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Monitoring integrity of operating structures has become a crucialneed in industrial applications while motivation for moresustainable materials pushes forward the development of naturalfibre composites (NFC). The complexity and variability of theirfailure behaviour and mechanical properties still limit theexploitation of their full potential. Acoustic Emission (AE) hasshown promising results to predict remaining service life ofstructures, allowing identification, localisation and assessment ofdamages in composite materials. Thus, embedment of AE sensors couldbe a reliable solution for real-time Structural Health Monitoring(SHM). This paper aims to quantify

Residual vibrations are a recurrent problem in MEMS actuators leading to a limitation of their dynamics and lifespan. This paper presents a voltage-controlled technique and its applicability to suppress residual vibrations in high voltage (about 100 V) electrostatic comb-drive actuators. The studied actuator is composed of a driving module and a clutch module devoted to the step by step driving of linear or circular gears. The proposed method is based on a command shaping technique well adapted to be integrated in an Application-Specific Integrated Circuit (ASIC), especially for nomadic applications. Firstly, an electrodynamic characterization is used to extract the key voltages of the optimized command signals. The key voltages correspond to the beginning and the end of the actual displacement. The command signals consist of two begin/end voltage jumps and a linear voltage rise/fall in an optimized time between the key voltages. Then, experimental validations investigated the influence of voltage fall time for a MEMS chip and the resulting dispersion for a set of 8 MEMS chips. The results show that residual vibrations are reduced by a factor higher than 20 in terms of the amplitude rate of bounces against back stop and the settling time of free oscillations. Finally, an analog circuit capable of building the optimized command signals is proposed and will be implemented in the next generation of the ASIC driving the electrostatic two-module actuator.

International audience; This paper presents a sensor using the mode localization phenomenon to detect a mass perturbation.It is composed of two cantilevers with different lengths and connected by a coupling beam. The shortcantilever is electrostatically actuated and by changing the applied DC voltage, we can reduce its stiffnessand reach the veering point, which corresponds to a balanced system. This principle allows us to overcomethe manufacturing defect which perturbs the initial system. An analytical model using the Euler-Bernoullibeam theory is developed for the design. The equation of the continuous system is discretized with theGalerkin method and simulations are performed. The designed device composed of polysilicon coupledmicrobeams is then fabricated with the Multi-User MEMS Processes and an experimental investigation iscarried out. Three devices with different coupling are considered with a length ratio of 0.98. This ratio issuitable to reach the veering point by using a DC balancing voltage around the half of the pull-in voltage.The comparison between theoretical and experimental results shows a good agreement for each device.

International audience; The preshaped curved beam is used as bistable mechanism in MEMS, its behavior is characterized by the snapping forces and stresses that evolve during deflection between the two sides of buckling. Based on analytical models, the influence of variating the material and dimension parameters on the behavior of the curved beam is analyzed. The limit of miniaturization of the beam based on the stress limits is identified. Further, a design optimization methodology is provided which allows selecting the miniature dimensions of the curved beam after defining the range of possible dimensions. This method ensures a required bistablity behavior in terms of stroke and holding forces, while respecting the design requirement. Several design constraints are defined including material and technological limitations and some other specifications. The results in different cases of optimization problems showed to be the same using a proposed optimization methodology and a standard gradient based optimization algorithm.

International audience; Current digital microrobots are mainly composed of bistable modules and flexible structures. Unlike conventional microrobots, they are based on mechanical stability instead of complex control strategies in order to reach precise and repeatable discrete positioning. By design, their number of stable positions depends on the number of bistable modules. As a consequence, increasing the robot workspace requires using several modules. In this case, the robot size increases and its miniaturization becomes complex and non-intuitive. To address this issue, a multistable module has been developed to reach several stable positions. In this letter, a new generation of digital microrobots is proposed. Based on two multistable modules and flexible structures, the new microrobot can reach a large workspace while having a small footprint. Concretely, the robot size decreases by 26% while the number of stable positions increases by 950% in comparison with the first generation of the digital microrobot. A prototype is designed, fabricated and characterized experimentally. Preliminary results show a good agreement between the expected and the achieved workspace. The robot achieves 169 stable positions with a discrete step of 4.125 μm and a resolution of 150 nm. With these capabilities, the robot paves the way for promising perspectives and applications, in particular precise micro-manipulation in confined environment such as a Scanning Electron Microscope.

