Films polymères électroactifs hautement déformables

National audienc

Elaboration et caractérisation de films épais piézoélectriques sérigraphiés sur alumine, silicium, aciers inoxydables et vitrocéramiques

Le travail traite de l'élaboration par sérigraphie de couches épaisses de ferroélectriques de quelques dizaines de microns d'épaisseur, et de leur caractérisation diélectrique et piézoélectrique, pour des applications dans les microsystèmes. L'emploi de substrats autres que l'alumine a nécéssité des modifications du procédé, notamment en ce qui concerne la recherche d'éléctrodes et de couches barrières adaptées, et l'abaissement du budget thermique par l'ajout d'aides au frittage. Ainsi sont réalisés des films de titanates de plomb sur vitrocéramiques et aciers inoxydables, avec des propriétés proches de celles des matériaux massifs, et des films PZT 52/48 sur silicium avec de bons coefficients d33(150pC/N) et Kt(0.45), ce dernier étant estimé à l'aide des équations des modéles à ondes planes. Des différences, entre les films épais et les céramiques massives, et entre les divers types de matériaux, sont mises en évidence et discutées.The work deals with the processing by screen-printing of ferroelectric thick films with thicknesses around tens microns, and their dielectric and piezoelectric characterization. These thick films can be used for microsystems applications. The use of other substrates instead of alumina needs to modify the process: convenient electrode and barrier layers must be found, and the sintering temperatures must be lowered by the addition of sintering aids. As a consequence lead titanate fims are made on glassceramics and stainless steels, with properties close to the bulk ceramic ones and PZT 52/48 films on silicon with good d33 (150 pC/N) and kt (0.45) coefficients. kt is estimated with the help of plane wave models equations. Some differences between the thick films and the bulk ceramics, and between different types of materials, are shown off and discussed.LIMOGES-ENSCI (870852305) / SudocVILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

A study on a polyurethane-based blend with enhanced electromechanical properties

International audienc

Enhancement of the magnetoelectric response of polyurethane polymer / piezoceramic bi-layer materials

International audiencetThis paper deals with the eddy current-induced magnetoelectric (ME) effect in a bi-layered structureconsisting of a piezoelectric ceramic and a thermoplastic polyurethane (PU) film with three differentvalues of Young’s modulus. It is observed a great effect of the elastic properties of the polymer on themagnetoelectric characteristics of the laminate samples.To study the influence of the elastic modulus (c) and damping coefficient () of the bilayers on theDC direct current magnetic induction (Bdc) induced piezomagnetic coefficient () and magnetoelectriccurrent magnitude (I), a model based on a forced damped elastic system has been developed to calculatec, , the first and second complex magnetoelectric coefficient ˛pand ˇpfor different samples. The effect ofthe polymer elastic modulus on the magnetoelectric response is presented and discussed. The calculatedvalues of the I(Bdc) and S(Bdc) obtained with this model are in good agreement with experimental data.The optimal value of the effective ME voltage coefficient (˛E t) was obtained for the stiffest polyurethanegrade

Development of large-strain and low-powered electro-active polymers (EAPs) using conductive fillers

International audienceDuring the last decade, Electro Active Polymers (EAPs) have attracted much attention especially because of their high level of generated strain. Mainly ferroelectric materials are used as fillers with elevated volume percentages in order to create a reasonable strain level. Aggregation problems should also be considered. With silicone or acrylic elastomers as the matrix, very high strains, even more than 300%, can today be obtained, however this requires a very high electric induction, e.g., 120 MV/m. Such a high electric requirement prevents these materials from being utilized with other electric components. There exist intermediate materials between traditional actuator materials, such as PZTs, and EAPs. These materials can generate higher strain levels than traditional PZT materials, and are expected to be driven with a low electric level. The present paper shows the easy fabrication method of such intermediate materials. Conductive fillers were incorporated into the polymeric material. As opposed to for ferroelectric filler materials which have many dipoles, there was no electric field inside the conductive fillers. As a consequence, electric charges were distributed over the surface of the filler particle surfaces. This mechanism increased the electric coefficient so that a high strain level could be obtained more efficiently than in the case of ferroelectric fillers. The improvement of electrostriction by adding very small volume percentages of fillers, 0.1-2 Vol.%, was thus confirmed. The composite films, fabricated by a very easy method, could generate more than 20% of strain at 15 MV/m

