Most electromagnetic interference standards specify that measurements of radiated emissions must be performed in the far field (FF), e.g. at an open-area test site or in a semi-anechoic chamber. Since near field (NF) measurements are cheaper, quicker and more flexible compared to FF tests, establishing a correlation between NF and FF data is of great research interest. One strategy to achieve this goal is to find a set of basic radiators comprising electric and magnetic dipoles that generate the same NF as the original source at selected observation points. This set of dipoles, based on the uniqueness theorem, can then be used to predict the FF radiation patterns. The uniqueness theorem requires that electric or magnetic fields are matched on a closed surface with respect to the magnitude and phase. The focus of this thesis is the investigation of FF prediction based on NF magnitude-only data. In this thesis, a robust NF-FF conversion model based on Genetic Algorithms (GAs) is built up to predict the radiation of printed circuit boards (PCBs). This is done by introducing a dipole moment magnitude range pre-selection before the initialisation step of GAs, customising the processes of selection, crossover and mutation for anti-sticking and checking the correlation between NF and FF fitness values. Since the performance of GAs is tightly related to the number of dipoles in the GA model, FF characteristics of generic radiation sources (such as a long wire and a large loop) are analysed using both analytical calculation and source modelling by GAs. For structures with simple FF patterns, if more dipoles than necessary are used, the computational cost of GAs is unnecessarily high. On the other side, for structures with complicated FF patterns, the GA modelling may not be able to well approximate the FF radiation, due to the limitation for GAs to tackle too many unknowns. Therefore the scope of the model applicability is discussed, and a dipole number N, depending on the electrical size of the source, is recommended for GA modelling. By applying GAs to get the equivalent dipole set of a radiating PCB from the magnetic NF magnitudes, NF sampling approaches are investigated in detail, including where to locate NF sampling planes, what plane coverage angle to choose, how many points to observe, what type of data to collect, what dynamic range to allow for the data, and how many planes to choose. Two case studies are presented for predicting the FF radiation of PCBs from magnetic NF magnitude-only observations, and validate the NF sampling approaches in this thesis.

L'écoulement de jeu est un phénomène très important dans les turbomachines. Il provient du mouvement relatif entre la pale et la paroi d'extrémité, et la différence de pression à travers la pale. L'écoulement de jeu est extrêmement complexe pour sa nature tridimensionnelle et instable, et son existence conduit à de nombreux effets défavorables, par exemple, les pertes de performance aérodynamique et les émissions de bruit. C'est pourquoi l'écoulement de jeu a motivé de nombreuses recherches expérimentales et numériques. Afin d'améliorer la compréhension du écoulement de jeu et le bruit de large bande associé, une campagne de recherche a été menée au LMFA. En ce qui concerne l'écoulement de jeu, cette campagne de recherche comprend une expérience avec des technologies de mesure avancées, un calcul zonal LES et une série de calculs RANS / URANS. L'expérience et les simulations considèrent une configuration simple de l'écoulement de jeu à un faible nombre de Mach. Les résultats expérimentaux et numériques sont analysés de façon systématique et approfondie dans la présente étude. Enfin, des efforts sont déployés pour la modélisation et la prédiction du bruit à large bande avec des résultats expérimentaux et numériques. On observe dans l'expérience un système à multiple-tourbillon, avec une tourbillon de jeu intense. Les différentes analyses sur les caractéristiques d'écoulement montrent un bon accord entre l'expérience et le ZLES dans la région du écoulement de jeu. L'approche zonale (RANS-LES) s'avère être un outil puissant pour fournir une description détaillée du écoulement de jeu, avec un coût de calcul limité. Cependant, les calculs RANS et URANS surestiment globalement la diffusion de la tourbillon. En outre, l'oscillation du tourbillon de jeu est étudiée en utilisant des champs instantanés de PIV et l'amplitude d'oscillation est évaluée. La réponse dynamique de la tourbillon de jeu est également étudiée avec URANS aux fréquences choisies. Deux modèles de prédiction du bruit en champ lointain, correspondant à deux sources acoustiques différentes, sont reformulés et mis en oeuvre avec les données de champ proche des simulations numériques. Ces prédictions sont comparées aux mesures à champ lointain. En utilisant les données ZLES, le modèle de l’écoulement de jeu sur-estime le bruit généré dans la région de jeu. Le modèle de bruit de bord de fuite est implémenté avec les données ZLES et les données RANS et fournit une très bonne prédiction dans une large bande de fréquence. / The tip-leakage flow is a common flow feature in turbomachines. It originates from the relative motion between the blade tip and the end-wall, and the pressure difference across the blade. The tip-leakage flow is extremely complex for its three-dimensional unsteady nature, and its existence leads to many unfavourable effects, such as aerodynamic performance losses and noise emissions. These issues have motivated extensive experimental and numerical researches from both aerodynamic and aeroacoustic points of view. In order to improve the understanding of the tip-leakage flow and its associated broadband noise, a research campaign has been carried out at LMFA. Regarding the tip-leakage flow, this research campaign includes an experiment with advanced measurement technologies, a zonal LES computation and a series of RANS/URANS computations. Both the experiment and the simulations consider a single-airfoil configuration at low Mach number. Experimental and numerical results are analysed systematically and thoroughly in the current study. Finally, efforts are put on the broadband noise modelling and prediction based on the experimental and numerical results. A multi-vortex system with an intense tip-leakage vortex is observed in the experiment. The various analyses of the flow characteristics show a good agreement between the experiment and the ZLES in the blade tip region. The zonal (RANS-LES) approach proves itself to be a powerful tool to provide a detailed description of the tip-leakage flow, with a limited computational cost. However, the RANS and URANS computations globally over-estimate the diffusion of the tip-leakage vortex. Furthermore, the random oscillation of the tip-leakage vortex is investigated using PIV instantaneous flow fields and the wandering amplitude is evaluated. The dynamic response of the tip-leakage vortex is also studied with URANS at selected frequencies. Two far-field noise prediction models, corresponding to two different acoustic sources, are reformulated and implemented with the near-field data from the numerical simulations. These predictions are compared to the far-field measurements. Using the ZLES data as input, the blade-tip self-noise model is found to over-estimate the noise generated in the blade-tip region. The trailing-edge noise model is implemented with the time-averaged ZLES and the RANS near-field data, and yields a very good prediction within a broad range of frequency.

