The Experts below are selected from a list of 145185 Experts worldwide ranked by ideXlab platform
Nuria Llombart - One of the best experts on this subject based on the ideXlab platform.
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holographic surface leaky wave lenses with circularly polarized focused Near Fields part ii experiments and description of frequency steering of focal length
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Darwin Blanco, Jose Luis Gomeztornero, Eva Rajoiglesias, Nuria LlombartAbstract:This paper reports experimental results which demonstrate the possibility to synthesize focused Near-Fields from a planar printed circuit which is fed with a simple coaxial probe. A prototype operating at 10 GHz has been manufactured and tested. As predicted by the theory described in the first part of this paper, high 75% focusing efficiency of circularly polarized Fields is obtained as a result of the proper modulation of the dimensions of the Archimedean-shaped printed slot. The designed coaxial feeding provides good matching (below -10 dB) in the entire frequency band. Finally, the scanning of the focal length as a function of the frequency is described in this paper, showing measured results and accurate theoretical explanation based on the frequency dispersion of the tapered leaky mode. This phenomenon is general for this type of two dimensional leaky-wave lenses, and might find many applications in imaging, sensing and heating.
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holographic surface leaky wave lenses with circularly polarized focused Near Fields part i concept design and analysis theory
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Jose Luis Gomeztornero, Darwin Blanco, Eva Rajoiglesias, Nuria LlombartAbstract:A novel concept of planar printed-circuit microwave lens, based on the transformation of a cylindrical surface wave into a modulated leaky wave, is presented in this paper. Inspired on holographic concepts, the TM0 cylindrical leaky wave is properly tapered across the two-dimensional surface by using an Archimedean-spiral shaped slotted printed-circuit, so that it is obtained a quadratic-phase, quasi-uniform amplitude aperture distribution which creates a highly focused circularly-polarized Near-field pattern. The first part of this paper describes the general analysis and synthesis methodology to obtain planar holographic lenses with high radiation and focusing efficiency. As an example, a printed-slot lens with 6λ0 diameter and focal ratio F/D = 1 operating at 10 GHz is designed and theoretically studied by simulations. The second part of the paper concentrates on the prototype and measurements.
Mostafa A. El-sayed - One of the best experts on this subject based on the ideXlab platform.
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Plasmonic Spheroidal Metal Nanoshells Showing Larger Tunability and Stronger Near Fields Than Their Spherical Counterparts: An Effect of Enhanced Plasmon Coupling
2015Co-Authors: Nasrin Hooshmand, Prashant K. Jain, Mostafa A. El-sayedAbstract:Two of the most tunable nanostructure geometries for nanoplasmonics include the metal nanoshell structure and the spheroidal geometry. We systematically investigate the effect of combining both geometries within the same nanostructure. Localized surface plasmon resonances (LSPRs) of spheroidal gold nanoshells are simulated as a function of their aspect ratio. The long-axis LSPR mode of a spheroidal nanoshell red shifts with decreasing shell thickness, similar to a spherical nanoshell. A higher aspect ratio spheroidal nanoshell shows a larger fractional LSPR red shift for the same thickness normalized by core dimensions. This is because coupling between the inner and outer surface plasmons of the nanoshell is stronger for the elongated spheroidal geometry as compared to that for the spherical case, increasing in strength with increasing aspect ratio. It is the result of this enhanced plasmon coupling that spheroidal nanoshells of aspect ratio 4 are over two times more tunable than spherical nanoshells. Also, the plasmonic field enhancement is an order of magnitude larger for the spheroidal nanoshells of aspect ratio 4 as compared to spherical nanoshells. These effects observed in the spheroidal nanoshell are analogous to those in a dimer of spheroidal nanopaticles
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Plasmonic Spheroidal Metal Nanoshells Showing Larger Tunability and Stronger Near Fields Than Their Spherical Counterparts: An Effect of Enhanced Plasmon Coupling
Journal of Physical Chemistry Letters, 2011Co-Authors: Nasrin Hooshmand, Prashant K. Jain, Mostafa A. El-sayedAbstract:Two of the most tunable nanostructure geometries for nanoplasmonics include the metal nanoshell structure and the spheroidal geometry. We systematically investigate the effect of combining both geometries within the same nanostructure. Localized surface plasmon resonances (LSPRs) of spheroidal gold nanoshells are simulated as a function of their aspect ratio. The long-axis LSPR mode of a spheroidal nanoshell red shifts with decreasing shell thickness, similar to a spherical nanoshell. A higher aspect ratio spheroidal nanoshell shows a larger fractional LSPR red shift for the same thickness normalized by core dimensions. This is because coupling between the inner and outer surface plasmons of the nanoshell is stronger for the elongated spheroidal geometry as compared to that for the spherical case, increasing in strength with increasing aspect ratio. It is the result of this enhanced plasmon coupling that spheroidal nanoshells of aspect ratio 4 are over two times more tunable than spherical nanoshells. Als...
