Selective thermal emission and infrared camouflage based on layered media

Infrared camouflage based on artificial thermal metasurfaces has recently attracted significant attention. By eliminating thermal radiation differences between the object and the background, it is possible to hide a given object from infrared detection. Infrared camouflage is an important element that increases the survivability of aircraft and missiles, by reducing target susceptibility to infrared guided threats. Herein, a simple and practicable design is theoretically presented based on a multilayer film for infrared stealth, with distinctive advantages of scalability, flexible fabrication, and structural simplicity. The multilayer medium consists of silicon substrate, carbon layer and zinc sulfide film, the optical properties of which are determined by transfer matrix method. By locally changing the thickness of the coating film, the spatial tunability and continuity in thermal emission are demonstrated. A continuous change of emissive power is further obtained and consequently implemented to achieve thermal camouflage functionality. In addition, other functionalities, like thermal illusion and thermal coding, are demonstrated by thickness-engineered multilayer films

Métamatériaux thermiques intelligents

This thesis mainly focuses on thermal metamaterials, including thermal metadevices that can actively manipulate heat flux, and thermally responsive metamaterials that can deform in response to external heat stimuli in a controlled manner. We propose a method to design arbitrarily shaped 3D thermal cloaks with anisotropic and homogeneous material properties. Based on this approach, we study the steady-state and transient cloaking performance of multilayered cloaks. Then we propose a general road map to build thermal harvesting devices with microstructure design. The device is realized by naturally available materials. Both numerical and experimental results demonstrate good thermal harvesting performance. In addition to the above mentioned works on in-plane heat conduction control, we further propose a multilayered medium approach to flexibly manipulate out-of-plane thermal radiation. Based on this approach we realize functionalities like infrared camouflage, thermal coding and thermal illusion. Finally, we propose thermomechanical metamaterials that can generate basic deformations (translation and rotation) in reaction to heat stimuli. We verify their accurate, stable and reversible thermally induced performance by simulations and experiments. Actuation operation is also investigated.Cette thèse porte principalement sur les métamatériaux thermiques, y compris les méta-composants thermiques qui peuvent manipuler activement un flux de chaleur, et les métamatériaux sensibles à la chaleur qui peuvent se déformer de manière contrôlée en réponse à des stimuli thermiques externes. Nous proposons une méthode pour concevoir des capes de camouflage thermique 3D de forme arbitraire. Sur la base de cette approche, nous étudions les performances de camouflage en régime permanent et transitoire. Ensuite, nous proposons une feuille de route générale pour construire des dispositifs de récupération thermique avec une conception de la microstructure. Le dispositif est réalisé avec des matériaux naturellement disponibles. Les résultats tant numériques qu'expérimentaux démontrent de bonnes performances de récupération thermique. En plus des travaux mentionnés ci-dessus sur le contrôle de la conduction thermique dans le plan, nous proposons également une approche de milieu multicouche pour manipuler de manière flexible le rayonnement thermique hors plan. Sur la base de cette approche, nous réalisons des fonctionnalités telles que le camouflage infrarouge, le codage thermique et l'illusion thermique. Enfin, nous proposons des métamatériaux thermomécaniques capables de générer des déformations élémentaires (translation et rotation) en réaction à des stimuli thermiques. Nous vérifions que les performances induites sont thermiquement précises, stables et réversibles par des simulations et des expériences. Le comportement d'actionnement est également étudié

