RADIATIVE COOLING STRUCTURES AND SYSTEMS

Abstract

Polymer-based selective radiative cooling structures are provided which include a selectively emissive layer of a polymer or a polymer matrix composite material. Exemplary selective radiative cooling structures are in the form of a sheet, film or coating. Also provided are methods for removing heat from a body by selective thermal radiation using polymer-based selective radiative cooling structures.

Claims

1. A selective radiative cooling structure, the structure comprising a selectively emissive layer comprising a polymer and a plurality of dielectric particles dispersed in the polymer, where the dielectric particles have an average size ranging from 3 μm to 30 μm; wherein the selective radiative cooling structure has an average emissivity ranging from 0.6 to 1.0 over the wavelength range 7 μm to 13 μm; the volume percentage of the dielectric particles in the selectively emissive layer ranges from 1% to 25%; and the selectively emissive layer is substantially solar transparent or translucent.

2. The selective radiative cooling structure of claim 1, wherein the structure is in the form of a sheet.

3. The selective radiative cooling structure of claim 1, wherein the selective radiative cooling structure provides a radiative heat flux from 50 W/m.sup.2 to 150 W/m.sup.2 at a working temperature in the range of −100° C. to 500° C.

4. The selective radiative cooling structure of claim 1, wherein the dielectric particles have an average size ranging from 3 μm to 15 μm.

5. The selective radiative cooling structure of claim 1, wherein the dielectric particles are selected from the group consisting of silicon dioxide (SiO.sub.2), calcium carbonate (CaCO.sub.3), silicon carbide (SiC), zinc oxide (ZnO), titanium dioxide (TiO.sub.2), and alumina (Al.sub.2O.sub.3).

6. The selective radiative cooling structure of claim 1, wherein the polymer of is selected from the group consisting of a 4-methyl-1-pentene polymer, a 4-methyl-1-pentene copolymer, polyvinyl fluoride, polyethylene terephthalate.

7. The selective radiative cooling structure of claim 1, wherein the polymer is a copolymer of poly(4-methyl-1 pentene) with a-olefins selected from the group consisting of 1-pentene, 1-hexene and 1-octene.

8. The selective radiative cooling structure of claim 1, wherein the selectively emissive layer has an average thickness of from 10 μm to 3 mm.

9. The selective radiative cooling structure of claim 1, wherein the selective radiative cooling structure further comprises a protective film that is solar-transparent and weather-resistant.

10. The selective radiative cooling structure of claim 1, wherein the selective radiative cooling structure has a solar absorptivity from 0 to 0.2 over a wavelength range of 0.3 μm to 3 μm.

11. The selective radiative cooling structure of claim 1, further comprising a solar reflective layer in contact with the selectively emissive layer, the solar reflecting layer comprising a metal film or metal substrate, wherein the selectively emissive layer has an emissivity ranging from 0.6 to 1.0 over the wavelength range 7 μm to 13 μm and the selective radiative cooling structure has a solar reflectivity ranging from 0.8 to 1 over the wavelength range 0.3 μm to 3 μm.

12. The selective radiative cooling structure of claim 10, wherein the metal film has an average thickness from 20 nanometers to 1000 nanometers.

13. The selective radiative cooling structure of claim 1, wherein the dielectric particles have an average effective diameter selected from the range of 3 μm to 30 μm

14. A method for removing heat from a body by selective thermal radiation, the method comprising the steps of: a. placing a selective radiative cooling structure according to claim 1 in thermal communication with a surface of the body, wherein the selective emissive layer of the selective radiative cooling structure is in thermal communication with the body, b. transferring heat from the body to the selective radiative cooling structure; and c. radiating heat from selectively emissive layer of the selective radiative cooling structure.

15. The method of 14, wherein the body is a solar panel, a roof or window of an automobile, a roof or window of a building, or a cold storage structure for energy, food, oil or other commodity.

16. The method of claim 14, wherein the selective radiative cooling structure further comprises a solar reflecting layer comprising a metal film or substrate and has a solar absorptivity from 0 to 0.2 over the wavelength range of 0.3 μm to 3 μm.

17. The method of claim 14, wherein the body is a passive thermosiphon or an active channel array and wherein the heat transfer fluid circulates inside the body.

18. A cold collection system comprising: a. a plurality of cold collection devices, each cold collection device configured to be in thermal communication with a heat transfer fluid; b. a plurality of selective radiative cooling structures, each selective radiative cooling structure in thermal communication with the surface of one of the plurality of cold collection devices; wherein each selective radiative cooling structure comprises a selectively emissive layer of claim 1.

19. A method for making a selective emissive layer, the method comprising the steps of: a. extruding a feed material comprising a polymer, in which a plurality of dielectric particles is dispersed, through a die to form a film or sheet, wherein the polymer is characterized by an absorptivity of 0.6 to 1.0 in the range 7 μm to 13 μm; wherein the plurality of dielectric particles has an average size ranging from 3 μm to 30 μm and the volume percentage of the plurality of dielectric particles in the polymer ranges from 15 to 25%; and b. cooling the film or sheet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1: spectral irradiance of AM1.5 on earth surface and radiation spectrum of a black body surface at 15° C. through the atmospheric transmission window;

[0066] FIG. 2: schematic illustration of an emissive layer 5 of polymer 20.

[0067] FIG. 3A: schematic illustration of an emissive layer 5 including polymer 20 including particles dispersed in polymer matrix 30.

[0068] FIG. 3B: the absorptivity/emissivity as a function of wavelength for a 50-μm-thick polymethylpentene film with 5% 8-μm-diameter solid silica microspheres.

[0069] FIG. 4A: schematic illustration of an emissive layer 5 including polymer 20 and particles 30 in contact with metal reflective layer 40.

[0070] FIG. 4B: schematic illustration of an emissive layer 5 including polymer 20 and particles 30; one face of the emissive layer is in contact with metal reflective layer 40 and the other face of the emissive layer is in contact with an anti-reflection layer 50, which in turn is in contact with a protection layer 60.

[0071] FIG. 4C: schematic illustration of an emissive layer 5 including polymer 20 and particles 30; one face of the emissive layer is in contact with a barrier layer 70, which in turn is in contact with a metal reflective layer 40 and the other face of the emissive layer is in contact with a protection layer 60.

[0072] FIG. 4D: schematic illustration of an emissive layer 5 including polymer 20 and particles 30; one face of the emissive layer is in contact with a barrier layer 70, which in turn is in contact with a metal reflective layer 40, which in turn is in contact with a thermal-conduction layer and the other face of the emissive layer is in contact with an anti-reflection layer 50, which in turn is in contact with a protection layer 60.

