CST_ MWS： small objects respect to the wavelength

there is someone who simulates small objects respect to the wavelength? for example: i'm trying to see the electric field intensity in 2 concentric spheres, 3.5 um and the other 3.4um.
one is dispersive, and the other one (the inner one) is dielectric.
i have problems with the mesh, and the simulation time...which is very very long.
the frequency interval is [0, 2.45] GHz.
some suggestions please?
thx

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