Near-field Thermal Radiation In Composite Metamaterials

Radiative Heat Transfer is a common process between arbitrary objects located at nonzero absolute temperatures,ordering from the incandescent bulbs,Sun,to nano-antenna.Owing to its photon tunneling of the evanescent wave and surface polariton effect,the nearfield radiation heat transfer can significantly surpass the blackbody radiation limit as established by the famous Planck’s law.These characteristics have been applied in micronano thermal photovoltaic systems and near-field thermal scanning microscopy.Micro/nano particle composite metamaterials exhibit novel physical properties that are not available in a single component by adjusting their microstructure and nanostructure.We will study the near-field thermal radiation behavior of composite metamaterials.This topic involves physics,materials science,engineering thermophysics,chemistry,and other disciplines.The research in this area not only has important academic value but also has a lot of potential application value in engineering and nanotechnology.In this dissertation,the form of fluctuational electrodynamics and fluctuational dissipation theory based on electromagnetic field theory is described.Combined with the effective media theory established for different composite metamaterials,the near-field thermal radiation characteristics of composite metamaterials are systematically studied,and thermal rectification device design is proposed.We start by demonstrating a strong photonic thermal rectification effect between the polar dielectrics plate and the composite metamaterials containing nonspherical polar dielectric nanoparticles with small volume fractions.Thermal rectification efficiency isfound to be adjusted by the volume fractions and the nanoparticles’ shape,and it can be as large as 80%when the polar dielectric nanoparticles are spherical in shape and are in the dilute limit with the volume fraction f=0.01.Physically,strong electromagnetic coupling between the surface phonon polaritons(SPhPs)mode of polar dielectrics plate and the localized surface phonon polaritons(LSPhPs)mode around polar dielectric nanoparticles.The results provide alternative new freedom for regulating energy flow and heat rectification efficiency in the near field and might be helpful in designing a multiparameter adjustable thermal diode.In order to consider the near-field radiative heat transfer(NFRHT)between a semiinfinite polar dielectric plate and a composite metamaterial containing semiconductor nanoparticles with spatial dispersion or nonlocality,a suitable theoretical technique is needed.To this end,we show that the enhancement of near-field heat radiation is found owing to the strong coupling of localized surface plasmon polaritons(LSPPs)in the composite metamaterials and surface phonon polaritons(SPhPs)excited between polar dielectric plate and air.The introduction of nonlocality is useful to significantly enhance the NFRHT as well as the rectification efficiency when the temperature difference is small.For a large volume fraction of semiconductor nanoparticles,the thermal rectification efficiency can be larger than 90%at a small temperature difference within 150 K.Our findings may pave a way for thermal devices based on composite metamaterial containing semiconductor nanoparticles.Meanwhile,exploiting the NFRHT with graded composite metamaterials still remains technologically intriguing for practical usage.Here,we theoretically investigate the nearfield radiative heat transfer(NFRHT)between two graded composite metamaterial plates composed of graded metal nanoparticles.Our study provides an in-depth analysis of the physical mechanism of NFRHT between graded composite plates,demonstrating that both the surface plasmon polariton(SPP)excited between the graded composite plate and air and the localized SPP(LSPP)excited in the graded composite plate can strongly couple and enhance NFRHT.In addition,the strength of NFRHT can be controlled by adjusting the gradation function and volume fraction of graded nanoparticles.Our study provides a theoretical basis and guidance for the related near-field thermal devices based on composite metamaterials containing graded nanoparticles.In this dissertation,by designing different composite metamaterials and numerically analyzing their NFRHT phenomena,the possible applications of various composite metamaterials are demonstrated and the profound physical implications behind them are revealed.Composite metamaterials can be used to control the radiative heat flux with a high degree of freedom and high efficiency by adjusting material parameters,particle shape and size,and the proportion of each component,and also improve the intensity of near-field heat radiation to a certain extent.In addition,a series of novel physical mechanisms and physical phenomena that are not available in bulk materials were presented.These innovations pave the way for the design and application of near-field thermal devices based on composite metamaterials.