[0073] FIG. 4E: schematic illustration of an emissive layer 5 including polymer 20 and particles 30; one face of the emissive layer is in contact with a barrier layer 70, which in turn is in contact with a metal reflective layer 40 and the other face of the emissive layer is in contact with an anti-reflection layer 50, which in turn is in contact with a protection layer 60.

[0074] FIG. 5: schematic illustration of a radiative cooling sheet directly attached to the top of a solar cell.

[0075] FIG. 6: schematic illustration of a radiative cooling sheet directly attached to a radiant ceiling panel.

[0076] FIG. 7A: schematic illustration of a radiative cooling sheet with reflective layer directly attached to the roof of a built structure.

[0077] FIG. 7B: schematic illustration of a radiative cooling sheet with reflective layer directly attached to the roof of a car.

[0078] FIGS. 8A and 8B: FIG. 8A: schematic illustration of a radiative cooling structure in contact with multiple cold collection devices and FIG. 8B: cross section through FIG. 8A along A-A.

[0079] FIGS. 8C and 8D: FIG. 8C: schematic illustration of a thermosiphon that can be used in contact with the radiative cooling structure to collect coldness enabled by radiative cooling structure and FIG. 8D: side view of the thermosiphon.

[0080] FIG. 9: schematic illustration of an active cooling system for buildings where radiative cooling structures is used to enable the cooling for the cold storage system.

[0081] FIG. 10A: schematic illustration of multiple cold collection devices for supplemental cooling for a power plant condenser.

[0082] FIG. 10B: an exemplary 12-hour operating schedule to enable cold collection and storage using a passive thermosiphon to collect the cold achieved using selective radiative cooling structure.

[0083] FIG. 11: schematic illustration of an apparatus for extrusion of a polymer-based film.

[0084] FIG. 12: schematic illustration of an apparatus for coating a film with oxides and metals.

[0085] FIG. 13A: emissivity/absorptivity as a function of wavelength for a 50-μm-thick bare polymethylpentene (TPX™) film and a 50 μm thick film with 5% volume fraction of 8-μm-diameter solid silica microspheres.

[0086] FIG. 13B: emissivity/absorptivity as a function of wavelength for polymethylpentene films of different thickness with 5% volume fraction of 8-μm-diameter solid silica microspheres.

[0087] FIG. 13C: absorptivity/emissivity as a function of wavelength for of 55-μm-thick polymethylpentene film with 5% volume fraction of 8-μm-diameter solid silica microspheres.

[0088] FIG. 14: emissivity as a function of glass bead concentration (volume fraction) for different size beads.

[0089] FIGS. 15A-15C: Glass-polymer hybrid metamaterial. FIG. 15A: schematic of the polymer-based hybrid metamaterial with randomly distributed SiO.sub.2 microsphere inclusions for large-scale radiative cooling. The polarizable microspheres interact strongly with infrared light, making the metamaterial extremely emissive across the full atmospheric transmission window while remaining transparent to the solar spectrum. FIG. 15B: normalized absorption (blue), scattering (red), and extinction (black) cross-sections of individual microspheres as a function of size parameter (k.sub.0a). The extinction, the sum of the scattering and absorption, peaks at a size parameter of 2.5, which corresponds to a microsphere radius of 4-μm. The inset shows the electric field distributions of two microspheres with 1- and 8-μm diameters, illuminated at a 10-μm wavelength. The scale bar is 4 μm. The smaller microsphere resonates at the electric dipolar resonance while higher order electric and magnetic modes are excited in the larger microsphere. FIG. 15C: an angular diagram for the scattering far-field irradiance of an 8-μm-diameter microsphere with 10-μm wavelength illumination. The incident field is polarized along the y-direction and propagating along the z-direction.

[0090] FIGS. 16A-16C: Fröhlich resonance and broadband infrared absorbance of the hybrid metamaterial. FIGS. 16A and 16B, respectively: the real and imaginary parts of the effective refraction index for the glass-polymer hybrid metamaterials. The metamaterial with 1-μm-diameter SiO.sub.2 microspheres (black curves) shows a strong Fröhlich resonance at its phonon-polariton frequency of 9.7 μm, while the metamaterial with 8-μm-diameter microspheres (red curves) shows significantly more broadband absorption across infrared wavelengths. The strong Fröhlich resonance not only limits the bandwidth of strong emissivity but also introduces strong reflectance of incident infrared radiation. In both cases, the metamaterial contains 6% SiO.sub.2 by volume. FIG. 16C: attenuation lengths of the two hybrid metamaterials, with the 8-μm-diameter SiO.sub.2 microsphere case showing an average attenuation length of ˜50 μm from λ=7 to 13 μm.

[0091] FIGS. 17A-17D: Spectroscopic response of the hybrid metamaterial. FIG. 17A: schematic of the hybrid metamaterial backed with a thin silver film. The silver film diffusively reflects most of the incident solar irradiance while the hybrid material absorbs all incident infrared irradiance and is highly infrared emissive. FIG. 17B: three-dimensional confocal microscope image of the hybrid metamaterial. The microspheres are visible due to the autofluorescence of SiO.sub.2. FIG. 17C: power density of spectral solar irradiance (AM1.5) and thermal radiation of a blackbody at room temperature. The sharply varying features in both spectra are due to the absorbance of the atmosphere (gas molecules). The radiative cooling process relies on strong emission between 8 and 13 μm, the atmospheric transmission window. FIG. 17D: measured emissivity/absorptivity (black curve) of the 50-μm-thick hybrid metamaterial from 300 nm to 25 μm. Integrating spheres are employed for the measurement of both solar (300 nm to 2.5 μm) and infrared (2.5 μm to 25 μm) spectra. Theoretical results for the same hybrid metamaterial structure (red curves) are plotted for comparison. Two different numerical techniques, RCWA and incoherent transfer matrix methods, are employed for the solar and infrared spectral ranges, respectively.

