Focusing high-power electromagnetic waves using time-reversal

A main aspect of this work has been to develop analytical and statistical models of the power efficiency of a time-reversal amplification system (TRAS).It is also important to evaluate the efficiency of a reverberation chamber. This allows quantifying the power received by one or more antenna when the reverberation chamber is excited. This factor is important when considering construction of the most efficient chamber for time-reversal amplification.Measurements assessing the loading effect of antennas in reverberation chambers when the field can be considered diffused were also undertaken. The study focuses on the evaluation of the varying quality factor when adding loaded antennas in the chamber.Another focus of this work is to evaluate the ratios between signals during calibration and focusing phase. An important aspect of the studies presented in this work thus concerns evaluation of the maximum value of the impulse response in a complex propagation system.We also present the power gain of time-reversal techniques and its statistical advantages compared to a classic use of a reverberation chamber.The development of a prototype required the design and implementation of each of the branches of the complete systems.The first measurement campaigns allowed the complete validation of the models.L'objectif de la thèse a été de mettre en place dans un premier temps des modèles analytiques et statistiques permettant d'évaluer les performances d'un système à retournement temporel de fortes-puissances puis de les vérifier grâce à des mesures.Des campagnes de mesures ont alors permis de vérifier les modèles. Des simulations numériques ont aussi montrées les possibilités offertes par un tel système.En parallèle, des travaux sur l'impact des antennes dans une chambre réverbérantes ont été menés afin d'évaluer les performances d'un système ayant plusieurs sorties.Les résultats de thèses ont permis l'élaboration de nouvelles métriques des performances du système.Le développement d'un prototype a nécessité la conception et la réalisation de chacune des branches du système complet.Les premières campagnes de mesures ont permis la validation complète des modèles

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

International audienceThe ability of reverberation chambers to generate high-intensity field levels from relatively low-power input signals is reexamined for the case of time-reversed signals, proving that they lead to a higher efficiency. Moreover, the strong statistical spread typical of time-harmonic excitations can be dramatically reduced, thus improving the reliability of radiative tests, while limiting the need for a large number of independent realizations. The two excitation schemes are compared when forcing their respective input signals to display the same peak instantaneous power. Experimental results are provided, supporting the conclusions of our theoretical analysis

Configurable EBEN: Extreme Bandwidth Extension Network to enhance body-conducted speech capture

This paper presents a configurable version of Extreme Bandwidth Extension Network (EBEN), a Generative Adversarial Network (GAN) designed to improve audio captured with body-conduction microphones. We show that although these microphones significantly reduce environmental noise, this insensitivity to ambient noise happens at the expense of the bandwidth of the speech signal acquired by the wearer of the devices. The obtained captured signals therefore require the use of signal enhancement techniques to recover the full-bandwidth speech. EBEN leverages a configurable multiband decomposition of the raw captured signal. This decomposition allows the data time domain dimensions to be reduced and the full band signal to be better controlled. The multiband representation of the captured signal is processed through a U-Net-like model, which combines feature and adversarial losses to generate an enhanced speech signal. We also benefit from this original representation in the proposed configurable discriminators architecture. The configurable EBEN approach can achieve state-of-the-art enhancement results on synthetic data with a lightweight generator that allows real-time processing.Comment: Accepted in IEEE/ACM Transactions on Audio, Speech and Language Processing on 14/08/202

Measurement techniques enhancements for MIMO 4G mobile communication systems. extension of mode stirred reverberation chambers (MSRCs) emulation capabilities

