{"id":55409,"date":"2022-11-30T12:29:20","date_gmt":"2022-11-30T10:29:20","guid":{"rendered":"https:\/\/www.iemn.fr\/?p=55409"},"modified":"2022-11-30T12:56:04","modified_gmt":"2022-11-30T10:56:04","slug":"these-x-d-lleshi-metasurface-absorbers-with-transverse-gradients","status":"publish","type":"post","link":"https:\/\/www.iemn.fr\/en\/theses-2022\/these-x-d-lleshi-metasurface-absorbers-with-transverse-gradients.html","title":{"rendered":"THESE : X.D LLESHI \u2013 Metasurface absorbers with transverse gradients"},"content":{"rendered":"<div id='layer_slider_1'  class='avia-layerslider main_color avia-shadow  avia-builder-el-0  el_before_av_heading  avia-builder-el-first  container_wrap sidebar_right'  style='height: 261px;'  ><div id=\"layerslider_58_1jb5blj7m5ala\" data-ls-slug=\"homepageslider\" class=\"ls-wp-container fitvidsignore ls-selectable\" style=\"width:1140px;height:260px;margin:0 auto;margin-bottom: 0px;\"><div class=\"ls-slide\" data-ls=\"duration:6000;transition2d:5;\"><img loading=\"lazy\" decoding=\"async\" width=\"2600\" height=\"270\" src=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2019\/01\/sliders_news1.jpg\" class=\"ls-bg\" alt=\"\" srcset=\"https:\/\/www.iemn.fr\/wp-content\/uploads\/2019\/01\/sliders_news1.jpg 2600w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2019\/01\/sliders_news1-300x31.jpg 300w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2019\/01\/sliders_news1-768x80.jpg 768w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2019\/01\/sliders_news1-1030x107.jpg 1030w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2019\/01\/sliders_news1-1500x156.jpg 1500w, https:\/\/www.iemn.fr\/wp-content\/uploads\/2019\/01\/sliders_news1-705x73.jpg 705w\" sizes=\"auto, (max-width: 2600px) 100vw, 2600px\" \/><ls-layer style=\"font-size:14px;text-align:left;font-style:normal;text-decoration:none;text-transform:none;font-weight:700;letter-spacing:0px;border-style:solid;border-color:#000;background-position:0% 0%;background-repeat:no-repeat;width:180px;height:30px;left:0px;top:231px;line-height:32px;color:#ffffff;border-radius:6px 6px 6px 6px;padding-left:50px;background-color:rgba(0, 0, 0, 0.57);\" class=\"ls-l ls-ib-icon ls-text-layer\" data-ls=\"minfontsize:0;minmobilefontsize:0;\"><i class=\"fa fa-quote-right\" style=\"color:#ffffff;margin-right:0.8em;font-size:1em;transform:translateY( -0.125em );\"><\/i>ACTUALITES<\/ls-layer><\/div><\/div><\/div><div id='after_layer_slider_1'  class='main_color av_default_container_wrap container_wrap sidebar_right'  ><div class='container av-section-cont-open' ><div class='template-page content  av-content-small alpha units'><div class='post-entry post-entry-type-page post-entry-55409'><div class='entry-content-wrapper clearfix'>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-lb3j82ux-61da4dad63bc12ca1805af8b21e7941f\">\n#top .av-special-heading.av-lb3j82ux-61da4dad63bc12ca1805af8b21e7941f{\nmargin:0 0 10px 0;\npadding-bottom:4px;\n}\nbody .av-special-heading.av-lb3j82ux-61da4dad63bc12ca1805af8b21e7941f .av-special-heading-tag .heading-char{\nfont-size:25px;\n}\n.av-special-heading.av-lb3j82ux-61da4dad63bc12ca1805af8b21e7941f .av-subheading{\nfont-size:15px;\n}\n<\/style>\n<div  class='av-special-heading av-lb3j82ux-61da4dad63bc12ca1805af8b21e7941f av-special-heading-h2  avia-builder-el-1  el_after_av_layerslider  el_before_av_hr  avia-builder-el-first'><h2 class='av-special-heading-tag'  itemprop=\"headline\"  >THESE : X.D LLESHI \u2013 Metasurface absorbers with transverse gradients <\/h2><div class=\"special-heading-border\"><div class=\"special-heading-inner-border\"><\/div><\/div><\/div>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-18u73nj-dad6a947580930e400fc42ba200e80f1\">\n#top .hr.av-18u73nj-dad6a947580930e400fc42ba200e80f1{\nmargin-top:5px;\nmargin-bottom:5px;\n}\n.hr.av-18u73nj-dad6a947580930e400fc42ba200e80f1 .hr-inner{\nwidth:100%;\n}\n<\/style>\n<div  class='hr av-18u73nj-dad6a947580930e400fc42ba200e80f1 hr-custom  avia-builder-el-2  