  Electromagnetic wave control using the concept of a reflecting surface is
first studied as a near-field and a far-field problem. Using a secondary source
present in a wireless communication environment, such as a backscatter tag, it
is possible to leverage the incoming radiation from the source as a
reference-wave to synthesize the desired wavefront across the reflecting
surface, radiating a field of interest. In this geometry, the phase grating,
which is synthesized using an array of sub-wavelength unit cells, is calculated
by interacting the incident reference-wave and the desired wavefront, similar
to a hologram. When illuminated by the reference-wave, the reflected wavefront
from the calculated phase grating is guaranteed to constructively add in the
direction of the desired radiation (beam-steering in the far-field) and also
focus at the intended depth (beam-focusing in the radiative near-field).
Leveraging a dynamic modulation mechanism in the context of an intelligent
reflective surface (IRS) illuminated by a backscatter tag, later, we present
that one can selectively focus and defocus at an arbitrarily positioned
receiver within the 3D field of view of the reflecting surface. This enables
the control of the amplitude of the radiated electric field at the receiver
location, paving the way for a spatial modulation mechanism by means of
reconfiguring the reflecting surface in a backscattered wireless communication
environment. In addition to the phase modification approach on a unit cell
level to reconfigure the aperture radiated wavefronts, we finally present a
time varying IRS concept making use of a time-delay based approach relying on a
delay adjustment between the reflection coefficients of the IRS' unit cell
lattices.
