  Due to the complicated environment of the plasma sheath, it is difficult to
experimentally measure plasma characteristics in the narrow geometry where
sheaths from opposite boundaries overlap. Since such geometries are often found
in industrial plasma applications, accurate measurements of this type are of
significant interests. In this paper, we employ micron-sized dust grains as
non-perturbative probes of the plasma environment. A particle-freefall
technique is then used to measure the sheath profiles produced by a rf plasma
within a glass box. The results show that this technique can identify the
plasma operating conditions for which the sheaths on opposite walls begin to
overlap as well as the magnitude of the effect.
