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Research Papers

Theory and Manufacturing Processes of Solar Nanoantenna Electromagnetic Collectors

[+] Author and Article Information
D. K. Kotter, S. D. Novack

 Idaho National Laboratory, 2025 Fremont Avenue, Idaho Falls, ID 83415

W. D. Slafer

 MicroContinuum, Inc., 57 Smith Place, Cambridge, MA 02138

P. J. Pinhero1

Department of Chemical Engineering, University of Missouri, Columbia, MO 65211pinherop@missouri.edu

1

Corresponding author.

J. Sol. Energy Eng. 132(1), 011014 (Jan 05, 2010) (9 pages) doi:10.1115/1.4000577 History: Received September 09, 2008; Revised September 20, 2009; Published January 05, 2010

The research described in this paper explores a new and efficient approach for producing electricity from the abundant energy of the sun, using nanoantenna (nantenna) electromagnetic collectors (NECs). NEC devices target midinfrared wavelengths, where conventional photovoltaic (PV) solar cells are inefficient and where there is an abundance of solar energy. The initial concept of designing NECs was based on scaling of radio frequency antenna theory to the infrared and visible regions. This approach initially proved unsuccessful because the optical behavior of materials in the terahertz (THz) region was overlooked and, in addition, economical nanofabrication methods were not previously available to produce the optical antenna elements. This paper demonstrates progress in addressing significant technological barriers including: (1) development of frequency-dependent modeling of double-feedpoint square spiral nantenna elements, (2) selection of materials with proper THz properties, and (3) development of novel manufacturing methods that could potentially enable economical large-scale manufacturing. We have shown that nantennas can collect infrared energy and induce THz currents and we have also developed cost-effective proof-of-concept fabrication techniques for the large-scale manufacture of simple square-loop nantenna arrays. Future work is planned to embed rectifiers into the double-feedpoint antenna structures. This work represents an important first step toward the ultimate realization of a low-cost device that will collect as well as convert this radiation into electricity. This could lead to a broadband, high conversion efficiency low-cost solution to complement conventional PV devices.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Calculated flow of THz currents to the antenna feedpoint. Red represents highest concentrated E field. Modeled with Ansoft HFSS (21).

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Figure 2

Typical electromagnetic radiation patterns of ground-plane spiral antenna. Antenna relative field strength (db) is plotted on a polar graph, where 0 deg=direct incidence. The physical size of the antenna is represented by the red ring and the effective electrical size of the antenna is the radiation pattern (approximate relative comparison only).

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Figure 3

Array of antenna-coupled microbolometers—(UCF image—Ref. 9) The bolometer element will be replaced with embedded rectifiers. A flexible panel of interconnected nantennas may one day replace heavy, expensive solar panels.

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Figure 4

Square FSS element and its RLC circuit analog

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Figure 5

Cross-sectional schematic of NEC structure showing path of incident wave

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Figure 6

Modeled spectral output of an NEC. Proof of concept based on loop antenna structure with a 10 μm resonance.

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Figure 7

Fabrication process flow for a square-loop IR FSS

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Figure 8

SEM of a small portion of the completed IR NEC made by e-beam lithography. The entire IR FSS covers 40 mm2 and is composed of 9.76×108 elements.

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Figure 9

Demonstrated success in energy collection. Validated using a spectral radiometer and FTIR.

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Figure 10

(a) SEM top view of Si wafer after anisotropic oxide etch. Narrow ridges along walls and “star” shape in square are residual e-beam resist layer (which are removed after subsequent oxide strip). (b) SEM cross section of patterned oxide layer of Fig. 1 (prior to DRIE step). Due to the unusual design of the structure, the initial etch width was slightly larger than the design for these experiments but higher accuracy is expected in the future as the etch process is further refined. (c) Tilted view SEM image of patterned oxide layer of Figs.  1111.

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Figure 11

Cross section of master template after DRIE step, showing oxide mask layer over bulk silicon

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Figure 12

(a) Schematic of pattern replication process. (b) Schematic of antenna and ground plane process.

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Figure 13

(a) and (b) SEM image of polymer replicas made from tooling (not shown) from wafer master template (top, normal view; bottom, tilted view)

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Figure 14

(a) Prototype FSS structure on flexible substrate and (b) 300 mm×600 mm nantenna sheet stitched together from 18 coupons

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Figure 15

(a) Experimental setup for thermal characterization of prototypes. (b) and (c) Optical (top) and graphical (bottom) experimental results from thermal characterization.

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