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Production of mm-Wave epiwafers of GaN on Si grown by NH3-MBE
No full textInternational audienceWith 5G-advanced, the data consumption between wireless equipment is predicted to follow exponential growth. To allow that, there is a need to increase the bandwidth with RF chips that fulfill 2 criteria: performance in the range of 24-100 GHz and affordability, for large scale deployment. Thanks to its remarkable properties, GaN is an ideal material that will deliver high power densities with high efficiency in the millimeter waves [1]. Two technologies coexist to answer these criteria: GaN-on-Silicon Carbide (SiC) and GaN-on-Silicon. GaN-on-SiC shows high performance [2], essentially because of the high thermal conductivity of SiC, however highly resistive SiC is expensive and the fabrication process of SiC generates 12 times more carbon emission than Si [3]. On the other hand, GaN-on-Si is affordable but lacks performance.Straightened by EasyGaN’s knowhow in terms of AlN grown on Silicon by NH3-MBE, we have developed step by step an epistack, named LeanGaN, that is 3 times thinner than standard MOCVD GaN-on-Si epistack, with a purity 100 times higher. It is directly translated on the performance of test devices, by establishing the state of the art of power added efficiency (PAE) at 40 GHz (Fig.1) [4]. The first reliability tests, such as High Temperature Operating Lifetime, show promising results. It reveals only a 0.2 dB drop in output power over 8 hours (Fig. 2). Epiwafers up to 200 mm diameter are produced using ammonia mode in a fully automated RIBER MBE 49 production reactor
Strain energy harvesting performances of piezoelectric composite transducers in rolling tires: a numerical study
No full textTire-pavement contact is responsible for mechanical strain energy which can be used to power autonomous smart devices in the context of automotive industry. Power harvesting capabilities of piezoelectric composites included in the host structure are numerically evaluated from finite element (FE) simulations. The transducer consists of a network of rectangular piezoelectric parallelepipeds embedded in a soft polymer matrix. At the local scale of the composite, optimal transducer geometries are identified with a brute force research. The procedure highlights a large sensitivity to the mechanical load, that justifies an analysis of the intrusiveness of the sensor integration in the host structure. Computations are performed at the tire scale to discuss the influence of the sensor on the strain energy distribution. The results show that a trade-off has to be made between the harvesting efficiency and the changes in mechanical behaviour of the host structure. These variations are considered with care in view of preserving the functional properties of the tire.</div
Robust attribute-based access control protocol over data-centric IoT-NDN networking
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Back Barrier Integration for > 4kV Blocking in GaN HEMTs on Sapphire without Field Plates
No full textInternational audienceThis work presents a significant advancement in optimizing the trade-off between on-resistance and breakdown voltage in GaN high electron mobility transistors (HEMTs) grown on sapphire substrates. By integrating an AlGaN back barrier and employing high carbon doping in the buffer layer, we achieve blocking voltages exceeding 4 kV while maintaining low on-resistance-without the use of gate dielectrics or field plates. In addition to improved electrical performance, transient measurements reveal a reduction in trapping effects thanks to the back barrier, which enhances carrier confinement and mitigates long recovery time traps. These findings highlight the potential of GaN-on-sapphire as a cost-effective and scalable platform for high-voltage power applications.</div
Designing an Artificial Intelligence Driving Assistance System (AIDAS) for train drivers
No full textInternational audienceThis paper propose system in order to promote a new task sharing approach for railway driving. The system depends on three monitoring modules for evaluating the driver's condition, driving performance, and the driver's instantaneous and anticipated workload, and two output modules to compute, compare and select the best approach. Initially, data on the driver and the train driving parameters are collected and utilised to generate indicators. Finally, the algorithms to propose a distribution of train driving tasks is analysed in relation to the indicator that has been previously calculated. The objective of the task distribution is twofold: firstly, to optimise the driver's workload, and secondly, to modify the distribution when the driver is under or overloaded. The algorithm has the capacity to enhance the driver's performance and skills, or to adapt the driver's workload
La redéfinition de l'ordre public économique à l'ère de la reconfiguration de la concurrence internationale
No full textArticle d'un volume de 15 pages, structuré en deux parties (I et II), elles-mêmes composées, chacune, deux sous-parties (A et B).Economic public order is not sufficiently defined by interventionism or ordoliberalism, nor by liberalism and neoliberalism, which repress it. This is undoubtedly due to the different ideological underpinnings that run through it depending on economic circumstances. Thus, economic public order cannot be defined in isolation by laissez-faire, nor by regulation, the market, or competition, which it exceeds, although it is identified at the heart of the latter, or even as one of its components, especially since it takes several forms, even different aspects in the era of "private economic orders," and is also presented as a by-product of globalization serving a societal project. The plasticity of this notion seems to allow its redefinition and therefore its readjustment, including that of public power, in the era of a reconfigured international competition which is becoming more exacerbated, through recourse to the notion of essential interests of the Nation, which favors a redeployment of this public power in economic matters, in a relatively new form.L’ordre public économique n’est pas suffisamment défini ni par l’interventionnisme ou l’ordolibéralisme, ni par le libéralisme et le néolibéralisme qui le refoulent. Sans doute en raison des différents soubassements idéologiques qui le traversent au gré des conjonctures économiques. Ainsi, l’ordre public économique ne peut se définir isolément ni par le laisser-faire, ni par la régulation, le marché ou la concurrence qu’il excède, bien qu’identifié au cœur de celle-ci, voire comme l’une de ses composantes, d’autant plus qu’il se décline sous plusieurs natures, même sous différents aspects à l’ère des « ordres privés économiques » et se présente par ailleurs comme un sous-produit de la mondialisation au service d’un projet de société. La plasticité de cette notion semble permettre sa redéfinition et donc sa réadaptation y compris celle de la puissance publique, à l’ère d’une concurrence internationale reconfigurée qui s’exacerbe, à travers le recours à la notion d’intérêts essentiels de la Nation, qui favorise un redéploiement de cette puissance publique en matière économique, sous une forme relativement nouvelle
Event-Triggered Adaptive Fault-Tolerant Control Based on Sliding Mode/Neural Network for Lane Keeping Assistance Systems in Steer-by-Wire Vehicles
No full textInternational audienceThis paper presents a new approach to Fault-Tolerant Control (FTC), addressing the complexities inherent in vehicle dynamics and steering actuator faults. By combining the sliding mode (SM) method and the Generalized Regression Neural Network (GRNN) for their compensation, this novel approach introduces a single estimator to consider a complete dynamic system that incorporates all nonlinearities and actuator faults. Inspired by conventional Model-Free Control (MFC) techniques, which often rely on specific model assumptions, we propose a new adaptive model-free control structure based on local measurements. Furthermore, we introduce an innovative event-triggered control mechanism that activates control actions only when necessary, where the system closed-loop stability is demonstrated through a rigorous Lyapunov theory analysis. This strategy not only enhances system efficiency but also reduces energy consumption and processing overhead in computing systems. The effectiveness of our approach is demonstrated through numerical simulations and experimental tests, particularly in lateral Lane-Keeping Assist (LKA) systems for Steer-by-Wire (SBW) vehicle. Overall, our contributions advance the field of fault-tolerant control, offering practical solutions for real-world applications.</div
Étude expérimentale de l’effet de la turbulence à haute intensité sur le sillage d’un corps allongé.
