Double toroidal spoof localized surface plasmon resonance excited by two types of coupling mechanisms

The double toroidal spoof localized surface plasmons (LSPs) on combined split ring resonators (SRRs) are proposed and experimentally demonstrated at microwave frequencies. Based on conventional printed circuit board techniques on a dielectric substrate, the designed metamaterial clearly shows two toroidal spoof LSP resonances. Two toroidal spoof LSP resonances are excited due to the conductive coupling and magneto-inductive coupling, respectively. Both numerical simulations and experiments are in good agreement. It is shown that the toroidal spoof LSP resonance is sensitivie to the local dielectric environments. Hence, the combined SRRs may be used as plasmonic sensors and find potential applications in the microwave and terahertz frequencies.