Casimir force in a compressive transformation medium

We consider an example of an idealized inhomogeneous metamaterial which, when introduced into a Casimir cavity, reduces the magnitude of the Casimir force. It has recently been argued, however, that Casimir-Lifshitz forces in inhomogeneous media are cutoff dependent; the stress tensor typically yields an infinite Casimir force, even in a case where the force must be zero. We demonstrate that, although the medium is inhomogeneous, it does not contribute any additional scattering events, but simply modifies the effective length of the cavity, and consequently the predicted force in this case is finite and can be stated exactly.