Tunable analog thermal material Xu, Guoqiang; Dong, Kaichen; Li, Ying ...
Nature communications,
11/2020, Letnik:
11, Številka:
1
Journal Article
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Abstract
Naturally-occurring thermal materials usually possess specific thermal conductivity (
κ
), forming a digital set of
κ
values. Emerging thermal metamaterials have been deployed to realize ...effective thermal conductivities unattainable in natural materials. However, the effective thermal conductivities of such mixing-based thermal metamaterials are still in digital fashion, i.e., the effective conductivity remains discrete and static. Here, we report an analog thermal material whose effective conductivity can be in-situ tuned from near-zero to near-infinity
κ
. The proof-of-concept scheme consists of a spinning core made of uncured polydimethylsiloxane (PDMS) and fixed bilayer rings made of silicone grease and steel. Thanks to the spinning PDMS and its induced convective effects, we can mold the heat flow robustly with continuously changing and anisotropic
κ
. Our work enables a single functional thermal material to meet the challenging demands of flexible thermal manipulation. It also provides platforms to investigate heat transfer in systems with moving components.
The sky is a natural heat sink that has been extensively used for passive radiative cooling of households. A lot of focus has been on maximizing the radiative cooling power of roof coating in the hot ...daytime using static, cooling-optimized material properties. However, the resultant overcooling in cold night or winter times exacerbates the heating cost, especially in climates where heating dominates energy consumption. We approached thermal regulation from an all-season perspective by developing a mechanically flexible coating that adapts its thermal emittance to different ambient temperatures. The fabricated temperature-adaptive radiative coating (TARC) optimally absorbs the solar energy and automatically switches thermal emittance from 0.20 for ambient temperatures lower than 15°C to 0.90 for temperatures above 30°C, driven by a photonically amplified metal-insulator transition. Simulations show that this system outperforms existing roof coatings for energy saving in most climates, especially those with substantial seasonal variations.
Abstract
The twisted stacking of two layered crystals has led to the emerging moiré physics as well as intriguing chiral phenomena such as chiral phonon and photon generation. In this work, we ...identified and theoretically formulated a non-trivial twist-enabled coupling mechanism in twisted bilayer photonic crystal (TBPC), which connects the bound state in the continuum (BIC) mode to the free space through the twist-enabled channel. Moreover, the radiation from TBPC hosts an optical vortex in the far field with both odd and even topological orders. We quantitatively analyzed the twist-enabled coupling between the BIC mode and other non-local modes in the photonic crystals, giving rise to radiation carrying orbital angular momentum. The optical vortex generation is robust against geometric disturbance, making TBPC a promising platform for well-defined vortex generation. As a result, TBPCs not only provide a new approach to manipulating the angular momentum of photons, but may also enable novel applications in integrated optical information processing and optical tweezers. Our work broadens the field of moiré photonics and paves the way toward the novel application of moiré physics.
Radiative cooling, what’s next? Dong, Kaichen; Wu, Junqiao
Next Energy,
March 2023, 2023-03-00, 2023-03-01, Letnik:
1, Številka:
1
Journal Article
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Radiative coatings make use of omnipresent surface thermal radiation for passive cooling of objects without consuming energy or emitting greenhouse gases, and are a promising energy-saving strategy ...at scale to address the climate change problem. In the last decade, thanks to advances in photonics and micro/nano-fabrication technologies, we have witnessed the emergence of high-performance radiative coatings with hundreds of different designs. In this work, the development timeline of radiative coatings is summarized and potential research directions in this field are analyzed. Existing challenges and opportunities, especially for passively switchable radiative coatings, are discussed. We hope this short review promotes radiative coating materials and products for serving the sustainability of our society in various markets such as buildings, vehicles, and space objects.
Novel magnetic ground states have been stabilized in two-dimensional (2D) magnets such as skyrmions, with the potential next-generation information technology. Here, we report the experimental ...observation of a Néel-type skyrmion lattice at room temperature in a single-phase, layered 2D magnet, specifically a 50% Co-doped Fe5GeTe2 (FCGT) system. The thickness-dependent magnetic domain size follows Kittel's law. The static spin textures and spin dynamics in FCGT nanoflakes were studied by Lorentz electron microscopy, variable-temperature magnetic force microscopy, micromagnetic simulations, and magnetotransport measurements. Current-induced skyrmion lattice motion was observed at room temperature, with a threshold current density, jth = 1 × 106 A/cm2. This discovery of a skyrmion lattice at room temperature in a noncentrosymmetric material opens the way for layered device applications and provides an ideal platform for studies of topological and quantum effects in 2D.
