Spoof surface plasmon polaritons on ultrathin metal strips with tapered grooves

The dispersions of spoof surface plasmon polaritons (spoof SPPs) on comb-shaped ultrathin metal strips are studied both experimentally and numerically. The electric field distributions on these metal strips are measured directly by adopting a near field scanning technique. The dispersions of spoof SPPs are thus obtained by means of Fourier transform of the field distributions. Both fundamental and second order modes are investigated and the measured dispersions agree well with numerical results calculated by using the finite element method. The shape effects of grooves on the dispersion relations are also studied. As the top width of grooves decreases, the dispersions undergo a red-shift, and the field confinement in the depth direction of the grooves intensifies. This provides us a simple way to modify the propagation of spoof SPPs by altering the subwavelength structure of the metal strips.