Mesure des coefficients de la matrice de diffusion d'une jonction mécanique

La caractérisation expérimentale des jonctions mécaniques souvent complexes rencontrées dans nombre d'applications industrielles est un élément essentiel intervenant dans l'élaboration de modèles vibratoires. Les jonctions permettant de relier des structures simples de type plaque ou poutre peuvent être représentées à l'aide de matrice de diffusion. L'objet de cette communication est de présenter un dispositif expéri mental permettant la mesure des caractéristiques d'une jonction constituée d'une masse symétrique raccordant deux poutres soumises à des vibrations de flexion. La méthode de mesure et ses conditions optimales de mise en oeuvre sont présentées et permettent d'obtenir les coefficients de transmission et de réflexion. Un modèle, tenant compte de l'élasticité des liaisons poutre/masse permet de rendre compte des coefficients mesurés et d'interpréter leur variation fréquentielle à l'aide du phénomène de masse bloquante

Mode conversion in High overtone Bulk Acoustic wave Resonators

International audienceHigh overtone Bulk Acoustic Resonators (HBAR) have been realized using the Smart Cut(TM) technology to transfer a thin X-cut LiNbO3 layer onto an X-cut LiNbO3 substrate. When the bonding of the two wafers is performed, an additional rotation along the normal axis is set to generate mode conversion between the two acoustic shear waves electromechanically coupled in X-cut LiNbO3. This enables excitation of only one of the two acoustic shear waves

Large Qxf Product for HBAR using Smart Cut (TM) transfer of LiNbO3 thin layers onto LiNbO3 substrate

International audienceIn this paper, we propose a novel approach for HBAR devices using the Smart Cut(TM) technology to obtain thin homogeneous X-cut single crystal films of LiNbO3. Sub-micron layers were successfully transferred onto LiNbO3 handle wafers. RF characterizations were performed around 1.95 GHz and quality factors in excess of 40 000 are extracted, proving the applicability of layer transfer by Smart Cut TM to acoustic devices. An excellent matching between simulations and experimental data as well as TCF measurements are presented in this pape

Self-referenced spectral interferometry for ultrashort infrared pulse characterization

Self-Referenced Spectral Interferometry is used for single shot pulse characterization over the 0.9-2.5 µm spectral range with a single spectrometer and an optimized optical setup. We characterize sub-55 fs pulses from 1.4 µm to 2 µm and broadband 2.5-cycle pulses at 1.65 µm (13 fs FWHM)

GaInP/AlGaAs metal-wrap-through tandem concentrator solar cells

III–V multi-junction solar cells are promising devices for photovoltaic applications under very high concentration levels of sunlight. Shadowing losses of the front side metallisation and ohmic resistance losses in the metal grid limit the practical cell size typically to around 1 cm2 at 1000 suns. The use of a full back-contact architecture, similar to the metal-wrap-through (MWT) technology known in silicon photovoltaics, can help to overcome this limitation. Furthermore, positioning both the positive and negative contact pads on the rear side of concentrator solar cells opens the possibility for efficient packaging solutions and the realisation of dense array receivers with low metal shadowing. The MWT technology addresses conventional concentrating photovoltaics as well as combined conventional concentrating photovoltaic-thermal applications and offers specific advantages for large-area devices at high intensities. This work presents the first experimental results for MWT architectures applied to III–V tandem solar cells and discusses specific challenges. An efficiency of 28.3% at 176 suns and 27.2% at 800 suns has been measured for the best MWT Ga0.51In0.49P/Al0.03Ga0.97As tandem solar cells

III-V multi-junction Metal-Wrap-Through (MWT) concentrator solar cells

III-V multi-junction solar cells are promising devices for photovoltaic applications under very high concentration levels of sunlight. Shadowing losses of the front side metallization and ohmic resistance losses in the metal grid limit the practical cell size typically to around 1 cm2 at 800 suns. The use of a full back-contact architecture, similar to the Metal Wrap-Trough (MWT) technology known in silicon photovoltaics, can help to overcome this limitation. Furthermore, positioning both the positive and negative contact pads on the rear side of concentrator solar cells opens the possibility for efficient packaging solutions and the realization of dense array receivers with low metal shadowing. The MWT technology addresses conventional concentrating photovoltaics as well as combined PV-thermal applications and offers specific advantages for large area devices at high intensities. This work presents first experimental results for MWT architectures applied to III-V tandem solar cells and discusses specific challenges. An efficiency of 28.3 % at 176 suns and 27.2% at 800 suns has been measured for the best MWT Ga0.51In0.49P/Al0.03Ga0.97As tandem solar cells