Junjie Liu - One of the best experts on this subject based on the ideXlab platform.
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Near Fields of gasper jet flows with wedged nozzle in aircraft cabin environment
Building and Environment, 2017Co-Authors: Zhanqi Tang, Nan Jiang, Yong Guo, Xujia Cui, Shen Dai, Junjie LiuAbstract:Abstract The geometry of the outlet nozzle has a direct effect on the Near Fields of turbulent jets. An attempt is made to modify the gasper jet nozzle by adding wedges of different sizes. The Near Fields of the wedged gasper jets are measured by a hot-wire anemometer. For the with-wedges cases, the mean velocity exhibits a more rapid decay in the axial direction, and the turbulent intensity is attenuated after the “second potential core.” The higher-order statistics, such as skewness and kurtosis, indicate no obvious difference in the downstream region. As the turbulent structures are formed, the energy spectra indicate that their average energy increases under the wedges' perturbation. Then, the anti-axial-symmetry of the transition flows is observed in two characteristic planes. The mean velocity does not exhibit a significant difference between the two planes, but the turbulent intensity in the perturbed plane embodies the wedges' influence. The wedged nozzle affects the energy intensity and diffusion angle of the turbulent structures in the perturbed plane, and the difference from the unperturbed plane is confirmed by the discrepancy spectra. Furthermore, the anti-axial-symmetry is characterized by turbulent intermittency and entrainment. The turbulent intermittency in the perturbed plane performs with a lower value in the Near-nozzle region, and evolves into axial-symmetry in the further downstream region. For turbulent entrainment, the entrainment ratio manifests that wedged nozzle reduces the flow mass in the entrainment of ambient air in the downstream region.
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turbulent characteristics in the Near Fields of gasper jet flows in an aircraft cabin environment intermittently energetic coherent structures
Building and Environment, 2017Co-Authors: Zhanqi Tang, Nan Jiang, Yong Guo, Xujia Cui, Shen Dai, Junjie LiuAbstract:Abstract In an aircraft cabin environment, a gasper nozzle is a type of air conditioning and part of the air-recirculation system, and its Near Fields are dominated by intermittently energetic coherent structures (IECSs). Based on the percentage of dissatisfied (PD) model, the turbulent intensity and the intermittent frequency of IECSs are investigated in this study as main factors of draught sensation. The gasper jet flow Fields at several Reynolds numbers (Re = 2000～17,047) are determined using a hot-wire anemometer, and a round-pipe jet flow is used for comparison. The mean velocity and streamwise gradient exhibit self-similarity after the reattachment point. Pre-multiplied energy spectra provide the energetic length scales of the intermittent coherent structures. Then, continuous wavelet transform is employed to detect the IECSs. The average waveform indicates that along the axis direction, the IECSs exhibit unstable coherence, symmetric and oscillating waveforms. All of these signatures are independent of the nozzle geometry and display an earlier emergence with an increase in Re. Furthermore, the mean turbulent intensity and waiting time of the IECSs are explored. Compared with the round-pipe jet, the IECSs in the gasper jet flows have a lower mean turbulent intensity. The analysis of the probability density function indicates that the waiting time between the successive IECSs is almost twice that of the energetic length scale, and the dimensionless result presents that the intermittent frequency has the self-similar distribution for all the cases in this study.
Jose Luis Gomeztornero - One of the best experts on this subject based on the ideXlab platform.