Thermally driven smart metamaterials

Cette thèse porte principalement sur les métamatériaux thermiques, y compris les méta-composants thermiques qui peuvent manipuler activement un flux de chaleur, et les métamatériaux sensibles à la chaleur qui peuvent se déformer de manière contrôlée en réponse à des stimuli thermiques externes. Nous proposons une méthode pour concevoir des capes de camouflage thermique 3D de forme arbitraire. Sur la base de cette approche, nous étudions les performances de camouflage en régime permanent et transitoire. Ensuite, nous proposons une feuille de route générale pour construire des dispositifs de récupération thermique avec une conception de la microstructure. Le dispositif est réalisé avec des matériaux naturellement disponibles. Les résultats tant numériques qu'expérimentaux démontrent de bonnes performances de récupération thermique. En plus des travaux mentionnés ci-dessus sur le contrôle de la conduction thermique dans le plan, nous proposons également une approche de milieu multicouche pour manipuler de manière flexible le rayonnement thermique hors plan. Sur la base de cette approche, nous réalisons des fonctionnalités telles que le camouflage infrarouge, le codage thermique et l'illusion thermique. Enfin, nous proposons des métamatériaux thermomécaniques capables de générer des déformations élémentaires (translation et rotation) en réaction à des stimuli thermiques. Nous vérifions que les performances induites sont thermiquement précises, stables et réversibles par des simulations et des expériences. Le comportement d'actionnement est également étudié.This thesis mainly focuses on thermal metamaterials, including thermal metadevices that can actively manipulate heat flux, and thermally responsive metamaterials that can deform in response to external heat stimuli in a controlled manner. We propose a method to design arbitrarily shaped 3D thermal cloaks with anisotropic and homogeneous material properties. Based on this approach, we study the steady-state and transient cloaking performance of multilayered cloaks. Then we propose a general road map to build thermal harvesting devices with microstructure design. The device is realized by naturally available materials. Both numerical and experimental results demonstrate good thermal harvesting performance. In addition to the above mentioned works on in-plane heat conduction control, we further propose a multilayered medium approach to flexibly manipulate out-of-plane thermal radiation. Based on this approach we realize functionalities like infrared camouflage, thermal coding and thermal illusion. Finally, we propose thermomechanical metamaterials that can generate basic deformations (translation and rotation) in reaction to heat stimuli. We verify their accurate, stable and reversible thermally induced performance by simulations and experiments. Actuation operation is also investigated

Achieving thermal magnification by using effective thermal conductivity

ABSTRACT: A thermal magnification device is proposed by using effective thermal conductivity. Different from transformation optics method, the magnification design is realized analytically by enforcing equality of effective thermal conductivity on the magnification device and the reference case in specified domains. The validity of theoretical analysis is checked by numerical simulation results, which demonstrates the magnifying effects of the proposed design. The device only needs isotropic and homogeneous materials that are easy to obtain in nature. It is also shown that the obtained magnifying conditions are the same as those derived by separation of variables. But the proposed method proves more flexible for multilayered materials and simpler for non-spherical objects under non-uniform thermal fields. It can also be extended to other fields and applications governed by Laplace equation. Keywords: Thermal magnification, Effective thermal conductivity, Separation of variable

Designs for thermal harvesting with nonlinear coordinate transformation

In this paper a thermal concentrating design method was proposed based on the concept of generating function without knowing the needed coordinate transformation beforehand. The thermal harvesting performance was quantitatively characterized by heat concentrating efficiency and external temperature perturbation. Nonlinear transformations of different forms were employed to design high order thermal concentrators, and corresponding harvesting performances were investigated by numerical simulations. The numerical results shows that the form of coordinate transformation directly influences the distributions of heat flows inside the concentrator, consequently, influences the thermal harvesting behaviors significantly. The concentrating performance can be actively controlled and optimized by changing the form of coordinate transformations. The analysis in this paper offers a beneficial method to flexibly tune the harvesting performance of the thermal concentrator according to the requirements of practical applications

Transformation Thermodynamics with Arbitrarily Shaped Non-Conformal Objects and Coatings

In this paper we apply transformation optics theory to thermodynamics and design thermal cloaks and concentrators with arbitrarily shaped non-conformal objects and coatings. Expressions of the required material parameters are derived analytically and then validated by numerical simulations. We apply this method to design a thermal cloak which can guide the heat flow around the inner domain without perturbation to external thermal fields. In this way, the object inside the inner domain is protected from the invasion of external heat fluxes. In contrast, a concentrator is designed to concentrate heat flows into a small region without disturbing outside temperature fields, which can considerably enhance the heat density in the designed domain. The proposed method extends the design flexibility in manipulating heat flux and will find wide applications in thermal protection systems, solar cells and so on

