Electromagnetic energy focusing based on localized spoof surface plasmon polaritons

We propose a self-similar linear chain of several metallic spirals whose sizes and separations are decreasing proportionally. This structure owns the ability of focusing electro-mag-netic energy on subwavelength scale, with the magnitude of local electric field intensity reaching 1435, located around the smallest spiral. Near-field response spectrum and near-field mapping are performed in the microwave regime and experimental results agree well with theoretical simulation. This study may have promising applications in surface enhanced Raman scattering and elec-tromaznetic near-field sensing.