Browsing by Author "Ivanov S."

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    Elucidation of the contribution of modified titania films over the performance of thin film humidity sensors
    (2013-05-21) Kozhukharov S.; Nenova Z.; Nenov T.; Ivanov S.; Machkova M.
    The present research focuses on comparative measurements of the influence of complex additives on the sensitivity of humidity sensors, prepared by the sol-gel metrhod. Three different dopants were added to the primary mixture in order to improve the properties of the films, expressed in water uptake capability, as follows: Bismuth acetate (CH3COO)3Bi, Vanadium-2,4 pentadionate (C15H21O6V), and Sodium tert-butoxide (CH3)3CONa. The properties of the obtained sensors were evaluated by determination of their electrical resistances in a chamber with controlled humidity. As a result, it was experimentally established that the most significant positive effect over both the increase of sensitivity and the measurement range enlargement come from V(III)-2,4 pentadionate with Sodium tert-butoxide.
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    Humidity Sensing Elements Based on Silica-Graphene Surface Layers
    (2024-01-01) Nedev N.; Nenova Z.; Kozhukharov S.; Ivanov S.; Nenov T.
    The paper presents humidity sensing elements based on silica-graphene surface layers, prepared via a sol-gel method. The samples were sintered at temperatures of 400 °C, 600 °C and 800 °C. Tetraethoxysilane was used as a precursor of SiO2 and as a dopant - graphene aggregates of nanoplatelets. A description of the sample preparation procedure is provided. Using a precise impedance analyzer and a calibrator for humidity and temperature, the changes in their resistance R were investigated with variations in relative humidity in the range of 30% to 90% at a temperature of 25 °C and at a frequency of 20 Hz. Morphological observations and map data analyses were carried out by Scanning Electron Microscopy (SEM) and Energy Dispersion Spectroscopy (EDX). The developed sensor elements have a good sensitivity to the humidity, and the resistance change reaches two orders of magnitude. Additions of graphene improve the sensitivity of the elements. The characteristics of the sensing elements at different sintering temperatures and different amounts of graphene dopant were modeled using an artificial neural network.