Cette thèse propose de prédire le bruit émis par des ventilateurs à basse vitesse et sa diffraction par des obstacles liés aux contraintes d’installation dans les applications industrielles. Les composantes tonale et à large bande du bruit sont étudiées. Les méthodes existant dans la littérature considèrent des hypothèses et des simplifications afin de traiter le problème du bruit des ventilateurs de façon analytique, comme par exemple l’approximation de champ lointain. Tout d’abord, l’hypothèse de champ lointain dans la formulation du bruit tonal est relaxée. En utilisant des sources artificielles, une comparaison entre deux expressions analytiques et une simulation numérique est effectuée pour la validation en champ libre. Ensuite, la diffraction du bruit tonal est étudiée par des techniques numériques et analytiques. Le champ acoustique d’un rotor fonctionnant dans un conduit fini est d’abord pris comme exemple en combinant les formulations analytiques avec la méthode d’éléments de frontière (BEM). Etant donné que cette dernière serait trop coûteuse en temps de calcul pour des applications haute fréquence, des techniques analytiques pour le problème de diffraction sont également présentées. La réflexion et la diffraction des ondes sonores par une plaque infinie sont d’abord considérées en remplaçant la plaque par une source image. Ensuite, une solution analytique exacte pour la diffraction du bruit tonal par un coin rigide est formulée. Un autre point abordé dans cette thèse est la prévision du bruit à large bande produit par un ventilateur axial à basse vitesse évoluant dans un écoulement turbulent. La théorie d’Amiet pour le bruit d’interaction de turbulence sur un profil fixe est considérée. Nous en proposons dans cette thèse une extension permettant de prédire le bruit du profil dans son champ proche géométrique l’aide d’outils semi-analytiques. La nouvelle formulation est comparée à solution classique d’Amiet et à une solution de référence obtenue par intégration numérique sans hypothèse de champ lointain géométrique. Des expériences sont également menées dans une soufflerie anéchoide où la turbulence est générée en amont du profil par une grille. Une autre hypothèse du modèle d’Amiet concerne l’écoulement uniforme arrivant sur le profil. Cette hypothèse n’est pas vérifiée dans la plupart des applications industrielles. Différentes méthodes existent dans la littérature pour traiter ce problème. Nous proposons une nouvelle approche pour prendre en compte des conditions d’écoulement variables en envergure. En intégrant toutes ces améliorations, la réponse acoustique large bande d’un profil fixe placé dans un jet turbulent et d’un ventilateur axial à basse vitesse placé dans un écoulement turbulent est étudiée et validée par comparaison avec l’expérience. Dans une dernière partie, la diffraction des ondes acoustiques générées par le profil et le ventilateur par des obstacles est déterminée numériquement et analytiquement. Puisque la méthode BEM n’est pas prévue pour résoudre directement le champ d’une source aléatoire, une approche innovante obtenue par la reformulation de la méthode déterministe de BEM est utilisée. Le modèle final est comparé aux solutions numériques, analytiques et expérimentales pour la validation. / This thesis proposes to predict the sound emitted from low-speed fans and its scattered-field by installation effects related to industrial applications. Both tonal and broadband components of fan noise are investigated. Methods existing in the literature contain assumptions and simplifications in order to deal with fan noise problems in analytical manner, such as consideration of an observer located in the far-field of the source. Firstly, the effect of far-field assumption in the tonal fan noise formulation is addressed. Using artificial blade sources, a comparison between two closed-form analytical solutions and a numerical technique is performed for validation in free-field. Secondly, the scattered field of the tonal fan noise is investigated using numerical and analytical techniques. The acoustic field of a rotor operating in a finite duct is first investigated combining the closed-form analytical formulations with the Boundary Element Method (BEM). Since BEM would be computationally demanding for high frequency applications, analytical scattering techniques are also introduced. Reflection and scattering of sound waves by a large plane are first addressed replacing the plane with an image source. Secondly, an exact analytical solution considering scattering of the tonal fan noise by a rigid corner is derived. Another point addressed in this thesis is the prediction of the broadband noise generated by a low-speed axial fan operating in turbulent stream. Amiet’s theory of turbulence-interaction noise for a stationary air foil is considered. One of the key points proposed in this thesis is an extension of Amiet’s method, allowing prediction of the acoustic field of the airfoil in its geometrical near-field in a semi-analytical perspective. The extended formulation is compared with Amiet’s classical solution and a reference solution obtained with numerical integration involving no geometrical far-field assumption. Experiments are also performed in anechoic chamber using an isolated airfoil located in grid generated turbulence. Another assumption made in Amiet’s theory is the consideration of uniform flow impinging onto the airfoil. However this assumption is not valid for most industrial applications. Different methods exist in literature to deal with this problem. A new approach is proposed in order to take the span wise varying flow conditions into account. Including all the improvements, the broadband acoustic responses of a stationary airfoil located in the developing region of a jet and of a low-speed axial fan operating in a turbulent stream are investigated and validated against measurements. Finally, scattering of the sound generated by the considered airfoil and fan by benchmark obstacles is addressed numerically and analytically. Since BEM is not capable to handle statistical source fields directly, an innovative approach obtained by re-formulating the deterministic BEM method is employed. The final model is compared to the numerical, analytical and experimental solutions for validation purposes.

