Infrarouge lointain | EPFL Graph Search

L'infrarouge lointain (IRL) est une région d'infrarouge du spectre électromagnétique ayant une fréquence inférieure à celle de la lumière visible et aux autres bandes d'infrarouge. L'infrarouge lointain se définit souvent comme tout rayonnement avec une longueur d'onde entre 15 micromètres (µm) et 1 mm (qui correspond à une plage entre 20 THz et 300 GHz). Différentes sources préfèrent d'autres délimitations pour son spectre ; par exemple, parfois les astronomes définissent l'infrarouge lointain dans une fourchette entre 25 µm et 350 µm. La norme ISO 20473:2007 définit quant à elle l'infrarouge lointain à la fourchette comprise entre 50 µm et 1 mm. La lumière visible représente une plage de rayonnements dont les longueurs d'onde se trouvent entre 400 nm et 700 nm, ce qui signifie que les photons du rouge lointain ont moins d'énergie que ceux de la lumière visible. Applications Astronomie Les objets dont la température est comprise entre 5 K et 340 K émettront

Infrared spectra of jennite and tobermorite from first-principles

Alfredo Pasquarello, Gabriele Sclauzero, Alexandre Vidmer

The infrared absorption spectra of jennite, tobermorite 14 angstrom, anomalous tobermorite 11 angstrom, and normal tobermorite 11 angstrom are simulated within a density-functional-theory scheme. The atomic coordinates and the cell parameters are optimized resulting in structures which agree with previous studies. The vibrational frequencies and modes are obtained for each mineral. The vibrational density of states is analyzed through extensive projections on silicon tetrahedra, oxygen atoms, OH groups, and water molecules. The coupling with the electric field is achieved through the use of density functional perturbation theory, which yields Born effective charges and dielectric constants. The simulated absorption spectra reproduce well the experimental spectra, thereby allowing for a detailed interpretation of the spectral features in terms of the underlying vibrational modes. In the far-infrared part of the absorption spectra, the interplay between Ca and Si related vibrations leads to differences which are sensitive to the calcium/silicon ratio of the mineral. (C) 2014 Elsevier Ltd. All rights reserved.

Elsevier2014

Numerical modeling of planar periodic structures in electromagnetics

Katarina Blagovic

Periodic structures, such as frequency-selective surfaces (FSSs) and photonic band-gap (PBG) materials, exhibit total reflection in specific frequency bands while total transmission in other bands. They find numerous applications in a large field of the electromagnetic (EM) spectrum. For example, in the microwave region, they are used to increase the efficiency of reflector antennas. In the far-infrared region they are used in designing polarizers, beam splitters, mirrors for improving the pumping efficiency in molecular lasers, as components of infrared sensors, etc. To set a solid basis for the analysis of periodic structures, we have first studied the most commonly used technique, the integral equation (IE) solved by the method of moments (MoM). IE-MoM is particularly well-suited for the analysis of printed planar structures. In any IE-MoM numerical implementation the efficient evaluation of the corresponding Green's functions (GFs) is of paramount importance. This is especially true for IE analysis of periodic structures whose GFs are slowly converging infinite sums. The systematic study of existing acceleration algorithms of general and specific types, used to accelerate the evaluation of periodic GFs, has been performed. We propose a new and efficient method for acceleration of multilayered periodic GFs that successfully combines the advantages of Shanks' and Ewald's transform. In structures operating at higher frequencies (thin films in millimeter and submillimeter wave bands or with self supporting metallic plates) the thickness of metallic screens must be taken into account. The existing full-wave approaches for simulating these structures double the number of unknowns as compared to that one of the zero-thickness case. Moreover, the thick aperture problem asks for the computation of cavity Green's functions, which is a difficult and time-consuming task for apertures of arbitrary cross-sections. This thesis addresses the problem of scattering by periodic apertures in conducting screens of finite thickness by introducing an approximate and computationally efficient formulation. This formulation consists in treating the thick aperture as an infinitely thin one and in using the correction term in integral equation kernel that accounts for the screen thickness. The number of unknowns remains the same as in the zero-thickness screens and evaluation of complicated cavity Green's functions is obviated, which yields computationally efficient routines.

EPFL2006

Far-infrared sensor with LPCVD-deposited low-stress Si-rich nitride absorber membrane—Part 2. Thermal property and sensitivity

Nico de Rooij, Fabio Jutzi

This is the second part of two articles reporting investigation on a thermal-detector-type far-infrared sensor operating in the 8–14 µm wavelength region using Low-Pressure Chemical Vapor Deposition (LPCVD) deposited low-stress Si-rich nitride (SiN) membrane as its thermal absorber. The use of the SixNy membrane material as a far-infrared radiation absorber has been reported in many papers, there are still few reports addressing its fundamental optical absorption property at thiswavelength region, in relation with its thermal properties, utilized in an infrared sensing device. After dealing with optical absorptivity of suchmembrane in the first paper, this second article deals with the thermal property, aswell as the overall sensitivity issue of the sensor. In this report, similarly, a combination of analytical modelling, numerical simulation, and experimental characterisation is carried out. The issue of scaling down is also addressed. Results show that the thermal sensitivity depends on the membrane size. A 1000µm×1000µm will achieve 80 K/(Wcm−2), while membrane as small as 10µm×10µm has only 0.15–0.3 K/(Wcm−2).

2009

Numerical modeling of planar periodic structures in electromagnetics

Katarina Blagovic

EPFL2006