[0092] FIGS. 18A-18C: Performance of scalable-manufactured hybrid metamaterial for effective radiative cooling. FIG. 18A: photograph showing the 300-mm-wide hybrid metamaterial thin film that was produced in a roll-to-roll manner, at a speed of 5 meters per minute. The film is 50 μm in thickness and not yet coated with silver. FIG. 18B: 72-hour continuous measurement of the ambient temperature (black) and the surface temperature (red) of an 8-in-diameter hybrid metamaterial under direct thermal testing. A feedback-controlled electric heater keeps the difference between ambient and metamaterial surface temperatures less than 0.2° C. over the consecutive three days. The heating power generated by the electric heater offsets the radiative cooling power from the hybrid metamaterial. When the metamaterial has the same temperature as the ambient air, the electric heating power precisely measures the radiative cooling power of the metamaterial. The shaded regions represent nighttime hours. FIG. 18C: the continuous measurement of radiative cooling power over three days where an average cooling power >110 W/m.sup.2 and a noon-time cooling power of 93 W/m.sup.2 between 11 am-2 pm are measured. The average nighttime cooling power is higher than that of the day-time, and the cooling power peaks after sunrise and before sunset. The measurement error of the radiative cooling power is well within 10 W/m.sup.2 (32).

[0093] FIG. 19A: the edge-to-edge concentration distribution of the silica microspheres in the 300-mm-wide metamaterial. The concentration variation is less than 0.4%. The inset shows an optical image of the metamaterial thin film. Scale bar: 40 μm. FIG. 19B: averaged emissivity distribution of all samples corresponding to the distribution in FIG. 19A.

[0094] FIG. 20A: photography showing the light-scattering effect of the translucent hybrid metamaterial. A 2-mm-diameter laser beam at a wavelength of 532 nm is greatly dispersed when transmitted through the film. FIG. 20B: chromaticity analysis of the metamaterial. The color of the hybrid metamaterial is centered in the color space (white-balanced) as a result of the strong scattering effect of visible light by the microspheres.

[0095] FIG. 21A: schematic of the direct thermal measurement apparatus with a feedback-controlled electric heater. The closed-loop electronics tracks the metamaterial surface temperature to be the same as that of the ambient environment, minimizing convective and conductive heat losses. This feedback-controlled measurement apparatus allows us to remove the HDPE protective film and let the hybrid metamaterial be directly exposed to the air for 24/7 continuously, with accurate measurement of the radiative cooling power. FIG. 21B: photograph of the experimental setup during operation.

[0096] FIG. 22A: ambient temperature and the hybrid metamaterial surface temperature measured over an 18-hour-period of time on Oct. 8.sup.th, 2016 in Boulder, Colo. The shaded region represents nighttime hours. With the feedback-controlled electric heater, the surface temperature closely follows the ambient temperature. The inset shows the initial dynamics when the control loop is switched on. FIG. 22B: temperature difference between the measured ambient temperature and the hybrid metamaterial surface. FIGS. 22C and 22D, respectively: histograms of the day- and nighttime temperature differences show small deviations of 0.2° C. and 0.1° C., respectively.

[0097] FIG. 23A: continuous measurement of the surface (red) and ambient temperature (black) temperature using electronic feedback control. FIG. 23B: distribution of the temperature difference between the surface and the ambient temperature over 24 hours. FIG. 23C: continuously measured cooling power (sampled at 1 sec) and its run-time average value (averaged over 5 min). There are momentary oscillations, shown in grey, for the real-time data due to the feedback control circuit. FIG. 23D: distribution of the difference between the instantaneously measured cooling power and its run-time average value. The measurement error is less than 10 watts and the momentary oscillation clearly overestimates the error in real-time power measurement.

[0098] FIGS. 24A-C: direct radiative cooling of a water body. FIG. 24A: schematic for the setup. FIG. 24B: the ambient temperature (Black), water tank surface temperature (Blue), water temperature (Green), and the metamaterial surface temperature (Red) as functions of time. At 3:10 am on Sep. 15.sup.th 2016, the metamaterial was exposed to the sky. FIG. 24C: the transient analysis of the cold energy stored in the water (Blue), the plastic water tank (Green), the stacked structure, including the metamaterial, silver-coated wafer, and the copper plate (Cyan), and the summation of the three (Red). The total convective and conductive heat loss (Magenta) through the Polystyrene foam box increased with the increasing temperature differences between the enclosure and ambient air. The total heat capacity is about 33 KJ/(m.sup.2.Math.K). The total radiative cooling power of the metamaterial (Black) is the sum of the heat loss and the cold stored in all materials, which was approximately 120 W/m.sup.2. The overshoot in the measured radiative cooling power at the beginning of the measurement was due to non-steady heat flows between the components of the measurement system.

DETAILED DESCRIPTION OF THE INVENTION

[0099] In the drawings, like reference numbers refer to like elements.

[0100] The electromagnetic spectrum can be classified into several regions. Regions referred to herein are the infrared region (wavelength approximately 1 mm to 750 nm), visible region (wavelength approximately 750 nm to 400 nm) and the ultraviolet region (wavelength approximately 400 nm to 40 nm). The infrared region has also been classified into sub-regions using various classification schemes; in the ISO classification scheme the mid-infrared is approximately 3 μm to 50 μm. As used herein the radiant flux is the radiant energy per unit time (e.g. W), the irradiance is the radiant flux received by a surface per unit area (e.g. Wm.sup.−2) and the spectral irradiance is the irradiance of a surface per unit wavelength (e.g. Wm.sup.−2nm.sup.−1).

[0101] Electromagnetic radiation emitted from matter at a temperature above absolute zero Kelvin may be referred to as thermal radiation. The solar spectrum refers to the distribution of electromagnetic radiation emitted by the sun, as a function of electromagnetic wavelengths. Most of the solar energy is over a wavelength from about 0.3 μm to about 3 μm, as can be seen from FIG. 1.

[0102] Emissivity specifies how well a real surface radiates electromagnetic energy as compared with a black-body and can range between 0 and 1. The directional spectral emissivity is the ratio of the emissive ability of the real surface to that of a black body. A total emissivity is averaged with respect to all wavelengths; a hemispherical emissivity is averaged with respect to all directions. As used herein, a selectively emissive layer is configured to emit electromagnetic radiation over a range of wavelength with a desirable emissivity between 0 and 1 at a temperature above absolute zero.

[0103] As used herein, a selectively emissive layer has an emissivity that is wavelength-selective. A selectively emissive layer is configured to thermally-generating electromagnetic emissions at temperatures other than absolute zero Kelvin and is not a blackbody. Since emissivity correlates with absorptivity, a selectively emissive layer is also a selectively absorptive layer. In embodiments, the selectively emissive layer has high emissivity in at least some portions of the infrared portion of the spectrum, but has limited emission in at least some portions of the solar spectrum. Such a selectively emissive layer is also selectively absorptive, having high absorption in at least some portions of the infrared portion of the spectrum, but limited absorption in at least some portions of the solar spectrum.

