  We show that engineered diffraction gratings can considerably simplify the
design and performance of acoustic devices. Acoustic reflecting gratings based
on rectangular cavities drilled on an acoustically rigid surface are designed
in such a way that all the incident energy is channeled towards the diffracted
mode traveling in the oposite direction of the incident field (retroreflection
effect), and this effect is used to cloak an object placed over a rigid
surface. Axisymmetric gratings consisting in rigid surfaces with just one
groove per unit cell are used to design acoustic thin acoustic carpet cloaks.
Finally, full wave numerical simulations are performed and a conical carpet
cloak is experimentally tested, showing an excellent scattering cancellation
effect.
