From Event: SPIE Commercial + Scientific Sensing and Imaging, 2018
Current technologies for optical gas imaging use one of the following methods: (1) single band-pass filter, which dictate a “man in the loop” for detection; (2) bi-channel sensors that need allocation of half of the detecting area for each band; (3) low rate and/or highly expensive multi/hyperspectral sensors. We suggest a low-cost, fast electrically-switchable notch-filter, based on liquid crystal (LC) in an infrared (IR) transparent cell which enables dynamic dual band sensing on the entire detector area.
We utilize fundamental properties of the LC: its molecular IR absorption bands (rovibrational modes) are overlapping those of gaseous (hydrocarbons, carbon dioxide , and more), and the transmittance of these bands depends on the orientation of the LC molecules relative to the polarization of the incident light (ordinary or extraordinary), Applying voltage on the LC cell affects the molecules' orientation, and therefore significantly changes the band transmittance. The high frequency response of LC cells to the electrical field enable detecting dynamic gas plumes.
We proved this concept experimentally using custom made polyamide-coated Germanium cells and a commercial LC, E7. The spectral response, measured by a fast spectro-radiometer, for wavelengths between 2 to 14 micrometer, shows several absorption lines overlapping those of hydro-carbonates hazardous and greenhouse gaseous that require monitoring, and we demonstrated the detection of the refrigerant gas R-134a. We are currently preforming an experimental imaging setup for gas detection based on this method, and the results will be presented in this talk.
Karni Wolowelsky, Amir Gil, Moshe Elkabets, and Carmel Rotschild, "Gas detection using absorption properties of liquid crystals (Conference Presentation)," Proc. SPIE 10661, Thermosense: Thermal Infrared Applications XL, 1066102 (Presented at SPIE Commercial + Scientific Sensing and Imaging: April 17, 2018; Published: 14 May 2018); https://doi.org/10.1117/12.2299834.5783306356001.
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