Wire medium considered as a realisation of artificial uniaxially anisotropic materials is an optically dense array of aligned wires which are embedded in a dielectric matrix. This thesis focuses on such medium and its use for two intriguing and important purposes. The first purpose is about controlling the radiative heat transfer and improvement of thermophotovoltaic systems. We started from an essential step and investigated the applicability of the effective medium model to the problems of radiative heat transfer through wire metamaterials. This initial study allowed us to move forward to next steps and introduce new practical designs for micron-gap thermophotovoltaic generators. In the proposed systems, using wire media we could achieve frequency-selective and super-Planckian radiative heat transfer. This important feature gave rise to the high ultimate efficiency and high electric output. Also, we theoretically showed that by employing wire media together with a particular type of emitter which supports surface plasmon/phonon polaritons, micron-gap thermophotovoltaic systems can operate at relatively low temperatures while we can still attain a noticeable conversion efficiency and remarkable electric output per unit area. The second purpose is associated with enhancement of subwavelength electric and magnetic emitters. Studying the wire medium whose wires are made of polaritonic materials, we uncovered two types of topological phase transition (between closed and open types of dispersion surfaces) which occur at the mid-infrared range. These topological phase transitions correspond to transverse magnetic waves and result in a striking and resonant radiation enhancement of subwavelength electric dipole which is embedded into the wire medium and oriented parallel to the optical axis. We showed that a broadband (and huge) enhancement is achievable by overlapping the corresponding resonance bands. Also, we revealed topological phase transition for transverse electric waves. Here, the suggested wire medium is composed of parallel wires which have high positive dielectric constant. In our previous studies, wires possess a negative dielectric constant. Interestingly, the highest resonant enhancement at the transition frequency corresponds to the subwavelength magnetic dipole.
|Julkaisun otsikon käännös||Wire Media for Enhancement of Radiative Heat Transfer and Spontaneous Emission|
|Tila||Julkaistu - 2017|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|