652 research outputs found
Analytic Design Techniques for MPT Antenna Arrays
Solar Power Satellites (SPS) represent one of the most interesting technological opportunities to provide large scale, environmentally clean and renewable energy to the Earth [1]‐[3]. A fundamental and critical component of SPSs is the Microwave Power Transmission (MPT) system, which is responsible for the delivery of the collected solar power to the ground rectenna [2]. Towards this end, the MPT array must exhibit a narrow main beam width (), a high beam efficiency (BWBE), and a low peak sidelobe level (). Moreover, reduced realization costs and weights are also necessary [3]. To reach these contrasting goals, several design techniques have been investigated including random methods [4] and hybrid deterministic‐random approaches [2][3]. On the contrary, well‐established design tools based on stochastic optimizers [5][6] are difficult to be employed, due to their high computational costs when dealing with large arrays as those of interest in SPS [3]
Generalized Analysis and Unified Design of EM Skins
A generalized formulation is derived for the analysis of the field
manipulation properties of electromagnetic skins (EMSs) in the working regimes
of interest for wireless communications. Based on such a theoretical framework,
a unified method for the design of anomalous-reflecting and focusing EMSs is
presented. Representative results, from a wide set of numerical experiments,
are reported and validated with full-wave HFSS simulations to give the
interested readers some insights on the accuracy, the effectiveness, and the
computational efficiency of the proposed analysis/synthesis tools
Optically-Transparent EM Skins for Outdoor-to-Indoor mm-Wave Wireless Communications
Optically-transparent opportunistic electromagnetic skins (OTO-EMSs) are
proposed to enable outdoor-to-indoor (O2I) millimiter-wave (mmW) wireless
communications with existing windows/glass-panels. More in detail, static
passive EMSs consisting of optically-transparent conducting patterned layers
attached to standard glass-panels are designed. Towards this end, both the
phase coverage and the optical transparency of a meshed copper-based meta-atom
printed on a non-dedicated insulated glass substrate are optimized.
Successively, the feasibility of OTO-EMSs able to support mmW high-efficiency
O2I transmissions along non-Snell refraction directions is numerically
demonstrated
Features and Potentialities of Static Passive EM Skins for NLOS Specular Wireless Links
The ability of passive flat patterned electromagnetic skins (EMSs) to
overcome the asymptotic limit of the total path attenuation (TPA) of flat
metallic reflectors of arbitrary size in non-line-of-sight (NLOS) specular
wireless links is assessed. Closed-form expressions for the achievable TPA in
EMS-powered NLOS links as well as the condition on the panel size of
EMS-screens to improve the performance of flat passive conductive screens
(PCSs) with the same aperture are derived and numerically validated by
considering different incidence angles, screen apertures, transmitter/receiver
distances, antenna gains, meta-atom geometries, and carrier frequencies
Memory-Enhanced Dynamic Evolutionary Control of Reconfigurable Intelligent Surfaces
An innovative evolutionary method for the dynamic control of reconfigurable
intelligent surfaces (RISs) is proposed. It leverages, on the one hand, on the
exploration capabilities of evolutionary strategies and their effectiveness in
dealing with large-scale discrete optimization problems and, on the other hand,
on the implementation of memory-enhanced search mechanisms to exploit the
time/space correlation of communication environments. Without modifying the
base station (BS) beamforming strategy and using an accurate description of the
meta-atom response to faithfully account for the micro-scale EM interactions,
the RIS control (RISC) algorithm maximizes the worst-case throughput across all
users without requiring that the Green's partial matrices, from the BS to the
RIS and from the RIS to the users, be (separately) known/measured.
Representative numerical examples are reported to illustrate the features and
to assess the potentialities of the proposed approach for the RISC
Unconditional adoption rules out the need for parent–offspring recognition in a single‐brooded colonial seabird
Parent–offspring
recognition (POR) is fundamental in colonial birds when the potential
intermingling of chicks is higher due to the large number and proximity of nests.
In species with isolated nests, where chick presence in the nest is strong contextual
evidence of kinship, there might be circumstances when the parent might doubt the
identity of the chick, but not enough to reject it. Olfactory-based
recognition of conspecifics
and nest sites in birds has gained strong evidence suggesting a potential role
of olfaction in POR. Despite that, there are no studies testing it. We used Scopoli's
shearwater (Calonectris diomedea) as model colonial single-brooded
species with a developed
olfactory sense, usually breeding in well-spaced
nests with low probability of
chicks mixing. We tested the parent's ability to selectively respond to their own chick
as opposed to a simpler rule of feeding any chick found in the nest by means of chick-fostering
experiments. We designed two cross-fostering
experiments using chicks of
different ages to test whether the ability of parents to recognize a related chick develops
over time, possibly after acquiring an own distinctive odour. Finally, we also manipulated
nests’ odour to disentangle the confounding effect of nest site recognition
from POR when parents return at night. All experimental chicks were adopted by parents
as the weight and bill growth of cross-fostered
chicks did not differ significantly
from the control group. We recorded a small difference in weight when foster chicks
were inside an odour-manipulated
nest; although we did not record weight loss in
experimental chicks, only a steeper increase in weight was observed in control chicks.
