1,721,041 research outputs found
Polarization Independent Unidirectional Scattering with Turnstile Nanoantennas
Full text linkWe study the scattering behavior of a dielectric cross-dipole nanoantenna in the near-infrared spectral range when it is excited by a circular polarized plane wave. We theoretically demonstrate, for optimized geometrical parameters of the proposed turnstile structure, the possibility to simultaneously obtain a unidirectional scattering and a specific circular polarization of the scattered field. Our results open new functionalities for metamaterials and optical nanoantennas
Impact of amplifier nonlinearities on OFDM transmission system performance
No full textThe power spectral density of an orthogonal frequency-division multiplexing (OFDM) signal after a saturated high-power amplifier (HPA) is analytically derived. The distortion of the HPA-processed OFDM signal is defined, and its power spectrum is computed. The spectra of the signal and of the distortion are used to get an accurate estimate of the bit-error rate of an OFDM transmission system and to derive compensation at the receiver, which leads to performance improvement
Comprehensive Analysis of Graphene Geometric Diodes: Role of Geometrical Asymmetry and Electrostatic Effects
Full text linkComprehensive Analysis of Graphene Geometric Diodes: Role of Geometrical Asymmetry and Electrostatic Effects
Full text linkA self-consistent Monte Carlo/3-D Poisson simulator has been developed to analyze the current asymmetry in graphene geometric diodes. The model couples ballistic transport in the graphene layer with 3-D electrostatics in the graphene and oxide substrate. Results are given in terms of transmission coefficients and currents at the two terminals of the diode. We prove that while the current asymmetry is mainly induced by ballistic transport in the asymmetric structure, the electrostatics plays a relevant role that tends to substantially counterbalance the geometrical effect
Lossless tapers, Gaussian beams, free-space modes: standing waves versus through-flowing waves
No full textNew Delhi - Indi
Nano-antenna array for high efficiency sunlight harvesting
Full text linkSolar rectennas are promising devices for energy harvesting. Capability of rectennas to convert incident light into useful energy depends on the antenna efficiency, that is the ratio between the power transferred to the load vs the incoming power. In this work, we first emphasize that for the efficiency to be calculated accurately, antennas need to be treated as receiving devices, not as transmitting ones. Then, we propose an arrangement of antennas that differs from those published so far in three respects: (1) the proposed arrangement is formed by an array of nano-antennas with sub-wavelength inter-element spacing, (2) it comprises a reflecting mirror, and (3) it allows for dual polarization operation. Through numerical simulations, we show that the small lattice pitch we use is responsible for frequency flattening of the lattice impedance over the whole solar spectrum, eventually allowing for excellent matching with the antennas’ loads. Also, the small pitch allows for a smooth dependence of the receiving efficiency on the angle of incidence of sunlight. Finally, we show numerically that the reflecting mirror also allows for an almost complete cancellation of light scattered by the receiving antennas. The final result is a polarization insensitive receiving theoretical efficiency larger than 70% over the whole 300-3000 nm spectral range, with a less than 10% energy wasting due to back-scattering of sunlight
Lossless tapers, Gaussian beams, free-space modes: Standing waves versus through-flowing waves
No full textModeling and optimization of graphene ballistic rectifiers
No full textWe present a simulation framework based on the combination of Monte Carlo transport and Landauer-Buttiker formalism to model and optimize ballistic rectifiers exploiting the long mean-free-path of graphene. The influence on the responsivity (i.e. the induced voltage normalized by the impinging power) of the main geometrical parameters, of bias and of different scattering mechanisms is critically analyzed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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