Along with the rapid development of hybrid electronic–photonic systems, multifunctional devices with dynamic responses have been widely investigated for improving many optoelectronic applications. ...For years, microelectro-opto-mechanical systems (MEOMS), one of the major approaches to realizing multifunctionality, have demonstrated profound reconfigurability and great reliability. However, modern MEOMS still suffer from limitations in modulation depth, actuation voltage, or miniaturization. Here, we demonstrate a new MEOMS multifunctional platform with greater than 50% optical modulation depth over a broad wavelength range. This platform is realized by a specially designed cantilever array, with each cantilever consisting of vanadium dioxide, chromium, and gold nanolayers. The abrupt structural phase transition of the embedded vanadium dioxide enables the reconfigurability of the platform. Diverse stimuli, such as temperature variation or electric current, can be utilized to control the platform, promising CMOS-compatible operating voltage. Multiple functionalities, including an active enhanced absorber and a reprogrammable electro-optic logic gate, are experimentally demonstrated to address the versatile applications of the MEOMS platform in fields such as communication, energy harvesting, and optical computing.
Efficient thermal management at the nanoscale is important for reducing energy consumption and dissipation in electronic devices, lab-on-a-chip platforms and energy harvest/conversion systems. For ...many of these applications, it is much desired to have a solid-state structure that reversibly switches thermal conduction with high ON/OFF ratios and at high speed. Here we describe design and implementation of a novel, all-solid-state thermal switching device by nanostructured phase transformation, i.e., modulation of contact pressure and area between two poly-silicon surfaces activated by microstructural change of a vanadium dioxide (VO
) thin film. Our solid-state devices demonstrate large and reversible alteration of cross-plane thermal conductance as a function of temperature, achieving a conductance ratio of at least 2.5. Our new approach using nanostructured phase transformation provides new opportunities for applications that require advanced temperature and heat regulations.
Optical materials with nearly zero refractive indices have driven emerging applications ranging from geometry-invariant optical tunneling, nonlinear optics, optical cloaking to thermal emission ...manipulation. In conventional dielectric photonic circuits, light scattering and back reflection at the waveguide bends and crossings leads to significant optical loss. Here we propose to use near-zero-index materials as a cladding layer for low-loss optical waveguides, where optical modes are tightly confined within the dielectric core region. Compared to conventional waveguides, the near-zero-index waveguides are superior in maintaining a high mode-filling factor for small device sizes close to the diffraction limit and reducing the crosstalk in between at a sub-wavelength separation. In addition, we found that light propagation is robust to waveguide bends in a small radius (∼µm) and geometry variation in the cross section. Hollow waveguides with near-zero-index cladding layers further support low-loss light propagation because materials absorption is minimized from the air core. Our work offers critical insights into future designs of low-loss and miniaturized photonic devices.
Overcooling is a major challenge of conventional passive radiative cooling materials, especially for thermal regulation of houses, electric vehicles, and space objects. In a recent paper published in ...Device, Qiao and co-workers reported a Janus film system that keeps objects cool in hot-weather daytime and warm in cold-weather nighttime.
Overcooling is a major challenge of conventional passive radiative cooling materials, especially for thermal regulation of houses, electric vehicles, and space objects. In a recent paper published in Device, Qiao and co-workers reported a Janus film system that keeps objects cool in hot-weather daytime and warm in cold-weather nighttime.
The cost of annual energy consumption in buildings in the United States exceeds 430 billion dollars ( Science 2019, 364 (6442), 760-763), of which about 48% is used for space thermal management ...(https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019), revealing the urgent need for efficient thermal management of buildings and dwellings. Radiative cooling technologies, combined with the booming photonic and microfabrication technologies ( Nature 2014, 515 (7528), 540-544), enable energy-free cooling by radiative heat transfer to outer space through the atmospheric transparent window ( Nat. Commun. 2024, 15 (1), 815). To pursue all-season energy savings in climates with large temperature variations, switchable and tunable radiative coolers (STRC) have emerged in recent years and quickly gained broad attention. This Perspective introduces the existing STRC technologies and analyzes their benefits and challenges in future large-scale applications, suggesting ways for the development of future STRCs.The cost of annual energy consumption in buildings in the United States exceeds 430 billion dollars ( Science 2019, 364 (6442), 760-763), of which about 48% is used for space thermal management (https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019), revealing the urgent need for efficient thermal management of buildings and dwellings. Radiative cooling technologies, combined with the booming photonic and microfabrication technologies ( Nature 2014, 515 (7528), 540-544), enable energy-free cooling by radiative heat transfer to outer space through the atmospheric transparent window ( Nat. Commun. 2024, 15 (1), 815). To pursue all-season energy savings in climates with large temperature variations, switchable and tunable radiative coolers (STRC) have emerged in recent years and quickly gained broad attention. This Perspective introduces the existing STRC technologies and analyzes their benefits and challenges in future large-scale applications, suggesting ways for the development of future STRCs.
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