Soft thermoplastic blends as antenna substrates : formulations and characterizations

La multitude des dispositifs communicants haute fréquence associée à l’avènement de l’électronique flexible ont suscité un intérêt croissant dans l’étude et le développement des polymères souples en tant que substrats légers et bas coût pour les antennes planaires. Néanmoins, les pertes diélectriques élevées des polymères simples limitent les performances finales de l’antenne. Dans ce contexte, l’objectif de cette thèse est de développer des mélanges thermoplastiques styréniques souples en tant que substrats diélectriques pour des antennes planaires (patch) en bande X. L’intérêt principal des mélanges thermoplastiques réside dans la possibilité de moduler les caractéristiques diélectriques et mécaniques. Ainsi, le choix des formulations des mélanges thermoplastiques à base de copolymères styréniques, a été guidé par la recherche d’un compromis entre pertes diélectriques et souplesse. Pour ce nouveau type de substrat souple, une méthodologie de caractérisation diélectrique large bande a été adaptée afin d’étudier l’effet de la composition du mélange sur les propriétés diélectriques. Les faibles pertes des mélanges en bande X ont démontré leur potentialité pour les applications en micro-ondes. Conséquemment, un protocole de fabrication d’antenne planaire a été présenté et les performances de rayonnement des antennes intégrant les mélanges thermoplastiques les plus prometteurs ont été analysées et comparées à l’état de l’art.The multitude of communicating systems operating at high frequencies associated to the evolution of flexible electronics have increased the interest in developing and studying soft polymers as light and low cost dielectric substrates for patch antenna. Nevertheless, due to their high loss at high frequencies, simple polymers hinder the final performances of the antenna. Regarding to that aspect, the main objective of the PhD project is to develop soft styrenic thermoplastic blends as substrates for patch antenna in the X-band. The main interest of the blends is that the final properties such as the dielectric and the mechanical ones can be tuned. Hence, the choice of the formulations of the thermoplastic blends based on styrenic copolymers was driven by the quest of a compromise between dielectric loss and softness. For the new soft developed substrates, a broadband dielectric characterization methodology has been established. The influence of the blends composition on the dielectric properties has been studied. The dielectric characteristics of the thermoplastic blends proved their potential as substrates for antenna operating at microwave frequencies. Consequently, the antenna fabrication protocol has been presented and the performances of antennas based on different blends have been analyzed and compared to literature

Characterization methodology up to 40 GHz of new low loss soft dielectric thermoplastic films for microwave applications

International audienceThis paper presents a soft low dielectric loss thermoplastic blend based on polyolefins as a dielectric material for microwave applications. To determine the dielectric properties, more precisely the relative permittivity εr and tan δ, characterization techniques and the elaboration of samples were customized to the 200-μm thick dielectric film. Dielectric properties were extracted from the peaks of the transmission coefficient S 12 measured from 10 MHz to 40 GHz with probe station and coplanar waveguide ring resonator. The measured dielectric constant and loss tangent of the investigated blends were found to be around ε r ≈ 2.45 and tan δ ≈ 0.01 in X-Band. A proof of concept of a patch antenna based on the developed soft dielectric film of polypropylene (PP)-based polymer blend was also made. The measured return loss of the antenna showed great agreement with simulation results with HFSS® software and reached -30 dB at an operating frequency of 9.7 GHz. An investigation of the radiation characteristics in the far field in anechoic room was made. The gain and the efficiency of the patch microstrip antenna, which were extracted and calculated from the radiation pattern attained 4.56 dB and 47% respectively. These here reported results are promising for the development of blend compositions for high frequency applications

Ring resonator characterization at microwave frequencies of a novel soft dielectric

International audienceRecent evolution in wireless communication and flexible electronics [1], where planar antennas are subject to external mechanical constraints such as bending requires to customize the main components such as the dielectric to make it more suitable for the upcoming trends. Developing soft dielectric brings many advantages as it significantly reduces the weight and permits to design engineered alternatives to the existing rigid antennas. For instance, it is of a great importance to develop soft dielectric substrate with low dielectric loss in order not to hinder the radiation of antenna. In this work, we present a novel soft dielectric thermoplastic elastomer based on standard polyolefins like polypropylene and polyethylene and to our knowledge, no characterization method was reported to similar blends in microwave frequencies. We propose an established methodology of dielectric characterization up to 40 GHz based on the ring resonator with grounded coplanar waveguide [2] by the GSG (Ground Signal Ground) probe that was tailored for a 200-µm thick soft dielectric thermoplastic elastomer. The rings were prepared via photolithography of the copper layer deposited by sputtering over a thermo-molded thermoplastic dielectric film. The proposed methodology first consists in extracting the dielectric permittivity and dielectric loss up to 10 kHz based on the metal insulator metal model, where measurements were carried out using impedance meter Agilent 4294A. Then the ring geometric dimensions were optimized by High frequency electromagnetic simulations. Different ring radiuses were tested to minimize the error in calculation of the dielectric properties and the results were obtained by using an Agilent E8364B Vector Network Analyzer (VNA) (bandwidth from 10 MHz to 50 GHz) and Cascade ACP40-AW-GSG probes (40 GHz bandwidth, 500 µm pitch). The whole test system was controlled using Wincal Cascade software. The measured dielectric constant and loss tangent up to 40 GHz were extracted from the resonant peaks of the S12 and were found to be r ~ 2.42 and tan ~ 0.008 at ~15 GHz respectively for a polyethylene octene copolymer (OBC) and styrene-ethylene-butadiene-styrene (SEBS) based blend (Young’s Modulus : ~5 MPa). The low dielectric loss in the X-band makes the soft dielectric blend promising for microwave devices such as antenna applications

