High Resolution Micro-Pirani Pressure Sensor Gauge with Transient Response Processing

International audienceA micro-Pirani pressure sensor which acts as a pressure dependent thermo-resistance gauge is traditionally exploited using a steady state resistance measurement. However any signal variation occurs over a constant voltage bias due to the initial resistance of the device which affects the sensor's sensitivity. Our work shows for the first time an experimental investigation of a micro-Pirani gauge based on its dynamical behavior when heated by a current step. Such a processing does magnify the pressure dependence of the gauge's signal in eliminating the initial resistance influences on the measurement. Furthermore, a first order low pass filter step response identification of the experimental transient signal strongly reduces the thermal noise influence on the measurement. The heating step, the recording of the time dependent signal and its post-processing can be easily achieved by a small-size controller. The proposed system provides a substantial enhancement of the micro-Pirani pressure sensor performance

Contribution aux systèmes électromécaniques d’actionnement et de mesure

Si des solutions à des problèmes pratiques ont été imaginées depuis des centaines, voire des milliers d’années, les micro-nano-technologies ont offert plus récemment des moyens de miniaturisation et d’intégration inédits. Ces travaux ont pour point de départ l’intégration de cuivre épais dans les procédés de la microélectronique. Impossible jusqu’au tournant du XXIème siècle, elle est aujourd’hui courante. Dans une première partie, la réalisation de micro-dispositifs en cuivre épais est présentée et l’application de cette technologie à la réalisation de transducteurs acoustiques – micro-haut-parleur et absorbeur acoustique haute performances – est décrite.Dans une deuxième partie, un nouveau saut technologique est présenté. L’application des technologies de la microélectronique à la réalisation de dispositifs polymères est étudiée et appliquée à la réalisation de capteurs de force souples. Des règles générales de dimensionnement des capteurs sont extraites par des moyens numériques et expérimentaux. Les limites ultimes de sensibilité et de gamme de mesure des capteurs utilisant des corps d’épreuves en PDMS ont été définies et atteintes

Case Study of a MEMS Snap-Through Actuator: Modeling and Fabrication Considerations

MEMS actuators rely on the deformation of silicon structures. Using dimensions smaller than dozens of micrometers reveals that the micro-electro-mechanical systems (MEMS) actuators are affected by fabrication inaccuracies, leading to hardly predictable forces and/or actuation results. In this paper, MEMS bistable buckled beam actuators are presented. A series of structures based on pre-shaped buckled beams of lengths ranging from 2 to 4 mm, constant width of 5 μm and actuation stroke ranging from 20 to 100 μm was fabricated. Experimental data show a significant difference with predictions from a conventional analytical model. The model commonly used for buckled beams design assumes a rectangular beam section, but it is not the case of the fabricated beams. Furthermore, only symmetric buckling modes (mode 1, mode 3…) are supposed to exist during snap-through. In this paper, new analytical models have been developed on the basis of the models of the literature to consider the effective beam shape. The first improved analytical model enabled prediction of the MEMS buckled beams mechanical behavior in a 30% margin on the whole range of operation. A second model has been introduced to consider both the effective shape of the beam and centro-symmetric buckling modes. This refined model exhibits the partial suppression of buckling mode 2 by a central shuttle. Therefore, mode 2 and mode 3 coexist at the beginning and the end of snap-through, while mode 3 quickly vanishes due to increasing rotation of the central shuttle to leave exclusive presence of mode 2 near the mid-stroke. With this refined model, the effective force-displacement curve can be predicted in a margin reduced to a few percentages in the center zone of the response curve, allowing the accurate prediction of the position switch force. In addition, the proposed model allows accurate results to be reached with very small calculation time

Integration of microcoils for on-chip immunosensors based on magnetic nanoparticles capture

Immunoassays using magnetic nanoparticles (MNP) are generally performed under the control of permanent magnet close to the micro-tube of reaction. Using a magnet gives a powerful method for driving MNP but remains unreliable or insufficient for a fully integrated immunoassay on lab-on-chip. The aim of this study is to develop a novel lab-on-chip concept for high efficient immunoassays to detect ovalbumin (Biodefense model molecule) with microcoils employed for trapping MNP during the biofunctionalization steps. The objectives are essentially to optimize their efficiency for biological recognition by assuring a better bioactivity (antibodies-ovalbumin), and detect small concentrations of the targeted protein (~10 pg/mL). In this work, we studied the response of immunoassays complex function of ovalbumin concentration. The impact of MNP diameter in the biografting protocol was studied and permitted to choose a convenient MNP size for efficient biorecognition. We realized different immunoassays by controlling MNP in test tube and in microfluidic device using a permanent magnet. The comparison between these two experiments allows us to highlight an improvement of the limit of detection in microfluidic conditions by controlling MNP trapping with a magnet. Keywords: Bacteria, Lab-on-chip, ELISA, Magnetic nanoparticles, Ovalbumin, Microcoils, Fluorescent microscop

