1,720,966 research outputs found
Retrieval of two-dimensional absorption coefficient structure from a scanning radiometer at 23.8 GHz
No full text
Propagation constant of HE mode near the cutoff frequency in a circular waveguide
No full textIn this letter, the propagation characteristics of
normal mode near the cutoff region of a circular waveguide surrounded
by a medium of finite conductivity and given permeability
is discussed. Several real-time applications require an accurate
solution of the characteristic equation at low computational cost.
A fast computed approximate solution for external medium with
infinite conductivity is available but inaccurate in the cutoff
region. Besides, field solvers and other numerical techniques give
a precise solution in the whole frequency range, but unacceptable
computational time. The proposed solution is derived by a
perturbation approach once the characteristic equation has been
expanded. A comparison between computed and exact values
shows that the approximate solution is quite good for a wide range
of conductivity and permeability values of the external medium
Effetti propagativi sul segnale radio ricevuto in ambito urbano: confronto fra tecniche di tracciamento dei raggi e metodi statistici
No full textEffetti propagativi sul segnale radio ricevuto in ambito urbano: confronto tra tecniche di tracciamento dei raggi e metodi statistici
No full textAnalysis of the influence of the Power Control and Discontinuous Trasmission on RF Exposure with GSM Mobile Phones
No full textAbstract—Biological studies and, in particular, epidemiological
ones require the estimation of the RF exposure induced by a mobile
phone. Due to the different techniques used by global system
mobile (GSM) and digital communication system (DCS) such as
power control and discontinuous transmission, the power emitted
by a handset is largely variable. As these parameters depend on the
environment and the network strategy, individual exposure level is
difficult to evaluate a priori. An analysis of the relative influence
of the main parameters is performed and a method of statistical
analysis based on measurement is proposed to estimate and characterize
the exposure level in an operating network. Using a test mobile
system, the data stream between the mobile and the base station,
and, in particular, the power control level, has been recorded
along routes in Paris and its vicinity. Statistical parameters such
as mean value, standard deviation, level crossing rate, and average
duration fading have been extracted from these data. These parameters,
which characterize the RF exposure induced by a GSM
handset in an operating network, have been applied to a generic
handset to evaluate the characteristics of the power absorbed by
specific biological tissues using the finite-difference time-domain
(FDTD) method
Determinazione della struttura del coefficiente di attenuazione (2D) mediante osservazioni radiometriche multiple alla frequenza 23.8 GHz
No full textDetection of anomalies inside hollow metal cylindrical structures
No full textThe evaluation of the physical conditions of a hollow metal cylindrical structure is critical in many applications, such as those involving oil or power generating industries or water pipeline networks. Direct and internal inspection is often not
possible or highly costly in terms of time and inspection tools. We present here a guided waves-based technique whose particularity is to detect and to quantify a circular anomaly inside a hollow metal cylindrical structure, while being
deployed. The technique requires only one measurement point to obtain information on remote sections that are hundreds of metres apart. Radar equipment sends an electromagnetic wave through an open end of the structure and it receives the backscattered field, which is produced by variations of the
internal hollow structure radius (deformations, welding joints, etc.). We derive the link between the recorded signal, which carries information on amplitude and propagation time, the circular anomalies parameters, defined by the percent radial reduction, and the deformation length, avoiding the
complications of the most classification algorithms. The anomaly identification is obtained through an inversion procedure that performs well with both the synthetic and real data. In the latter case, the estimated parameters of a given anomaly are in good agreement with the actual ones
Tomographic radiometric inversion with poor angular coverage: the benefit of a regularization scheme.
No full textIn this work the authors present some aspects about the retrieval of the atmospheric bidimensional
structure of the atmospheric specific attenuation coefficient through inversion of
the observed brightness temperature values using a tomographic approach. The poor angular
coverage is one of the main limiting factors, together with the parameterization of both model
and data space, i.e. the structure of the observed scenario and the number of acquisitions
in realistic experimental condition. The attention is focused on the aspects concerning the
regularization scheme, which helps in improving the quality of the retrieved values either by
adding a priori knowledge about the model or by contrasting the effect of noise. A preliminary
analysis is performed applying different strategies on two synthetic examples.
Keywords: inverse problems, regularization, radiometric tomograph
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