Negative group velocity characteristics of spoof surface plasmon polaritons

Although there have been many discussions on negative group velocity (NGV), disagreements over its counter-intuitive explanations are still on the way. In this paper, it is proposed that the negative group velocity is just a component of the actual wave group, which has to be accompanied by a positive group velocity (PGV) component. A composite wave with the NGV component propagates forward in the form of a tumbling vortex as an attenuated or evanescent wave. Negative group velocity exists only in the anomalous dispersion band with resonance absorption. This wave group model is confirmed by the NGV characteristics of spoof surface plasmon polaritons (SSPPs) of spiral-shaped periodic units. In this case, the PGV and NGV waves are formed by the resonance coupling of periodic cells, and the composite SSPP modes have both resonance absorption attenuation and vortex cancellation attenuation.

Automated summary

Although there have been discussions on negative group velocity, disagreements over its explanations are still ongoing. This paper proposes that negative group velocity is just a part of the actual wave group and needs to be accompanied by positive group velocity. A composite wave with negative group velocity propagates forward as a tumbling vortex in the form of an attenuated or evanescent wave. The existence of negative group velocity is limited to the anomalous dispersion band with resonance absorption. This wave group model is confirmed by the characteristics of spoof surface plasmon polaritons.