  In this study, we reveal noncontact frictional forces between surfaces in the
presence of peristaltic permittivity modulation. Our setup comprises a
conducting medium, an air gap, and a dielectric substrate on which we have a
space-time-modulated grating that emits electromagnetic radiation. The
radiation receives energy and momentum from the grating, which is eventually
absorbed by the conducting medium or propagates away from the grating on the
dielectric side, resulting in electromagnetic power loss and lateral forces at
the surfaces.
