229 research outputs found
Theoretical and experimental investigations inside electromagnetic reverberation chambers
No full textCarousel Stirrer Efficiency Evaluation by a Volumetric Lattice-Based Correlation Matrix
No full textRecently, a new stirrer shape, the carousel stirrer, has been proposed to improve the reverberation chamber performances. In this contribution, we propose a method to compute the number of uncorrelated positions of the carousel stirrer. This method works by counting the low-correlation elements of a 3D lattice-based correlation matrix, each elements of the matrix being the Pearson correlation between two random vectors sampled at two different stirrer locations. We use adhoc FDTD code to simulate the Cartesian fields within the reverberation (lattice) region, for a large number of stirrer positions. Our analysis highlights dependence on the considered volume dimensions, the number of lattice field samples, and their spatial distance. The study also reveals the presence of periodic frequencies where uncorrelation dramatically reduces. A parametric analysis is presented to investigate the reason of this phenomenon which is evident only for two Cartesian field components
Accuracy Evaluation of the Huygens Subgridding Method
No full textIn this work, an application of the recent Huygens Subgridding (HSG) method to
study lossy materials with the ̄nite-di®erence time-domain (FDTD) scheme is presented and
a related error analysis discussed. Achieved HSG results showed a good agreement with a full
higher-resolution reference guide for di®erent electrical parameter values, indicating a negligible
numerical dispersion on the transverse section. Moreover, the increasing decimation factor e®ect
has been investigated to evaluate the subgridding accuracy. Findings are of interest in the
numerical prediction of planar screens e®ectiveness, material parameters retrieval and microwave
spectroscopy
Effect of losses on the maximum-to-mean value in a mode-stirred reverberation chamber
No full textPerformances of reverberation chambers exhibit a non-trivial dependence on distributed losses. It is shown through numerical simulations that the average maximum-to-mean chamber field/power do not decrease with increasing losses as expected. Rather, it reaches an optimal value at moderate losses. Interestingly, the chamber field uniformity is also optimized at the same amount of losses. This behavior is accompanied by a progressive reduction of the quality factor and of the number of independent stirrer positions, indicating that losses augment the unstirred components as partial field coherence develops. A statistical model, the random coupling model, based on wave-chaos is used to shed light on the role of modal fluctuations and losses in the achievement of an optimal stress. It is found that the optimal condition is reached when losses extend the cavity bandwidth up to the average mode-to-mode spacing. Then, further increasing losses results in a suboptimal condition, for which the open-cavity behavior takes over, i.e., the ratio decreases
Dependence of reverberation chamber performance on distributed losses: A numerical study
No full textFinite-difference time-domain simulations of reverberation chambers exhibit a strong frequency dependence of field/power fluctuations on distributed losses. The performances of a reverberation chamber are calculated at different loss conditions and in a wide frequency band in terms of backscatter coefficient, and number of independent positions. Those performance indicators are related to field and power statistics through the scattering coefficients. A goodness-of-fit test is applied to analyze the statistical distribution functions of the numerical transmission scattering coefficient. Strong deviations from idealized distribution functions, some unexpected, are observed varying the chamber loading at both low- and high-frequencies. Observed phenomena are confirmed from the random coupling model, which reconciliates findings with the universal behavior of wave chaotic systems, as well as with previous studies of other investigators
Numerical Modeling of the Reverberation Chamber Method for the Measurement of Material Absorbing Cross Section
No full textReverberation chamber (RC) test facility allows to determine the absorbing cross section (ACS) of lossy materials under a random field excitation. Measurements are based on the quality factor variation produced by the sample under test presence with respect to the empty chamber condition. Simulations are based on the representation of the RC electromagnetic field by means of a random plane wave superposition. A finite-difference time-domain (FDTD) code is used to compute the material absorbed power and to recover a numerical ACS. The method sensibility is stressed by application to small size samples. Comparison between numerical and experimental data reveals a satisfactory agreement. The simulation technique can be applied to study the absorbing properties of absorbers with arbitrary geometry during the early design stage
Reverberation chamber as a multivariate process: FDTD evaluation of correlation matrix and independent positions
No full textThis paper evaluates the mode-stirring effciency in terms
of uncorrelated positions of a mechanical stirrer operating inside a reverberation chamber (RC). The actual RC is simulated and viewed as a multivariate random process: the chamber field is sampled in a lattice of spatial points distributed uniformly over a volume of arbitrary dimensions. By adopting such a grid, the stirrer effciency is then
computed through the correlation matrix, accounting for the residual correlation between stirrer positions. The second-order statistics are calculated averaging over the sampling volume. Results are presented for two stirrers that move in both synchronous and interleaved mode. A comparison with the traditional circular correlation (CC) method, for the determination of the uncorrelated positions, is done showing how CC overestimates stirrer effciency
Electromagnetic Reverberation: The Legacy of Paolo Corona
No full textThis paper reviews some significant achievements in the research activity and academic career of Paolo Corona, with particular focus on electromagnetic reverberation theory and measurements. An annotated selection is presented for some of his celebrated publications as well as some lesser well-known unpublished works.Some of his recorded views on issues and directions for future research on reverberation chambers are also included
Correlation matrix methods to assess the stirring performance of electromagnetic reverberation chambers
No full text© 2018 The use of correlation matrices to evaluate the number of uncorrelated stirrer positions of electromagnetic reverberation chambers has widespread applications in electromagnetic compatibility. We present a review of recent methods based on multivariate correlation functions that relates statistical inhomogeneities in space (frequency) to the reduction of uncorrelated cavity configurations. Full wave finite-difference time domain simulations of an actual reverberation chamber are performed through an in-house parallel code. The efficiency of this code allows for capturing extensive inhomogeneous/anisotropic reverberation fields at frequencies close to the lowest usable frequency (LUF) of the chamber. The concept of effective independent position is revised in light of random sampling and a model-driven relation with the probability distribution of correlation matrix entries is used to take into account spatial (frequency) inhomogeneities. Driven by extensive simulation data, an empirical probability density function is found for the correlation matrix elements to be non-central t-student distributed with asymmetry increasing towards low frequencies
A statistical model of the interaction between reverberation fields and lossy materials
No full textIn this work, a thermodynamic model for random fields was used to study lossy materials in a reverberation chamber (RC). In particular, angular spectrum (AS) statistics were obtained inside the material and the deterministic alteration of the incidence angle at the boundary was used to find the probability density function (PDF) of the effective refraction angle. The statistical model was validated by a discrete approach and a semi-empirical model was derived to calculate the power transmitted inside a nested RC through an aperture covered by a lossy thin slab. A preliminary experimental result is presented in order to have a first check of the proposed formulation
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