[ENG] Mobile communications have experienced a brutal raise over the past 15 years. What started as a voice communication system (GSM or 2G) has finished yet as a data communication system of any kind, which in some cases has come to replace the conventional cabled data access infrastructure. This change in the use given to mobile devices necessarily entails a change in the underlying technology, which should be capable to provide the transmission speeds that these new applications require. This has emerged in recent years an increasing interest in multiple antenna techniques, usually referred as multiple-input multiple-output (MIMO) techniques, as they increase the spectral efficiency (and thus the transmission rate for a given bandwidth) of wireless systems. In this thesis, some of the factors limiting the ideal advantages of these multiantenna techniques are studied, in order to quantify the differences between the ideal behavior of 4G devices and behavior that users will experience in actual use conditions. The effect that the user has on the final performance of the devices is one of the main limitations that these devices are in daily use. Mobile phones are used almost all the time in the vicinity of the user, causing a decrease in the richness of the multipath electromagnetic environment (and thus a reduction of the MIMO benefits). As a result of this reduction, the number of signal paths that reach the user is also reduced. In this thesis both factors (user influence and influence of the number of signal paths) will be studied both for passive devices (antenna prototypes) and active devices (commercial phones). The second part of this thesis consist on the study of how to transfer some of these factors reducing the isotropicity of the environment, to one of the most promising measurement techniques, as it is the mode-stirred reverberation chamber (MSRC). This technique emulates naturally an isotropic rich multipath environment with the signal strength following a Rayleigh distribution. However, in this thesis two new techniques are proposed that allow the emulation of less isotropic environments without altering the basic operating principle of the MSRC. [SPA] Las comunicaciones móviles han experimentado un aumento brutal en los últimos 15 años. Lo que comenzó como un sistema de comunicación de voz (GSM o 2G) ha terminado todavía como un sistema de comunicación de datos de cualquier tipo, que en algunos casos ha llegado a sustituir la infraestructura de cableado convencional de acceso a datos. Este cambio en el uso que se da a los dispositivos móviles implica necesariamente un cambio en la tecnología subyacente, que debe ser capaz de proporcionar las velocidades de transmisión que estas nuevas aplicaciones requieren. Esto se ha convertido en los últimos años un creciente interés en las técnicas de múltiples antenas, normalmente se conoce como técnicas de múltiple entrada y múltiple salida (MIMO), ya que aumentan la eficiencia espectral (y por lo tanto la velocidad de transmisión para un ancho de banda dado) de los sistemas inalámbricos. En esta tesis, algunos de los factores que limitan las ventajas ideales de estas técnicas de múltiples antenas son estudiados, con el fin de cuantificar las diferencias entre el comportamiento ideal de dispositivos 4G y comportamiento que los usuarios experimentarán en condiciones reales de uso. El efecto que el usuario tiene sobre el rendimiento final de los dispositivos es una de las principales limitaciones que estos dispositivos son de uso diario. Los teléfonos móviles se utilizan en casi todo el tiempo en la proximidad del usuario, causando una disminución en la riqueza del entorno electromagnético trayectos múltiples (y por tanto una reducción de los beneficios MIMO). Como resultado de esta reducción, el número de trayectorias de señal que llegan al usuario también se reduce. En esta tesis ambos factores (la influencia del usuario y la influencia del número de caminos de señal) se estudió tanto para dispositivos pasivos (prototipos de antenas) y los dispositivos activos (los teléfonos comerciales). La segunda parte de esta tesis consisten en el estudio de cómo transferir algunos de estos factores que reducen la isotropicity del medio ambiente, a una de las técnicas de medición más prometedores, como es la cámara de agitación de modos (MSRC). Esta técnica emula naturalmente un entorno isotrópico multipath rico con la intensidad de la señal después de una distribución de Rayleigh. Sin embargo, en esta tesis, dos nuevas técnicas que se proponen permitir la emulación de entornos isotrópicos menos sin alterar el principio de funcionamiento básico del MSRC.Universidad Politécnica de Cartagen

Returning radiation in strong gravity around black holes: Reverberation from the accretion disc

We study reflected X-ray emission that returns to the accretion disc in the strong gravitational fields around black holes using General Relativistic ray tracing and radiative transfer calculations. Reflected X-rays that are produced when the inner regions of the disc are illuminated by the corona are subject to strong gravitational light bending, causing up to 47 per cent of the reflected emission to be returned to the disc around a rapidly spinning black hole, depending upon the scale height of the corona. The iron K line is enhanced relative to the continuum by 25 per cent, and the Compton hump by up to a factor of three. Additional light travel time between primary and secondary reflections increases the reverberation time lag measured in the iron K band by 49 per cent, while the soft X-ray lag is increased by 25 per cent and the Compton hump response time is increased by 60 per cent. Measured samples of X-ray reverberation lags are shown to be consistent with X-rays returning to the accretion disc in strong gravity. Understanding the effects of returning radiation is important in interpreting reverberation observations to probe black holes. Reflected X-rays returning to the disc can be uniquely identified by blueshifted returning iron K line photons that are Compton scattered from the inner disc, producing excess, delayed emission in the 3.5-4.5keV energy range that will be detectable with forthcoming X-ray observatories, representing a unique test of General Relativity in the strong field limit.Comment: 20 pages, 14 figures. Accepted for publication in MNRA

