  Rectennas formed from nanodipole antennas terminated by plasmonic
metal-insulator-metal (MIM) travelling wave transmission line rectifiers are
developed for ambient thermal energy harvesting at 30 THz. The transmission
lines are formed from two strips coupled either vertically or laterally. A
systematic design approach is presented, that shows how different components
can be integrated with each other with maximum radiation receiving nantenna
efficiency, maximum coupling efficiency between nantenna and rectifier, and
maximum MIM diode rectifier efficiency. The tunneling current of the rectifier
is calculated using the transfer matrix method (TMM) and the nonequilibrium
Green's function (NEGF). The figures of merit of the rectifier are analyzed,
and the effect of the metals and insulator choices on these merits is
investigated. A detailed parametric study of the coupled strips plasmonic
transmission lines is presented and thoroughly discussed. The overall
efficiencies of the proposed travelling wave rectennas are fully expressed and
compared. Due to the extremely small spacing between its two strips, the
nanodipole terminated by vertical coupled strips plasmonic transmission line
offers significantly higher efficiency than that terminated by a lateral
coupled strips line. However, the overall efficiency of the vertical coupled
strips rectenna is still very low due to the extremely low efficiency of the
MIM rectifier.
