Design optimization of dual-band and double-polarization ir perfect absorbers using adjoint sensitivities

In this work, we utilize adjoint sensitivity approach within a constrained optimization algorithm to design a dual band infrared perfect absorber (IR-PA). The structure is composed of a silver circular ring and an elliptic cross centered on top of a two layer substrate. Dimensions of the ring and crossed ellipses in addition to the thicknesses are considered the design parameters. Careful parameters' optimization leads to a dual-band and near unity absorber at 2.7 μm and 6.0 μm, respectively. The symmetry of the design allows the operation at a polarization free electromagnetic excitation. The absorption peak wavelengths and their bandwidths can be tailored to match with a wide range of applications such as detection, energy harvesting, imaging, and stealth technologies.