| Periodic microstructure surface exhibits some special radiation properties when electromagnetic wave is incident onto it, forexmaple the wavelength-selective property, and we can active control the radiation properties by designing different microstructure surfaces. Under the background of infrared detection, this paper did some researchs about two-dimensional metal/dielectric/metal film grating structures in order to get dual-frequency absorption properties at 3~5μm and 8~10μm. Using RCWA method to calculate the radiation properties of the structures, and its absorptance mechanism is studied.Two-dimensional square ring array has the property of polarization insensitive and we can obtain absorptance peak in the required band by designing the structural parameters. And its mechanism can be attributed to the excitation of magnetic polaritons(MP) in the dielectric layer. However, the absorptance peak shifts to shorter wavelengths when the incident angle incease due to the excitation of surface plasma poaritons(SPP) and coupled with MP. Only odd-order MPs can be excited when normal incidence, and in the case of oblique incidence can appear even order MPs. So, the MP has the property of angle-selective the same as wavelength-selective.Comparative analysis the absorption property of the square ring structure and the patch structure. Because of the influence of the square cavity, the higher MPs shift to shorter wavelength. In order to widen the absorption bandwidth, we redesigned the square ring structure with the method of multi-layer stack. In this way, we can effectively broaden the width of absorption peak, and keep the height at the same time.By using different parts of the same structure excite magnetic polaritons in different wavelength, we can obtain dual-band high absorption properties. Here, with the method of nestification, we design a double square ring structure and a square ring embedded a path structure, and use the RCWA to calculate and analysis their absorption properties. |
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