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Using Terahertz Time-Domain Spectroscopy to Discriminate among Water Contamination Levels in Diesel Engine Oil
摘要： Terahertz time-domain spectroscopy (THz-TDS) in the range of 0.5 to 2.0 THz was evaluated for discriminating among water contamination levels (0%, 0.1%, and 0.2%) in diesel engine oil (SAE 15W-40). The absorption coefficient demonstrated potential to discriminate among the three water contamination levels with significant differences among all three levels across the 1.111 to 1.332 THz and 1.669 to 1.934 THz ranges. At each of these frequency ranges, each water contamination level was significantly different from the other two. The 0% water contamination level had the lowest absorption coefficient, while 0.2% water had the highest absorption coefficient. The refractive index demonstrated greater potential to discriminate among water contamination levels with significant differences among all three water levels across the 0.5 to 1.5 THz range. The refractive index of 0% water was the lowest and 0.2% water was the highest across the THz range. Linear regression analysis of the refractive index as a predictor of water contamination level yielded a highly significant equation (p < 0.0001, R2 = 0.99, RMSE = 0.01) when using the refractive indices at 0.5 THz. The refractive indices of these oil samples were promising for discrimination of water contamination. THz spectroscopy should be evaluated for discriminating other engine oil contaminants.
关键词： Terahertz spectroscopy,Diesel,Engine oil,Water contamination
更新于2025-09-09 09:28:46
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Plasmon confinement by carrier density modulation in graphene
摘要： We investigate plasmon resonances in graphene with periodic carrier density modulation. The period is 8 μm, and each period consists of 1.7- and 6.3-μm-wide ribbons with di?erent density. Using terahertz spectroscopy, we show two plasmon modes with their electric ?eld mostly localized in the 1.7- or 6.3-μm-wide ribbon arrays. We also show that plasmons are excited only in one of the micro-ribbon arrays when the Fermi energy of the other micro-ribbon array is set close to the charge neutrality point. These results indicate that plasmons can be con?ned by the carrier density modulation. ? 2018 The Japan Society of Applied Physics
关键词： carrier density modulation,plasmon resonances,graphene,terahertz spectroscopy
更新于2025-09-04 15:30:14
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Active Thermal Control of 5 nm Gap Terahertz Antennas
摘要： Metallic nanostructures are combined with various active materials for electrical, optical, and thermal modulations of their optical properties. In particular, for the thermal modulation, deformation of metallic nanostructures at high temperatures limits the applications to relatively low temperatures, where thermal expansion of metals is negligible. Here, a unique regime is reported where terahertz (THz) waves transmitting through 5 nm wide slot antennas can be significantly modulated via controlled thermal expansion of metals without active materials. The normalized amplitude is modulated by 20% and the resonant frequency by 22% at an elevated temperature of 150 °C, indicating a decrease in the gap width by 50%. The extreme width-to-length ratio of the THz slot antennas compensates the small thermal expansion coefficient of metals, enabling the gap width to be considerably changed. COMSOL simulation and coupled-mode method (CMM) calculation quantitatively support the experimental data. This works suggests a new possibility of thermally active metallic nanostructures.
关键词： metamaterials,active modulation,terahertz spectroscopy,nanogaps,thermal expansion
更新于2025-09-04 15:30:14
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Encyclopedia of Spectroscopy and Spectrometry || Terahertz Imaging and Spectroscopy Methods and Instrumentation
摘要： Terahertz Imaging and Spectroscopy Methods and Instrumentation
关键词： Instrumentation,Terahertz,Spectroscopy,Imaging
更新于2025-09-04 15:30:14