  In this paper, we discuss recent progress in magnet-free non-reciprocal
structures based on a synthetic form of angular momentum bias imparted via
spatiotemporal modulation. We discuss how such components can support metrics
of performance comparable with traditional magnetic-biased ferrite devices,
while at the same time offering distinct advantages in terms of reduced size,
weight, and cost due to the elimination of magnetic bias. We further provide an
outlook on potential applications and future directions based on these
components, ranging from wireless full-duplex communications to metasurfaces
and topological insulators.
