{"id":55407,"date":"2023-02-03T17:00:18","date_gmt":"2023-02-03T15:00:18","guid":{"rendered":"https:\/\/www.iemn.fr\/?p=55407"},"modified":"2023-02-03T17:00:18","modified_gmt":"2023-02-03T15:00:18","slug":"these-r-chamseddine-metasurfaces-fonctionelles-controlees-par-cristaux-liquides","status":"publish","type":"post","link":"https:\/\/www.iemn.fr\/en\/these\/these-2021\/these-r-chamseddine-metasurfaces-fonctionelles-controlees-par-cristaux-liquides.html","title":{"rendered":"THESIS: R. CHAMSEDDINE- Functional metasurfaces controlled by liquid crystals"},"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_bkcfz092cqxp\" 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-55407'><div class='entry-content-wrapper clearfix'>\n\n<style type=\"text\/css\" data-created_by=\"avia_inline_auto\" id=\"style-css-av-lb3fz51p-9efd37c2b78bf891c1d565da4689dd8c\">\n#top .av-special-heading.av-lb3fz51p-9efd37c2b78bf891c1d565da4689dd8c{\nmargin:0 0 10px 0;\npadding-bottom:4px;\n}\nbody .av-special-heading.av-lb3fz51p-9efd37c2b78bf891c1d565da4689dd8c .av-special-heading-tag .heading-char{\nfont-size:25px;\n}\n.av-special-heading.av-lb3fz51p-9efd37c2b78bf891c1d565da4689dd8c .av-subheading{\nfont-size:15px;\n}\n<\/style>\n<div  class='av-special-heading av-lb3fz51p-9efd37c2b78bf891c1d565da4689dd8c 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 : R. CHAMSEDDINE &#8211; M\u00e9tasurfaces fonctionelles contr\u00f4l\u00e9es par cristaux liquides <\/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><u>CHAMSEDDINE R.<\/u><br \/>\n<\/strong><\/p>\n<p>Soutenance : <strong>16 d\u00e9cembre 2021<br \/>\n<\/strong><br \/>\nTh\u00e8se de doctorat en Electronique, micro\u00e9lectronique, nano\u00e9lectronique et micro-ondes, Universit\u00e9 de Lille, ENGSYS Sciences de l\u2019ing\u00e9nierie et des syst\u00e8mes.<\/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>Le but principal de cette th\u00e8se a \u00e9t\u00e9 de contr\u00f4ler dynamiquement la r\u00e9flectivit\u00e9 d\u2019une m\u00e9tasurface par cristaux liquides. Les m\u00e9tasurfaces, dont les propri\u00e9t\u00e9s \u00e9lectromagn\u00e9tiques sont contr\u00f4l\u00e9es \u00e9lectriquement par l\u2019orientation des mol\u00e9cules LC, fonctionnent en r\u00e9flexion et pr\u00e9sentent un tr\u00e8s fort contraste entre une absorption quasi-totale et un faible niveau de r\u00e9flexion, dans le but de r\u00e9aliser un modulateur d\u2019amplitude. Des r\u00e9seaux p\u00e9riodiques de type \u2018patchs\u2019 ont \u00e9t\u00e9 optimis\u00e9s par simulation num\u00e9rique de type \u2018 full wave\u2019 et \u00e0 l\u2019aide d\u2019une approche analytique de type lignes de transmission. Leurs propri\u00e9t\u00e9s \u00e9lectromagn\u00e9tiques ont ensuite \u00e9t\u00e9 valid\u00e9es exp\u00e9rimentalement par des mesures de spectres de r\u00e9flectivit\u00e9, sans ou avec tension de commande, dans la bande 26-40 GHz. Un d\u00e9calage fr\u00e9quentiel de la fr\u00e9quence de r\u00e9sonance du r\u00e9seau de plus de 5.8 GHz, correspondant \u00e0 une agilit\u00e9 en fr\u00e9quence de 17 %, \u00e0 l\u2019origine d\u2019un contraste de plus de 30 dB, a ainsi pu \u00eatre d\u00e9montr\u00e9 par l\u2019infiltration d\u2019un cristal liquide de forte anisotropie avec des valeurs de permittivit\u00e9 longitudinale de 4 et transversale de 2. 6. Pour le travail de conception, une attention particuli\u00e8re a \u00e9t\u00e9 port\u00e9e \u00e0 la condition de r\u00e9sonance des r\u00e9seaux qui d\u00e9pend principalement de la dimension lat\u00e9rale des patchs et \u00e0 celle de couplage critique qui correspond \u00e0 l\u2019\u00e9galit\u00e9 des coefficients de radiation et de dissipation. Au plan exp\u00e9rimental, deux contributions essentielles ont \u00e9t\u00e9 apport\u00e9es avec d\u2019une part la caract\u00e9risation des propri\u00e9t\u00e9s di\u00e9lectriques des LC dans la bande 26-40 GHz \u00e0 l\u2019aide d\u2019une cellule guides d\u2019onde, les cristaux liquides \u00e9tant orient\u00e9s sous champ magn\u00e9tique et la mise en oeuvre d\u2019un banc bi-statique de mesure en espace libre des param\u00e8tres de la matrice de r\u00e9partition dans cette m\u00eame bande. L\u2019ing\u00e9nierie de phase par le contr\u00f4le de l\u2019argument du coefficient complexe ainsi que l\u2019introduction de variations locales gr\u00e2ce \u00e0 des m\u00e9tasurfaces pix\u00e9lis\u00e9es, en vue de contr\u00f4ler en temps r\u00e9el les diagrammes de rayonnement, \u00e0 l\u2019aide de m\u00e9tasurfaces, constituent les prochaines \u00e9tapes de ce travail.<\/p>\n<h5>Abstract:<\/h5>\n<p>The main goal of this thesis was to dynamically control the reflectivity of a liquid crystal metasurface. The metasurfaces, whose electromagnetic properties are electrically controlled by the orientation of the LC molecules, operate in reflection and present a very strong contrast between a quasi-total absorption and a low level of reflection, in order to realize an amplitude modulator. Periodic arrays of the \u2018patch\u2019 type were optimized by full wave numerical simulation and by an analytical approach of the transmission line type. Their electromagnetic properties were then experimentally validated by reflectivity spectra measurements, without or with control voltage, in the 26-40 GHz band. A frequency shift of the resonant frequency of the grating of more than 5.8 GHz, corresponding to a frequency agility of 17%, resulting in a contrast of more than 30 dB, was demonstrated by the infiltration of a liquid crystal of high anisotropy with longitudinal permittivity values of 4 and transverse permittivity of 2. In the design work, particular attention has been paid to the resonance condition of the gratings which depends mainly on the lateral dimension of the patches and to the critical coupling condition which corresponds to the equality of the radiation and dissipation coefficients. At the experimental level, two essential contributions have been made with the characterization of the dielectric properties of LCs in the 26-40 GHz band using a waveguide cell, the liquid crystals being oriented under magnetic field and the implementation of a bi-static bench for free space measurement of the parameters of the distribution matrix in this same band. Phase engineering by controlling the argument of the complex coefficient as well as the introduction of local variations thanks to pixelated metasurfaces, in order to control in real time the radiation patterns, with the help of metasurfaces, are the next steps of this work.<\/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":[317],"tags":[],"class_list":["post-55407","post","type-post","status-publish","format-standard","hentry","category-these-2021"],"_links":{"self":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/55407","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=55407"}],"version-history":[{"count":0,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/posts\/55407\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/media?parent=55407"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/categories?post=55407"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.iemn.fr\/en\/wp-json\/wp\/v2\/tags?post=55407"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}