From MEMS to NEMS: closed-loop actuation of resonant beams beyond the critical Duffing amplitude

International audienceBecause of its moderate cost in terms of electronics, resonant sensing has become commonplace in the context of MEMS and NEMS devices. It is usual to drive such resonators below the critical open-loop Duffing amplitude, above which the oscillations become unstable. However, when scaling sensors down to NEMS, nonlinearities may occur at very low amplitudes, making oscillations very difficult to detect. This paper describes a very general way to compute the critical amplitude in open-loop operation for beam resonators, before it focuses on closed-loop Duffing-type resonators. The major contribution of this paper is the use of describing function analysis validated by numerical simulations to show that it is possible to obtain stable oscillations with amplitudes much larger than the critical Duffing amplitude. As a practical consequence, the measured currents are significantly increased and the constraints on the sensing electronics can be relaxed

Large amplitude dynamics of micro/nanomechanical resonators actuated with electrostatic pulses

International audienceIn the field of resonant NEMS design, it is a common misconception that large-amplitude motion, and thus large signal-to-noise ratio, can only be achieved at the risk of oscillator instability. In the present paper, we show that very simple closed-loop control schemes can be used to achieve stable largeamplitude motion of a resonant structure, even when jump resonance (caused by electrostatic softening or Duffing hardening) is present in its frequency response. We focus on the case of a resonant accelerometer sensing cell, consisting in a nonlinear clamped-clamped beam with electrostatic actuation and detection, maintained in an oscillation state with pulses of electrostatic force that are delivered whenever the detected signal (the position of the beam) crosses zero. We show that the proposed feedback scheme ensures the stability of the motion of the beam much beyond the critical Duffing amplitude and that, if the parameters of the beam are correctly chosen, one can achieve almost full-gap travel range without incurring electrostatic pull-in. These results are illustrated and validated with transient simulations of the nonlinear closed-loop system

Architectures pour des circuits fiables de hautes performances

Nanometric technologies led to a decrease of electronic circuit reliability, especially against external phenomena. Those may change the state of storage components, or interfere with logical components. In fact, this issue is more critical for memories, as they are more sensitive to external radiations. The error correcting codes are one of the most used solutions. However, reliability constraints require codes that are more and more complex. These codes have a negative effect on the system bandwidth. We propose a generic methodology that removes the timing penalty of error correcting codes during memory's write operation. Moreover, it limits the speed penalty for read operation only in the rare case an error is detected. To proceed, the circuit is decontaminated after uncorrected data were propagated inside the circuit. This technique may require restoring some past states of few storage components by adding some FIFO. An algorithm that identifies these components was also created. Then we try to evaluate the impact of such a technique for the following issue: the global state restoration of a circuit to erase all kinds of soft errors, everywhere inside the circuit.Les technologies nanométriques ont réduit la fiabilité des circuits électroniques, notamment en les rendant plus sensible aux phénomènes extérieurs. Cela peut provoquer une modification des composants de stockage, ou la perturbation de fonctions logiques. Ce problème est plus préoccupant pour les mémoires, plus sensibles aux perturbations extérieures. Les codes correcteurs d'erreurs constituent l'une des solutions les plus utilisées, mais les contraintes de fiabilité conduisent à utiliser des codes plus complexes, et qui ont une influence négative sur la bande passante du système. Nous proposons une méthode qui supprime la perte de temps due à ces codes lors de l'écriture des données en mémoire, et la limite aux seuls cas où une erreur est détectée lors de la lecture. Pour cela on procède à la décontamination du circuit après qu'une donnée erronée ait été propagée dans le circuit, ce qui nécessite de restaurer certains des états précédents de quelques composants de stockage par l'ajout de FIFO. Un algorithme identifiant leurs lieux d'implémentation a également été créé. Nous avons ensuite évalué l'impact de cette méthode dans le contexte plus large suivant : la restauration d'un état précédent de l'ensemble du circuit en vue de corriger une erreur transistoire susceptible de se produire n'importe où dans le circuit