Returning radiation in strong gravity around black holes: reverberation from the accretion disc

We study reflected X-ray emission that returns to the accretion disc in the strong gravitational fields around black holes using General Relativistic ray-tracing and radiative transfer calculations. Reflected X-rays that are produced when the inner regions of the disc are illuminated by the corona are subject to strong gravitational light bending, causing up to 47 per cent of the reflected emission to be returned to the disc around a rapidly spinning black hole, depending upon the scale height of the corona. The iron Kα line is enhanced relative to the continuum by 25 per cent, and the Compton hump by up to a factor of 3. Additional light traveltime between primary and secondary reflections increases the reverberation time lag measured in the iron K band by 49 per cent, while the soft X-ray lag is increased by 25 per cent and the Compton hump response time is increased by 60 per cent. Measured samples of X-ray reverberation lags are shown to be consistent with X-rays returning to the accretion disc in strong gravity. Understanding the effects of returning radiation is important in interpreting reverberation observations to probe black holes. Reflected X-rays returning to the disc can be uniquely identified by blueshifted returning iron K line photons that are Compton scattered from the inner disc, producing excess, delayed emission in the 3.5–4.5 keV energy range that will be detectable with forthcoming X-ray observatories, representing a unique test of General Relativity in the strong field limit

Neural architecture for echo suppression during sound source localization based on spiking neural cell models

