Stirrer efficiency in FOA reverberation chambers. Evaluation of correlation coefficients and chi-squared tests

Lunden, O.; Bäckström, Mikael

doi:10.1109/isemc.2000.875529

Cited by 70 publications

(40 citation statements)

References 3 publications

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“…The number of independent samples N ind is calculated with the classical autocorrelation function method [27]. The offset ∆, i.e., the number of samples at which the correlation coefficient is dropped to 1/e is found, and we have: N ind = N mes /∆.…”

Section: Statistical Properties Of the Lasmea's Msrcmentioning

confidence: 99%

Mode Stirred Reverberation Chamber (Msrc): A Large and Efficient Tool to Lead High Frequency Bioelectromagnetic in Vitro Experimentation

Lalléchère¹,

Girard²,

Roux³

et al. 2010

PIER B

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Abstract-An important aspect of the studies undertaken in bioelectromagnetism relates to the choice of exposure facility. The characteristics of a real electromagnetic environment are far more complex compared to the one plane wave irradiation set-up used in the majority of bioelectromagnetic studies. Moreover, biological requirements should represent the starting point in the design of an in vitro exposure system. Indeed it is important to avoid altering the electromagnetic properties of the exposure system in the presence of biological equipments. Related to these two essential points, this article contributes to show the advantages of a Mode Stirred Reverberation Chamber (MSRC) to guarantee a controlled electromagnetic environment around biological materials for in vitro experimentation. An example of irradiation of in vitro human skin cells cultures is considered to illustrate this paper. In order to show that the biological conditions and the physical requirements for in vitro experiments are checked, two aspects are described. Firstly we achieved the characterization of the electromagnetic field generated around the biological system (both equipments and cultures). Secondly the analysis of the Specific Absorption Rate (SAR) inside the biological medium was evaluated both numerically and experimentally. Initially, the statistical properties of fields inside the MSRC were checked with or without the biological devices in order to verify their electromagnetic transparency with respect to the reverberating properties of the electromagnetic environment (inside MSRC). We checked the good agreement of the experimental electromagnetic power distribution with the theoretical one.The computation of electromagnetic energy absorbed by biological medium (SAR) was based upon Finite Difference in Time Domain (FDTD) technique. A numerical analogy was achieved between the MSRC behavior and a free-space finite sum of random plane waves. Simulations are able to provide both an estimation of SAR distribution inside each biological culture dish and a computation of the coupling effects between dishes. Relying on the previous conclusions, temperature measurements were led to evaluate the experimental SAR levels and its time variations inside the MSRC. Two high-frequency (900 MHz) environments were considered: A 10 minutes exposure with field amplitude inside the biological incubator of 7.87 V/m and 30 minutes with 41 V/m (SAR ranged from 2.6 mW/kg to 73 mW/kg, mean values). Numerical and experimental results prove the ability of MSRC to provide a large and efficient tool to achieve bioelectromagnetic experiments at high frequencies.

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Section: Statistical Properties Of the Lasmea's Msrcmentioning

confidence: 99%

Mode Stirred Reverberation Chamber (Msrc): A Large and Efficient Tool to Lead High Frequency Bioelectromagnetic in Vitro Experimentation

Lalléchère¹,

Girard²,

Roux³

et al. 2010

PIER B

View full text Add to dashboard Cite

show abstract

“…Furthermore, we modify the recursion in (4) by replacing and by computationally more attractive quantities. More specifically, we consider the modifications of (4) in which for for for (7) and for for for (8) with the subscripts representing the "sign," "relay correlation," and "modulus," respectively. Equation (4) will lead to the classic sign algorithm in the case for , see, e.g., [14]- [16].…”

Section: Derivation Of Tracking Formulasmentioning

confidence: 99%

“…Furthermore, correlation techniques are used in room acoustics as a measure for the diffuseness of a sound field [3], as a judgment of the quality of a sound field [4], as a tool in the field of architectural acoustics [5]- [7], LPC analysis for speech coding [8], time delay of arrival (TDOA) [9], feature detector [10], and system identification [11]. An overview of tracking applications in audio-video object localization is given by [12].…”

Section: Introductionmentioning

confidence: 99%

Efficient tracking of the cross-correlation coefficient

Aarts

Irwan

Janssen

2002

IEEE Trans. Speech Audio Process.

