| 1. |
- Anoshkin, Ilya V., et al.
(author)
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Freeze-Dried Carbon Nanotube Aerogels for High-Frequency Absorber Applications
- 2018
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:23, s. 19806-19811
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Journal article (peer-reviewed)abstract
- A novel technique for millimeter wave absorber material embedded in a metal waveguide is proposed. The absorber material is a highly porous carbon nanotube (CNT) aerogel prepared by a freeze-drying technique. CNT aerogel structures are shown to be good absorbers with a low reflection coefficient, less than -12 dB at 95 GHz. The reflection coefficient of the novel absorber is 3-4 times lower than that of commercial absorbers with identical geometry. Samples prepared by freeze-drying at -25 degrees C demonstrate resonance behavior, while those prepared at liquid nitrogen temperature (-196 degrees C) exhibit a significant decrease in reflection coefficient, with no resonant behavior. CNT absorbers of identical volume based on wet-phase drying preparation show significantly worse performance than the CNT aerogel absorbers prepared by freeze-drying. Treatment of the freeze-dried CNT aerogel with n- and p-dopants (monoethanolamine and iodine vapors, respectively) shows remarkable improvement in the performance of the waveguide embedded absorbers, reducing the reflection coefficient by 2 dB across the band.
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| 2. |
- Lioubtchenko, Dmitri V., et al.
(author)
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W-band phase shifter based on optimized optically controlled carbon nanotube layer
- 2017
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In: 2017 IEEE MTT-S International Microwave Symposium (IMS). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509063604 ; , s. 1188-1191
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Conference paper (peer-reviewed)abstract
- Phase shifting in a dielectric rod waveguide (DRW), loaded with carbon nanotube (CNT) layers of different thickness, was studied experimentally under light illumination in the frequency range of 75-110 GHz. The dependence of efficiency of the phase shifting, in terms of phase shift per light intensity and millimeter wave attenuation, on the optical transparency of the CNT-layer is investigated in this paper. The best result, a phase shifter of 0-15° with less than 0.1 dB additional signal loss in the W-band was achieved for a 95% transparent CNT layer at 23 mW/mm2 light intensity of a tungsten halogen lamp (main radiation spectrum is 550-680 nm). The overall insertion loss of the phase shifter including two DRW tapering sections serving as transitions to rectangular waveguides are 3 to 5 dB in the W-band, about 2 dB is attributed to the CNT DRW section. This comprises, for the first time, an optically-controlled CNT-based DRW phase shifter with phase shift and insertion loss levels suitable for practical applications.
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| 3. |
- Smirnov, Serguei, et al.
(author)
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Optically controlled dielectric properties of single-walled carbon nanotubes for terahertz wave applications
- 2018
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In: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 10:26, s. 12291-12296
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Journal article (peer-reviewed)abstract
- Materials with tunable dielectric properties are valuable for a wide range of electronic devices, but are often lossy at terahertz frequencies. Here we experimentally report the tuning of the dielectric properties of single-walled carbon nanotubes under light illumination. The effect is demonstrated by measurements of impedance variations at low frequency as well as complex dielectric constant variations in the wide frequency range of 0.1-1 THz by time domain spectroscopy. We show that the dielectric constant is significantly modified for varying light intensities. The effect is also practically applied to phase shifters based on dielectric rod waveguides, loaded with carbon nanotube layers. The carbon nanotubes are used as tunable impedance surface controlled by light illumination, in the frequency range of 75-500 GHz. These results suggest that the effect of dielectric constant tuning with light, accompanied by low transmission losses of the carbon nanotube layer in such an ultra-wide band, may open up new directions for the design and fabrication of novel Terahertz and optoelectronic devices.
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| 4. |
- Chicherin, Dmitry, et al.