[0104] As used herein, average size refers to the numerical average or arithmetic mean of the effective diameter. In an embodiment, for example, average size refers to the sum of effective diameters of all particles divided by the number of particles. Given that average size refers to effective diameter, particles may have various shapes are not limited to spherical or sphere-like particles. Distributions of particles may also vary, for example, particles may have narrow or broad distributions and may be monodisperse or polydisperse.

[0105] As used herein, absorptivity is defined as the fraction of radiation energy incident on a surface of a body that is absorbed by the body. The incident radiation depends on the radiative conditions at the source of the incident energy. In an embodiment, the average absorptivity is a hemispherical absorptivity averaged over the wavelength range of interest.

[0106] As used herein, transmissivity is defined as the fraction of radiation energy incident on the surface of a body that is transmitted by the body. As used herein, transmissive material has a transmissivity on average greater than zero for radiation in the specified wavelength range. y. In an embodiment, the average transmissivity is a hemispherical transmissivity averaged over the wavelength range of interest. In some embodiments a transparent material has a transmissivity greater than 0.9 for the specified wavelength range.

[0107] As used herein reflectivity is defined as the fraction of radiation energy incident on a body that is reflected by the body. Solar reflectivity is defined as the fraction of radiation energy incident on a body that is reflected by the body in a specified region of the solar spectrum (e.g. 0.3 μm to 3 μm). In an embodiment, the solar reflectivity is averaged over the specified region of the spectrum. In an embodiment, the average reflectivity is a hemispherical reflectivity averaged over the wavelength range of interest.

[0108] As used herein, room temperature is approximately 20° C. to 30° C.

[0109] Embodiments of the present invention also pertain to methods for manufacturing radiative cooling structures on size scales useful for relevant cooling applications. In some embodiments of the present invention, polymers or polymer-based materials is fed into an extruder, optionally an industrial extruder or die-caster, and is melted and extruded into thin sheets. As examples, the polymer fed to the extruder is in pellets, powdered, or any other dry form. In embodiments for producing composite emissive layers, the non-polymer materials, e.g., the dielectric or glass particles discussed above, are mixed into the polymer prior to, during or after melting of the polymer, and before extrusion. The non-polymer materials can be mixed in any manner and may be mixed to a uniform or near-uniform blend of the polymer and non-polymer materials. As discussed above, such polymer-based sheets can be 3 μm to several millimeters in thickness. The extruded sheets can be cast onto solid substrates or, in one embodiment, formed onto chilled rollers, forming standalone thin films.

[0110] In other embodiments, the polymer or polymer-based sheet can be manufactured by any one or combination of a variety of polymer production methods, including without limitation liquid or solution casting, blowing or blow molding, spinning, compression molding, spraying methods, and injection molding. For example, the initial polymer material may be mixed with non-polymer particles, melted, and the melted mixture blown, compressed, or otherwise molded into any thickness sheets. In other embodiments, the polymer may be provided in a fluid or liquid form so that the polymer may be applied directly to a surface, for example, by painting, brushing, coating or spraying. In some embodiments, the liquid polymer may have particles dispersed throughout. The polymer may require a curing process upon application or may dry to form the desired polymer layer.

[0111] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. All references cited herein are hereby incorporated by reference to the extent not inconsistent with the disclosure herewith. All references throughout this application, for example patent documents including issued or granted patents or equivalents; patent application publications; and non-patent literature documents or other source material; are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference, to the extent each reference is at least partially not inconsistent with the disclosure in this application (for example, a reference that is partially inconsistent is incorporated by reference except for the partially inconsistent portion of the reference).

[0112] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art, in some cases as of their filing date, and it is intended that this information can be employed herein, if needed, to exclude (for example, to disclaim) specific embodiments that are in the prior art. For example, when a compound is claimed, it should be understood that compounds known in the prior art, including certain compounds disclosed in the references disclosed herein (particularly in referenced patent documents), are not intended to be included in the claim.

[0113] When a group of substituents is disclosed herein, it is understood that all individual members of those groups and all subgroups, including any isomers and enantiomers of the group members, and classes of compounds that can be formed using the substituents are disclosed separately. When a compound is claimed, it should be understood that compounds known in the art including the compounds disclosed in the references disclosed herein are not intended to be included. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure.

[0114] Every formulation or combination of components described or exemplified can be used to practice the invention, unless otherwise stated. Specific names of compounds are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same compounds differently. When a compound is described herein such that a particular isomer or enantiomer of the compound is not specified, for example, in a formula or in a chemical name, that description is intended to include each isomers and enantiomer of the compound described individual or in any combination. One of ordinary skill in the art will appreciate that methods, device elements, starting materials and synthetic methods other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such methods, device elements, starting materials and synthetic methods are intended to be included in this invention. Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure.

[0115] As used herein, “comprising” is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, “consisting of” excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any recitation herein of the term “comprising”, particularly in a description of components of a composition or in a description of elements of a device, is understood to encompass those compositions and methods consisting essentially of and consisting of the recited components or elements. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[0116] The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

[0117] In general the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The preceding definitions are provided to clarify their specific use in the context of the invention.

[0118] Although the description herein contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. For example, thus the scope of the invention should be determined by the appended claims and their equivalents, rather than by the examples given.

[0119] The invention may be further understood by the following non-limiting examples.

EXAMPLE 1

Polymethylpentene-Based Radiative Cooling Films

[0120] FIG. 13A shows the emissivity/absorptivity as a function of electromagnetic wavelength for a 50-μm-thick bare polymethylpentene (TPX™) films and a 50 μm thick film with 5% 8-μm-diameter solid silica microspheres. The trace for the TPX™ film is lighter gray than the trace for the composite film. Polymethylpentene is index-matched with silica in the solar spectrum, but not in the infrared spectrum. The polymethylpentene film mixed with silica microspheres results in a high emissivity at IR wavelengths of 7-13 μm. Without wishing to be bound by any particular belief, the silica spheres are believed to act as infrared scatterers and resonantly interact with infrared radiation, contributing to improved infrared emissivity of the films.

[0121] FIG. 13B shows the emissivity/absorptivity as a function of wavelength for polymethylpentene films of different thickness with 5% volumetric fraction of 8-μm-diameter solid silica microspheres. (key: 50 μm film darker gray solid line, 80 μm film dashed line, 120 μm film lighter gray solid line), The thicker polymethylpentene film with silica microspheres increases the emissivity at IR wavelength of 7-13 μm without significant absorption effect in solar spectrum.