Gas migration regimes and outgassing in particle-rich suspensions

Understanding how gasses escape from particle-rich suspensions has important applications in nature and industry. Motivated by applications such as outgassing of crystal-rich magmas, we map gas migration patterns in experiments where we vary (1) particle fractions and liquid viscosity (10–500 Pa s), (2) container shape (horizontal parallel plates and upright cylinders), and (3) methods of bubble generation (single bubble injections, and multiple bubble generation with chemical reactions). We identify two successive changes in gas migration behavior that are determined by the normalized particle fraction (relative to random close packing), and are insensitive to liquid viscosity, bubble growth rate or container shape within the explored ranges. The first occurs at the random loose packing, when gas bubbles begin to deform; the second occurs near the random close packing, and is characterized by gas migration in a fracture-like manner. We suggest that changes in gas migration behavior are caused by dilation of the granular network, which locally resists bubble growth. The resulting bubble deformation increases the likelihood of bubble coalescence, and promotes the development of permeable pathways at low porosities. This behavior may explain the efficient loss of volatiles from viscous slurries such as crystal-rich magmas

Architectures pour des circuits fiables de hautes performances

Les technologies nanométriques ont réduit la fiabilité des circuits électroniques, notamment en les rendant plus sensible aux phénomènes extérieurs. Cela peut provoquer une modification des composants de stockage, ou la perturbation de fonctions logiques. Ce problème est plus préoccupant pour les mémoires, plus sensibles aux perturbations extérieures. Les codes correcteurs d'erreurs constituent l'une des solutions les plus utilisées, mais les contraintes de fiabilité conduisent à utiliser des codes plus complexes, et qui ont une influence négative sur la bande passante du système. Nous proposons une méthode qui supprime la perte de temps due à ces codes lors de l'écriture des données en mémoire, et la limite aux seuls cas où une erreur est détectée lors de la lecture. Pour cela on procède à la décontamination du circuit après qu'une donnée erronée ait été propagée dans le circuit, ce qui nécessite de restaurer certains des états précédents de quelques composants de stockage par l'ajout de FIFO. Un algorithme identifiant leurs lieux d'implémentation a également été créé. Nous avons ensuite évalué l'impact de cette méthode dans le contexte plus large suivant : la restauration d'un état précédent de l'ensemble du circuit en vue de corriger une erreur transistoire susceptible de se produire n'importe où dans le circuit.Nanometric technologies led to a decrease of electronic circuit reliability, especially against external phenomena. Those may change the state of storage components, or interfere with logical components. In fact, this issue is more critical for memories, as they are more sensitive to external radiations. The error correcting codes are one of the most used solutions. However, reliability constraints require codes that are more and more complex. These codes have a negative effect on the system bandwidth. We propose a generic methodology that removes the timing penalty of error correcting codes during memory's write operation. Moreover, it limits the speed penalty for read operation only in the rare case an error is detected. To proceed, the circuit is decontaminated after uncorrected data were propagated inside the circuit. This technique may require restoring some past states of few storage components by adding some FIFO. An algorithm that identifies these components was also created. Then we try to evaluate the impact of such a technique for the following issue: the global state restoration of a circuit to erase all kinds of soft errors, everywhere inside the circuit.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Spin Correlations in the Geometrically Frustrated Pyrochlore Tb2Mo2O7

We report neutron scattering studies of the spin correlations of the geometrically frustrated pyrochlore Tb2Mo2O7 using single crystal samples. This material undergoes a spin-freezing transition below Tg~24 K, similar to Y2Mo2O7, and has little apparent chemical disorder. Diffuse elastic peaks are observed at low temperatures, indicating short-range ordering of the Tb moments in an arrangement where the Tb moments are slightly rotated from the preferred directions of the spin ice structure. In addition, a Q-independent signal is observed which likely originates from frozen, but completely uncorrelated, Tb moments. Inelastic measurements show the absence of sharp peaks due to crystal field excitations. These data show how the physics of the Tb sublattice responds to the glassy behavior of the Mo sublattice with the associated effects of lattice disorder.Comment: 4 pages, 4 figure