(author)
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Analog-type millimeter-wave phase shifters based on MEMS tunable high-impedance surface and dielectric rod waveguide
- 2011
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In: International Journal of Microwave and Wireless Technologies. - : Cambridge University Press and the European Microwave Association. - 1759-0787. ; 3:5, s. 533-538
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Journal article (peer-reviewed)abstract
- Millimeter-wave phase shifters are important components for a wide scope of applications. An analog-type phase shifter for W-band has been designed, analyzed, fabricated, and measured. The phase shifter consists of a reconfigurable high-impedance surface (HIS) controlled by micro-electromechanical system (MEMS) varactors and placed adjacent to a silicon dielectric rod waveguide. The analog-type phase shift in the range of 0–32° is observed at 75 GHz whereas applying bias voltage from 0 to 40 V to the MEMS varactors. The insertion loss of the MEMS tunable HIS is between 1.7 and 5 dB, depending on the frequency.
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| 5. |
- Chicherin, Dmitry, et al.
(author)
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MEMS based high-impedance surface for millimetre wave dielectric rod waveguide phase shifter
- 2010
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In: European Microwave Week 2010, EuMW2010. - 9782874870163 ; , s. 950-953
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Conference paper (peer-reviewed)abstract
- Analogue type millimetre wave phase shifter based on a dielectric rod waveguide with adjacent MEMS tuneable high-impedance surface is proposed. Applying bias voltage to the MEMS varactors of the high-impedance surface allow controlling its effective impedance and consequently the phase factor of the propagation constant inside the waveguide. The measured phase difference between the phase shifter with adjacent high-impedance surface and phase shifter with low impedance surface is up to 378°. The insertion loss of the high-impedance surface as phase shifting element at 80-90 GHz is 0.5-2.7 dB depending on the distance to the dielectric rod waveguide.
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| 6. |
- Chicherin, Dmitry, et al.
(author)
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MEMS tunable metamaterials surfaces and their applications
- 2010
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In: APMC 2010. - 9781424475902 - 9784902339215 ; , s. 239-242
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Conference paper (peer-reviewed)abstract
- Microelectromechanical systems (MEMS) are proposed as a technological solution for fabrication of metamaterials. This enables tunability of metamaterials effective properties and allows using metamaterials in wide range of applications. Low loss of the MEMS devices allows the metamaterials application to be extended to millimeter and submillimeter wave frequencies without compromising on performance. Electronic beam steering by MEMS tunable metamaterials at millimeter wavelength is considered and a prototype of a W band analog tunable phase shifter is demonstrated. The insertion loss of the fabricated MEMS tunable metamaterials surface varies from 0.7 dB to a maximum of 3.5 dB (at a resonance frequency). MEMS varactors have shown reliable and repeatable analog operation over 108 cycles.
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| 7. |
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| 8. |
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| 9. |
- Demchenko, P., et al.
(author)
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Study of optical pumping influence on carbon nanotubes permittivity in THz frequency range
- 2018
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In: Journal of Physics. - : Institute of Physics Publishing.
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Conference paper (peer-reviewed)abstract
- Equivalent complex permittivity of carbon nanotubes (CNT) was measured with/without light illumination at the frequency range of 0.2-1 THz. It was shown that we can tune the dispersion of the CNT complex conductivity during varying of optical pumping (wavelength of 980 nm). These results mean that CNT is perspective candidate for development of THz tunable attenuators and phase shifters.
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| 10. |
- Drozdz, Piotr, et al.
(author)
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W-band waveguide embedded nanofiber absorber
- 2021
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In: 2021 46Th International Conference On Infrared, Millimeter And Terahertz Waves (IRMMW-THZ). - : Institute of Electrical and Electronics Engineers (IEEE).
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Conference paper (peer-reviewed)abstract
- A novel type of absorber integrate into a standard WR-10 metal waveguide of is developed and measured. The absorber is based on alumina nanofibers covered with single or multi- carbon layers. Employing this technique for the CNT based absorbers offers a material with micron scales-oriented 3D microstructures, that is hybrid alumina nanofibers covered with carbon layer. These microstructures result in a low level of reflectance and good absorbance at 75-110 GHz frequency band due to the highly porous and low conductivity.
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