  This paper derives and investigates a time-varying k-domain modulation in
vector form using a time-reversal (TR) field decomposition theory proposed for
the first time. First, the proposed theory illustrates that the TR field can
exhibit super-resolution property from the perspective of spatial focusing
pattern if a point sink is set at the initial source point. Afterward, the
instantaneous TR fields with and without the point sink, as well as their
k-domain patterns are compared to illustrate the time-varying k-domain
modulation, which accounts for the superresolution property. The phenomenon
observed and derived in this paper shows great potential in the applications
empowered by super-resolution focusing, such as wireless communication carrying
the subwavelength information and high spatial resolution wireless power
transfer.
