Metallic metamaterials comprised of subwavelength slits can replace conventional dielectric materials for interaction with convection electrons. Moving electrons can excite effective surface plasmons in subwavelength slits which behaves as Cerenkov radiation. Threshold-free of electron energy and robustness against breakdown for compact and high-power beam-wave interaction are the benefits of metallic metamaterials.
The effective surface plasmons in metamaterials can be manipulated by geometric modulation that induces radiation to free space. The radiation power is turned out to be much higher than Smith-Purcell radiation from ordinary reflection gratings. Understanding such manipulation of trapped electromagnetic modes is quite important for efficient interaction with both light and convection electrons in such subwavelength scale.