Nonreciprocal microwave transmission in metastructures with transversely magnetized ferrite plate and a grating of resonant elements

Nonreciprocal transmission of a linearly polarized electromagnetic wave at a ferromagnetic resonance (FMR) frequency has been observed in a metastructure comprising a transversely magnetized ferrite plate and a grating of resonant elements. The nonreciprocity of wave transmission is observed for the metastructure arranged along the axis of a rectangular waveguide and even in the free space between transmitting and receiving waveguides, where the effect does not take place when there is no grating. The observed phenomenon is explained by the formation of a surface wave with elliptic or circular polarization on the grating. The nonreciprocity reaches maximum (>35 dB) under the conditions of mutual influence between the FMR and the resonance of grating elements for certain values of the certain frequency and magnetic field, which depend on the distance between the ferrite plate and the grating. The nonreciprocal effects have been observed for grating elements in the form of double split rings, polyhedral loops, and dipoles. The results may be of interest for the development of new nonreciprocal devices and multifunctional metastructures such as decoupling elements for quasi-optical systems and two-frequency decoupling filters for counterpropagating waves in the gigahertz and terahertz range.