  Conventional concentrators with inhomogeneous coating materials that fully
enclose the destined region pose great challenges for fabrication. In this
paper, we propose to design an EM concentrator with homogeneous materials.
Distinguished from conventional ones, the elaborately designed EM concentrator
features a concentrator region that is open to the outer-world, which is
achieved with multi-folded transformation optics method by compressing and
folding the coating materials to create window(s). Based on this concept, we
also investigate open-rotator and open rotational-concentrator devices, which
could simultaneously rotate and store the EM waves in the central destined
region. Due to the open nature of our proposed designs, we believe they will
find potential applications in remote controlling with impressive new
functionalities.