Zusammenfassung Diese Arbeit untersucht die biologischen Ursachen des psycho-akustischen Präzedenz Effektes, der Menschen in die Lage versetzt, akustische Echos während der Lokalisation von Schallquellen zu unterdrücken. Sie enthält ein Modell zur Echo-Unterdrückung während der Schallquellenlokalisation, welches in technischen Systemen zur Mensch-Maschine Interaktion eingesetzt werden kann. Die Grundlagen dieses Modells wurden aus eigenen elektrophysiologischen Experimenten an der Mongolischen Wüstenrennmaus gewonnen. Die dabei erstmalig an der Wüstenrennmaus erzielten Ergebnisse, zeigen ein besonderes Verhalten spezifischer Zellen im Dorsalen Kern des Lateral Lemniscus, einer dedizierten Region des auditorischen Hirnstammes. Die dort sichtbare Langzeithemmung scheint die Grundlage für die Echounterdrückung in höheren auditorischen Zentren zu sein. Das entwickelte Model war in der Lage dieses Verhalten nachzubilden, und legt die Vermutung nahe, dass eine starke und zeitlich präzise Hyperpolarisation der zugrundeliegende physiologische Mechanismus dieses Verhaltens ist. Die entwickelte Neuronale Modellarchitektur modelliert das Innenohr und fünf wesentliche Kerne des auditorischen Hirnstammes in ihrer Verbindungsstruktur und internen Dynamik. Sie stellt einen neuen Typus neuronaler Modellierung dar, der als Spike-Interaktionsmodell (SIM) bezeichnet wird. SIM nutzen die präzise räumlich-zeitliche Interaktion einzelner Aktionspotentiale (Spikes) für die Kodierung und Verarbeitung neuronaler Informationen. Die Basis dafür bilden Integrate-and-Fire Neuronenmodelle sowie Hebb'sche Synapsen, welche um speziell entwickelte dynamische Kernfunktionen erweitert wurden. Das Modell ist in der Lage, Zeitdifferenzen von 10 mykrosekunden zu detektieren und basiert auf den Prinzipien der zeitlichen und räumlichen Koinzidenz sowie der präzisen lokalen Inhibition. Es besteht ausschließlich aus Elementen einer eigens entwickelten Neuronalen Basisbibliothek (NBL) die speziell für die Modellierung verschiedenster Spike- Interaktionsmodelle entworfen wurde. Diese Bibliothek erweitert die kommerziell verfügbare dynamische Simulationsumgebung von MATLAB/SIMULINK um verschiedene Modelle von Neuronen und Synapsen, welche die intrinsischen dynamischen Eigenschaften von Nervenzellen nachbilden. Die Nutzung dieser Bibliothek versetzt sowohl den Ingenieur als auch den Biologen in die Lage, eigene, biologisch plausible, Modelle der neuronalen Informationsverarbeitung ohne detaillierte Programmierkenntnisse zu entwickeln. Die grafische Oberfläche ermöglicht strukturelle sowie parametrische Modifikationen und ist in der Lage, den Zeitverlauf mikroskopischer Zellpotentiale aber auch makroskopischer Spikemuster während und nach der Simulation darzustellen. Zwei grundlegende Elemente der Neuronalen Basisbibliothek wurden zur Implementierung als spezielle analog-digitale Schaltungen vorbereitet. Erste Silizium Implementierungen durch das Team des DFG Graduiertenkollegs GRK 164 konnten die Möglichkeit einer vollparallelen on line Verarbeitung von Schallsignalen nachweisen. Durch Zuhilfenahme des im GRK entwickelten automatisierten Layout Generators wird es möglich, spezielle Prozessoren zur Anwendung biologischer Verarbeitungsprinzipien in technischen Systemen zu entwickeln. Diese Prozessoren unterscheiden sich grundlegend von den klassischen von Neumann Prozessoren indem sie räumlich und zeitlich verteilte Spikemuster, anstatt sequentieller binärer Werte zur Informationsrepräsentation nutzen. Sie erweitern das digitale Kodierungsprinzip durch die Dimensionen des Raumes (2 dimensionale Nachbarschaft) der Zeit (Frequenz, Phase und Amplitude) sowie der zeitlichen Dynamik analoger Potentialverläufe. Diese Dissertation besteht aus sieben Kapiteln, welche den verschiedenen Bereichen der Computational Neuroscience gewidmet sind. Kapitel 1 beschreibt die Motivation dieser Arbeit welche aus der Absicht rühren, biologische Prinzipien der Schallverarbeitung zu erforschen und für technische Systeme während der Interaktion mit dem Menschen nutzbar zu machen. Zusätzlich werden fünf Gründe für die Nutzung von Spike-Interaktionsmodellen angeführt sowie deren neuartiger Charakter beschrieben. Kapitel 2 führt die biologischen Prinzipien der Schallquellenlokalisation und den psychoakustischen Präzedenz Effekt ein. Aktuelle Hypothesen zur Entstehung dieses Effektes werden anhand ausgewählter experimenteller Ergebnisse verschiedener Forschungsgruppen diskutiert. Kapitel 3 beschreibt die entwickelte Neuronale Basisbibliothek und führt die einzelnen neuronalen Simulationselemente ein. Es erklärt die zugrundeliegenden mathematischen Funktionen der dynamischen Komponenten und beschreibt deren generelle Einsetzbarkeit zur dynamischen Simulation spikebasierter Neuronaler Netzwerke. Kapitel 4 enthält ein speziell entworfenes Modell des auditorischen Hirnstammes beginnend mit den Filterkaskaden zur Simulation des Innenohres, sich fortsetzend über mehr als 200 Zellen und 400 Synapsen in 5 auditorischen Kernen bis zum Richtungssensor im Bereich des auditorischen Mittelhirns. Es stellt die verwendeten Strukturen und Parameter vor und enthält grundlegende Hinweise zur Nutzung der Simulationsumgebung. Kapitel 5 besteht aus drei Abschnitten, wobei der erste Abschnitt die Experimentalbedingungen und Ergebnisse der eigens durchgeführten Tierversuche beschreibt. Der zweite Abschnitt stellt die Ergebnisse von 104 Modellversuchen zur Simulationen psycho-akustischer Effekte dar, welche u.a. die Fähigkeit des Modells zur Nachbildung des Präzedenz Effektes testen. Schließlich beschreibt der letzte Abschnitt die Ergebnisse der 54 unter realen Umweltbedingungen durchgeführten Experimente. Dabei kamen Signale zur Anwendung, welche in normalen sowie besonders stark verhallten Räumen aufgezeichnet wurden. Kapitel 6 vergleicht diese Ergebnisse mit anderen biologisch motivierten und technischen Verfahren zur Echounterdrückung und Schallquellenlokalisation und führt den aktuellen Status der Hardwareimplementierung ein. Kapitel 7 enthält schließlich eine kurze Zusammenfassung und einen Ausblick auf weitere Forschungsobjekte und geplante Aktivitäten. Diese Arbeit möchte zur Entwicklung der Computational Neuroscience beitragen, indem sie versucht, in einem speziellen