Laurent Robert

Miniaturized pH biosensors based on electrochemically modified electrodes with biocompatible polymers.

Potentiometric pH sensors based on linear polyethylenimine (L-PEI) and linear polypropylenimine(L-PPI), two synthetic enzymes and biocompatible polymers, films were prepared by electropolymerization of three different monomers: ethylenediamine (EDA), 1,3-diaminopropane (1,3-DAP) and diethylenetriamine (DETA) in order to be used in clinical, dermatological and biological applications, such as in vivo analysis. In a first step a biosensor was tested which consisted in a platinum wire protruded from glass sheath. The polymer film coated on these platinum electrodes showed good linear potentiometric responses to pH changes from pH 3 to 10. Resulting electrodes present both good reversibility and good stability versus time. The effect of the different polymer film thicknesses to potentiometric responses was also studied. This study allowed us to develop a miniaturized pH biosensor in the second step. This sensor was fabricated using photo-lithography, followed by sputtering and lift-off processes, and it included an electronic detection system. We have also successfully studied the potentiometric responses to pH changes of this device over a period of 1 month, and so we propose this new pH micro-biosensor as an alternative to classical pH sensors currently used in dermatology.

Microgrippers fabricated by the LIGA technique

A study devoted to the design and fabrication of microgrippers using the LIGA technique is described in this paper. The design method is presented and validated by the use of finite-element analysis. Technological topics are detailed to illustrate the fabrication process. Also, experimental data concerning the mechanical behaviour of one of the microgrippers are reported. These data are used to improve the previous finite-element analysis. Finally, a comparison between experiments and theoretical predictions is discussed.

Surface acoustic wave trapping in a periodic array of mechanical resonators

The existence of two families of surface acoustic modes trapped by steep ridges on a piezoelectric substrate, shear horizontal and vertically polarized surface modes, is demonstrated experimentally using high aspect ratio interdigital transducers fabricated on lithium niobate. The experimental variation of the resonance frequencies of the various surface modes is obtained experimentally, and up to an order of magnitude slowing of surface waves is observed, with the phase velocity dropping from 4000 down to 450m∕s. It is argued that the observed resonances are surface modes trapped by the ridge electrodes.

Discriminated measures of strain and temperature in metallic specimen with embedded superimposed long and short fibre Bragg gratings

We propose a superimposed fibre Bragg gratings device to measure, localize and discriminate strain and temperature effects simultaneously for structural health monitoring. Long period grating (LPG) and fibre Bragg grating (FBG) exhibit different responses to an applied perturbation; thus, strain and temperature influences can be determined separately by measuring the corresponding wavelength shifts. In this paper, we present a configuration based on the use of these two grating types: a LPG and a FBG written in the same fibre section which allows us to discriminate the contributions of these two main perturbations. The sensor is calibrated in a temperature range from 22 °C to 120 °C and in a strain range from 0 to 1400 μe. The reported errors are estimated to be within ± 0.4 °C and ±5 μe respectively. Our sensor is compared to those suggested in the literature for the discrimination between strain and temperature with Bragg gratings. We propose a parameter E which allows us to compare the relative uncoupling efficiency of those techniques. These sensors were embedded and tested in metallic material plates for the purpose of validating structural health monitoring.

Highly selective electroplated nickel mask for lithium niobate dry etching

A sulfur hexafluoride based reactive ion etching process allowing to etch several micron deep holes with diameters of the order of a few microns in lithium niobate is reported. Etching of deep structures with aspect ratios up to 1.5 was made possible through the use of an electroplated nickel mask exhibiting a selectivity as high as 20 with respect to lithium niobate. Several crystallograpic orientations were investigated, although particular interest was paid to Y-axis oriented substrates. Photoresist as well as metal masks were also tested and their selectivity was compared. The influence of process parameters such as applied rf power or operating pressure on the sidewall slope angle of the etched patterns was investigated. The technique has been successfully applied to the fabrication of phononic crystals consisting of periodical arrays of 9 μm diameter, 10 μm deep holes, with a 10 μm period, and presenting sidewall angles as high as 73° etched in Y-axis oriented lithium niobate.

