According to the Equivalence Principle, any distribution of electromagnetic fields can be
generated within a closed region by suitable electric and magnetic sources lying on its
bounding surface. In electromagnetic theory, these sources have been used as fictitious
analytical tools. However, this has changed in recent years with the development of
“Huygens's metasurfaces,” which are subwavelength thin sheets of artificial active and/or
passive elements. With proper configuration, these elements can physically approximate the …