No description available.

Physical implementations of cryptographic algorithmscan leak sensitive information through different kindsof side-channels. This information can potentially be used forrecovering the secret key used in the algorithms. Recently, sidechannelattacks on CPU implementations of Advanced EncryptionStandard (AES) has been presented. Some of these attacksuse far-field electromagnetic radiation.In this thesis, we investigate if cross correlation can be used tolocate the part of the signal corresponding to the execution of theAES-encryption. We gather side-channel signal data containingencryption activity to create and test multiple templates forcorrelation. By evaluating the performance of the templates indifferent scenarios, we conclude that the method is useful andrelatively easy to implement compared to previous methods.Furthermore, our extraction method has a low execution timewhich gives it potential to be used in real-time attacks. / Fysiska implementationer av krypteringsalgoritmerkan läcka känslig information genom olika typer avsidokanaler. Informationen kan potentiellt användas för att återskapa algoritmernas hemliga krypteringsnycklar. Senastetiden har sidokanalsattacker mot CPU-implementationer av AdvancedEncryption Standard (AES) presenterats. Vissa av dessaattacker nyttjar utstrålande elektromagnetiska fjärrfält. I denna rapport undersöker vi om korskorrelation kananvändas för att hitta tidpunkten i signalen då AES-krypteringengenomfördes. Vi samlar in signaldata från sidokanalen sominnehåller krypteringsaktivitet, detta för att skapa och testa olikakorrelationsmallar. Genom att utvärdera mallarnas prestanda iolika scenarion kan vi sluta oss till att denna metod är användbarsamt lätt att implementera jämfört med tidigare metoder. Därtillvisar vår metods korta körtid att den har potential att användasi en realtidsattack. / Kandidatexjobb i elektroteknik 2021, KTH, Stockholm

