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The availability of low cost, integrated, radiation sources in the infrared with a narrow-band emission spectrum is of great importance in a variety of applications such as infrared sensing, thermophotovoltaics, radiation cooling, and thermal circuits [1]. An easy way to obtain infrared radiation is to take advantage of thermal emission form a heated body. However, the spectral and directional control of thermal emission is a challenging task due to the incoherent behavior (both spatially and temporally) of the thermal radiation. We investigate the possibility of spatially and spectrally controlling the thermal infrared emission by exploitation of the Yagi–Uda antenna design. Hybrid antennas composed of alternating SiC and Au elements are considered. As a starting point we considered SiC dipole antennas as feeders, operating at 400 K. The length and section of the rods have between designed in order to have a single resonance in the wavelength range around 12 micron. We used Au elements to work as the reflector and the directors elements. Indeed, gold is a low emissivity material and the mirror and directors are supposed to be slightly detuned with respect to the emitting wavelength. However, all the elements are at the same temperature and contribute to the final bandwidth of emission and efficiency. The numerical study was performed by modifying a previously developed model based on the fluctuational electrodynamics approach and on the discretization of the resulting volume integral equation to calculate relative emissivity and spatial emission pattern of nanoparticle ensembles [2]. We show that despite of the chaotic nature of thermal radiation it is possible to obtain efficient highly directional and narrow bandwidth antennas in the mid to far IR by adapting the Yagi-Uda scheme with a combination of metallic and polar materials. We compare the performances obtained with hybrid antennas with respect to all metallic antennas and discuss how to improve specific features for different kind of applications.
References
[1] A. Lochbaum et al. “On-Chip Narrowband Thermal Emitter for Mid-IR Optical Gas Sensing”, ACS Photonics, 4, 1371−1380, (2017)
[2] M. Centini et al., “Midinfrared thermal emission properties of finite arrays of gold dipole nanoantennas”, Phys. Rev. B. 92 205411 (2015)
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