International audience; In this paper, the effects of initial deflection on the static and dynamic behaviors of circular capacitive transducers are experimentally investigated. The obtained results are in good agreement with numerical simulations. It is shown that the initial deflection has a major impact on the static response of the resonator by shifting the pull-in voltage, and on its dynamic response by increasing the resonance frequency and modifying the bifurcation topology from softening to hardening behavior. Moreover, the dynamic behavior of the microplate may display nonlinear periodic and quasiperiodic responses due to geometric and electrostatic nonlinearities.

Acoustic Emission (AE) is a non-destructive technique suitable for monitoring structural damages in complex systems. Interpretation of AE data is generally made by an unsupervised learning approach called clustering. A clustering method divides a dataset into different groups called clusters, which are expected to have a physical interpretation in terms of damages. The set of groups, called partition, is then evaluated through an external criterion. Since the number of clusters is a priori unknown, the standard approach for AE clustering consists in running a clustering method for different number of clusters and then to select the partition with the best value of the external criterion. The external criterion can vary across publications and aims at evidencing “natural” clusters. According to the criterion, the selected partition and its interpretation can be subjected to variability. In this publication, we explore a clustering method in which the parameters of clusters are optimised jointly with the number of clusters through an objective function and an optimisation procedure designed for that purpose. To our knowledge, it is the first method of this class in AE literature. Experimental results concern real data from tightening test.

International audience; The ability of Capacitive Micromachined Ultrasonic Transducer (CMUTs) todesign broadband sensors for Structural Health Monitoring (SHM) is studiedthrough both multi-frequency and bandwidth aspects. Elementary cells arecomposed of circular membranes fabricated using the standard MUMPS Process. The multi-frequency aspect, which involves different individual membranes from 50 µm to 250 µm radius, is theoretically addressed through anumerical modeling. The targeted frequency range, consistent with the SHMapplication, is then between 80 kHz and 2 MHz. Geometrical features induced by the manufacturing process greatly affect the dynamic properties ofthe membranes and this is experimentally validated. The bandwidth aspectis also addressed on an array of identical 100 µm radius membranes thusinvolving their intrinsic capabilities. Harmonic excitation with targeted frequencies 300 kHz, 530 kHz and 800 kHz, below and beyond the resonancefrequency of the membranes, are performed. The influence of the bias voltage VDC on the signal-to-noise ratio is studied according to the excitationfrequency. As a result, a signal-to-noise of 20 dB is achieved around the resonance frequency. Finally, the circular membranes array is tested for acousticemission sensing through a pencil lead break test. In spite of a low signal-tonoise ratio, acoustic events are clearly detected. The multi-frequency aspectand the large bandwidth capability of the CMUTs are hence demonstratedand highlight the adaptability of the sensor to its environment.

International audience; The present paper deals with the analysis of the squeeze film effects in circular capacitive micromachined ultrasound transducers (CMUT) operating in air, with emphasis on improved bandwidth. Firstly, a 1D analytical approach based on parallel plate approximation is recalled. The opposing influences of the electrostatic softening and the squeeze film stiffening make the resonant frequency dependent on the bias voltage with respect to air spring constant to mechanical spring constant ratio. In a second part, FEM models using COMSOL Multiphysics® are built to analyze the influences of the plate flexibility and the lateral venting boundary conditions on the squeeze film effects. The associated numerical results show that viscous losses are involved in sealed air-filled cavities. Moreover, the dimensionless elastic and viscous damping forces do not depend on the lateral venting boundary conditions for high squeeze number range, usual for CMUT operation. Finally, 2D full coupled simulations of flexible CMUT are compared with experimental data. Thus, the squeeze film damping increases bandwidth of air-coupled CMUTs with both sealed and laterally vented cavities.

International audience; Objective: go further in structural and multifunctional applications• to master the natural resources• to control the mechanical properties in a specific environment• to optimize the architecturation of the composite

International audience; Among the various experimental techniques used for Structural Health Monitoring (SHM), acoustic emission (AE) allows real time monitoring of large structures with the possibility to detect, characterize and locate damages. In practice, its implementation can be complex, especially for mobile structures. The main difficulties are related to the integration of sensors in the structure, electricalinterconnections, different sources of noise, the detection and processing of transient signals and the management of massive data streaming. Generally, AE are collected through piezoelectric sensors. We propose an AEbased SHM methodology using an alternative technology in breakthrough with piezoelectric transduction: Capacitive micro-machined ultrasonic transducers (CMUTs). These sensors have many advantages. One advantage lies in the size of the sensors allowing a little intrusive integration into the material. Following a previous work published in EWSHM’̣18, we report on the design, fabrication, and experimental demonstration of a new CMUT transducer specifically designed for the measurement of AE events. A data preprocessing methodology dedicated to interpret the obtained AE streaming is presented. We compare the results with standard piezoelectric sensors to detect damages during tensile tests on composite plates.