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holographic surface leaky wave lenses with circularly polarized focused Near Fields part ii experiments and description of frequency steering of focal length
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Darwin Blanco, Jose Luis Gomeztornero, Eva Rajoiglesias, Nuria LlombartAbstract:This paper reports experimental results which demonstrate the possibility to synthesize focused Near-Fields from a planar printed circuit which is fed with a simple coaxial probe. A prototype operating at 10 GHz has been manufactured and tested. As predicted by the theory described in the first part of this paper, high 75% focusing efficiency of circularly polarized Fields is obtained as a result of the proper modulation of the dimensions of the Archimedean-shaped printed slot. The designed coaxial feeding provides good matching (below -10 dB) in the entire frequency band. Finally, the scanning of the focal length as a function of the frequency is described in this paper, showing measured results and accurate theoretical explanation based on the frequency dispersion of the tapered leaky mode. This phenomenon is general for this type of two dimensional leaky-wave lenses, and might find many applications in imaging, sensing and heating.
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holographic surface leaky wave lenses with circularly polarized focused Near Fields part i concept design and analysis theory
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Jose Luis Gomeztornero, Darwin Blanco, Eva Rajoiglesias, Nuria LlombartAbstract:A novel concept of planar printed-circuit microwave lens, based on the transformation of a cylindrical surface wave into a modulated leaky wave, is presented in this paper. Inspired on holographic concepts, the TM0 cylindrical leaky wave is properly tapered across the two-dimensional surface by using an Archimedean-spiral shaped slotted printed-circuit, so that it is obtained a quadratic-phase, quasi-uniform amplitude aperture distribution which creates a highly focused circularly-polarized Near-field pattern. The first part of this paper describes the general analysis and synthesis methodology to obtain planar holographic lenses with high radiation and focusing efficiency. As an example, a printed-slot lens with 6λ0 diameter and focal ratio F/D = 1 operating at 10 GHz is designed and theoretically studied by simulations. The second part of the paper concentrates on the prototype and measurements.
Darwin Blanco - One of the best experts on this subject based on the ideXlab platform.
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holographic surface leaky wave lenses with circularly polarized focused Near Fields part ii experiments and description of frequency steering of focal length
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Darwin Blanco, Jose Luis Gomeztornero, Eva Rajoiglesias, Nuria LlombartAbstract:This paper reports experimental results which demonstrate the possibility to synthesize focused Near-Fields from a planar printed circuit which is fed with a simple coaxial probe. A prototype operating at 10 GHz has been manufactured and tested. As predicted by the theory described in the first part of this paper, high 75% focusing efficiency of circularly polarized Fields is obtained as a result of the proper modulation of the dimensions of the Archimedean-shaped printed slot. The designed coaxial feeding provides good matching (below -10 dB) in the entire frequency band. Finally, the scanning of the focal length as a function of the frequency is described in this paper, showing measured results and accurate theoretical explanation based on the frequency dispersion of the tapered leaky mode. This phenomenon is general for this type of two dimensional leaky-wave lenses, and might find many applications in imaging, sensing and heating.
-
holographic surface leaky wave lenses with circularly polarized focused Near Fields part i concept design and analysis theory
IEEE Transactions on Antennas and Propagation, 2013Co-Authors: Jose Luis Gomeztornero, Darwin Blanco, Eva Rajoiglesias, Nuria LlombartAbstract:A novel concept of planar printed-circuit microwave lens, based on the transformation of a cylindrical surface wave into a modulated leaky wave, is presented in this paper. Inspired on holographic concepts, the TM0 cylindrical leaky wave is properly tapered across the two-dimensional surface by using an Archimedean-spiral shaped slotted printed-circuit, so that it is obtained a quadratic-phase, quasi-uniform amplitude aperture distribution which creates a highly focused circularly-polarized Near-field pattern. The first part of this paper describes the general analysis and synthesis methodology to obtain planar holographic lenses with high radiation and focusing efficiency. As an example, a printed-slot lens with 6λ0 diameter and focal ratio F/D = 1 operating at 10 GHz is designed and theoretically studied by simulations. The second part of the paper concentrates on the prototype and measurements.