As more and more modern systems and products use built-in microcontrollers, hardware security becomes more important to protect against cyber-attacks. Internet of things devices, like Bluetooth devices, usually use an encryption algorithm to keep data safe from hackers. Advanced Encryption Standard (AES) is a commonly used encryption algorithm. AES itself is hard to break. However, it is possible to utilize the information leaking from a system during the execution of encryption, called side-channel, to recover the key or part of the key used by the encryption algorithm. This kind of attack is called a side-channel attack (SCA). In this study, two deep learning (DL) models are trained to attack the Bluetooth microcontroller unit Nordic nRF52 development kit equipped with an nRF52832 chip. The DL models are trained using the far-field electromagnetic emissions that the microcontroller unintentionally generates and transmits through the antenna while encrypting data. All encryptions are executed with a fixed key and random plaintext. The attack is conducted in two stages: the profiling and attack stages. In the profiling stage, where the attacker is assumed to have full system control, 100 000 traces holding encryption information are sampled and used to train the DL models to classify a sub-byte of the fixed key given a trace. In the attack stage, traces are captured in two different environments. The first is an entirely isolated environment, while the second adds a specific Wi-Fi access point and client connection that execute HTTP requests and responses in this isolated environment referred to as the system environment. Given traces obtained from one of the two attack environments, the performance of the trained models at classifying the correct sub-key is evaluated.  To summarize the results of this study, twelve SCAs are performed on six datasets captured in two different environments using two different DL models for each dataset. The correct key byte can be retrieved in three of these SCAs. All three successful attacks are made in an isolated environment without any interfering noise. The best performance is achieved with the multi-layer perceptron DL architecture, processing traces each composed of 10 averaged traces of the identical encryption, and the correct key-byte is recovered after 8198 traces.

La caractérisation des sources de rayonnement électromagnétique par des techniques de champ proche est aujourd'hui largement utilisée. Ces techniques consistent à mesurer le champ rayonné à proximité de la source pour en déduire, par traitement mathématique, le champ dans d'autres zones de l'espace (champ proche ou champ lointain). Les applications sont nombreuses comme par exemple la caractérisation des diagrammes de rayonnement des antennes ou la détermination des périmètres de sécurité autour des antennes de station de base. Par ailleurs, la mesure en champ proche trouve également des applications dans le diagnostic des sources.Ce travail de thèse porte sur une nouvelle méthode de calcul des coefficients du développement modal à partir d'une mesure sur une surface échantillonnée irrégulièrement ou arbitraire. Ces coefficients permettent ensuite d'évaluer le diagramme de rayonnement de la structure rayonnante dans toutes les directions de l'espace.Le principe de la méthode matricielle consiste à mesurer les composantes tangentielles du champ électromagnétique sur une surface. Les coefficients modaux sont obtenus par l'inversion d'un système d'équations linéaires reliant le champ électrique mesuré et les fonctions d'ondes.Cette méthode permet de désolidariser la géométrie de la surface de mesure du système de coordonnées dans lequel est exprimé le développement modal. Il en résulte de nombreux avantages, comme le choix d'une surface de mesure quelconque, pour des raisons de compacité, de simplicité de mise en œuvre ou de suppression d'erreur de troncature. / The characterization of electromagnetic radiation sources by near field techniques is now widely used. These involve measuring the radiated field close to the source to deduce, by mathematical processing, the field in other areas of space (near field and far field). There are many applications such as the evaluation of the antenna far field radiation patterns or the determination of safety perimeters around base station antennas. Furthermore, the near-field measurement technique can be used in the sources diagnostic.In our study, we present a new method for calculating the modal expansion coefficients from irregularly sampled or arbitrary measurement surfaces. The calculation of these modal coefficients allows the assessment of the radiation pattern of the antenna under test in every spatial directions.The principle of the matrix method is to calculate the modal coefficients by solving a system of linear equations relating the measured electric field and wave functions. Once the modal coefficients are known the far field of the structure is achieved.This method allows the separation between the geometry of the measuring surface and the coordinate system wherein the modal expansion is expressed. This leads to many advantages, such as selecting any measurement surfaces, for the reasons of compactness, implementation simplicity or truncation errors suppression.

The aim of this thesis is to improve the operational performance of the communication antennas mounted on complex platforms such as aircrafts and warships by arranging placements of these antennas. Towards this aim, primarily, in order to gain insight on the influence of geometrically simple structures composing the platform on antenna performance, a quarter wavelength monopole antenna placed at the center of a finite square ground plane is studied by using uniform Geometrical Theory of Diffraction (GTD). Besides, the change of far field radiation pattern and complex diffraction functions due to the variation of the width of a square ground plane is examined. Secondly, electromagnetic analysis of two Ultra High Frequency (UHF) antennas mounted on geometrically simple structures composing simplified F-4 aircraft is carried out by using transient solver of Computer Simulation Technology (CST) Microwave Studio&reg / (MWS), in order to conceive the influence of each structure on antenna performance. Then, electromagnetic analysis of these antennas mounted on simplified and original F-4 aircrafts is performed, in order to determine the optimal location of the lower UHF antenna (newly installed antenna) for the operational performance of this antenna to be optimum in terms of electromagnetic coupling and far field radiation pattern. Finally, electromagnetic analysis of the communication antennas mounted on a warship is performed by using transient solver of CST MWS&reg / , in order to determine the optimal locations of these antennas for the operational performance of these antennas to be optimum in terms of electromagnetic coupling and far field radiation pattern.

