Theory Optical rectenna

figure 3. image showing skin effect @ high frequencies. dark region, @ surface, indicates electron flow lighter region (interior) indicates little no electron flow.

because of simplifications used in typical rectifying antenna theory, there several complications arise when discussing optical rectennas. @ frequencies above infrared, of current carried near surface of wire reduces effective cross sectional area of wire, leading increase in resistance. effect known “skin effect”. purely device perspective, i-v characteristics appear no longer ohmic, though ohm’s law, in generalized vector form, still valid.

another complication of scaling down diodes used in larger scale rectennas cannot operate @ thz frequencies without large loss in power. large loss in power result of junction capacitance (also known parasitic capacitance) found in p-n junction diodes , schottky diodes, can operate @ frequencies less 5 thz. ideal wavelengths of 0.4–1.6 μm correspond frequencies of approximately 190–750 thz, larger capabilities of typical diodes. therefore, alternative diodes need used efficient power conversion. in current optical rectenna devices, metal-insulator-metal (mim) tunneling diodes used. unlike schottky diodes, mim diodes not affected parasitic capacitances because work on basis of electron tunneling. because of this, mim diodes have been shown operate @ frequencies around 150 thz.