Selective reflective and absorptive surfaces and methods for resonantly coupling incident radiation
Methods and apparatus for providing a tunable absorption band in a wavelength selective surface are disclosed. A device for selectively absorbing incident electromagnetic radiation includes an electrically conductive surface layer including an arrangement of multiple surface elements. The surface layer is disposed at a nonzero height above a continuous electrically conductive layer. An electrically isolating intermediate layer defines a first surface that is in communication with the electrically conductive surface layer. The continuous electrically conductive backing layer is provided in communication with a second surface of the electrically isolating intermediate layer. The arrangement of surface elements couples at least a portion of the incident electromagnetic radiation between itself and the continuous electrically conductive backing layer, such that the resonant device selectively absorbs incident radiation, and reflects a portion of the incident radiation that is not absorbed.
1. A device for selectively absorbing incident electromagnetic visible or infrared radiation comprising:
a selective surface comprising:
a first electrically conductive layer including a plurality surface elements;
an electrically isolating intermediate layer defining a first surface in communication with the electrically conductive surface layer; and
a second, continuous electrically conductive layer in communication with a second surface of the electrically isolating intermediate layer,
wherein the selective surface has a primary resonant absorption band for selectively absorbing incident visible or infrared radiation responsive to a resonant electromagnetic coupling between the plurality of surface elements and the continuous electrically conductive layer, and
wherein the primary resonant absorption band has a central wavelength λc and a bandwidth Δλ, where Δλ/λc is 0.1 or less.
2. The device of claim 1 , wherein the plurality of surface elements comprises a plurality of discrete electrically conductive elements.
3. The device of claim 2 , wherein the thickness of the electrically isolating intermediate layer is about 0.01 λc or less.
4. The device of claim 2 , wherein the plurality discrete electrically conductive elements comprises an array of uniformly shaped elements, wherein the uniformly shaped elements are selected from the group consisting of: closed curves; ellipses; circles; rectangles; squares; polygons; triangles; hexagons; parallelograms; annular structures; and star-shaped structures having at least three members each extending from a central portion of the star shape to a point of the star-shape.
5. The device of claim 1 , wherein the thickness of the electrically isolating intermediate layer is less than one tenth of the central wavelength λc of the primary resonant absorption band.
6. The device of claim 1 , wherein the surface elements have a size of less than about 50 micrometers.
7. The device of claim 6 , wherein the surface elements have a size of less than about 0.5 micrometers.
8. The device of claim 1 , wherein at least one of the first and second electrically conductive layers is formed from a metal.
9. The device of claim 1 , wherein at least one of the first and second electrically conductive layers is formed from an electrically conductive semiconductor.
10. The device of claim 1 , wherein the plurality of surface elements are arranged in an array, said array selected from the group consisting of: a rectangular grid; a square grid; a triangular grid; an Archimedean grid; an oblique grid; a centered rectangular grid; a hexagonal grid; and a random array.
11. The device of claim 1 , wherein the at least one of λc and Δλ of the primary resonant absorption band is determined by the dimensions of each surface element of the plurality of surface elements of the first electrically conductive layer.
12. The device of claim 1 , wherein the selective surface has a secondary resonant absorption band determined by the spacing between surface elements of the plurality of surface elements.
13. The device of claim 1 , wherein the electrically conductive surface layer comprises an electrical conductor defining a plurality of discrete through holes, and wherein the plurality of discrete through holes correspond to the plurality of surface elements.
14. The device of claim 13 , wherein the plurality of discrete through holes comprise an array of uniformly shaped elements, wherein the uniformly shaped elements are selected from the group consisting of: closed curves; ellipses; circles; rectangles; squares; polygons; triangles; hexagons; parallelograms; annular structures; star-shaped structures each having at least three members each extending from a central portion of the star shape to a point of the star-shape; and annular shapes.
15. The device of claim 13 , wherein the plurality of discrete through holes are arranged in an array, selected from the group consisting of: rectangular grids; square grids; triangular grids; Archimedean grids; oblique grids; centered rectangular grids; hexagonal grids; and random arrays.
16. The device of claim 1 , wherein the at least one of λc and Δλ of the primary resonant absorption band are determined at least one of: a thickness of the first electrically conductive layer; a thickness of the intermediate layer; a physical property of the intermediate layer; a physical property of each of the electrically conducting surface elements of the plurality of electrically conducting surface elements.
17. The device of claim 1 , wherein the device comprises a secondary resonant absorption band determined by at least one of: a spacing between surface elements of the plurality of surface elements; thickness of the first electrically conductive layer; thickness of the intermediate layer; physical properties of the intermediate layer; physical properties of each of the electrically conducting surface elements of the plurality of electrically conducting surface elements.
18. A method of selectively reflecting incident visible or infrared radiation comprising:
providing a selective surface comprising:
a first electrically conductive layer including a plurality surface elements;
an electrically isolating intermediate layer defining a first surface in communication with the electrically conductive surface layer; and
a second, continuous electrically conductive layer in communication with a second surface of the electrically isolating intermediate layer,
wherein the selective surface has a primary resonant absorption band for selectively absorbing incident visible or infrared radiation responsive to a resonant electromagnetic coupling between the plurality of surface elements and the continuous electrically conductive layer,
receiving the incident visible or infrared radiation with the selective surface to absorb a portion of the incident visible or infrared radiation in the primary resonant absorption band; and
reflecting at least a portion of the incident radiation outside of the primary resonant absorption band;
wherein the primary resonant absorption band has a central wavelength λc and a bandwidth Δλ, where Δλ/λc is 0.1 or less.
19. The method of claim 18 , wherein the plurality of surface elements comprises a plurality of discrete electrically conductive elements.
20. The method of claim 18 , wherein the electrically conductive surface layer comprises an electrical conductor defining a plurality of discrete through holes, and wherein the plurality of discrete through holes correspond to the plurality of surface elements.
21. The method of claim 20 , wherein the thickness of the electrically isolating intermediate layer is about 0.01 λc or less.
22. The method of claim 20 , wherein the surface elements have a size of less than about 50 micrometers.
23. The method of claim 20 , wherein the surface elements have a size of less than about 0.5 micrometer.
24. The method of claim 18 , wherein the thickness of the electrically isolating intermediate layer is less than one tenth of the central wavelength λc of the primary resonant absorption band.
25. The method of claim 18 , wherein the selective surface has a secondary resonant absorption band determined by the spacing between surface elements of the plurality of surface elements.