el_after_av_heading  el_before_av_textblock  hr-left hr-icon-no'><span class='hr-inner inner-border-av-border-thin'><span class=\"hr-inner-style\"><\/span><\/span><\/div>\n<section  class='av_textblock_section av-jriy64i8-2f4600354c0449b610997916bbd9b6bc'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" >\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-13ewzjw-68e036126b913e5028f77311dc66b825\">\n.av_font_icon.av-13ewzjw-68e036126b913e5028f77311dc66b825{\ncolor:#bfbfbf;\nborder-color:#bfbfbf;\n}\n.av_font_icon.av-13ewzjw-68e036126b913e5028f77311dc66b825 .av-icon-char{\nfont-size:60px;\nline-height:60px;\n}\n<\/style>\n<span  class='av_font_icon av-13ewzjw-68e036126b913e5028f77311dc66b825 avia_animate_when_visible av-icon-style- avia-icon-pos-left avia-icon-animate'><span class='av-icon-char' aria-hidden='true' data-av_icon='\ue8c9' data-av_iconfont='entypo-fontello' ><\/span><\/span>\n<p><strong>X.D LLESHI <\/strong><\/p>\n<p>Soutenance : <strong>30 novembre 2022<br \/>\n<\/strong><span class=\"titre\">Th\u00e8se de doctorat en Acoustique, Universit\u00e9 de Lille, ENGSYS Sciences de l\u2019ing\u00e9nierie et des syst\u00e8mes<\/span><\/p>\n<\/div><\/section>\n<section  class='av_textblock_section av-jtefqx33-628129dba2299b2ecd65ebfc92eac29d'   itemscope=\"itemscope\" itemtype=\"https:\/\/schema.org\/BlogPosting\" itemprop=\"blogPost\" ><div class='avia_textblock'  itemprop=\"text\" ><div  class='hr av-kjh3zw-4dff888f744b728a1aca9b3a0971493a hr-default  avia-builder-el-6  avia-builder-el-no-sibling'><span class='hr-inner'><span class=\"hr-inner-style\"><\/span><\/span><\/div>\n<h5>Summary:<\/h5>\n<p>Les absorbants \u00e9lectromagn\u00e9tiques ont \u00e9t\u00e9 largement utilis\u00e9s depuis la seconde guerre mondiale dans diverses applications : r\u00e9duction de la signature radar d\u2019avion, att\u00e9nuation des effets d\u2019interf\u00e9rence entre antennes proches ou pr\u00e9vention de la r\u00e9flexion des signaux parasites dans les chambres an\u00e9cho\u00efques. Depuis ces vingt derni\u00e8res ann\u00e9es, beaucoup d\u2019\u00e9tudes ont \u00e9t\u00e9 consacr\u00e9es aux absorbants de type m\u00e9tamat\u00e9riaux. En effet ils sont tr\u00e8s compacts, peuvent satisfaire simultan\u00e9ment de multiples contraintes et pr\u00e9senter de tr\u00e8s hautes performances en termes de fen\u00eatre d\u2019absorption tr\u00e8s large bande ou de grande robustesse angulaire. Cependant, l\u2019accroissement actuel de la densification des \u00e9l\u00e9ments dans les syst\u00e8mes, notamment rayonnants, ainsi que leur utilisation sur une tr\u00e8s large gamme de fr\u00e9quences, demande la recherche de nouvelles structures absorbantes innovantes capable de faire face \u00e0 ces d\u00e9fis futurs. Dans le cadre de ce travail de th\u00e8se, des m\u00e9tasurfaces absorbantes sont \u00e9tudi\u00e9es en visant trois objectifs : i) l\u2019obtention d\u2019un niveau d\u2019absorption proche de l\u2019unit\u00e9, ii) donner des directives pour d\u00e9velopper de nouveaux mat\u00e9riaux absorbants ayant les propri\u00e9t\u00e9s RF souhait\u00e9es et iii) le contr\u00f4le du niveau d\u2019absorption. La premi\u00e8re \u00e9tude a trait \u00e0 l\u2019obtention d\u2019un niveau d\u2019absorption de l\u2019\u00e9nergie de l\u2019onde incidente sup\u00e9rieur \u00e0 90% sur une bande tr\u00e8s large (sup\u00e9rieure \u00e0 une octave) pour diff\u00e9rents \u00e9tats de polarisation et angles d\u2019incidence. Dans ce but, des structures multi-mat\u00e9riaux de forme pyramidale en marches d\u2019escalier, ont \u00e9t\u00e9 analys\u00e9es. La deuxi\u00e8me \u00e9tude porte sur les absorbeurs basse fr\u00e9quence qui utilisent des m\u00e9tamat\u00e9riaux aux propri\u00e9t\u00e9s magn\u00e9tiques. Pour obtenir une absorptivit\u00e9 quasi unitaire, diverses solutions sont propos\u00e9es, comme la combinaison de r\u00e9sonateurs di\u00e9lectriques avec des mat\u00e9riaux magn\u00e9tiques ou la conception d&rsquo;un absorbeur aux propri\u00e9t\u00e9s \u00e9lectromagn\u00e9tiques non encore d\u00e9velopp\u00e9es par les industries. La troisi\u00e8me \u00e9tude a pour but d\u2019obtenir un niveau d\u2019absorption quasi-constant dans la bande de fonctionnement entre quelques pourcents et 100%. Ces structures \u00e0 r\u00e9flexion partielles nous permettront de concevoir un profil graduel d\u2019absorption dans les directions transversales \u00e0 la direction de propagation de l\u2019onde incidente, r\u00e9duisant les effets de diffraction aux bords d\u2019\u00e9l\u00e9ments m\u00e9talliques. Pour ces \u00e9tudes sur les structures \u00e0 r\u00e9flexions partielle et totale, les aspects conception \u00e9lectromagn\u00e9tique et de caract\u00e9risation, en particulier pour les mesures des spectres de r\u00e9flectance en espace libre sont pr\u00e9sent\u00e9s et discut\u00e9s.<\/p>\n<h5>Abstract:<\/h5>\n<p>Electromagnetic absorbers have been widely used since World War II in various applications: reduction of aircraft radar signature, mitigation of interference effects between nearby antennas or prevention of reflection of spurious signals in anechoic chambers. For the last twenty years, many studies have been devoted to metamaterial absorbers. Indeed, they are very compact, can simultaneously satisfy multiple constraints and present very high performances in terms of very wide band absorption window or high angular robustness. However, the current increase in the densification of elements in systems, especially radiating systems, as well as their use over a very wide range of frequencies, requires the search for new innovative absorbing structures able to face these future challenges. In this thesis, absorbing metasurfaces are studied with three objectives: i) to obtain an absorption level close to unity, ii) to give guidelines to develop new absorbing materials with the desired RF properties and iii) to control the absorption level. The first study deals with the achievement of an absorption level of the incident wave energy higher than 90% over a very wide band (greater than one octave) for different polarization states and incidence angles. For this purpose, multi-material structures with a pyramidal staircase shape have been analyzed. The second study deals with low frequency absorbers using metamaterials with magnetic properties. In order to obtain a quasi-unity absorptivity, various solutions are proposed, such as the combination of dielectric resonators with magnetic materials or the design of an absorber with electromagnetic properties not yet developed by the industries. The third study aims at obtaining a quasi-constant absorption level in the operating band between a few percent and 100%. These partial reflection structures will allow us to design a gradual absorption profile in directions transverse to the direction of propagation of the incident wave, reducing the effects of diffraction at the edges of metallic elements. For these studies on partial and total reflection structures, the electromagnetic design and characterization aspects, in particular for free space reflectance spectra measurements are presented and discussed.<\/p>\n<\/div><\/section>","protected":false},"excerpt":{"rendered":"","protected":false},"author":20,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[316],"tags":[],"class_list":["post-55409","post","type-post","status-publish","format-standard","hentry","category-theses-2022"],"_links":{"self":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/55409","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/users\/20"}],"replies":[{"embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/comments?post=55409"}],"version-history":[{"count":0,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/55409\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/media?parent=55409"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/categories?post=55409"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/tags?post=55409"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}