  The presence of active forces in various biological and artificial systems
may change how those systems behaves under forcing. We present a minimal model
of a suspension of passive or active swimmers driven on the boundaries by
time-dependent forcing. In particular, we consider a time-periodic drive from
which we determine the linear response functions of the suspension. The meaning
of these response functions are interpreted in terms of the storage and
dissipation of energy through the particles within the system. We find that
while a slowly driven active system responds in a way similar to a passive
system with a re-defined diffusion constant, a rapidly driven active system
exhibits a novel behavior related to a change in the motoring activity of the
particles due to the external drive.
