  Analysis of the properties of resonant modes in a reentrant cavity structure
comprising of a post and a ring was undertaken and verified experimentally. In
particular we show the existence of higher order reentrant cavity modes in such
a structure. Results show that the new cavity has two re-entrant modes, one
which has a better displacement sensitivity than the single post resonator and
the other with a reduced sensitivity. The more sensitive mode is better than
the single post resonator by a factor of 2 to 1.5 when the gap spacing is below
100 $ \mu$m. This type of cavity has the potential to operate as a highly
sensitive transducer for a variety of precision measurement applications, in
particular applications which require coupling to more than one sensitive
transducer mode.