Anwendungsfeld die Lücke zwischen biologischen Erkenntnissen, rechentechnischen Modellen und Hardware Engineering zu schließen. Sie empfiehlt ein neues räumlich-zeitliches Paradigma der dynamischen Informationsverarbeitung zur Erschließung biologischer Prinzipien der Informationsverarbeitung für technische Anwendungen.This thesis investigates the biological background of the psycho-acoustical precedence effect, enabling humans to suppress echoes during the localization of sound sources. It provides a technically feasible and biologically plausible model for sound source localization under echoic conditions, ready to be used by technical systems during man-machine interactions. The model is based upon own electro-physiological experiments in the mongolian gerbil. The first time in gerbils obtained results reveal a special behavior of specific cells of the dorsal nucleus of the lateral lemniscus (DNLL) - a distinct region in the auditory brainstem. The explored persistent inhibition effect of these cells seems to account for the base of echo suppression at higher auditory centers. The developed model proved capable to duplicate this behavior and suggests, that a strong and timely precise hyperpolarization is the basic mechanism behind this cell behavior. The developed neural architecture models the inner ear as well as five major nuclei of the auditory brainstem in their connectivity and intrinsic dynamics. It represents a new type of neural modeling described as Spike Interaction Models (SIM). SIM use the precise spatio-temporal interaction of single spike events for coding and processing of neural information. Their basic elements are Integrate-and-Fire Neurons and Hebbian synapses, which have been extended by specially designed dynamic transfer functions. The model is capable to detect time differences as small as 10 mircrosecondes and employs the principles of coincidence detection and precise local inhibition for auditory processing. It consists exclusively of elements of a specifically designed Neural Base Library (NBL), which has been developed for multi purpose modeling of Spike Interaction Models. This library extends the commercially available dynamic simulation environment of MATLAB/SIMULINK by different models of neurons and synapses simulating the intrinsic dynamic properties of neural cells. The usage of this library enables engineers as well as biologists to design their own, biologically plausible models of neural information processing without the need for detailed programming skills. Its graphical interface provides access to structural as well as parametric changes and is capable to display the time course of microscopic cell parameters as well as macroscopic firing pattern during simulations and thereafter. Two basic elements of the Neural Base Library have been prepared for implementation by specialized mixed analog-digital circuitry. First silicon implementations were realized by the team of the DFG Graduiertenkolleg GRK 164 and proved the possibility of fully parallel on line processing of sounds. By using the automated layout processor under development in the Graduiertenkolleg, it will be possible to design specific processors in order to apply theprinciples of distributed biological information processing to technical systems. These processors differ from classical von Neumann processors by the use of spatio temporal spike pattern instead of sequential binary values. They will extend the digital coding principle by the dimensions of space (spatial neighborhood), time (frequency, phase and amplitude) as well as the dynamics of analog potentials and introduce a new type of information processing. This thesis consists of seven chapters, dedicated to the different areas of computational neuroscience. Chapter 1: provides the motivation of this study arising from the attempt to investigate the biological principles of sound processing and make them available to technical systems interacting with humans under real world conditions. Furthermore, five reasons to use spike interaction models are given and their novel characteristics are discussed. Chapter 2: introduces the biological principles of sound source localization and the precedence effect. Current hypothesis on echo suppression and the underlying principles of the precedence effect are discussed by reference to a small selection of physiological and psycho-acoustical experiments. Chapter 3: describes the developed neural base library and introduces each of the designed neural simulation elements. It also explains the developed mathematical functions of the dynamic compartments and describes their general usage for dynamic simulation of spiking neural networks. Chapter 4: introduces the developed specific model of the auditory brainstem, starting from the filtering cascade in the inner ear via more than 200 cells and 400 synapses in five auditory regions up to the directional sensor at the level of the auditory midbrain. It displays the employed parameter sets and contains basic hints for the set up and configuration of the simulation environment. Chapter 5: consists of three sections, whereas the first one describes the set up and results of the own electro-physiological experiments. The second describes the results of 104 model simulations, performed to test the models ability to duplicate psycho-acoustical effects like the precedence effect. Finally, the last section of this chapter contains the results of 54 real world experiments using natural sound signals, recorded under normal as well as highly reverberating conditions. Chapter 6: compares the achieved results to other biologically motivated and technical models for echo suppression and sound source localization and introduces the current status of silicon implementation. Chapter 7: finally provides a short summary and an outlook toward future research subjects and areas of investigation. This thesis aims to contribute to the field of computational neuroscience by bridging the gap between biological investigation, computational modeling and silicon engineering in a specific field of application. It suggests a new spatio-temporal paradigm of information processing in order to access the capabilities of biological systems for technical applications