Metamaterial Control of Thermal Radiation

The observation and use of thermal radiation has a long history. Significant advance was made in 1879 when Josef Stefan found that “the total radiated power per unit surface area of a black body across all wavelengths is directly proportional to the fourth power of its temperature”, which was later named the Stefan–Boltzmann law. The Stefan–Boltzmann law sets a limit for the thermal radiation from most of natural materials, since their total radiated energy is proportional to the fourth power of their temperature. Thus, use of natural materials for the control and manipulation of thermal emission is hindered from further development. Metamaterials are artificial materials consisting of sub-wavelength unit cells, and good candidates to break these limitations, since the optical properties of metamaterials originates from their geometrical designs, as opposed to their chemical composition. Here we propose and demonstrate the idea of metamaterial based on microelectromechanical system capable of dynamically tailoring the energy emitted from a surface, with its emission performance going beyond the Stefan–Boltzmann law. Our dynamic metamaterial emitters have great application prospects in energy harvesting, space exploration, sensing and detecting, and many other areas. In addition, our results are not limited to the thermal infrared band, demonstrate here, but may be scaled to nearly any sub-optical range of the electromagnetic spectrum, and verify the potential of MEMS metamaterials to operate as reconfigurable multifunctional devices with unprecedented energy control capabilities.

Although metamaterial may yield advanced thermal emission control, they are difficult to apply to some applications, such as in thermal imaging and energy harvesting with thermophotovoltaics. This is because they are typically fashioned with metallic materials and thus possess low melting points, high Ohmic loss, and high thermal conductivity. Here we present an all dielectric metamaterial absorber/emitter. By overlapping the electric and magnetic dipole resonances, a high absorptive / emissive state can be achieved. Due to its great thermal properties, such as heat localization and thermal stability, an all dielectric metamaterial absorber/ emitter can replace metal-based metamaterial in some application areas, and offers a new route for applications in thermophotovoltaics, imaging, and sensing.

This dissertation consists of seven chapters. The first chapter gives a brief introduction to thermal radiation, metamaterials, metamaterial absorbers, and all dielectric metamaterials. The second chapter discusses in detail thermochromic infrared metamaterials. The third chapter demonstrates a reconfigurable room temperature metamaterial infrared emitter. The fourth chapter shows a THz all dielectric metamaterial absorber. The fifth chapter gives another example of all dielectric metamaterial emitters that can be used in thermophotovoltaic systems. The sixth chapter is a summary. The seventh chapter is an executive summary of original contributions.