An electromagnetic absorber is a device that converts incoming electromagnetic waves into other forms of energy. Since Landy et al. (2008) proposed a metal-insulator-metal-based narrow-band absorber, a wide range of absorbers have emerged. Because the broadband electromagnetic absorbers are widely used in photodetector, solar cells, cooling coolers, and photochemical devices, they have been a hot spot of research in recent years, and the broadband electromagnetic absorbers worked in visible light, infrared, terahertz, microwave, and other bands have been widely reported. UV absorbers have important applications in ultraviolet-related fields such as ultraviolet photocatalyst, but there are few reports on this type of absorber. Although most absorption bands of previously designed absorbers involve the ultraviolet band, they don’t completely cover the ultraviolet band, and the absorption effect of the ultraviolet band is not better than that of the other bands, with an average absorption rate of only about 60%. In terms of material and performance, most applications of the absorbers are focused on fields such as energy collection, but ultraviolet protection is less explored. It is critical to design a broadband efficient absorption device that fully covers the ultraviolet band in order to improve the absorption performance and give full play to the performance of the ultraviolet band, combined with its adopted material characteristics and design structure, and to understand the physical mechanism behind it.

A multigroove ultraviolet absorber was designed using Bi_1.5Sb_0.5Te_1.8Se_1.2(BSTS) material. First, modeling was done with COMSOL software. The incident and reflection ports were assigned to port 1, while the transmission port was assigned to port 2. To account for the diffraction effects of levels 0 and ±1, two diffraction levels were set under each port. Periodic boundary conditions were set on the left and right sides to ensure the structure’s periodic setting. The grid was then finely divided to ensure the accuracy of the calculation and the results. The field distribution of this absorber was then simulated, and the simulation results showed that the physical mechanism of the absorber was surface plasma resonance and optical cavity resonance. Finally, a frequency domain parameterized solution is used to calculate the effect of different structure parameters and incidence angles on absorption performance.

After numerous simulations, relatively optimized structural parameters were obtained: number of grooves N is 10, BSTS thickness t₁ is 100 nm, SiO₂ width t₂ is 145 nm, groove width W is 600 nm, minimum depth h_min is 1225 nm, and maximum depth h_max of grooves is 1800 nm. The diagrams show the absorber’s absorption rate, reflectance, and transmission rate at zero incidences (Fig. 4). As can be seen in Fig. 4, the absorption curve maintains a good absorption effect, up to more than 90%, allowing for high broadband absorption across the entire ultraviolet band range. To illustrate the absorption characteristics of the absorber at different angles, the contour diagram of the absorption at 0° to 85° is given in Fig. 5, which shows that absorption of about 90% can be achieved at 0°-60°. The overall absorption effect in the 0°-70° range can reach over 80%, achieving a wide-angle high absorption in the ultraviolet band range. The normalized magnetic field distributions at 210 nm, 250 nm, 320 nm, and 360 nm in the zero incident case were showed in Fig. 6 to analyze the physical mechanism of this absorber absorption. This absorber’s absorption mechanism is the surface plasma resonance effect and the optical cavity resonant effect, as shown in Fig. 6. The groove region of the structure is the grating region, because surface plasma resonance occurs at the surface of the BSTS material, causing strong absorption at different wavelengths. When the incident electromagnetic wave meets the resonance conditions, the field is localized within this region, resulting in strong absorption. Furthermore, in order to analyze the dependence between the absorption performance of the absorber and the structural parameters, in the case of zero incidences, combined with the field distribution at a specific wavelength, the effects of changing the width of air groove W, thickness t₁ of BSTS, width t₂ of SiO_2,minimum depth h_min of groove, maximum depth h_max of groove and number N of air groove on absorption performance were analyzed respectively. The results are shown in (Figs.7-12).

This article describes the design of a multigroove-type ultraviolet absorber with absorption conditions spanning the entire ultraviolet band, from 200 to 400 nm. The finite element method was used to investigate the relationship between the absorption mechanism or the absorption characteristics and the incident wavelength, angle of incidence, and structural parameters. The structure is intended to benefit from the combination of both materials and structures, with the BSTS material exhibiting good plasma properties in the ultraviolet band and the dielectric constant of the medium layer silica changing with wavelength. The absorber achieves high absorption in the ultraviolet band due to the effective combination of the two materials and the reasonable structural design. Through extensive simulation calculations, the absorptivity can reach the range of over 80% between 200 to 400 nm at 0°-70°, and at 0°-60°the absorptivity of about 90% is basically achieved with optimized structural parameters, realizing the broadband wide-angle absorption in the ultraviolet band. With zero incidences, the overall absorptivity exceeds 90%. The absorption mechanism of the zero-degree incidence case is highlighted when combined with the magnetic field distribution under the optimization parameters. Broadband and efficient absorption were caused by the interaction of the surface plasma resonance and the optical cavity resonance. A reasonable absorber size design provides a theoretical foundation for the actual production of the ultraviolet absorber. Furthermore, the absorber’s design is expected to have important applications in ultraviolet sensing, ultraviolet photoelectric detection, ultraviolet protection, and other fields.