Miniaturisation des antennes large bande à l'aide de matériaux artificiels

Dans le domaine de la guerre électronique, la maîtrise du spectre électromagnétique est primordiale. Les antennes doivent donc posséder une couverture fréquentielle extrêmement large. Leur bande de fréquences de fonctionnement peut dépasser la décade, i.e. un rapport 10 entre fréquences haute et basse. De plus, la fréquence basse peut être voisine de la centaine de MHz augmentant de ce fait l'encombrement de l'antenne dans le sens de l'épaisseur. L'intégration d'antenne bande basse sur porteur constitue donc un enjeu majeur. Les antennes classiques dédiées a la guerre électronique font habituellement appel a des antennes dites " indépendantes de la fréquence " chargées par une cavité absorbante. Les travaux présentes dans ce manuscrit ont pour but de supprimer les absorbants présents dans les antennes pour a la fois augmenter leur efficacité et réduire leur épaisseur. Nos recherches se sont orientés vers les matériaux dits " artificiels ", les conducteurs magnétiques artificiels (CMA) et des matériaux a bandes interdites électromagnétiques (BIE), permettant la réalisation pratique de réflecteur magnétique. Apres un état de l'art sur les méthodes analytiques, numériques et expérimentales, nous étudions le comportement de l'antenne spirale d'Archimède en espace libre puis en présence de réflecteurs théoriques: conducteur électrique parfait et conducteur magnétique parfait. Nous avons proposé et validé expérimentalement une méthodologie innovante pour la conception d'antenne large bande faible épaisseur. Enfin, nous avons présenté un réflecteur hybride exploitant les propriétés des conducteurs électriques et magnétiques afin d'étendre la bande de fréquences des antennes.In the field of electronic warfare, control of the electromagnetic spectrum is essential. Antennas must have an extremely broad frequency coverage. Their frequency band of operation may exceed the decade, i.e. a ratio of 10 between high and low frequencies. In addition, the low frequency can be close to a hundred MHz thereby increasing the size of the antenna in the direction of thickness. The integration of low-band antenna is a major challenge. Frequency independent antennas loaded by a cavity absorbent are conventional antennas dedicated to electronic warfare commonly used. The work presented in this manuscript are intended to remove the absorbent present in antennas to increase efficiency and reduce their thickness. Our research was oriented towards artificial materials, such as artificial magnetic conductor (amc) and electromagnetic band gap materials (ebg), enabling the practical realization of magnetic reflector. After a state of the art of analytical, numerical and experimental methods, we study the behavior of an archimedean spiral antenna in free space and then with two types of theoretical reflectors: perfect electric conductor (pec) and perfect magnetic conductor (pmc). We proposed and experimentally validated an innovative methodology to design a wideband and low profile antenna. Finally, we presented a hybrid reflector composed of electrical and magnetic conductors. These two types of conductors are combined to extend the operating bandwidth of the antenna. Using an archimedean spiral, we show that antenna have exploitable properties at low and high frequency.PARIS-Télécom ParisTech (751132302) / SudocSudocFranceF

Reprocessable Covalent Elastomeric Networks from Functionalized 1,4-cis-Polyisoprene and -Polybutadiene

International audienceTo obtain and maintain rubber properties such as elasticity, strength, creep, and chemical resistance, or stiffness over time, rubbers must be chemically cross-linked, mainly by sulfur vulcanization. However, the materials produced in this manner result in irreversibly cross-linked networks and are consequently difficult to recycle, which leads to large quantities of rubber waste each year. In this paper, a new route to synthesize reversibly cross-linked 1,4-cis-polyisoprene (PI) and -polybutadiene (PB) based on the Diels–Alder chemistry is investigated. Furan groups are first grafted along the polymeric backbone and at chain ends. In a second step, a bis-maleimide compound is added to the modified liquid material, leading to the formation of a thermo-reversible cross-linked elastomer. Mechanical properties of the resulting rubber can be easily tuned and depend on the bis-maleimide/furan ratio as well as on the nature of the polymeric precursor (polyisoprene vs polybutadiene). The good reprocessability of these materials was demonstrated by remolding them five times without any loss of properties between the first and the last cycle

DAMPs and RAGE Pathophysiology at the Acute Phase of Brain Injury: An Overview

Early or primary injury due to brain aggression, such as mechanical trauma, hemorrhage or is-chemia, triggers the release of damage-associated molecular patterns (DAMPs) in the extracellular space. Some DAMPs, such as S100B, participate in the regulation of cell growth and survival but may also trigger cellular damage as their concentration increases in the extracellular space. When DAMPs bind to pattern-recognition receptors, such as the receptor of advanced glycation end-products (RAGE), they lead to non-infectious inflammation that will contribute to necrotic cell clearance but may also worsen brain injury. In this narrative review, we describe the role and ki-netics of DAMPs and RAGE at the acute phase of brain injury. We searched the MEDLINE database for “DAMPs” or “RAGE” or “S100B” and “traumatic brain injury” or “subarachnoid hemorrhage” or “stroke”. We selected original articles reporting data on acute brain injury pathophysiology, from which we describe DAMPs release and clearance upon acute brain injury, and the implication of RAGE in the development of brain injury. We will also discuss the clinical strategies that emerge from this overview in terms of biomarkers and therapeutic perspective