W. Zhang, W. M. Zhu, E. E. M. Chia, Z. X. Shen, H. Cai, Y. D. Gu, W. Ser, and A. Q. Liu
Abstract
Wednesday, 30 April 2014
A pseudo-planar metasurface for a polarization rotator
W. Zhang, W. M. Zhu, E. E. M. Chia, Z. X. Shen, H. Cai, Y. D. Gu, W. Ser, and A. Q. Liu
Abstract
Tuesday, 29 April 2014
Electrothermally actuated microelectromechanical systems based omega-ring terahertz metamaterial with polarization dependent characteristics
Chong Pei Ho, Prakash Pitchappa, Yu-Sheng Lin, Chia-Yi Huang, Piotr Kropelnicki and Chengkuo Lee
Abstract
We present the design, simulation, fabrication, and characterization of a continuously tunable Omega-ring terahertz metamaterial. The tunability of metamaterial is obtained by integratingmicroactuators into the metamaterial unit cell. Electrothermal actuation mechanism is used to provide higher tuning range, larger stroke, and enhanced repeatability. The maximum achieved tuning range for the resonant frequency is around 0.30 THz for the input power of 500 mW. This shows the potential of using electrothermally actuated microactuators based tunablemetamaterial design for application such as filters, absorbers, sensors, and spectral imagers.
Abstract
Friday, 25 April 2014
Structural and chemical modification of nontronite associated with microbial Fe(III) reduction: Indicators of “illitization”
Tae-hee Kooa, Young-nam Jangb, Toshihiro Kogurec, Jae Hoon Kimd, Byung Cheol Parkd, Don Sunwooe, Jin-wook Kima,
Abstract
The smectite-to-illite reaction, termed illitization, is a ubiquitous process in siliciclastic sedimentary environments and plays a significant role in biogeochemical cycling, plant nutrition, petroleum maturation/migration, particle dispersion–aggregation, and contaminant uptake. The change in the redox state of structural Fe in smectite as a consequence of microbial Fe respiration, in part, controls the physicochemical properties of smectite, but knowledge of the chemical/structural modification at a nanoscale, particularly the reversibility of the structure and K fixation at various Fe-redox states that could control illitization, is limited. The present study focused on measuring indicators of illitization at a nanoscale, utilizing transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS) and terahertz time-domain spectroscopy (THz-TDS), as well as chemical analysis, including cation exchange capacity (CEC) and Fe(III) reduction. Nontronite (NAu-1) of the size fraction less than 0.2 m was inoculated with the Fe-reducing bacteria Shewanella oneidensis MR-1 in M1 medium with structural Fe(III) in NAu-1 as the sole electron acceptor and Na-lactate as the electron donor. Incubation continued for up to 12 months in an anaerobic chamber. Two sets of microbial structural Fe(III) reduction experiments were performed, and then one set was re-oxidized by bubbling pure oxygen gas through an autoclaved needle for 24 hours. The reaction was stopped at various time points by freezing the samples with liquid N2. The extent of Fe(III) reduction reached 26%; 5% of residual Fe(II) was detected upon re-oxidation. TEM and X-ray diffraction (XRD) analyses confirmed the presence of an illite-like packet with collapsed 10-Å basal spacing in the Fe-reduced nontronite sample and permanently fixed K after long-term incubation. The proportion of K fixation in the interlayer increased with the extent of Fe(III) reduction and the amount of residual Fe(II) upon re-oxidation. The values of CEC increased corresponding to the extent of Fe(III) reduction; the CEC was not restored after re-oxidation, most likely due to the increase in residual Fe(II), secondary phase mineral (vivianite) precipitation, and permanent K fixation. Nondestructive THz-TDS depicted the chemical/structural modification of bioreduced nontronite and its reversibility. In the present study, true illite was not formed because of the low value of Al/Si; however, the progressive increase in K/(K + 2Ca) and Al/Si in the packets of 10-Å layers as well as the chemical/structural irreversibility upon re-oxidation with increasing incubation time strongly suggested illitization.
Abstract
Thursday, 24 April 2014
From mm-wave to THz: Scalable Filter Design for Ultra-low Cost Applications
W. J. Otter, F. Hu, J. Hazell and S. Lucyszyn
Abstract
Full Article:
Abstract
This paper shows simulated and measured results of ultra-low cost metal mesh filters in the millimetre-wave and THz bands. It provides a broad overview of the filters currently available and their suitability for ultra-low cost applications. We demonstrate scalable conventional metal mesh filters on standard 525 µm fused silica substrates. In additional, trapped-mode excitation is used to improve out-of-band rejection at higher frequencies. The measured results show that these filters are scalable in the THz range using cost-effective micromachining manufacturing. This potentially opens up the possibility of using metal mesh filters for ultra-low cost applications.
Full Article:
Thursday, 17 April 2014
Frequency Dependent Optical and Dielectric Properties of Zinc Sulfide in Terahertz Regime
Abstract
Frequency dependent optical and dielectric properties for several grades of chemical vapor deposited (CVD) zinc sulfide (standard, elemental, and multi-spectral) was performed using a terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.15 THz to 2.5 THz. Zinc sulfide exhibits low frequency vibrational modes characterized by the THz-TDS. Two low-frequency phonon resonance lines were revealed at 0.78, and 2.20 THz. These samples were also characterized in the GHz range using a backward wave oscillator (BWO) source quasi-optical spectrometer, and the data obtained by both approaches were compared. Experimental data were also compared with an undamped harmonic oscillator model. These results compare well with the literature values obtained using other methods.
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