X-ray characterization of residual stresses in electroplated nickel used in LIGA technique

Pertinent simulations of micro-electromechanical systems using powerful computer-aided design tools depend on a systematic characterization of the electrical, optical, magnetic, and mechanical properties of the different materials involved in the fabrication of microdevices. Among these properties, we focused our attention on the residual stresses, which may be responsible for the degradation of the mechanical performances of micro-actuators and sensors. We report in this paper a detailed investigation of the residual stresses arising during nickel electroplating used in the LIGA technique. X-ray analysis and, in particular, the sin2 Ψ method allow a local characterization of the structural properties of the material as well as the residual stress tensor. The experimental results obtained on our nickel plates obtained with a nickel sulphamate electrolyte show that the structural properties and the residual stresses are tightly linked to the nature of the substrates used for the depositions (silicon and copper), the densities of current, the amount of NiCl2 in the bath and the thickness of the layers. In order to obtain the intrinsic stresses, the thermoelastic contribution to the global stresses is estimated with a finite element method and subtracted to the experimental values. In the final part of this paper, we present the effect of residual stresses in the mechanical behavior of a microgripper fabricated by LIGA.

A speckle texture image generator

We propose a framework for obtaining synthetic speckle-pattern images based on successive transformations of Perlins coherent noise function. In addition we show how a given displacement function can be used to produce deformed images, making this framework suitable for performance analysis of speckle-based displacement/strain measurement techniques, such as Digital Image Correlation, widely used in experimental mechanics.

Position-referenced microscopy for live cell culture monitoring

Position-referenced microscopy (PRM) is based on smart sample holders that integrate a position reference pattern (PRP) in their depth, allowing the determination of the lateral coordinates with respect to the sample-holder itself. Regions of interest can thus be retrieved easily after culture dish transfers from a cell incubator to the microscope stage. Images recorded at different instants in time are superimposed in a common coordinate system with subpixel accuracy. This paper presents such smart Petri culture dishes and their use for live cell culture monitoring. The impact of the PRP on the light budget is discussed and performances are demonstrated. First results on the application of PRM to the observation of apoptotic body internalization are reported.

An integrated reading and editing environment for scholarly research on literary works and their handwritten sources

We present an integrated system devoted to the visualization and the editing of hypermedia documents from literary material including document images and structured text. First, capabilities are offered to transcribe manuscript images. Transcribing the text consists in coupling lines typed on the keyboard with their corresponding text lines in the manuscript images. A semi-automatic system based on computer-human interaction and document analysis is proposed for performing this task. This system provides editing capabilities for linking document images and the corresponding structured textual representations (encoded by means of a logical markup language). Finally, application-specific visualization tools have been developed in order to provide users with an idea of the overall organization of the hyperdocument and help them to navigate.

An instrumented station for the survey of ozone and climate change in the southern tropics

The assessment of changes induced by human activities on Earth atmospheric composition and thus on global climate requires a long-term and regular survey of the stratospheric and tropospheric atmospheric layers. The objective of this paper is to describe the atmospheric observations performed continuously at Reunion Island (55.5 degrees east, 20.8 degrees south) for 15 years. The various instruments contributing to the systematic observations are described as well as the measured parameters, the accuracy and the database. The LiDAR systems give profiles of temperature, aerosols and ozone in the troposphere and stratosphere, probes give profiles of temperature, ozone and relative humidity, radiometers and spectrometers give stratospheric and tropospheric integrated columns of a variety of atmospheric trace gases. Data are included in international networks, and used for satellite validation. Moreover, some scientific activities for which this station offers exceptional opportunities are highlighted, especially air mass exchanges nearby dynamical barriers: (1) On the vertical scale through the tropical tropopause layer (stratosphere-troposphere exchange). (2) On the quasi-horizontal scale across the southern subtropical barrier separating the tropical stratospheric reservoir from mid- and high latitudes.