Stress analysis, dielectric, piezoelectric, and ferroelectric properties of PZT thick films. Fabrication of a 50MHz Tm-pMUT annular array

PZT films up to 35 μm thick were fabricated, using a composite sol gel route combining a PZT powder and a PZT sol. The maximum temperature for the process was 710°C. A demonstration of single layer and multilayer structures was given to show the flexibility of this technology. With Stoney’s Equation, studies of the in-situ film stress development as a function of the film thickness and density was effectuated. It helped to understand that the internal forces increase considerably with the film thickness and density. This study yields to set up experimental conditions in which a crack free surface finish of a 28μm thick film revealed the adaptability of the spin coating technique to fabricate thick films. The wet etching technology revealed the possibility of a great adaptability to pattern and shape innovative devices such as bars 10 μm wide of 21μm PZT thick film. The results open the way to a wide range of new industrial application requiring small features and/or multilayer PZT thick film with embedded electrodes. The single element and annular array devices have been shown to resonate at approximately 60MHz in air and 50 MHz in water. Three types of the composite thick film – 2C+4S, 2C+5S and 2C+6S – were used to fabricate the Tm-pMUT devices. In each case the most effective poling was obtained by maintaining the poling field of 8.4V/μm during cooling from the poling temperature (200ºC) to ‘freeze’ poled domains in place. This ‘freezing’ was required to prevent the tensile stresses within the film from reorienting the domains at high temperatures when the poling field is removed. Increasing values of thickness mode coupling coefficient (kt) were observed with increasing levels of sol infiltration (decreasing density). Such behaviour is thought to be due to non linear effects on the piezoelectric coefficient (e33) at high levels of porosity. For very dense thick film material a kt of 0.47 was observed which is comparable to that observed for the bulk material

New Advances in Forming Functional Ceramics for Micro Devices

Micro electromechanical systems (MEMS) are finding uses in an increasing number of diverse applications. Currently the fabrication techniques used to produce such MEMS devices are primarily based on 2-D processing of thin films. The challenges faced by producing more complex structures (e.g. high aspect ratio, spans, and multi-material structures) require the development of new processing techniques. Potential solutions to these challenges based on low temperature processing of functional ceramics, selective chemical patterning, and micro-moulding are presented to show that it is possible to create complex functional ceramic structures which incorporate non-ceramic conducting and support structures. The capabilities of both techniques are compared and the relative advantages of each explored

1-3 Piezocomposite design optimised for high frequency kerfless transducer arrays

Piezocomposites that can operate at frequencies above 30 MHz without spurious modes are required in order to develop sufficiently sensitive high frequency arrays for high resolution imaging. However, scaling down of conventional piezocomposite fabrication techniques becomes increasingly difficult as dimensions decrease with increasing frequency. The approach presented here is to use micro-moulded 1-3 piezocomposites and a distribution of piezoelectric segment size and separation. Innovative approaches to composite pattern design, based on a randomized spatial distribution, are presented. Micro-moulding techniques are shown to be suitable for fabricating composites with dimensions required for high frequency composites. Randomized piezocomposite patterns are modeled and are shown to suppress spurious modes

Les résultats des grandes banques internationales en 2005 et au premier semestre 2006.

Les grands groupes internationaux ont bénéficié, depuis 2005, d’un environnement économique et financier particulièrement favorable. Leurs performances pourraient toutefois se dégrader face à la montée des risques.Concentration bancaire, opérations transfrontalières, produit net bancaire, produit net d’intermédiation, charges d’exploitation, coefficient net d’exploitation, coût du risque de crédit, résultat net, coefficient de rentabilité.

Les résultats des grandes banques internationales en 2004 et au premier semestre 2005.

concentration bancaire, opérations transfrontalières, produit net bancaire, produit net d’intermédiation, charges d’exploitation, coefficient net d’exploitation, coût du risque de crédit, opérations sur immobilisations financières, résultat net, coefficient de rentabilité.

Comparaison entre quatre solutions pour échanger de l'énergie entre systèmes de forte capacité de stockage

International audienceL'électrification de systèmes toujours plus puissants est habituellement corrélée à de plus grands besoins de fiabilité, continuité de service et échanges d'énergie entre sources. Dans le domaine des systèmes de stockage électrochimique d'énergie, ces besoins sont souvent satisfaits en parallélisant des batteries. La déconnexion de deux batteries en parallèle est un processus simple et bien maîtrisé. En revanche, la connexion est un processus bien plus long et compliqué qui requière de l'électronique de puissance adaptée car cela revient à connecter en parallèle deux sources de tension. Basé sur un cas concret d'application et grâce à des simulations, cet article propose une comparaison entre quatre solutions pour échanger de l'énergie entre systèmes batterie lithium-ion et maitriser la connexion en parallèle de ceux-ci

Variable-number tandem-repeat markers for typing Mycobacterium intracellulare strains isolated in humans

<p>Abstract</p> <p>Background</p> <p><it>Mycobacterium intracellulare</it>, a species of the <it>Mycobacterium avium complex</it>, may be the cause of severe lung, lymphatic node, skin and bone/joint infections, as well as bacteriemia. The goal of this work was to identify Mycobacterial Interspersed Repetitive Unit-Variable Number Tandem Repeat (MIRU-VNTR) markers and to study their variability in a collection of isolates of <it>M. intracellulare </it>collected in humans. We studied 61 isolates collected in humans between 2001 and 2008, as well as the reference strain, <it>M. intracellulare </it>ATCC 13950.</p> <p>Results</p> <p>We identified 45 MIRU-VNTR candidates, of which 17 corresponded to the MIRU-VNTR identified in the genome of <it>M. intracellulare </it>ATCC 13950. Among the 45 potential MIRU-VNTR, seven were selected for use in a MIRU-VNTR assay applied to our collection of isolates. Forty-four patterns were found by MIRU-VNTR typing and the discriminatory power of the assay was high with a Hunter-Gaston diversity index of 0.98. We do not have evidence of a particular distribution of MIRU-VNTR polymorphism according to clinical situation.</p> <p>Conclusions</p> <p>Our results suggest that MIRU-VNTR typing could be used for molecular epidemiological studies applied to <it>M. intracellulare</it>.</p