New low loss soft thermoplastic blends for microwave applications

International audienceAll organic soft dielectrics are growing more and more interest in the electronic industry owing to their light weight, low cost and the flexibility they yield compared to the rigid devices. In the specific field of microwave communicating devices planar printed (patch) antennas on a soft dielectric substrate are sought for their conformability and advantageous compactness. In this article, two soft thermoplastic elastomer blends based on polypropylene (PP) or low-density polyethylene (LDPE) were tested. The fabrication process and the established characterization steps have been fully presented. More specifically, in order to characterize the dielectric film up to 40 GHz, the microstrip ring resonator with coplanar waveguide access has been adapted to a new configuration specimen sample. The results of the characterizations obtained showed very encouraging performances for microwave applications. Indeed, the measured dielectric constant and loss tangent up to 40 GHz were found to be ε_r≈2.45 and tan δ≈0.01 for both blends. The fabrication and the radiation characteristics of a patch antenna on a new performing PP or LDPE-based elastomer blends as the soft dielectric substrate was demonstrated and analysed. The proof of the concept of the investigated device consists of a microstrip patch antenna with an operation frequency of about 10 GHz. These dielectric features render the polyolefin based blends very promising as a soft material for microwave engineering, which is confirmed by the measured antenna properties: the gain, the directivity as well as the efficiency have been calculated from the measured radiation pattern and were recorded as 4.6 dB, 7.7 dB and 46% respectively for the r-PP based blend and 4.8 dB, 8.1 dB and 51% for the LDPE based blend

Mélanges élastomères thermoplastiques souples à faible pertes diélectriques pour applications antennaires en bande X

National audienceLe développement de substrats souples suscite un intérêt croissant pour les dispositifs communicants en bande X. En particulier, les polymères souples apportent un degré de liberté supplémentaire pour une intégration plus aisée des antennes planaires à des dispositifs conformables. Dans cet article, le choix des composants d’un mélange élastomère thermoplastique (TPE) en tant que substrat diélectrique est présenté. Les méthodes de caractérisation diélectrique ont été adaptées à ce type de matériau. Ainsi, la mesure des pertes diélectriques par la méthode des anneaux résonateurs jusqu’à 40GHz a donné des valeurs de tan δ~5.10-3 à 15GHz. La fabrication de l’antenne patch ainsi que les mesures du coefficient de réflexion pour un mélange TPE ont mis en évidence le potentiel des TPE comme substrats diélectriques souples

Optical absorption signature of a self-assembled dye monolayer on graphene

A well-organized monolayer of alkylated perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) has been formed onto CVD graphene transferred on a transparent substrate. Its structure has been probed by scanning tunnelling microscopy and its optical properties by polarized transmission spectroscopy at varying incidence. The results show that the transition dipoles of adsorbed PTCDI are all oriented parallel to the substrate. The maximum absorption is consistent with the measured surface density of molecules and their absorption cross section. The spectrum presents mainly a large red-shift of the absorption line compared with the free molecules dispersed in solution, whereas the relative strengths of the vibronic structures are preserved. These changes are attributed to non-resonant interactions with the graphene layer and the neighbouring molecules

Potentialities of flexoelectric effect in soft polymer films for electromechanical applications

International audienceAmong the transduction mechanisms of interest for sensing and/or actuationapplications at nano/micro scale, the piezoelectric effect has been widely exploited owing tothe solid state nature of piezoelectrics, the large ability of specific classes of materials for themechanical-to-electrical energy conversion and easy integration. However, every piezoelectric(also generally ferroelectric) presents well-known intrinsic drawbacks such as required polingstep and related aging. In contrast, uniquely flexoelectric materials do not suffer from thesedisadvantages because flexoelectricity, a universal effect in all dielectric solids defined as theelectrical polarization induced by a strain gradient, does not imply preliminary electric fieldinducedmacroscopic polarization. Besides, strain gradient may be easily obtained by bendingplate or cantilever-shaped structure and in this case it is nothing but the local curvature of theflexible system. Thus, as strain gradient (curvature) inversely scales with both elastic stiffnessand thickness, this study will focus on the evaluation of the potentialities of flexoelectric effectin soft polymer films for electromechanical applications, with an emphasis on the thicknessinfluence. In this way, analytical results combined to experimentally obtained effectiveflexoelectric coefficients for some typical polymer classes may provide guidelines for thedevelopment of soft and low frequency flexoelectric mechanical transducers