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Abstract-In many (audio) processing algorithms, involving manipulation of discrete-time signals, the performance can vary strongly over the repertoire that is used. This may be the case when the signals from the various channels are allowed to be strongly positively or negatively correlated. We propose and analyze a general formula for tracking the (time-dependent) correlation between two signals. Some special cases of this formula lead to classical results known from the literature, others are new. This formula is recursive in nature, and uses only the instantaneous values of the two signals, in a low-cost and low-complexity manner; in particular, there is no need to take square roots or to carry out divisions. Furthermore, this formula can be modified with respect to the occurrence of the two signals so as to further decrease the complexity, and increase ease of implementation. The latter modification comes at the expense that not the actual correlation is tracked, but, rather, a somewhat deformed version of it. To overcome this problem, we propose, for a number of instances of the tracking formula, a simple warping operation on the deformed correlation. Now we obtain, at least for sinusoidal signals, the correct value of the correlation coefficient. Special attention is paid to the convergence behavior of the algorithm for stationary signals and the dynamic behavior if there is a transition to another stationary state; the latter is considered to be important to study the tracking abilities to nonstationary signals. We illustrate tracking algorithm by using it for stereo music fragments, obtained from a number of digital audio recordings.

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“…For complex stirrer optimization, paddle shape analysis requires numerical tools for their optimization [12]- [17]. To enhance the chamber performances a second stirrer can be added [18], [19] even if a different efficiency can be obtained when two stirrers are moved in a synchronized or in an interleaved mode [10]. Full wave simulations of RC [20] allows to check the performance of the stirrer(s) using the parameters described in the IEC standard [21] like independent positions or field uniformity.…”

Section: Introductionmentioning

confidence: 99%

Reverberation chamber as a statistical relaxation process: Entropy analysis and fast time domain simulations

Gradoni

Primiani

Moglie

2012

International Symposium on Electromagnetic Compatibility - EMC EUROPE

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In this contribution, we investigate the entropy growth in a mode-stirred cavity simulated by the FDTD method. The adopted reverberation chamber is efficiently stirred by multiple paddles and excited by a Gaussian pulse. It is observed that the entropy starts growing quadratically in time, then it increases linearly during the energy buildup, and it saturates after a few nanoseconds, when the full onset of chaotic regime is developed. This allows for terminating the numerical simulations well before the Richardson time, as the asymptotic entropy is rapidly achieved. The analysis is based on the eigenvalues of the correlation matrix, calculated over a dense grid of spatial points, thus supporting the perspective of the reverberation chamber as a statistical multivariate process. The number of orthogonal eigenvectors (principal components) can be estimated and used as the number of statistically independent stirrer positions (degrees of freedom, cavity realizations). It is found that letting the chamber evolve for a very long time would gain only a few principal components, thus adding a negligible improvement in the stirring performances. Different mode-stirrer shapes can be investigated and their efficiency quantified by this method.

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Stirrer efficiency in FOA reverberation chambers. Evaluation of correlation coefficients and chi-squared tests

Cited by 70 publications

References 3 publications

Mode Stirred Reverberation Chamber (Msrc): A Large and Efficient Tool to Lead High Frequency Bioelectromagnetic in Vitro Experimentation

Mode Stirred Reverberation Chamber (Msrc): A Large and Efficient Tool to Lead High Frequency Bioelectromagnetic in Vitro Experimentation

Efficient tracking of the cross-correlation coefficient

Reverberation chamber as a statistical relaxation process: Entropy analysis and fast time domain simulations

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