University of Rhode IslandUnited States of America
Thermal radiative transport yields unique thermal characteristics of microscopic thin films—wavelength selectivity. This chapter focuses on a methodology about adjusting the wavelength selectivity of thin films embedded with nanoparticles in the far‐field and near‐field regimes. For nanostructured layered media doped with nanoparticles, Maxwell‐Garnett‐Mie theory is applied to determine the effective dielectric function for the calculation of radiative thermal transport. The thermal radiative wavelength selectivity can be affected by volume fraction and/or the size of the embedded nanoparticles in thin films. To characterize wavelength selectivity and optical property of nanostructured materials, both real and imaginary parts of effective refractive index need to be analyzed. It has been shown that the nanoparticles made of polar or metallic materials have different influence on thermal radiative wavelength selectivity of microscopic thin films.
Part of the book: Nanoscaled Films and Layers
We discuss concepts of radiative thermal diodes demonstrating dynamic control and modulation of radiative heat transfer. These concepts are analogous to electronic diodes and display high degree of asymmetry in radiative heat transfer. Change in optical properties of vanadium dioxide VO 2 upon phase transition are exploited to influence thermal radiation. The first concept is based on a simple multi-layer structure containing a layer of VO 2 to attain dynamic optical response in the far-field regime. The active terminal of the diode changes from highly reflecting to highly absorbing upon phase transition of VO 2 . In the second concept, a near-field thermal diode is considered that utilizes period gratings of VO 2 . Radiative heat transfer across the near-field gap is modulated by altering tunneling of surface waves when phase change in VO 2 occurs. For minimal temperature difference of 20 K, rectification ratios have been reported and they are maximum in existing literature for comparable operating temperatures and configurations.
Part of the book: Heat Transfer