  The electronic conductance of graphene-based bilayer flake systems reveal
different quantum interference effects, such as Fabry-P\'erot resonances and
sharp Fano antiresonances on account of competing electronic paths through the
device. These properties may be exploited to obtain spin-polarized currents
when the same nanostructure is deposited above a ferromagnetic insulator. Here
we study how the spin-dependent conductance is affected when a time-dependent
gate potential is applied to the bilayer flake. Following a Tien-Gordon
formalism we explore how to modulate the transport properties of such systems
via appropriate choices of the $ac$-field gate parameters. The presence of the
oscillating field opens the possibility of tuning the original antiresonances
for a large set of field parameters. We show that interference patterns can be
partially or fully removed by the time-dependent gate voltage. The results are
reflected in the corresponding weighted spin polarization which can reach
maximum values for a given spin component. We found that differential
conductance maps as functions of bias and gate potentials show interference
patterns for different $ac$-field parameter configurations. The proposed
bilayer graphene flake systems may be used as a frequency detector in the THz
range.
