Tailoring radiative properties with magnetic polaritons in deep gratings and slit arrays based on structural transformation

Magnetic polaritons which refer to the couplings between incident electromagnetic waves with magnetic excitation inside the structures play an important role in tailoring thermal radiative properties. Many researchers devote themselves to studying the geometric effects of the micro/nanostructures based on magnetic polaritons, and many wavelength-selective devices are designed. However, the links between different structures on thermal radiative properties based on structural transformation are not investigated yet. In this work, the idea that deep slit arrays and deep gratings can be equivalent conversion approximately when studying the radiative properties is proposed. Magnetic polariton resonant conditions of deep metal gratings and slit arrays are investigated. Considering the symmetry of the structures, when gratings and slit arrays have same geometry parameters except that the slit heights are twice that of the grating depths, the phenomena that they have almost identical magnetic polariton resonant frequencies are observed. The reason for almost identical magnetic polariton resonant conditions is attributed to that the symmetry of the structures leads to the similar electromagnetic field distributions. Moreover, equivalent inductor-capacitor circuit model is also used to analytically illuminate and confirm almost same MP resonant frequencies. The idea provided in this paper may benefit design of the wavelength-selective devices based on magnetic polaritons and further studies on tailoring radiative properties from perspective of structural transformation.