  We describe a Casimir setup consisting of two aligned sinusoidally corrugated
Ni surfaces, one of which is "hidden" by a thin opaque layer of gold with a
flat exposed surface. The gold layer acts as a low-pass filter that allows for
a clean observation of the controversial thermal Casimir force between the
corrugations, with currently available Casimir apparatuses. The proposed scheme
of measurement, based on the phase-dependent modulation of the Casimir force,
requires no electrostatic calibrations of the apparatus, and is unaffected by
uncertainties in the knowledge of the optical properties of the surfaces. This
scheme should allow for an unambiguous discrimination between alternative
theoretical prescriptions that have been proposed in the literature for the
thermal Casimir effect.