In conclusion, adoption in Scopoli's shearwater seems to follow the rule "if the young is
in my nest, accept it" proposed by Beecher (1991) for species with spatially separated
nests and low chick mobility.Fundação para a Ciência e Tecnologia - FCTinfo:eu-repo/semantics/acceptedVersio
Reconfigurable and Static EM Skins on Vehicles for Localization
Electromagnetic skins (EMSs) have been recently considered as a booster for
wireless sensing, but their usage on mobile targets is relatively novel and
could be of interest when the target reflectivity can/must be increased to
improve its detection or the estimation of parameters. In particular, when
illuminated by a wide-bandwidth signal (e.g., from a radar operating at
millimeter waves), vehicles behave like \textit{extended targets}, since
multiple parts of the vehicle's body effectively contribute to the
back-scattering. Moreover, in some cases perspective deformations challenge the
correct localization of the vehicle. To address these issues, we propose
lodging EMSs on vehicles' roof to act as high-reflectivity planar
retro-reflectors toward the sensing terminal. The advantage is twofold:
\textit{(i)} by introducing a compact high-reflectivity structure on the
target, we make vehicles behave like \textit{point targets}, avoiding
perspective deformations and related ranging biases and \textit{(ii)} we
increase the reflectivity the vehicle, improving localization performance. We
detail the EMS design from the system-level to the full-wave-level considering
both reconfigurable intelligent surfaces (RIS) and cost-effective static
passive electromagnetic skins (SP-EMSs). Localization performance of the
EMS-aided sensing system is also assessed by Cram\'er-Rao bound analysis in
both narrowband and spatially wideband operating conditions
Site Classification Assessment for Estimating Empirical Attenuation Relationships for Central-Northern Italy Earthquakes
The aim of this article is to investigate the ground motion attenuation of the most industrialized and populated regions of Italy, evaluating the capability of different approaches to estimate site dependent models. The 5.2 magnitude earthquake on November 24, 2004 shocked the areas of Northern Italy producing damage of about 215 million euros. The data set, including 243 earthquakes of local magnitude up to 5.2, has been collected in the period December 2002–October 2005 by 30 threecomponent seismic stations managed by Istituto Nazionale di Geofisica e Vulcanologia, Sezione of Milano (INGV-MI). Empirical attenuation relationships have been estimated for horizontal peak ground velocity (PGHV), acceleration (PGHA), displacement (PGHD), and for response spectral acceleration (SA) for periods between 0.1 and 1.5 s. To estimate suitable attenuation models, in particular for sites characterized by thick sedimentary geological formations, a soil discrimination based on EU8 code can lead to wrong evaluations. On the contrary, a classification based on H/V spectral ratios of seismic ambient noise (NHV) allows the models to fit better real and predicted data and to reduce the uncertainties of the process. For each receiver, NHV have been strengthened by additional H/V spectral ratio of earthquake data (EHV), calculated considering different portions of the analysed signals. In order to validate the PGHA attenuation relationship for greater magnitudes, accelerometric records, relative to Central-Northern Italy strong motions occurring in the last 30 years, have been collected and superimposed to our attenuation curves
A microtremor survey in the area shocked by the ml 5.2 Salò earthquake (north Italy): an empirical approach to determine the effects of ground motions
In this work the results of a quick microtremor survey performed in the municipalities situated in the epicentre area of the Ml 5.2 2004 Salò earthquake (North Italy) are presented. The aim of this study is to understand if the large amount of damage caused by the event (about 215 millions of euros only in the areas near to the epicenter) is correlated more to the local surface geology conditions or to the vulnerability of ancient Italian historical centers. A preliminary seismic zonation was carried out in 5 villages including about 30 measurements of microtremors analysed by the Nakamura technique (hereinafter HVNR). The points of measurement were carefully selected considering sites located both near damaged buildings and over different local geology conditions (alluvium deposits, fluvial-glacial deposits, debris fans and rock). In order to strengthen the HVNR results and to evaluate the reliability of the Nakamura analysis, a comparison with spectral ratios calculated on earthquakes (hereinafter HVSR) recorded at the strong motion station of Vobarno was made. In general, the outcomes of the survey highlight a possible correlation between local geology conditions and ground motion amplification for different frequency bands. In order to check if this evidence is linked with the damage, a series of macroseismic intensities values were collected for different zones of the investigated area, and a non parametric correlation approach was used to establish a possible correlation between damage and ground motion amplification for selected frequency bands. The results show, from a statistical point of view, that in the area surrounding the epicenter of the 24 November 2004 mainshock, the damage pattern is not strongly dependent upon the local surface geology but more correlated to the low quality of the civil structures present in the area, including old buildings of the last century
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