Transparent heat-mirror
First Claim
1. A composite film consisting of three continuous and discrete layers, one of said layers being metallic silver in a thickness of from about 30 A to about 200 A and the other two layers being transparent and positioned on opposite sides of said metallic silver layer, each of said transparent layers having a thickness within the range of from about 150 A to about 500 A, and said transparent layers being ones which cooperate to provide the composite film with an integrated solar transmission, α
-
eff, of at least about 0.5 and a ratio of integrated solar transmission to integrated heat reflectivity, α
eff /ε
eff, of at least about 5 where integrated solar transmission (α
eff) and integrated heat reflectivity (ε
eff) are defined as;
##EQU2## wherein Tr(λ
)=Transmission of heat-mirror at wavelength λ
R(λ
)=Reflectivity of heat-mirror at wavelength λ
A(λ
)=Solar energy spectrumWB (TB,λ
)=Energy distribution for a blackbody at an operating temperature TB.
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Abstract
Transparent heat-mirrors are disclosed which are comprised of composite films. These films include a discrete and continuous layer of metallic silver sandwiched between a transparent, outer, protective, anti-reflection layer and a transparent, phase-matching layer. This combination of layers is chosen to provide high solar transmission with minimum loss of thermal radiation. Transparent heat-mirrors are useful in the collection and trapping of solar energy, and in other applications where it is desired or necessary to have high infrared reflectivity with high solar transmission.
153 Citations
26 Claims
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1. A composite film consisting of three continuous and discrete layers, one of said layers being metallic silver in a thickness of from about 30 A to about 200 A and the other two layers being transparent and positioned on opposite sides of said metallic silver layer, each of said transparent layers having a thickness within the range of from about 150 A to about 500 A, and said transparent layers being ones which cooperate to provide the composite film with an integrated solar transmission, α
-
eff, of at least about 0.5 and a ratio of integrated solar transmission to integrated heat reflectivity, α
eff /ε
eff, of at least about 5 where integrated solar transmission (α
eff) and integrated heat reflectivity (ε
eff) are defined as;
##EQU2## wherein Tr(λ
)=Transmission of heat-mirror at wavelength λR(λ
)=Reflectivity of heat-mirror at wavelength λA(λ
)=Solar energy spectrumWB (TB,λ
)=Energy distribution for a blackbody at an operating temperature TB. - View Dependent Claims (2)
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eff, of at least about 0.5 and a ratio of integrated solar transmission to integrated heat reflectivity, α
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3. In a transparent heat-mirror comprising a single, continuous, discrete layer of metallic silver having a thickness of from about 30 A to about 200 A and an outer, transparent, protective, anti-reflection coating on one side of said metallic silver layer having a thickness of from about 150 A to about 500 A:
the improvement of providing a transparent coating having a thickness of from about 150 A to about 500 A on the inner side of said metallic silver layer, said transparent coating on the inner side of said metallic silver layer being one which cooperates with said outer, transparent, anti-reflection coating to provide the transparent heat-mirror with an α
eff of at least about 0.5 and an α
eff /ε
eff ratio of at least about 5.- View Dependent Claims (4, 5, 6, 7, 8)
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9. An article comprising a transparent substrate having a composite film thereon, said composite film having a single, continuous, discrete layer of metallic silver having a thickness from about 30 A to about 200 A, said metallic silver layer being sandwiched between an outer, protective, transparent, anti-reflection layer and an inner, adherent, transparent layer each having a thickness of from about 150 A to about 500 A, said outer and inner transparent layers providing said composite film with an α
-
eff of at least about 0.5 and an α
eff /ε
eff ratio of at least about 5. - View Dependent Claims (10, 11, 12)
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eff of at least about 0.5 and an α
-
13. In the collection of solar energy by using an absorber to absorb radiation from the sun, the improvement of using a transparent, heat-mirror in combination with the absorber wherein said heat-mirror comprises a composite film formed from a single, continuous, discrete layer of metallic silver having a thickness of from about 30 A to about 200 A sandwiched between an outer, transparent, protective, anti-reflection coating and an inner, adherent, transparent coating, said inner and outer coatings providing the composite film with an α
-
eff of at least 0.8 and an α
eff /ε
eff ratio of at least about 10.
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eff of at least 0.8 and an α
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14. A transparent heat-mirror consisting of a transparent substrate with a composite film, said composite film consisting of a single, continuous, discrete layer of metallic silver having a thickness of from about 30 A to about 200 A and two discrete layers of titanium dioxide located on opposite sides of said metallic silver layer and both having a thickness within the range of from about 150 A to about 500 A, said layers of titanium dioxide being sufficient to provide said transparent heat-mirror with an α
-
eff of at least about 0.5 and an α
eff /ε
eff ratio of at least about 5.
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eff of at least about 0.5 and an α
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15. In the formation of a composite film, which transmits visible light energy and reflects infrared light energy, on a substrate:
the improvement comprising respectively sputtering onto said substrate a first transparent layer, a silver layer, and a second transparent layer, under sputtering conditions which produce discrete layers in thicknesses which provide cooperation between said layers to provide a composite film having significantly increased visible light energy transmission compared to said silver layer alone and having high infrared light energy reflectivity. - View Dependent Claims (16)
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17. A composite film comprising a sputtered, continuous, discrete, silver layer sandwiched between two sputtered, continuous, discrete layers of titanium dioxide, said silver and titantium dioxide layers having thicknesses that cooperate to provide said composite film with significantly higher solar energy transmission compared to said silver layer alone and having high infrared reflectivity.
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18. A composite film consisting of a layer of metallic silver sandwiched between layers of titanium dioxide, each of said layers being continuous, discrete and having a thickness of about 180 A.
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19. A method of producing a composite film on a substrate, said composite film having high solar energy transmission and high infrared reflectivity, comprising:
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sputtering a first, continuous, discrete, transparent layer over said substrate; subsequently, sputtering a continuous, discrete, silver layer over said first layer; and
,thereafter, sputtering a second, continuous, discrete, transparent, layer over said silver layer, said first and said second transparent layers and said silver layer each being sputtered to a thickness so that all three layers cooperate to provide a composite film having significantly increased solar energy transmission compared to said silver layer alone and having high infrared reflectivity. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26)
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Specification