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There are two main infrared (IR) spectrophotometers: dispersive IR spectrometers and Fourier transform infrared (FTIR) spectrometers. In a dispersive IR spectrometer, a beam of infrared radiation produced by a hot wire is divided into two parallel equal-intensity beams using mirrors. One beam passes through the sample, while another is a reference beam. The beams then move through the monochromator, which separates the radiations into a continuous spectrum of different frequencies. The...
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When electromagnetic radiation passes through a material, atoms or molecules transition from a lower to a higher energy state by absorbing radiation corresponding to the energy difference between the two states. The absorption of infrared (IR) radiation causes transitions between vibrational energy levels in a molecule. Therefore, IR spectroscopy is a useful analytical tool for determining the molecular structure of molecules.
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IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the...
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The absorbance of UV and visible (UV–visible) radiations is measured using a UV–visible spectrophotometer. Deuterium lamps, which emit UV radiation, and tungsten lamps, which produce radiation in the visible region, are used as light sources in UV–visible spectrophotometers. A monochromator or prism is used for diffraction grating, i.e., to split the incoming radiation into different wavelengths. A system of slits is used to focus the desired wavelength on the sample cell.
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Virtual Spectral Selectivity in a Modulated Thermal Infrared Emitter with Lock-In Detection.

David Santalices1, Juan Meléndez1, Susana Briz1

  • 1LIR-Infrared Laboratory, Department of Physics, Universidad Carlos III de Madrid, 28911 Leganés, Spain.

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Summary
This summary is machine-generated.

Researchers developed virtual emitters using modulated MEMS thermal emitters and lock-in amplifiers. This technique allows for spectral selectivity, enabling the differentiation of gases like CO2 and CH4.

Keywords:
CO2Fourier seriesblackbodygas detectionlock-in amplifiermethaneoptical gas sensorspectral selectivitythermal emittervirtual emitter

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Area of Science:

  • * Microelectromechanical Systems (MEMS)
  • * Optical Gas Sensing
  • * Lock-in Amplification

Background:

  • * MEMS-based thermal emitters offer a low-power solution for optical gas sensors.
  • * Their low thermal mass allows for easy modulation and detection with lock-in amplifiers.
  • * Traditional methods may lack spectral selectivity for complex gas mixtures.

Purpose of the Study:

  • * To demonstrate the theoretical and experimental basis of virtual emitters generated from modulated thermal emitters.
  • * To explore the spectral profiles of signals obtained using different reference signals with lock-in amplification.
  • * To showcase a novel application for enhanced gas sensing selectivity.

Main Methods:

  • * Theoretical analysis using Fourier series expansion of emitted radiance.
  • * Experimental validation using a modulated infrared (IR) emitter and an IR camera with six spectral filters.
  • * Lock-in amplification implemented via software for signal processing.

Main Results:

  • * Confirmed that modulated thermal emitters produce different spectral profiles based on the reference signal frequency.
  • * Demonstrated that distinct spectral signatures, unique to each harmonic, can be retrieved.
  • * Successfully distinguished between CO2 and CH4 gases using multiple virtual emitters.

Conclusions:

  • * The concept of virtual emitters provides a new method for spectral analysis in modulated thermal systems.
  • * This technique enhances spectral selectivity, crucial for accurate gas detection.
  • * Virtual emitters offer a promising pathway for developing advanced, selective optical gas sensors.