Wave Manipulation by Topology Optimization - Solid Mechanics

4.4 Effect of polarization and background material[P2] 25
Figure 4.4 The cloak (a) for 1 symmetry line is near perfect at 0 o (b) whereas significant
scattering is generated at 5 o (c) The dielectric layout (e) for the cloak optimized to operate
in an interval from -5 o to 5 o are effective both for incident angles of 0 o (f) and 5 o (g). The
robust design for small variation in the angle of incidence comes at the cost of increased
scattering (d).
make the cloak more versatile to various angles of incidence, more symmetry lines
are added to the design domain at the cost of increased objective value.
As mentioned above a slight variation in the incident angle results in a deteriorated
cloaking performance. The cloak for 1 symmetry line is near perfect at
0 o whereas significant scattering is generated at 5 o as shown in figures 4.4(b) and
(c). A robust design for small perturbations in the angle of incidence is obtained
by illuminating with uniform waves incident in an interval from -5 o to 5 o on the
design domain and cylinder. The optimization is formulated as a min/max problem,
i.e. the load case, which yields the highest scattering in each iteration step is
minimized. The angle sweep in figure 4.4(d) and the fields patterns in figures 4.4(f)
and (g) clearly shows that the cloak from figure 4.4(e) can be operated in a broader
incident angle interval at the cost of increased scattering.
4.4 Effect of polarization and background material[P2]
Finishing the initial study we wanted to pursue a realization of an all-dielectric fully
enclosing optical cloak designed by topology optimization. In a possible future experimental
setup it may be easier to confine the polarized propagating wave in a
material with higher index than free space and let spatial distributed areas of free
space constitute the optimized design profile of the cloak. This is the ”inverse”
case of the previous study, which was based on distributing material with a higher
permittivity than the background material (free space). Intuitively, distributing dielectric
material having a lower permittivity than the background material would
result in cloaking performance on the same level or better, however, this is not the