied by using the finite element method. The electromagnetic loss and distributions of SF6 gas velocity, temperature, and breakdown margin in the GIS busbar chamber were carefully analyzed, and the influences of SF6 gas velocity and temperature variations on ultrasonic propagation performances in the GIS chamber were discussed in detail. It is found that the SF6 gas breakdown margin in the GIS busbar chamber is mainly affected by the electric field intensity. When I = 3300 A and U  = 1050 kV, the minimum SF6 gas breakdown margin in the GIS busbar chamber is 7.98 kV/mm, which is located at top of busbar conductor A, where the thermal breakdown risk is relatively high. Furthermore, it is noted that, when natural convection in GIS busbar chamber is weak, the influences of SF6 gas velocity and temperature variations on sound propagation would be insignificant. For this case, when acoustic propagation simulation is performed, the SF6 gas would be assumed to be stationary and its temperature would be set to the average gas temperature of natural convection in the GIS chamber, which would be beneficial to reduce the computational time and maintain the simulation accuracy as well.