Lateral Shift Makes a Ground-Plane Cloak Detectable

We examine the effectiveness of the ground-plane invisibility cloak generated from quasiconformal mapping of electromagnetic space. This cloak without anisotropy will generally lead to a lateral shift of the scattered wave, whose value is comparable to the height of the cloaked object, making the object detectable. This can be explained by the fact that the corresponding virtual space is thinner and wider than it should be. Ray tracing on a concrete model shows that for a bump with a maximum height of 0.2 units to be hidden, the lateral shift of a ray with 45 degree incidence is around 0.15 units.