Le thermo-photovoltaïque (TPV), conversion du rayonnement thermique par des cellules photovoltaïques (PV), est un dispositif qui a suscité un intérêt croissant depuis deux décennies, notamment pour son efficacité supérieure à celle de la conversion photovoltaïque classique. Ceci est essentiellement dû à l'accord entre le spectre du rayonnement de la source thermique et le spectre de conversion de la cellule PV. Les rendements maximaux sont obtenus pour des sources thermiques cohérentes, émettant dans une gamme spectrale étroite, énergétiquement au-dessus de l'énergie de la bande interdite de la cellule PV. On propose dans ce travail d'appliquer une méthode d'optimisation stochastique, en l'occurrence l'optimisation par essaims de particules, pour concevoir et optimiser de telles sources. On aboutit alors à des structures unidimensionnelles simples, à base de films minces de diélectriques, métaux et de semi-conducteurs. Les propriétés radiatives de ces sources, stables pour des températures allant jusqu'à 1000 K, sont aisément contrôlables à l'aide de paramètres simples comme les épaisseurs des films ou la concentration de dopage. Finalement, on propose une étude d'optimisation paramétrique des propriétés optiques des matériaux susceptibles de maximiser l'échange radiatif en champ proche entre deux milieux plans semi-infinis. Cette étude aboutit à un outil pratique, sous forme d'abaques, permettant de guider le choix des matériaux pertinents afin de maximiser les puissances au même temps que l'efficacité des systèmes TPV nanométriques. / Thermo-photovoltaic conversion of thermal radiation is a concept that has been thoroughly investigated during the two last decades because of its high efficiency when compared to classical photovoltaics (PV). These high performances are mainly due to the good-matching between the thermal source radiation spectrum and the PV cell conversion spectrum. Maximal efficiencies areobtained with coherent sources that emit in narrow spectral bands, just above the band gap energy of the cell. In this report, a stochastic method to design and optimize such sources, the particle swarm optimization in this case, is firstly presented. This method leads to simple one-dimensional structures, composed of thin films of dielectrics, metals and semiconductors. The radiativeproperties of these sources are easily tunable with control parameters as simple as films thicknesses and doping concentrations. They are stable at high temperatures up to 1000 K. Second, a parametric optimization study of usual materials optical properties models (Drude and Lorentz) is presented in order to maximize radiative heat transfer between semi-infinite planes separated by nanometric gaps. This leads to a simple tool in the form of abacuses which would guide the choice of relevant materials to maximize the output power of nano thermo-photovoltaic devices.

This thesis is an examination of one of the main technologies to be developed on the path to Space Solar Power (SSP): Wireless Power Transfer (WPT), specifically power beaming. While SSP has been the main motivation for this body of work, other applications of power beaming include ground-to-ground energy transfer, ground to low-flying satellite wireless power transfer, mother-daughter satellite configurations, and even ground-to-car or ground-to-flying-car power transfer. More broadly, Wireless Power Transfer falls under the category of radio and microwave signals; with that in mind, some of the topics contained within can even be applied to 5G or other RF applications. The main components of WPT are signal transmission, propagation, and reception. This thesis focuses on the transmission and propagation of wireless power signals, including beamforming with Phased Array Antennas (PAAs) and evaluations of transmission and propagation efficiency. Signals used to transmit power long distances must be extremely directive in order to deliver the power at an acceptable efficiency and to prevent excess power from interfering with other RF technology. Phased array antennas offer one method of increasing the directivity of a transmitted beam through off-axis cancellation from the multi-antenna source. Besides beamforming, another focus of this work is on the equations used to describe the efficiency and far field distance of transmitting antennas. Most previously used equations, including the Friis equation and the Goubau equation, are formed by examining singleton antennas, and do not account for the unique properties of antenna arrays. Updated equations and evaluation methods are presented both for the far field and the efficiency of phased array antennas. Experimental results corroborate the far field model and efficiency equation presented, and the implications of these results regarding space solar power and other applications are discussed. The results of this thesis are important to the applications of WPT previously mentioned, and can also be used as a starting point for further WPT and SSP research, especially when looking at the foundations of PAA technology.