[0122] FIG. 13C shows the absorptivity/emissivity as a function of wavelength for a 55-μm-thick polymethylpentene film with 5% volumetric fraction of 8-μm-diameter solid silica microspheres. The net day-time cooling power is 113 W/m.sup.2 with <4% averaged solar absorptivity and >0.8 IR emissivity on average. Percentages of fillers given in FIGS. 13A-13C are by volume.

[0123] FIG. 14 shows the projected radiative cooling power of an emissive layer with a reflective layer. The emissive layer includes a polymer sheet with embedded dielectric spheres according to different volume ratios of embedded spheres and film thicknesses.

EXAMPLE 2

Scalable-Manufactured Randomized Glass-Polymer Hybrid Metamaterial for Day-Time Radiative Cooling

[0124] Passive radiative cooling draws heat from surfaces and radiates it into space as infrared radiation to which the atmosphere is transparent. However, the energy density mismatch between solar irradiance and the low infrared radiation flux from a near-ambient-temperature surface require materials that strongly emit thermal energy and barely absorb sunlight. We embedded resonant polar dielectric microspheres randomly in a polymeric matrix, resulting in a metamaterial that is fully transparent to the solar spectrum while having an infrared emissivity greater than 0.93 across the atmospheric window. When backed with silver coating, the metamaterial shows a noon-time radiative cooling power of 93 W/m.sup.2 under direct sunshine. More critically, we demonstrated high-throughput, economical roll-to-roll manufacturing of the metamaterial, vital for promoting radiative cooling as a viable energy technology.

[0125] Radiative cooling—deposition of blackbody radiation from a hot object through the infrared transparency window of the atmosphere to the cold sink of outer space—is an appealing concept for the 21st century, where most daily necessities, from power generation to data centers, generate excess heat. In contrast to most of the currently employed cooling methods which require energy and resources to carry heat away, radiative cooling is a passive enhancement of the earth's natural method of cooling itself. Efficient nighttime radiative cooling systems have been extensively investigated in the past, with promising infrared-emissivity in both organic and inorganic materials including pigmented paints (1-5). Day-time radiative cooling, however, presents a different challenge because solar absorbance of just a few percent exceeds the cooling power and effectively heat the surface. Proposed nanophotonic devices can effectively reject solar irradiance but emit strongly in infrared (6-7), promising for day-time radiative cooling. However, the nanophotonic approach requires stringent, nanometer-precision fabrication, which is difficult to scale up cost-effectively to meet the large area requirements of the residential and commercial applications that can benefit most from radiative cooling.

[0126] Polymeric photonics is a growing field attractive for economy and scalability (8-11). Hybridization of random optical metamaterials with polymer photonics can be a promising approach for efficient day-time radiative cooling—To date harnessing randomness in photonic systems has yielded amplified spontaneous emission (12,13), extremely localized electromagnetic hotspots (14-16), improved light-trapping efficiency of photovoltaic cells (17,18), and negative permeability and switching devices with multi-stability (19,20). When electromagnetic resonators in a random metamaterial are collectively excited, the extinction and the optical path length in the material are both enhanced, resulting in nearly perfect absorption at the resonance (21,22). This implies the great potential for utilizing metamaterials with randomly distributed optical resonators for effective radiative cooling if perfect absorption (emissivity) across the entire atmospheric transmission window can be achieved.

[0127] Provided herein are efficient day- and nighttime radiative cooling methods and devices with a randomized, glass-polymer hybrid metamaterial. In an embodiment, the metamaterial consists of a visibly transparent polymer encapsulating randomly distributed silicon dioxide (SiO.sub.2) microspheres. The spectroscopic response spans two orders of magnitude in wavelength (0.3 to 25 μm). The hybrid metamaterial is extremely emissive across the entire atmospheric transmission window (8-13 μm) due to phonon-enhanced Fröhlich resonances of the microspheres. A 50-μm-thick metamaterial film containing 6% of microspheres by volume has an averaged infrared emissivity >0.93 and reflects approximately 96% of solar irradiance when backed with a 200-nm-thick silver coating. We experimentally demonstrate an average noon-time (11 am-2 pm) radiative cooling power of 93 W/m.sup.2 under direct sunshine during a three-day field test, and an average cooling power >110 W/m.sup.2 over the continuous 72-hour day and night test. The metamaterial was fabricated in 300-mm-wide sheets at a rate of 5 m/min, such that in the course of experiment we produced hundreds of square meters of the material.

[0128] The structure of the randomized, glass-polymer hybrid metamaterial described in this example contains micrometer-sized SiO.sub.2 spheres randomly distributed in the matrix material of polymethylpentene (TPX) (FIG. 15A). TPX was used due to its excellent solar transmittance. Other visibly transparent polymers such as Poly(methyl methacrylate) and polyethylene can be used. Because both the polymer matrix material and the encapsulated SiO.sub.2 microspheres are lossless in the solar spectrum, absorption is nearly absent and direct solar irradiance does not heat the metamaterial.

[0129] At infrared wavelengths, the encapsulated SiO.sub.2 microspheres have drastically different optical properties than that of the surrounding matrix material due to the existence of strong phonon-polariton resonances at 9.7 μm (23). We calculated the normalized absorbance (σ.sub.abs/a.sup.2), scattering (σ.sub.sca/a.sup.2), and extinction (σ.sub.ext/a.sup.2) cross-sections of an individual microsphere encapsulated in TPX as a function of its size parameter, k.sub.0a, for an incident wavelength of 10 μm (FIG. 15B). Here k.sub.0 is the wavevector in free space and a is the radius of the microsphere. The extinction peaks at a size parameter of ˜2.5, corresponding to a microsphere radius of ˜4 μm. The size parameter of the microsphere plays a key role in designing the hybrid metamaterial for radiative cooling. At the small particle (quasi-static) limit, the resonance is purely electric-dipolar in character (FIG. 15B inset). At the extinction peak, high-order Fröhlich resonances including both electric and magnetic modes are also strongly excited, which is evidenced by the strong forward scattering shown in FIG. 15C, the three-dimensional power scattering function (far-field scattering pattern) (24).

