A Review of Nonmagnetic Nonreciprocal Electronic Devices: Recent advances in nonmagnetic nonreciprocal components

Reciprocity is an underlying symmetry within a physical system that dates back to the work of Green in electrostatics in 1828
[1]
. Later on, through the works of Helmholtz, Rayleigh, and Lorentz, reciprocity theorems were developed in different fields, such as optics, acoustics, elastodynamics, and electromagnetics
[2]
,
[3]
. The electromagnetic reciprocity theorem states that, for a system with symmetrical permittivity and permeability tensors, which is passive, linear, and time invariant, the transmission and reception between two points in space are identical in opposite directions regardless of any spatial asymmetry within the channel between them.