Cherenkov radiation can also radiate in an arbitrary direction using properly engineered one dimensional metamaterials. The latter is designed to introduce a gradient of phase retardation along the trajectory of the fast travelling particle ( d ϕ ϕ / d x ), reversing or steering Cherenkov emission at arbitrary angles given by the generalized relation: cos ⁡ ⁡ θ θ = 1 n β β + n k 0 ⋅ ⋅ d ϕ ϕ d x