[0130] The intrinsically narrow linewidth of phonon-polaritons, often a superior advantage in the applications such as infrared sensing (25,26), can limit here the bandwidth of the highly emissive infrared region. We obtained broadband emissivity across the entire atmospheric window by accessing the high-order Fröhlich resonances of the polar dielectric microspheres (27). The real and the imaginary parts of the extracted effective index of refraction, n+iκ=√{square root over (ε.sub.eff.Math.μ.sub.eff)}, are functions of wavelength and microsphere sizes, as illustrated in FIGS. 16A and 16B, respectively, for 1- and 8-μm-diameter microspheres. Given the low concentration (6% by volume) and assuming that the microspheres are uniform in size and distribution, we retrieved the effective permittivity and permeability of the hybrid metamaterial from ε.sub.eff=ε.sub.p[1+iγ(S.sub.0+S.sub.1)], and μ.sub.eff=1+iγ(S.sub.0−S.sub.1), respectively (28), where S.sub.0 and S.sub.1 are the forward and backward scattering coefficients of an individual microsphere in the encapsulating medium, and the factor γ incorporates the volume fraction, f, and the size parameter,

[00001]$k_{0}a\left(\gamma =\frac{3f}{2{\left(k_{0}a\right)}^3}\right).$

In the case of large microspheres, modal interference between higher order modes makes the hybrid metamaterial strongly infrared-absorbing. Importantly, it becomes nearly dispersionless in the infrared. The dispersion of both the real and imaginary part of the effective index of refraction is less than 9×10.sup.−5/nm across the entire infrared wavelength range (FIGS. 16A and 16B), in stark contrast to the strong dispersion of polar, dielectric bulk SiO.sub.2, ˜5×10.sup.−3/nm in this same range. The low dispersion provides excellent broadband impedance matching of the metamaterial to free space, resulting in extremely low reflectance for both solar and infrared radiation. A hybrid metamaterial as thin as 50-μm can provide uniform and sufficiently strong absorbance across the entire atmospheric window, resulting in perfect broadband infrared emission for radiative cooling (FIG. 16C). In contrast, when the microspheres are small (k.sub.0a<<1), a sharp resonance occurs (FIG. 16B), which limits the high infrared emissivity to the polariton resonance wavelength only. Moreover, the resonance introduces strong reflectance, further reducing the overall emissivity.

[0131] The hybrid metamaterial strongly reflects solar irradiation when backed with a 200-nm-thick silver thin film (FIG. 17A) prepared by electron beam evaporation. We characterized the spectroscopic performance of the metamaterial thin film in both the solar (0.3 μm to 2.5 μm) and infrared (2.5 μm to 25 μm) regions using a UV-VIS-NIR spectrophotometer and Fourier transform infrared spectrometer (FTIR), respectively (FIG. 17C and FIG. 17D). We used integrating spheres to account for the scattered light from the full solid angle in both spectral regions. The measured spectral absorptivity (emissivity) of the sample (FIG. 17D) indicates that the 50-μm-thick film reflects ˜96% solar irradiation while possessing a nearly saturated emissivity >0.93 between 8 and 13 μm—yielding greater than 100 W/m.sup.2 radiative cooling power under direct sunlight at room temperature. The experimental results agree well with theory, where the spectroscopic discrepancies near 3 and 16 μm wavelengths primarily due to the absorbance of water and air during the FTIR measurement in ambient conditions. We must employ different theoretical approaches for calculating the emissivity in the solar and infrared wavelength ranges. We used the generalized, incoherent transfer-matrix method in the infrared region (29). In the solar region, we instead used rigorous coupled wave analysis (RCWA) because the extracted effective parameters of the metamaterial are inaccurate when the size of the microsphere is greater than the relevant wavelengths (30). We note that the high emissivity in the second atmospheric window between 16 and 25 μm might be harnessed for additional radiative cooling (31).

[0132] Using a polymer as the matrix material for radiative cooling has the advantages of being lightweight and easy to laminate on curved surfaces. It can accommodate small variations in microsphere size and shape with negligible impact on the overall performance. TPX has excellent mechanical and chemical resistance, offering potentially long lifetimes for outdoor use. However, one of the most compelling advantages of developing a glass-polymer hybrid metamaterial lies in the possibility of cost-effective scalable fabrication. A roll of 300-mm-wide and 50-μm-thick hybrid metamaterial film may be produced at a rate of 5 m/min (FIG. 18A). Control of the volume concentration of the SiO.sub.2 microspheres may be accomplished by using gravimetric feeders. The resultant film has a homogeneous distribution of microspheres, with fluctuations in concentration of less than 0.4% (32) (FIG. 19A). The hybrid metamaterial films are translucent due to the scattering of visible light from the microsphere inclusions (FIG. 20A). Additionally, when backed with a 200-nm-thick reflective silver coating, the hybrid metamaterial has a balanced white color (32) (FIG. 20B). The strongly scattering and nonspecular optical response of the metamaterial will avoid back-reflected glare, which can have detrimental visual effects for humans and interfere with aircraft operations (33).

[0133] Real-time, continuous radiative cooling is demonstrated by conducting thermal measurements using an 8-inch-diameter, scalably-fabricated hybrid metamaterial film over a series of clear autumn days in Cave Creek, Ariz. (33°49′32″N, 112°1′44″W, 585 m altitude) (FIG. 18B, FIG. 18C). The metamaterial was placed in a foam container that prevents heat loss from below. The top surface of the metamaterial faced the sky and was directly exposed to the air (32) (FIGS. 21A and 21B). The surface temperature of the metamaterial was kept the same as the measured ambient temperature using a feedback-controlled electric heater placed in thermal contact with the metamaterial to minimize the impacts of conductive and convective heat losses. The total radiative cooling power is therefore the same as the heating power generated by the electric heater if there is no temperature difference between the surface and the ambient air. With the feedback control, the surface temperature follows the measured ambient temperature within ±0.2° C. accuracy during the day and less than ±0.1° C. at night (32) (FIGS. 22A-22D). Continuously measuring radiative cooling power gives an average radiative cooling power >110 W/m.sup.2 over a continuous 72-hr day-/nighttime measurement (FIG. 18C). The average cooling power around noon reaches 93 W/m.sup.2 with normal-incidence solar irradiance greater than 900 W/m.sup.2. We observed higher average nighttime radiative cooling than during the day. However, the cooling power peaks after sunrise and before sunset when the ambient temperature is changing rapidly and solar irradiance is incident at large oblique angles. To further demonstrate the effectiveness of radiative cooling, we also used water as cold storage medium and show cold water production with the scalably-fabricated hybrid metamaterial (32) (FIGS. 24A-C). Applying chemical additives and high-quality barrier coatings may enhance their outdoor performance including lifetime and reliability. Many polymeric thin films are currently available and designed with extended outdoor lifetime (34).

