  We estimate the dominating frequencies contributing to the Casimir energy in
a cavity of metamaterials mimicking de Sitter space, by solving the eigenvalue
problem of Maxwell equations. It turns out the dominating frequencies are the
inverse of the size of the cavity, and the degeneracy of these frequencies also
explains our previous result on the unusually large Casimir energy. Our result
suggests that carrying out the experiment in laboratory is possible
theoretically.
