Time-Reversed Excitation of Reverberation Chambers: Improving Efficiency and Reliability in the Generation of Radiated Stress

Vallon, Henri; Cozza, Andréa; Monsef, Florian; Chauchat, Anne-Sophie

doi:10.1109/temc.2015.2478420

Cited by 8 publications

(10 citation statements)

References 15 publications

(14 reference statements)

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“…As TR applications cover bandwidths that would span a large number of resonant modes of a chamber, standard requirements for modal overlapping can be relaxed. Losses also have an impact on the efficiency of TR and GTR, as they directly control the intensity of the generated wavefront for a given input peak power [10].…”

Section: Methodsmentioning

confidence: 99%

“…GTR is entirely dependent on the availability of a medium capable of supporting diffusefield propagation, a statistically isotropic case of multipath propagation, also known as Rayleigh diffusion. Reverberation chambers comply with these requirements and bring at the same time a further advantage, energy efficiency, being closed systems with weak losses; when used with TR signals their efficiency can be further increased [10].…”

Section: Background and Motivationsmentioning

confidence: 99%

“…Applications of GTR-based synthesis are currently in progress and range from hardening shielded systems to high-power microwaves, imaging and generating stable highintensity fields without the statistical uncertainty found in standard reverberation chambers [10].…”

Section: Background and Motivationsmentioning

confidence: 99%

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Steering Focusing Waves in a Reverberation Chamber With Generalized Time Reversal

Cozza

Monsef

2017

IEEE Trans. Antennas Propagat.

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Generalized time reversal was introduced in a previous paper from a theoretical point of view. In this paper experiments are conducted to demonstrate its application to a reverberation chamber, as a method for generating coherent wavefronts in a medium displaying random propagation. Wavefronts thus generated were sampled over a planar surface, confirming that they propagate as if in a free-space environment. The accuracy with which they match their free-space counterpart is not affected by changing their features, e.g., direction of arrival and focus. These results prove that a single excitation antenna can generate complex wavefronts when coupled to diffusive wave propagation.

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Section: Methodsmentioning

confidence: 99%

Section: Background and Motivationsmentioning

confidence: 99%

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Steering Focusing Waves in a Reverberation Chamber With Generalized Time Reversal

Cozza

Monsef

2017

IEEE Trans. Antennas Propagat.

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“…Being highly reverberant systems, the necessary conditions for TR to be reliable were derived and verified in [19], [22] to require that the ratio B T /B c ≫ 1, with B c ≃ 1/τ the coherence time of the medium, here power grids. Hence, a minimum bandwidth requirement reads…”

Section: Reverberation Relaxation Time and Minimummentioning

confidence: 99%

Electromagnetic Time Reversal as a Correlation Estimator: Improved Metrics and Design Criteria for Fault Location in Power Grids

He¹,

Cozza²

2020

IEEE Trans. Electromagn. Compat.

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Recently published papers have proven the effectiveness of Electromagnetic time reversal (EMTR) in locating the position of faults such as phase-to-ground shunt connections in power grids. EMTR directly transposes the idea of focusing energy back to its source introduced in original time-reversal methods. The current interpretation of EMTR, based on metrics measuring energy or peak-amplitude of focusing, is shown to suffer from ambiguities that increase the risk of inaccurate fault location. After pointing out under what conditions time-reversal focusing occurs, an original frequency-domain reformulation of EMTR is introduced, showing that EMTR should more accurately be interpreted as a correlation estimator. New metrics based on this observation are introduced, taking into account the inhomogeneous transmission of electrical energy throughout complex networks, enabling a direct quantitative evaluation of the likelihood of locating a fault. Extensive numerical simulations confirm that the proposed formulation systematically improves the reliability of EMTR location estimates when faults occur in power grids of realistic complexity, highlighting the accrued risk that comes with the use of metrics that measure the scale of time-reversal focusing rather than its quality. Index Terms-Fault location, power grids, time reversal. I. INTRODUCTION T HE proper operation of power grids can be severely disrupted by events such as shunt faults where two or more conductors, subject to different potentials, become electrically connected through a low-impedance path, e.g., because of electrical arcs or phase-to-ground faults. The occurrence of such shunt faults is followed by transient signals that can be detected by a monitoring station, or probe, and subsequently used in order to estimate the fault position. A large number of methods has been introduced in the last decades for fault location in power grids, among which those based on travelling waves are of interested in the context of this paper [1]-[4]. A recent proposal for fault location is Electromagnetic Time Reversal (EMTR) [5], which is inspired by the idea of timereversal (TR) focusing [6], [7]. Its main appeal is its ability to locate faults from the transient signals they generate, as measured from a single probe. Its performance has been shown to depend on what kind of metrics are used, e.g., by monitoring S. He and Y. Xie are with

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“…For perfectly diffuse fields, it is equal to 1. The other term in (24) is the diversity factor, ( , ̅ ) = 1 + ( − 1) ̅ (26) which measures the effective number of degrees of freedom introduced by the transmission antennas, for an average correlation coefficient ̅ between the ( ) time-reversal transfer functions.…”

Section: How Accurate Are Time-reversed Fields In Diffusive Media?mentioning

confidence: 99%

Time Reversal in Diffusive Media

Cozza

Monsef

2017

Electromagnetic Time Reversal

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Erreur ! Utilisez l'onglet Accueil pour appliquer Heading 1 au texte que vous souhaitez faire apparaître ici. 2 Yet, diffusion is not only important in understanding propagation at optical frequencies. Diffusion actually happens quite often with microwaves, too. As a matter of fact, non-line-of-sight propagation in rooms and urban canyons share some of the characteristics of wave diffusion, which is better known as the class of Rayleigh channels in telecommunication theory [3]. Perhaps more important is the fact that wave diffusion can be useful. Reverberation chambers are the champions of wave diffusion, as their peculiar characteristics heavily depend on the ability to turn coherent excitations into a chaos of waves propagating along (ideally) every possible directions at the same time. When used as the basis for time reversal applications, diffusive media can be shown to take a whole new dimension that makes them suddenly appear as very appealing media for wave propagation, rather than the messy and uncontrollable medium we are used to expect with harmonic excitations. This chapter presents a summary of the work done in applying time reversal to diffusive media. It is organized into three parts. First, the main features of diffusive media are presented, starting from their physical origin leading to the derivation of black-box statistical models; these properties will be fundamental in the derivation of the results presented later. Time-reversed excitations are then considered, first for the generation of fields and the transmission of signals. The powerful self-averaging enabled by diffusive media is demystified, proving why it can only happen with such media. Self-averaging powers all of the properties of time reversal in diffusive media, as its ability to generate well-polarized fields in a medium considered as incapable of doing it. These results are then pushed a step further, by studying the generation of coherent wavefronts. Diffusive media are shown to be a potentially more effective solution for this task than free-space-based wave generators: a single antenna is shown to be capable of generating a large number of focusing wavefronts just by playing on the signals applied to it. Applications presented throughout the chapter are based on the use of reverberation chambers. Erreur ! Utilisez l'onglet Accueil pour appliquer Heading 1 au texte que vous souhaitez faire apparaître ici. 6

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Time-Reversed Excitation of Reverberation Chambers: Improving Efficiency and Reliability in the Generation of Radiated Stress

Cited by 8 publications

References 15 publications

Steering Focusing Waves in a Reverberation Chamber With Generalized Time Reversal

Steering Focusing Waves in a Reverberation Chamber With Generalized Time Reversal

Electromagnetic Time Reversal as a Correlation Estimator: Improved Metrics and Design Criteria for Fault Location in Power Grids

Time Reversal in Diffusive Media

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