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Erratum published on 17 December 2018, see Sensors 2018, 18(12), 4459.
Open AccessArticle

Error Sources and Distinctness of Materials Parameters Obtained by THz-Time Domain Spectroscopy Using an Example of Oxidized Engine Oil

1
Terahertz Systems Technology Group, Department of Electrical Engineering and Information Technology, Technische Universitat Darmstadt, Merckstr. 25, 64283 Darmstadt, Germany
2
Plant, Soil and Agricultural Systems, Southern Illinois University, MC 4415, Carbondale, IL 62901, USA
3
Department of Agricultural Machines and Equipment, College of Agriculture, Baghdad University, Baghdad 10071, Iraq
*
Authors to whom correspondence should be addressed.
Sensors 2018, 18(7), 2087; https://doi.org/10.3390/s18072087
Received: 9 May 2018 / Revised: 4 June 2018 / Accepted: 25 June 2018 / Published: 29 June 2018
(This article belongs to the Special Issue THz Imaging Systems and Sensors)
Gasoline engine oil (SAE 5W-20) was subjected to thermal oxidization (TO) for four periods of time (0 h, 48 h, 96 h and 144 h) and exposed to THz-time domain spectroscopy (TDS) measurement. Error contributions from various error sources, such as repeatability errors, assembly errors of the probe volume and errors caused by the TDS system were evaluated with respect to discernibility and significance of measurement results. The most significant error source was due to modifications of the TDS setup, causing errors in the range of 0.13% of the refractive index for samples with a refractive index around 1.467 and a probe volume length between 5 and 15 mm at 1 THz. The absorption coefficient error was in the range of 8.49% for an absorption around 0.6 cm−1. While the average of measurements taken with different setup configurations did not yield significant differences for different TO times, a single, fixed setup would be able to discern all investigated oil species across the entire frequency range of 0.5–2.5 THz. The absorption coefficient measurement showed greater discernibility than the measurement of the refractive index. View Full-Text
Keywords: Terahertz spectroscopy; optical path length; engine lubrication oil; error sources; thermal oxidation Terahertz spectroscopy; optical path length; engine lubrication oil; error sources; thermal oxidation
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Méndez Aller, M.; Abdul-Munaim, A.M.; Watson, D.G.; Preu, S. Error Sources and Distinctness of Materials Parameters Obtained by THz-Time Domain Spectroscopy Using an Example of Oxidized Engine Oil. Sensors 2018, 18, 2087.

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