Inverse Design Method On Radiative Properties Of One Dimensional Micro/Nano Scale Grating

Micro/nano scale grating exhibits wavelength-selective property whenelectromagnetic wave is incident onto its surface. Based on this property, it is widelyused for tailoring radiative properties. Under the background of aircraft thermalcontrolling, the thesis inversely designs grating emitters, the aim of which is to have anemittance peak and a broad one if possible at wavelength10μm. And inverse designingof gratings needs combining both the forward and the inverse problem methods. Thisthesis uses rigorous coupled wave analysis as forward problem method and geneticalgorithm as inverse problem method. Groove gratings, thin film gratings and movablegratings that can shift the emittance peak are analyzed in the thesis.Groove gratings include rectangular grating and dual groove grating. After inverseanalysis, both of them can achieve emittance peak at wavelength10μm along thenormal direction when subjected to transverse magnetic (TM) wave. And its mechanismcan be attributed to the excitation of magnetic polaritons (MP) in the deep groove.However, with the increasing of zenith angle, excitation of surface plasma polaritons(SPP) intervenes MP, which makes the emittance peak shifts to longer wavelengths anddisappear gradually. This problem can be solved by including angle in the objectivefunction, but the corresponding grating period is relatively smaller and the ratio ofgroove depth to width is greater.For thin film grating after inverse designing, an angle-independent emittance peakis achieved at wavelength10μm, the mechanism of which is also attributed to magneticpolaritons. The thesis gives an analysis of the grating parameters and finds that thewavelength to excite MP is linearly proportional to the width of metal strip. By virtue ofthis property, the thesis gives an optimization of complex thin film grating andmulti-layer thin film grating. Both achieve broad emittance peaks and large effectivebandwidth due to the collective effect of several MPs. The former includes multi-sizedmetal strips in one period while the latter has several layers with different width.Also, the thesis inversely designs double-strip thin film grating and overlappingthin film grating and analyzes the changing of the radiative properties with the lateralshift of the metal strip. The former has an emittance peak shift from10μm to8.5μm, butthe emittance decreases gradually and becomes angle-dependent. The latter has a peakshift from7μm to12μm and the emittance peak keeps high and angle-independent.