No full textThe resurgence of slow-flying aircraft operating in disturbed environments requires taking into account realistic unsteady conditions (turbulence, variability of loads…) and their coupling with the intrinsic wake dynamics. We propose to study the near wake of a slender ellipsoidal body, which serves as a simple yet representative demonstrator of real geometries (airships, submarines). The wake is first investigated in isolation, then subjected to high-intensity turbulent forcing.This research is based on experimental campaigns carried out in a water channel. Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) measurements were performed to provide both extensive spatial distributions and high-resolution temporal signatures.The first objective is to generate canonical decaying turbulence using fractal grids specifically designed to maximize turbulent intensity. The resulting decaying turbulence is characterized (Taylor microscale, turbulent kinetic energy, dissipation rate…) and compared with the literature. Notably, this study leverages PIV data to examine the common assumptions of homogeneity and isotropy (the “frozen turbulence” approximation).The second objective is to investigate the effect of this turbulent forcing on the statistical properties of the ellipsoid’s wake. Self-similarity and longitudinal evolution laws are identified under turbulent conditions and compared to the baseline case. We observe a reduction in entrainment and turbulent production, alongside a sustained feeding of the wake by the ambient turbulent kinetic energy.The third objective is to highlight the mechanisms of production and inter-scale transfers in the wake, with and without turbulent perturbation. To this end, we employ an approach still little known in this field: the Hilbert–Huang transform. This method decomposes the dynamics without relying on a preestablished mode basis and allows estimation of the local spectral signature at every point in the velocity field.La résurgence des aéronefs lents, opérant dans un environnement perturbé, nécessite la prise en compte de conditions réalistes instationnaires (turbulences, variabilité des contraintes…) et de leurs couplages avec les dynamiques intrinsèques de sillages. On se propose d’étudier le sillage proche d'un corps élancé ellipsoïdal, qui constitue un démonstrateur simple mais représentatif de géométries réelles (dirigeables, sous-marins). Le sillage est étudié seul puis est soumis à un forçage turbulent de haute intensité.Ces recherches s’appuient sur des campagnes expérimentales menées dans un canal hydraulique. Des mesures de Vélocimétries par Images de Particules (PIV) et Laser Doppler (LDV) ont été effectuées pour fournir à la fois une distribution spatiale étendue et des signatures temporelles haute résolution.Le premier objectif est de générer l’écoulement turbulent canonique à l’aide de grilles fractales spécialement conçues pour maximiser l’intensité turbulente. La turbulence en déclin ainsi obtenue est caractérisée (micro-échelle de Taylor, énergie cinétique turbulente, dissipation…) et confrontée à la littérature. Notons que cette étude tire avantage de la PIV pour discuter des hypothèses d’homogénéité et d’isotropie généralement utilisées (approximation de turbulence gelée).Le deuxième objectif est d’étudier l’effet de ce forçage turbulent sur les propriétés statistiques du sillage de l’ellipsoïde. L’auto-similitude et les lois d’évolution longitudinale sont identifiées dans le cas turbulent et comparées au cas de référence. On observe une diminution de l’entrainement et de la production turbulente et parallèlement, une alimentation continue du sillage par l’énergie cinétique turbulente ambiante.Le troisième objectif est la mise en évidence des mécanismes de production et de transferts inter-échelle dans le sillage avec et sans perturbation turbulente. Dans ce but, on propose une approche encore peu connue dans le domaine : la transformée de Hilbert-Huang. Cette méthode décompose la dynamique sans base de modes préétablie et permet d’estimer la signature spectrale locale en tout point du champ de vitesse
Optomechanical Su-Schrieffer–Heeger States in a Nanobeam Cavity
No full textInternational audienceWe design an optomechanical nanobeam cavity based on the Su–Schrieffer–Heeger (SSH) model,created via alternating two mechanical/optical domains at the interface through controlled holes and stubsspacing. The system provides topologically protected photon–phonon coupling (g/2π = 782 KHz) and a highoptical quality factor (Q = 3.77×105)