Study and modeling of an electrostrictive polyurethane diaphragm loaded with conductive carbon black

International audienc

Modified approach for high frequency dielectric characterization of thinly metallized soft polymer film using grounded coplanar waveguide

International audienceIn this paper, we introduce the dielectric characterization of soft polymer, polyurethane (PU), between 1 and 31 GHz frequency band using Grounded CoPlanar Waveguide (GCPW) lines with a modified analytical method. The unavoidable thin metallization (1 μm) of GCPW lines on polyurethane yields high conductor losses, which contribute to the extracted global losses up to 58% at 4 GHz. In order to get more precisely the dielectric losses, a modification of an already existing analytical model by coupling it with 3D electromagnetic simulations is proposed, which allows to estimate and subtract quickly the conductor losses. The measurements indicated that polyurethane relative permittivity ranges from 3.49 to 2.65 and the loss tangent was about 0.08, which is in agreement with the state of the art on this grade of PU as well as the Metal-Insulator-Metal capacitors characterizations (from 10−1 to 107 Hz and from 2 × 108 to 5 × 109 Hz). The proposed approach may open a fast and simple way for precisely determining the microwave dielectric properties of (ultra) soft polymers in a large bandwidth

Magnetoelectric coupling in Fe3O4/P(VDF-TrFE) nanocomposites

International audienceNanocomposite films composed of nanoparticles Fe3O4 embedded in copolymers of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) (70/30) have been elaborated. The effect of Fe3O4 content on the cristallinity ratio, dielectric and magnetoelectric properties of the nano-piezo-composites was studied and discussed. Dielectric characterization showed an increase of the permittivity and a decrease of the resistivity with the increasing ratio of nanofillers. Thermal analysis revealed a decrease of the cristallinity of the composite. Poling process was found to be difficult for Fe3O4 contents higher than 1%, because of the low breakdown fields and diminished resistivity with increasing Fe3O4 content. As a consequence, magnetoelectric measurements were conducted only on nanocomposites with Fe3O4 contents lower than 0.5% in the case of poled samples. The optimal value of the first order magnetoelectric (ME) coefficient αpαp was obtained for a nanoparticles content of 0.3% wt

Enhancement of dielectric, piezoelectric, ferroelectric, and electrocaloric properties in slightly doped (Na 0.5 Bi 0.5 ) 0.94 Ba 0.06 TiO 3 ceramic by samarium

International audienceWe investigated the structural, dielectric, piezoelectric, ferroelectric, and electrocaloric properties of the samarium doped (Na0.5Bi0.5)(0.94)Ba0.06TiO3 (NBT-6BT) ceramic. X-ray diffraction and Raman spectra confirm the coexistence of the rhombohedral and tetragonal structures for a low amount of Sm (<= 8 mol. %), while the compositions with a higher amount of Sm2O3 (11 mol. %) have a pseudocubic structure. The thermal dependency of the dielectric permittivity revealed two phase transitions from ferroelectric to antiferroelectric at low temperatures, then to paraelectric phase at higher temperatures. The substitution of NBT-6BT with 2 mol. % of Sm2O3 remarkably enhances the ferroelectric and the piezoelectric properties of the (Na0.5Bi0.5)(0.94)Ba0.06TiO3 ceramic. Furthermore, a large electrocaloric effect (Delta T = 1.4K) was directly measured on the ceramic doped with 2 mol. % of Sm2O3 under an applied electric field of 50 kV/cm. Published under license by AIP Publishing

Electrostrictive thermoplastic polyurethane-based nanocomposites filled with carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH): Properties and improvement of electromechanical activity

International audienc