Credit: Xiao Tian Yan et al., doi 10.1117/1.AP.3.2.025001 Surface plasmon polaritons (SPPs) are highly localized surface waves on the interface between metal and dielectric in the optical frequency band. SSPs do not naturally exist in the microwave and terahertz frequencies, so "spoof" surface plasmon polaritons (SSPPs) are necessary for operations in those lower frequency bands. Like optical SPPs, microwave SSPPs exhibit highly localized electromagnetic fields, subwavelength resolution, and extraordinary field confinement. Therefore, SSPP transmission lines (TLs) have been proposed as novel types of microwaveguides that offer new solutions for miniaturization, signal integrity, and low crosstalk in compact circuits for use in wireless communications and wearable electronics.