[0134] Supplementary Text

[0135] Distribution of Microspheres in the Polymer Matrix

[0136] The uniformity of the silica microsphere distribution in the polymer matrix was quantified, and it was shown that the edge-to-edge uniformity was achieved for the 300-mm-wide metamaterial thin films. As shown in FIG. 19A, the concentration variation is less than 0.4%, and the corresponding emissivity variation is even less (FIG. 19B).

[0137] Optical Diffusivity of the Hybrid Metamaterial

[0138] An inherent beneficial attribute of the glass-polymer hybrid metamaterial is optical diffusivity. We showed this optical characteristic by shining a simple laser pen at a wavelength of 532nm through the film approximately 1 m away from a wall. Scattering of the 2-mm beam within the 50-μm sample results in an 80 cm diameter at the wall (FIG. 20A). We further analyzed the visible appearance of the sample, when backed by a silver film by chromaticity analysis, and found it to be a pure balanced white color (FIG. 20B).

[0139] Direct Thermal Measurement of Radiative Cooling Power with Feedback-Controlled Electric Heater

[0140] Large temperature differences observed between the metamaterial and the ambient air can induce severe convective and conductive heat losses in an open environment, particularly during the day when the ambient temperature fluctuation is large. Given the complexity of heat exchange with varying boundary conditions and stochastic environmental parameters such as forced convection by wind, we implemented a feedback-controlled system to keep the metamaterial surface temperature the same as the ambient temperature and accurately assess the true radiative cooling power. The measurement uncertainty due to convective and conductive heat exchange between ambient air and the metamaterial was therefore substantially suppressed. It allowed us to remove the top HDPE protective film and perform direct thermal measurement with the hybrid metamaterial fully exposed to the air (see the apparatus, FIGS. 21A-B)—a preferred configuration for practical applications.

[0141] As shown in FIG. 22A, the surface temperature of the metamaterial tightly follows the ambient air temperature during both day- and nighttime hours. The inset shows the dynamic behavior when the feedback loop was switched on. The integral time constant is about 5 min, and the temperature difference between the ambient and the metamaterial surface can be brought and maintained below 0.2° C. within 30 min. The temperature difference between ambient and the surface of metamaterial over the same period of 18 hours is shown in FIG. 22B. The peak temperature difference was less than ±1° C. during the entire course of experiment. The occasional sudden jumps in temperature were mainly due to gusty wind, from which it took the feedback system approximately 30 min to reestablish tracking. The histograms of the temperature difference between the ambient and the metamaterial surface are shown in FIG. 22C and D for day- and nighttime, respectively. Considering the natural convection of ˜5 W/(m.sup.2.Math.K) and conduction at the air-metamaterial interface under such a small temperature difference, the electric heating power applied through the feedback electronics accurately measures the real-time radiative cooling power.

[0142] With the feedback-controlled direct thermal measurement apparatus, we measured the radiative cooling power of the hybrid metamaterial over a series of clear autumn days in Cave Creek, Ariz. (33°49′32″N, 112°1′44″W, 585 m altitude). A consecutive three-day measurement is presented in FIG. 18. We demonstrated a 72-hr average cooling power >110 W/m.sup.2 and a noon-time (11 am-2 pm) average cooling power of 93 W/m.sup.2.

[0143] The measurement error of the radiative cooling power is less than 10 W/m.sup.2 as defined by the histogram width reflecting 24-hr continuous measurement—and this is in fact overestimated due to the nature of the feedback controlled measurement system. As shown in FIG. 23A and FIG. 23B, the feedback controlled system causes the metamaterial surface temperature to trace the ambient temperature. The mismatch between the two temperatures is much less than 1° C. over the 24-hr period. In FIG. 23C, we show the instantaneous power and the time-averaged power, and the histogram of the difference is shown in FIG. 23D. Momentary oscillations in the feedback control loop cause the measurement error of cooling power to appear incorrectly large. For this reason, we therefore characterize the hybrid metamaterial using its run-time average value for the cooling power.

[0144] Direct Cooling of Water

[0145] We further demonstrate the effectiveness of radiative cooling for a relatively large thermal mass using water as a cold storage medium. The experimental setup is outlined in FIG. 24A. A plastic water tank was placed underneath the radiative cooling glass-polymer hybrid metamaterial, putting water in close contact with the heat-conducting copper plate. Since the water is stationary in the experiment, its large heat capacity substantially slows down the cooling process. We therefore used a 10-μm-thick HDPE film on top of the Polystyrene foam box in this setup to reduce convective heat loss and improve thermal isolation. FIG. 24B shows the ambient temperature (T.sub.air), the water tank surface temperature (T.sub.tank), the water temperature (T.sub.water), and the surface temperature of the metamaterial (T.sub.surface) as functions of time after we exposed the hybrid metamaterial to a clear sky at 3:10 am. The water temperature continuously dropped, reaching more than 8° C. below ambient after two hours of exposure.

[0146] Based on the temperature change, we calculated the amount of heat stored in each material involved in the experiment, including the water, the plastic water tank, and the material stack including the hybrid metamaterial, silver-coated silicon wafer, and the copper plate, as shown in FIG. 24C, as functions of time. FIG. 24C also shows the heat loss from the Polystyrene foam box and the total radiative cooling power, which is the summation of the heat loss and the total heat stored in all materials. The results once again demonstrated a radiative cooling power of more than 100 W/m.sup.2 during the night, and, more importantly, the effectiveness of the radiative cooling by a low-cost, scalably-manufactured glass-polymer hybrid metamaterial for cold water production, which could have applications in cooling of buildings, data centers and even thermoelectric power plants.

REFERENCES

[0147] (1) S. Catalanotti, V. Cuomo, G. Piro, D. Ruggi, V. Silvestrini, G. Troise, The radiative cooling of selective surfaces, Solar Energy, 17, 83 (1975).

[0148] (2) C. G. Granqvist and A. Hjortsberg, Radiative cooling to low temperatures: General considerations and application to selectively emitting SiO films, J. Appl. Phys., 52, 4205 (1981).

[0149] (3) B. Orel, M. Klanjs̆ek Gunde, and Ales̆ Krainer, Radiative cooling efficiency of white pigmented paints, Solar Energy, 50, 477 (1993).

[0150] (4) A. R. Gentle, G. B. Smith, A Subambient Open Roof Surface under the Mid-Summer Sun, Adv. Sci., 2, 1500119 (2015).

