  Micromegas detectors, thanks to the good spatial and temporal discrimination
capabilities, are good candidates for rare event search experiments. Recent
X-ray background levels achieved by these detectors in the CAST experiment have
motivated further studies in the nature of the background levels measured. In
particular, different shielding configurations have been tested at the Canfranc
Underground Laboratory, using a microbulk type detector which was previously
running at the CAST experiment. The first results underground show that this
technology, which is made of low radiative materials, is able to reach
background levels up to $2 \times 10^{-7}$keV$^{-1}$s$^{-1}$cm$^{-2}$ with a
proper shielding. Moreover, the experimental background measurements are
complemented with Geant4 simulations which allow to understand the origin of
the background, and to optimize future shielding set-ups.
