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In this article, a multiband, planar, direct energy rectification, and dual polarized infrared plasmonic nanoantenna is presented and numerically simulated using finite element method (FEM). Broadband characteristics are highly suitable for energy harvesting applications. The proposed nanoantenna structure comprises cross bowtie aluminum structures deposited on the silicon dioxide (SiO2) substrate. In the proposed device, incoming thermal electromagnetic energy is first enhanced by micro‐lenses through focusing the thermal energy onto the nanoantenna. Then, further enhancement is achieved using several nanoantennas, each with different resonance length, to achieve enough electrical field for electron field emission from sharp metallic tips in their gaps. Each nanoantenna resonates in the proper wavelength, electrical field is enhanced in the gap, and finally, a total current is generated from electron field emissions. The calculated current, based on Fowler‐Nordheim theory, matches well with the simulation results. The total current of the proposed nanostructure is superposition of the produced current of each nanoantenna. To our best knowledge, this is the first report on a multiband nanostructure for energy harvesting. As a typical implementation, a structure is designed for energy absorption in the mid infrared wavelengths, 1‐4 µm.

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Unlike the solar energy, infrared radiation from black bodies around us is always available. In this paper, a novel energy harvesting device is proposed for absorption of the infrared radiation from hot objects around us at temperatures beyond 300 K, in the vicinity of 10 μm wavelength, or from the Earth itself. Electron field emission from sharp edges in vacuum, based on Fowler‐Nordheim (FN) theory, is proposed as a means of rectification. A large number of nanoantennas are placed in an array to achieve high electric field, required for FN electron emission. The issue of wave spatial coherence is discussed in the paper, and it is shown that the device can operate with small affection. Using the proposed device, the MIM/MIIM diode, which is usually used for rectification and has a very low efficiency, is avoided and therefore efficiency is highly improved. A planar spiral series nanoantenna array (SSNA) is designed, as an example, to demonstrate the concept. Bowtie and cross bowtie antenna geometries are considered and their performances are compared.