Planar Spoof SPP Transmission Lines: Applications in Microwave Circuits

In the optical regime, surface plasmon polaritons (SPPs) are attractive topics for physicists, chemists, biologists, and material scientists [1]-[13]. The concept of SPPs, which is widely applied in the field of surface science, can be dated to the 1950s [14]. SPPs are surface wave modes that propagate along the interface between a dielectric and a conductor (usually a metal) at optical frequencies. They are formed by interaction between the light or other electromagnetic (EM) waves trapped on the surface and the free electrons of the metal [1], [2]. Because of this interaction, the EM energy is tightly confined around the interface.