Continuously tunable absorption bands in electromagnetic absorber implemented by a dual phase-transition thermal metamaterial

Abstract

Metamaterial electromagnetic absorbers (MMAs) are emerging as innovative solutions for applications such as radiation detection, electromagnetic stealth, and optoelectronic devices. Traditional MMAs rely on fixed materials and structures to create absorption for given bands, which often leads to invalidations of electromagnetic stealth when the detection bands change. Thus, it is urgent to study and design an electromagnetic absorber with continuously tunable absorption bands, particularly to include intermediate a given band, to adapt to changing detection bands for effective stealth. To overcome this dilemma, we design a graphite-based MMA that incorporates a Ni_1-xFe_xS-VO₂ phase transition thermal concentrator for enhancing electromagnetic absorption at high temperatures and realizing a continuous variation of electromagnetic absorption bands. Although the phase transition leads to abrupt changes in the electromagnetic parameters, the continuous evolution of the phase transition interface makes it possible to manipulate the temperature distribution in the graphite region, thus realizing continuously adjustable electromagnetic absorption bands for MMA. Simulations demonstrate that the phase transition significantly broadens the effective absorption bandwidth (EAB) of the proposed absorber, expanding it from 1.5 GHz to 6.3 GHz. Moreover, the system allows for switching between wideband and narrowband absorption, as well as achieving tunable intermediate absorption bands. This tunability opens new possibilities for active electromagnetic stealth, broadband communication, and sensing functionalities.