Retournement temporel | EPFL Graph Search

Le retournement temporel est un procédé physique connu de longue date dans différents domaines du spectre électromagnétique (visible, micro-onde, etc.) (et appliqué aux ultrasons par Mathias Fink à l'École supérieure de physique et de chimie industrielles de la ville de Paris) qui permet à une onde de retourner vers sa source dans le cas d'une propagation non dissipative. Description Ce procédé permet de résoudre le problème inverse ou plus clairement le renversement du temps d'une action. Par exemple refaire parcourir à une boule de billard le chemin qu'elle a parcouru depuis le tir, reste inobservable du fait du chaos déterministe : une modification même mineure de la position ou de la vitesse initiale modifierait la position finale. Toutefois lorsqu'il s'agit d'ondes acoustiques ou électromagnétiques, ce problème peut avoir une solution grâce à ce procédé. Le retournement temporel permet de focaliser spatialement et temporellement un signal électromagnétique dans un mi

Electromagnetic Time Reversal: Theory, Application to Fault Location in Power Networks and Experimental Validation

Zhaoyang Wang

The time-reversal invariance is readily described and universally embodied in most laws of nature, either in a strict or in a soft sense. Based on this underlying physical principle, time-reversal theory has been theoretically and experimentally studied in the field of acoustics first, and later introduced into electromagnetism, under the general denomination of Electromagnetic Time Reversal (EMTR). With the development of modern power system, especially represented by the technology of Smart Grids and Active Distribution Networks (ADNs), a reliable and efficient fault detection and location functionality is increasingly required to ensure the security and quality of supply. It has recently been shown that an EMTR-based fault location technique can provide superior performance with respect to existing techniques in terms of location accuracy and robustness against uncertainties. At the same time, several theoretical and technological challenges have to be addressed before such a technique can be used in real-world applications. The present work aims at addressing these challenges, which are summarized hereunder. Time reversal cavity applied to power networks. The concept of the time-reversal cavity was proposed by Cassereau and Fink for acoustic waves and later extended to electromagnetic waves. It is accepted that a time-reversal cavity is a theoretical concept and cannot be realized experimentally because it requires in principle an infinite number of transducers covering a closed surface around the medium to obtain information about all wavefronts propagating in all directions. Although this is true in a 3D situation, we believe that in the case of power networks in which waves are confined in a specific region of the space and propagate along the longitudinal direction of the lines (1D situation), such a time-reversal cavity is realizable. We propose to design, simulate, and experimentally validate such a cavity for the case of inhomogeneous power networks. Improving the performance of EMTR-based fault locating techniques. The currently-developed EMTR-based technique requires multiple simulations to identify the location of the fault. We will investigate possible ways of reducing the number of required simulation runs. Practical implementation of an EMTR-based fault locator. The EMTR-based method technologically requires the use of a hardware platform, such as a Field Programmable Gate Array (FPGA), capable of performing Electromagnetic Transient (EMT) simulations and post Digital Signal Processing (DSP). In order to address constraints of application in real-world power networks and robustness requirements, further improvement and optimization will be considered, namely, the determination of the minimum time-reversal window required to achieve a certain location accuracy, the development of a library of transmission lines and cables commonly used in power networks, analysis of the location error caused either by incomplete knowledge of the network, or other disturbances such as those originated by lightning, as well as limitations associated with the measurement. The final aim of the thesis is to further develop a fault location hardware platform integrating EMTR theory with numerous functionalities, like EMT simulations, DSP, interactive communication. Its performance will be verified by hardware-in-the-loop tests, and eventually by live tests in real power networks.

EPFL2020

Design and development of a haptic feedback demonstrator using time-reversal method and FPGAS

Andrés Chica Linares

The EPFL-LAI is investigating on haptic technologies to give vibrotactile feedback in digital musical interfaces. The aim is to develop an interactive surface that can render a multi-touch vibrotactile stimulus using piezoelectric actuators. The signals that will be sent to the piezoelectric system are generated using deep-learning strategies. Then, they will be simultaneously sent using a FPGA. After this stage there will be a power supply circuit to amplify the digital signals and finally send them to the piezoelectric system. When using these haptic technologies, the sensations of playing a real instrument will be recreated and the player will enjoy the digital instrument through the touch as well. This will make the experience of playing a digital instrument richer.

2021

Electromagnetic Time Reversal: Theory, Application to Fault Location in Power Networks and Experimental Validation

Zhaoyang Wang

EPFL2020