  Superconducting reentrant cavities can be used in parametric transducers for
Gravitational Wave antennas. The Mario Schenberg detector, which is being built
by the GRAVITON group at Instituto Nacional de Pesquisas Espaciais (INPE),
basically consists of a resonant mass (ball) and a set of parametric
transducers in order to monitor the fundamental modes of vibration. When
coupled to the antenna, the transducer-sphere system will work as a mass-spring
system. In this work the main task is the development of parametric transducers
consisting of reentrant superconducting cavity with high performance to be
implemented in the Mario Schenberg detector. Many geometries, materials and
designs have been tested and compared to optimize parameters such as electric
and mechanical Q-factor. The aim is the construction of a complete set of nine
parametric transducers that, attached to the spherical antenna, will possibly
reach the sensitivity $h$ $\sim$ 10$^{-22}$ $Hz$$^{-1/2}$ in the near future.
