  We introduce a metasurface-based system for the microwave hyperthermia
treatment of brain tumors, where the metasurface is designed by the
time-reversal technique for optimal focusing at the location of the tumor.
Compared to previous time-reversal microwave hyperthermia systems, which are
based on antenna arrays, the proposed system offers two advantages: 1) it
provides superior focal resolution, due to the finer sampling capability of its
deeply-subwavelength metasurface particles compared to that of typical array
antenna elements, 2) it features much lower complexity and cost, due to its
direct illumination principle compared to the heavy feeding network of the
array system. The system leverages reflecting metallic walls and a rich
scattering structure in combination with the metasurface to achieve high
hyperthermia performance with maximal simplicity. The metasurface system is
demonstrated by full-wave simulation results, which show that it represents a
viable novel noninvasive hyperthermia technology.
