From the final link:
‘Invisibility Cloak’ Undone ScienceDaily, Sep. 3, 2008Chinese scientists have proposed a theoretical “anti-cloak” that would partially cancel the effect of an invisibility cloak.
PhysOrg covered this as well with a some detail on what the anti-cloak is actually about and how it could be implemented.
An even greater problem for anyone who has aspirations to be concealed in public one day is that invisibility achieved through transformation media is a two-way street. With no light penetrating a perfect invisibility cloak, there would be no way for an invisible person to see outside. In other words, invisible people would also be blind—not exactly what Harry Potter had in mind.
But now, Chen and his colleagues have developed way to partially cancel the invisibility cloak’s cloaking effect. Their “anti-cloak” would be a material with optical properties perfectly matched to those of an invisibility cloak. (In technical jargon, an anti-cloak would be anisotropic negative refractive index material that is impedance matched to the positive refractive index of the invisibility cloak).
While an invisibility cloak would bend light around an object, any region that came into contact with the anti-cloak would guide some light back so that it became visible. This would allow an invisible observer to see the outside by pressing a layer of anti-cloak material in contact with an invisibility cloak