RESUMO
In this work, we investigate dynamically dual-tunable dual-band, triple-band, and four-band metamaterial absorbers (MAs) based on a bulk Dirac semimetal (BDS) and vanadium dioxide (VO2). Due to the bright-bright mode coupling between BDS rods, the dual-band, triple-band, and four-band MAs can be realized when the VO2 is in a fully metallic state. The average absorptivity of the absorption peaks in the three MAs reaches 97%, 98.6%, and 96.4% respectively. The physical mechanism can be explained by the radiating two-oscillator model. The resonant frequencies and absorptance intensities at absorption peaks in each MA can be dynamically tuned by varying the BDS Fermi energy and the VO2 conductivity.
RESUMO
An acoustic illusion device that can act as an invisible cloak or a shifting medium depending on the value of shift distance, which is about twice the circum-radius of the outer polygon, is proposed and designed based on linear coordinate transformation. A multi-folded transformation approach is used to design an illusion device with a circular opening window that allows for information interaction with the outside world. The results show that the proposed device can hide objects with arbitrary shapes or positions. Furthermore, in order to remove the material anisotropy of the proposed illusion device, a layered structure composed of homogenous and isotropic material is used based on the effective medium theory. The combination of the layered structure and the circular opening provide a flexible and feasible approach to achieve the partial implementation of the illusion device. It is hoped that these results may open an avenue for designing and implementing invisibility cloaks or illusion devices, and speed up potential applications for noise shielding, target camouflage, or target protection from active sonar signals.
