  Incorporating time-varying elements into electromagnetic systems has shown to
be a powerful approach to challenge well-established performance limits, for
example bounds on absorption and impedance matching. So far, the majority of
these studies have concentrated on time-switched systems, where the material
undergoes instantaneous modulation in time while the input field is entirely
contained within it. This approach, however, necessitates accurate timing of
the switching event and limits how thin the system can ultimately be due to the
spatial width of the impinging pulse. To address these challenges, here we
investigate the periodic temporal modulation of highly lossy materials,
focusing on their relatively unexplored parametric absorption aspects. Our
results reveal that, by appropriately selecting the modulation parameters, the
absorption performance of a periodically modulated absorber can be greatly
improved compared to its time-invariant counterpart, and can even exceed the
theoretical bound for conventional electromagnetic absorbers, namely, the
"Rozanov bound". Our findings thus demonstrate the potential of periodic
temporal modulations to enable significant improvements in absorber performance
while circumventing the limitations imposed by precise timing and material
thickness in time-switched schemes, opening up new opportunities for the design
and optimization of advanced electromagnetic absorber systems for various
applications.
