On the “Absorption” Mechanism of Metamaterial Absorbers

Several papers have appeared in the literature where periodic structures known as metamaterials are being used as RF absorbers. However, these structures lack enough lossy materials to absorb the electromagnetic energy in the same way that traditional RF absorbers do. Traditional RF absorbers convert electromagnetic energy to thermal energy. Since the first law of thermodynamics must hold, where does the energy carried as power in the electromagnetic wave go? In this paper it is shown that rather than absorb, the metamaterial structure redirects the energy away from the specular directions. Understanding how the power is reflected is key to being able to use these materials as RF absorbers in antenna ranges or to treat structures to reduce the RCS.