A mainland China homogenized historical temperature dataset for 1951-2004

The China Homogenized Historical Temperature (CHHT) dataset (1951-2004) version 1.0 consists of monthly and daily surface observations from all national stations in mainland China. The primary objective of CHHT 1.0 is to build a set of homogenized observational climatic datasets to reduce uncertainty in the detection of observed climatic change and variability. CHHT version 1.0 covers the years 1951-2004 in two formats that are stations and grids with 2.5°×2.5° spatial resolution and dataset is developed by using observations of daily mean, minimum and maximum temperatures from a total of 731 national weather stations distributed throughout mainland China. CHHT 1.0 quality control starts with fundamental checks that include the checking of range and limiting values, checking the internal consistency and, checking the measurements against each other. The CHHT 1.0 temperature data include two different datasets that are the original data and a homogeneity-adjusted version

Interlayer torsional sliding and strain localization in bilayer graphene

International audienceTwisted bilayer graphene can demonstrate extraordinary optical and electrical characteristics due to its interlayer interactions. The strong coupling of normal and tangential van der Waals interactions at the interface results in inhomogeneous interlayer deformations and further changes the bilayer graphene’s physical properties. Herein, theoretical and numerical models are established to study the torsional deformation behaviour of twisting a graphene flake over a rigid graphene substrate. It is found that in-plane deformations have significant influences on the interlayer potential energy density of AA stacking, but seldom affect other stacked domains. The deformation process is thus approximated by first twisting the graphene flake rigidly, and then relaxing the rigid constraints. The bilayer graphene system minimizes its energy by reducing (enlarging) the size of high-energy (low-energy) domains through additional rotations. The additional angles of the graphene flake are derived analytically based on a mechanical model following the principle of minimum potential energy. Results show that the influences of graphene film deformations get significant at small-twist-angles (typically less than 2∘). This work reveals the torsional deformation evolution mechanism of bilayer grapheneand provides beneficial guidance on achieving intriguing physical properties

Interactions of Self-Assembled Bletilla Striata Polysaccharide Nanoparticles with Bovine Serum Albumin and Biodistribution of Its Docetaxel-Loaded Nanoparticles

: Amphiphilic copolymers of stearic acid (SA)-modified Bletilla striata polysaccharides (BSPs-SA) with three different degrees of substitution (DSs) were synthesized. The effects of DS values on the properties of BSPs-SA nanoparticles were evaluated. Drug state, cytotoxicity, and histological studies were carried out. The affinity ability of bovine serum albumin (BSA) and the BSPs-SA nanoparticles was also characterized utilizing ultraviolet and fluorescence spectroscopy. Besides, the bioavailability and tissue distribution of docetaxel (DTX)-loaded BSPs-SA nanoparticles were also assessed. The results demonstrated that the DS increase of the hydrophobic stearic acid segment increased the negative charge, encapsulation efficiency, and drug-loading capacity while decreasing the critical aggregation concentration value as well as the release rate of docetaxel from the nanoparticles. Docetaxel was encapsulated in nanoparticles at the small molecules or had an amorphous status. The inhibitory capability of DTX-loaded BSPs-SA nanoparticles against 4T1 tumor cells was superior to that of Duopafei®. The ultraviolet and fluorescence results exhibited a strong binding affinity between BSPs-SA nanoparticles and bovine serum albumin, but the conformation of bovine serum albumin was not altered. Additionally, the area under the concentration–time curve (AUC0–∞) of DTX-loaded BSPs-SA nanoparticles was about 1.42-fold higher compared with Duopafei® in tumor-bearing mice. Docetaxel levels of DTX-loaded BSPs-SA nanoparticles in some organs changed, and more docetaxel accumulated in the liver, spleen, and the tumor compared with Duopafei®. The experimental results provided a theoretical guidance for further applications of BSPs-SA conjugates as nanocarriers for delivering anticancer drugs