Smart-MEMS based inertial measurement units: gyro-free approach to improve the grade

Microsystem Technologies - Inertial measurement units (IMU) are essentially a combination of acceleration and rotation rate sensors, generating position and attitude information. For tactical and...     

Noise analysis of a first-order thermal ΣΔ architecture for convective accelerometers

This paper presents the study of an original closed-loop conditioning approach for fully-integrated convective inertial sensors. The method is applied to an accelerometer manufactured on a standard CMOS technology using an auto-aligned bulk etching step. Using the thermal properties of the sensor, a first order sigma-delta modulator is built. This “electro-physical” modulator realizes an analog-to-digital conversion of the acceleration signal. Besides, the feedback mode of operation improves the sensor overall performance.     

A Behavioral Model of MEMS Convective Accelerometers for the Evaluation of Design and Calibration Strategies at System Level

This paper presents a behavioral model that can be used to improve the manufacturability of systems based on MEMS convective sensors. This model permits to handle faults related to process scattering, taking into account not only the electrical and lateral geometrical parameters but also the influence of the cavity depth. Moreover correlations between conductive and convective phenomena are included. The model is validated with respect to FEM simulations and a very good agreement is obtained between the behavioral model and FEM results. The proposed model can then be used in system-level simulations, for instance to evaluate the impact of process scattering on the performances of the sensing part and/or to investigate different design and calibration strategies with respect to the system robustness.     

Improvement of Power Supply Rejection Ratio in Wheatstone-bridge based piezoresistive MEMS

This paper deals with the design of MEMS-based sensors with piezoresistive transduction. It is demonstrated that when the sensor topology does not allow a perfect matching of resistances in the conditioning circuit (typically a Wheatstone bridge), the resolution of the system is limited by the ability to reject power supply noise. As this ability increases when the output offset of the bridge decreases, the proposed architecture implements a feedback loop to control MOS transistors inserted in the Wheatstone bridge to compensate resistor mismatches. This zero-offset bridge exhibits a very good offset cancellation and therefore a better resolution.     

Resistive transition of superconducting wire networks. Influence of pinning and fluctuations

We have studied the resistive transition of several 2-D superconducting wire networks of various coupling strengths, which we characterize in terms of the Kosterlitz-Thouless transition temperature and the ratio /a of the coherence length to the array period. In the extreme strong coupling limit where the mesh size is of the order of the zero-temperature coherence length, the superconducting behavior is well described by the mean-field properties of the superconducting wave function. Extending to 2-D array, the 1-D phase slippage model explains the dissipative regime observed above the Ginzburg-Landau depairing critical current. On the other hand, when the coupling is weak, phase fluctuations below the Ginzburg-Landau transition and vortex depinning dominate the resistive behavior. An activated dissipation is observed even below the depairing critical current. Results obtained in this regime for critical temperature, magnetoresistance or critical current versus temperature, and magnetic field are shown; their periodic oscillations are discussed in terms of depinning of vortices on the array. A simple periodic pinning potential for a vortex in a wire network is calculated, and compared with the case of pinning in Josephson junction arrays. We show that this model explains qualitatively the experimental results observed for small /a.     

Study of an Electrical Setup for Capacitive MEMS Accelerometers Test and Calibration

This paper deals with the development of a fully electrical method to estimate the sensitivity of capacitive MEMS accelerometers in batch fabrication. The objectives are to test and calibrate them without the need of costly and time-consuming mechanical test equipments. Alternate electrical test measurements are introduced and two methods are evaluated. The first one is based on the analytical study of the relations between the electrical test parameters and the sensitivity. The second one is based on a regression analysis of these relations on a learning batch of sensors. Both are evaluated on a case study accelerometer with Monte Carlo simulations. Applying the methods for calibration shows that the dispersion of the sensitivity can be improved. Results show that the second method is more promising.     

Leachate pre-treatment strategies before recirculation in landfill bioreactors.

Nitrified leachate recirculation represents a promising strategy for a more sustainable landfill management. Our objective was to determine the reactions involved in nitrate reduction in municipal solid waste batch biodegradation tests. Anaerobic digestion of waste in the three control reactors showed a good reproducibility. In two test reactors, nitrate was added at various moments of the waste degradation process. We observed that: (1) H2S concentration controlled the nitrate reduction pathway: above a certain threshold of H2S, dissimilatory nitrate reduction to ammonium (DNRA) replaced denitrification. (2) N2O/N2 ratio varied with the organic carbon concentration: the lower the easily biodegradable carbon concentration, the higher the N2O/N2 ratio. (3) N2 was consumed after denitrification. The possibility of a nitrogen fixation reaction in the presence of NH4 is discussed. Nitrified leachate recirculation during acidogenesis should be avoided because of higher H2S production which could induce DNRA.     

Vortex Avalanches in a Type II Superconductor

We report on a study of the spatiotemporal variation of magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. A sizable fraction of the increase in the local vortex population occurs in abrupt jumps. We compare the size distribution of these avalanches with the predictions of self-organized-criticality models for vortex dynamics.