Embodiments described herein generally relate a multi-mode heat transfer system. The heat transfer system includes an emitter device. The emitter device includes an inner core, a composite material pattern, and a surface coating pattern. The inner core is surrounded by an outer core having a thickness and an outer surface. The composite material pattern extends through at least a portion of the outer surface and at least a portion of the thickness of the outer core and is thermally coupled to the inner core. The surface coating pattern is on the outer surface and is changeable between a low emissivity state and a high emissivity state based on a surface temperature of the emitter device. In the low emissivity state, the emitter device transmits an omni-directional radiation and, in the high emissivity state, the emitter device transmits a focused radiation via the composite material pattern.

Various aspects as described herein are directed to a radiative cooling device and method for cooling an object. As consistent with one or more embodiments, a radiative cooling device includes a solar spectrum reflecting structure configured and arranged to suppress light modes, and a thermally-emissive structure configured and arranged to facilitate thermally-generated electromagnetic emissions from the object and in mid-infrared (IR) wavelengths.

Systems and methods for radiative cooling and heating are provided. For example, systems for radiative cooling can include a top layer including one or more polymers, where the top layer has high emissivity in at least a portion of the thermal spectrum and an electromagnetic extinction coefficient of approximately zero, absorptivity of approximately zero, and high transmittance in at least a portion of the solar spectrum, and further include a reflective layer including one or more metals, where the reflective layer has high reflectivity in at least a portion of the solar spectrum.

Embodiments described herein relate to a system with an electroactive substrate, a plurality of nanoparticles, and a control unit. The plurality of nanoparticles deposited in communication with the electroactive substrate. The control unit is configured to manipulate a shape of the electroactive substrate between an unactuated mode and an actuated mode to change an absorption band or an emission band of the plurality of nanoparticles. When the electroactive substrate shape is manipulated, the absorption band or the emission band of the plurality of nanoparticles is changed to tune the system for a radiative cooling based on a current dominating wavelength.

Disclosed are methods and functional elements for enhanced thermal management of predominantly enclosed spaces. In particular, the invention enables the construction of buildings with reduced power requirements for heating and/or air-conditioning systems since under certain conditions less energy for heating or cooling is required to maintain, within certain boundaries, desirable temperatures inside such buildings, habitats, or other enclosed spaces.

In some instances the invention is in part based on dynamically changing functional elements with variable properties, or effective properties, in terms of their electromagnetic radiative behavior and/or their thermal energy storage properties, or the spatial distribution of the stored thermal energy, which permits the application of methods and algorithms to control the overall thermal behavior of the entire structure in such a way that desired levels of inside temperature can be reached with reduced consumption of external energy (typically electricity, gas, oil, or coal).

In some instances no conventional heating of cooling is required at all, whereas in other instances the expenditure of external energy for conventional heating or cooling is reduced. In some instances the invention enables the reduction of the time to reach desired temperatures inside such buildings, habitats, or other predominantly enclosed spaces.

Examples of heat exchanger systems for active radiative cooling are described. In one example, the system includes a heat exchanger and a spectrally selective surface material on at least one surface of the heat exchanger. The spectrally selective surface material exhibits high reflectivity at shorter wavelengths and high emissivity at longer wavelengths. The system can also include an active cooling system in some cases to actively transfer heat to the heat exchanger. The use of spectrally selective surfaces that operate at temperatures exceeding that of the outdoor ambient for which convective losses augment radiation losses have advantages over passive cooling, such as but not limited to: providing a better match to cooling loads, reducing the heat rejection surface area required to achieve a desired cooling rate, and increasing the heat transferred to deep space through the atmospheric window so as to simultaneously cool infrastructure, devices, buildings, and Earth.

The present disclosure provides a polyolefin film including a fibrous polyolefin having an average diameter of 0.1 μm or more and less than 1.0 μm, wherein the polyolefin film has a connected-void structure, has a void ratio a of 50% to 90%, has a thickness d in μm, which satisfies, together with the void ratio a, a relation of 40≤(d×(100−a)/100)≤200, and is used as a radiative cooling film, and a radiative cooling structure body including the polyolefin film.

The present disclosure provides a polyolefin film including a fibrous polyolefin having an average diameter of 0.1 μm or more and less than 1.0 μm, wherein the polyolefin film has a connected-void structure, has a void ratio a of 50% to 90%, has a thickness d in μm, which satisfies, together with the void ratio a, a relation of 40≤(d×(100−a)/100)≤200, and is used as a radiative cooling film, and a radiative cooling structure body including the polyolefin film.

A coating including a relatively thin visible-absorptive layer atop a relatively thick non-absorptive, solar-scattering underlayer. The thin top layer enables efficient absorption of appropriate visible wavelengths to show specific colors, and minimizes absorption in the infrared radiation in sunlight due to its relatively small thickness. Meanwhile, the bottom layer maximizes the backscattering of infrared light without absorption to reduce solar heating.

Systems and techniques are described that provide for enhanced gain and radiation characteristics of antennas. The systems and techniques employ layers or cards of fractal plasmonic surfaces to provide gain to the antennas. The fractal plasmonic surfaces each include a close-packed arrangements of resonators having self-similar or fractal shapes, which may be referred to as “fractal cells.” The cards can be held by a frame adapted to fit an antenna. The FPS cards can provide benefits for gain, field emission, directivity, increased bandwidth, power delivery, and/or heat management. One or more dielectric layers or cards may be used to enhance gain and/or directivity characteristics.