[0151] (5) Md. M. Hossain, M. Gu, Radiative Cooling: Principles, Progress, and Potentials, Adv. Sci., 4, 1500360 (2016).

[0152] (6) E. Rephaeli, A. Raman, and S. Fan, Ultrabroadband photonic structures to achieve high-performance daytime radiative cooling, Nano Letters, 13, 1457 (2013).

[0153] (7) A. P. Raman, M. A. Anoma, L. Zhu, E. Rephaeli, and S. Fan, Passive radiative cooling below ambient air temperature under direct sunlight, Nature, 515, 540 (2014).

[0154] (8) M. F. Weber, C. A. Stover, L. R. Gilbert, T. J. Nevitt, A. J. Ouderkirk, Giant Birefringent Optics in Multilayer Polymer Mirrors, Science 287, 2451 (2000).

[0155] (9) S. D. Hart, G. R. Maskaly, B. Temelkuran, P H. Prideaux, J. D. Joannopoulos, Y. Fink, External Reflection from Omnidirectional Dielectric Mirror Fibers, Science 296, 510 (2002).

[0156] (10) J. K. Gansel, M. Thiel, M. S. Rill, M. Decker, K. Bade, V. Saile, G. von Freymann, S. Linden, M. Wegener, Gold Helix Photonic Metamaterial as Broadband Circular Polarizer, Science 325, 1513 (2009).

[0157] (11) R. D. Rasberry, Y. J. Lee, J. C. Ginn, P. F. Hines, C. L. Arrington, A. E. Sanchez, M. T. Brumbach, P. G. Clem, D. W. Peters, M. B. Sinclair, S. M. Dirk, Low loss photopatternable matrix materials for LWIR-metamaterial applications, Journal of Materials Chemistry, 21, 13902 (2011).

[0158] (12) H. E. Türeci, L. Ge, S. Rotter, and A. D. Stone, Strong Interactions in Multimode Random Lasers, Science, 320, 643 (2008).

[0159] (13) D. S. Wiersma, The physics and applications of random lasers, Nature Phys. 4, 359 (2008).

[0160] (14) S. Grésillon, L. Aigouy, A. C. Boccara, J. C. Rivoal, X. Quelin, C. Desmarest, P. Gadenne, V. A. Shubin, A. K. Sarychev, and V. M. Shalaev, Experimental observation of localized optical excitations in random metal-dielectric films, Phys. Rev. Lett. 82, 4520 (1999).

[0161] (15) L. Sapienza, H. Thyrrestrup, S. Stobbe, P. D. Garcia, S. Smolka, and P. Lodahl, Cavity quantum electrodynamics with Anderson-localized modes, Science, 327, 1352 (2010).

[0162] (16) M. Segev, Y. Silberberg, and D. N. Christodoulides, Anderson localization of light, Nature Photonics 7, 197 (2013).

[0163] (17) E. Yabolonovinch, Statistical ray optics, J. Opt. Soc. Am. 72, 899 (1982).

[0164] (18) H. A. Atwater, and A. Polman, Plasmonics for improved photovoltaic devices, Nature Materials 9, 205 (2010).

[0165] (19) B. J. Seo, T. Ueda, T. Itoh, and H. Fetterman, Isotropic left handed material at optical frequency with dielectric spheres embedded in negative permittivity medium, Appl. Phys. Lett., 88, 161122 (2006).

[0166] (20) P. Jung, S. Butz, M. Marthaler, M. V. Fistul, Juha Leppakangas, V. P. Koshelets, and A. V. Ustinov, Multistability and switching in a superconducting metamaterial, Nature Communications 5, 3730 (2014).

[0167] (21) X. P. Shen, Y. Yang, Y. X. Zang, J. Q. Gu, J. G. Han, W. L. Zhang, and T. J. Cui, Triple-band terahertz metamaterial absorber: Design, experiment, and physical interpretation, Appl. Phys. Lett. 101, 154102, (2012).

[0168] (22) J. Hao, É. Lheurette, L. Burgnies, É, Okada, and D. Lippens, Bandwidth enhancement in disordered metamaterial absorbers, Appl. Phys. Lett. 105, 081102 (2014).

[0169] (23) E. D. Palik, Handbook of Optical Constants of Solids (Academic, Orlando, 1985)

[0170] (24) W. Liu, J. Zhang, B. Lei, H. Ma, W. Xie, and H. Hu, Ultra-directional forward scattering by individual core-shell nanoparticles, Optics Express, 22, 16178 (2014).

[0171] (25) N. Ocelic, and R. Hillenbrand, Subwavelength-scale tailoring of surface phonon polaritons by focused ion-beam implantation, Nature Materials 3, 606 (2004).

[0172] (26) I. Balin, N. Dahan, V. Kleiner, E. Hasman, Slow surface phonon polaritons for sensing in the midinfrared spectrum, Appl. Phys. Lett. 94, 111112 (2009).

[0173] (27) Y. Zhao, M. A. Belkin, and A. Alù, Twisted optical metamaterials for planarized ultrathin broadband circular polarizers, Nature communications, 3, 870 (2012).

[0174] (28) M. S. Wheeler, J. S. Aitchison, J. I. Chen, G. A. Ozin, and M. Mojahedi, Infrared magnetic response in a random silicon carbide micropowder, Physical Review B, 79, 073103 (2009).

[0175] (29) C. C. Katsidis, and D. I. Siapkas, General transfer-matrix method for optical multilayer systems with coherent, partially coherent, and incoherent interference, Applied Optics, 41, 3978 (2002).

[0176] (30) L. F. Li, Use of Fourier series in the analysis of discontinuous periodic structures, J. Opt. Soc. Am. A 13, 1870 (1996).

[0177] (31) H. W. Yates, and J. H. Taylor, Infrared transmission of the atmosphere, No. NRL-5453, Naval Research Lab, Washington D.C., (1960).

[0178] (32) Materials and Methods can be found as Supplementary Materials on Science Online.

[0179] (33) X. H. Xua, K. Vignaroobanc, B. Xud, K. Hsua, A.M. Kannana, Prospects and problems of concentrating solar power technologies for power generation in the desert regions, Renewable and Sustainable Energy Reviews, 53, 1106 (2016).

[0180] (34) H. Price, E. Lupfert, D. Kearney, E. Zarza, G. Cohen, R. Gee, and R. Mahoney, Advances in parabolic trough solar power technology, Journal of solar energy engineering, 124, 109 (2002).