LINEAR AND NON LINEAR BEHAVIOUR OF MECHANICAL RESONATORS FOR OPTIMIZED INERTIAL ELECTROMAGNETIC MICROGENERATORS

Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838)International audienceThe need for wearable or abandoned microsystems, as well as the trend to a lower power consumption of electronic devices, make miniaturized renewable energy generators a viable alternative to batteries. Among the different alternatives, an interesting option is the use of inertial microgenerators for energy scavenging from vibrations present in the environment. These devices constitute perpetual energy sources without the need for refilling, thus being well suited for abandoned sensors, wireless systems or microsystems which must be embedded within the structure, without outside physical connections. Different electromagnetic energy scavenging devices have been described in the literature [1,2,3], based on the use of a velocity damped resonator, which is well suited for harvesting of vibrational energy induced by the operation of machines. These vibrations are characterized by a well defined frequency (in the range between few Hz’s and few kHz’s) and low displacement amplitudes. Adjusting the resonant frequency of the system to that of the vibrations allows amplification of these low amplitude displacements. Moreover, for these applications, the use of an electromagnetic device has the potential advantages of a good level of compatibility with Si Microsystem technology, as well as the possibility of relatively high electromechanical coupling with simple designs

Porous Polymer Based Flexible Pressure Sensors for Medical Applications

This paper focuses on the use of microporous PDMS foams as a highly deformable film to improve the sensitivity of flexible capacitive pressure sensor dedicated to wearable use. A fabrication process allowing the mechanical properties of foams to be adjusted is proposed together with a non-linear behavioral model used to objectively estimate the sensor performances in terms of sensitivity and measurement range. Sensors fabricated and characterized in this study show that the sensitivity and the measurement range can be adjusted from 0.14%/kPa up to 13.07%/kPa, and from 594 kPa to 183 kPa, respectively, while the PDMS film porosity ranges from 0% up to 85%

Influence of the Porosity of Polymer Foams on the Performances of Capacitive Flexible Pressure Sensors

This paper reports on the study of microporous polydimethylsiloxane (PDMS) foams as a highly deformable dielectric material used in the composition of flexible capacitive pressure sensors dedicated to wearable use. A fabrication process allowing the porosity of the foams to be adjusted was proposed and the fabricated foams were characterized. Then, elementary capacitive pressure sensors (15 × 15 mm2 square shaped electrodes) were elaborated with fabricated foams (5 mm or 10 mm thick) and were electromechanically characterized. Since the sensor responses under load are strongly non-linear, a behavioral non-linear model (first order exponential) was proposed, adjusted to the experimental data, and used to objectively estimate the sensor performances in terms of sensitivity and measurement range. The main conclusions of this study are that the porosity of the PDMS foams can be adjusted through the sugar:PDMS volume ratio and the size of sugar crystals used to fabricate the foams. Additionally, the porosity of the foams significantly modified the sensor performances. Indeed, compared to bulk PDMS sensors of the same size, the sensitivity of porous PDMS sensors could be multiplied by a factor up to 100 (the sensitivity is 0.14 %.kPa−1 for a bulk PDMS sensor and up to 13.7 %.kPa−1 for a porous PDMS sensor of the same dimensions), while the measurement range was reduced from a factor of 2 to 3 (from 594 kPa for a bulk PDMS sensor down to between 255 and 177 kPa for a PDMS foam sensor of the same dimensions, according to the porosity). This study opens the way to the design and fabrication of wearable flexible pressure sensors with adjustable performances through the control of the porosity of the fabricated PDMS foams

Efficiency optimization of an electrodynamic MEMS microspeaker

International audienceThis paper presents the optimization of a novel planar structure of MEMS electrodynamics microspeaker. The mobile part of the device is a microstructured silicon membrane suspended by a whole set of silicon springs. Its actuation principle relies on the Lorentz force, exactly like in conventional microspeakers broadly used in mobile electronics devices. The presented structure includes a planar coil electroplated on top of the silicon membrane, and a permanent magnet part based on magnet rings bonded onto the silicon substrate. Four different configurations of the permanent magnet part are studied. In each case, the dimensions of the planar coil are determined in order to maximize the electroacoustic conversion efficiency. The optimization method takes into account technological limits of microfabrication. Simulations based on analytical and finite element modelling show that the efficiency of optimized MEMS microspeaker could be up to ten times greater than that of conventional electrodynamics microspeakers used in mobile phones. The simulation results are confirmed by experimental measurements on MEMS microspeaker prototypes

Integration of commercial microspeakers in an acoustic absorbing liner

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