This paper investigates the mass sensing in a mode-localized sensor composed of two weakly coupled MEMS cantilevers with lengths 98μm and 100μm. The two resonators are connected by a coupling beam near the fixed end, and the shortest cantilever is electrostatically actuated with a combined AC-DC voltage. The DC actuation voltage is tuned to compensate the length difference and geometrical imperfections in order to dynamically equilibrate the system. An analytical model of the device using the Euler Bernoulli beam theory is presented and the required DC voltage to reach the balanced state is used. A mass perturbation is then added on the long cantilever and the eigenstate shifts and amplitude ratios in each mode are calculated for different couplings. Results show that the amplitude ratio of the second mode is the best output metric for the mass detection. For the validation of the model, an experimental investigation is carried out by using devices fabricated with the Multi-User MEMS Processes. Three different couplings are considered and the long cantilever is designed with a mass attached at its end. Instead of adding a mass on the device, we remove this part with a probe to introduce the perturbation. When the mass is removed, the experimental frequency responses of the device show localized vibrations, which are in good agreement with the theoretical results.

International audience; In this article, an original approach to model the squeeze film effects in capacitive circular microplates is developed. The nonlinear von Kàrmàn plate theory is used while taking into consideration the electrostatic and geometric nonlinearities of the clamped edge microplate.The fluid underneath the plate is modeled using the nonlinear Reynolds equation with a corrected effective dynamic viscosity due to size effect. The strongly coupled system of equations is solved using the Differential Quadrature Method (DQM) by discretizing the structural and the fluid domains into a set of grid points. The linear effects of the squeeze film on the microplate have been investigated based onthe complex eigenfrequencies of the multiphysical problem. It is shown that the air film can alter the resonance frequencies by adding stiffness as well as damping to the system. The model has been validated numerically with respect to a Finite Element Model (FEM)implemented in ANSYS and experimentally on a fabricated circular microplates. The nonlinear effects of the squeeze film have been studied by determining the steady state solution of the system using the finite difference method (FDM) coupled with the arclength continuation technique. It is shown that the decrease of the static pressure shifts the resonance frequency and leads to an increase of the vibration amplitude due to the reduction of the damping coefficient, while the increase in the pressure enlarges the bistability domain. The developed model can be exploited as an effective tool to predict the nonlinear dynamic behavior of microplates under the effect of air film for the design of Capacitive Micromachined Ultrasonic Transducers (CMUTs).

International audience; Dynamic range improvement based on geometric nonlinearity and initial deflection is demonstrated with imperfect circular microplates under electrostatic actuation. Depending on design parameters, we prove how the von Kármán nonlinearity and the plate imperfections lead to a significant delay in pull-in occurrence. These promising results open the way towards an accurate identification of static parameters of circular microplates and the development of a predictive model for the nonlinear dynamics of imperfect capacitive micromachined ultrasonic transducers.

The ability of capacitive micromachined ultrasonic transducer (CMUTs) to design broadband sensors for structural health monitoring (SHM) is studied through both multi-frequency and bandwidth aspects. Elementary cells are composed of circular membranes fabricated using the standard MUMPS Process. The multi-frequency aspect, which involves different individual membranes from 50 to 250 μ m radius, is theoretically addressed through a numerical modeling. The targeted frequency range, consistent with the SHM application, is then between 80 kHz and 2 MHz. Geometrical features induced by the manufacturing process greatly affect the dynamic properties of the membranes and this is experimentally validated. The bandwidth aspect is also addressed on an array of identical 100 μ m radius membranes thus involving their intrinsic capabilities. Harmonic excitation with targeted frequencies 300, 530 and 800 kHz, below and beyond the resonance frequency of the membranes, are performed. The influence of the bias voltage VDC on the signal-to-noise ratio is studied according to the excitation frequency. As a result, a signal-to-noise of 20 dB is achieved around the resonance frequency. Finally, the circular membranes array is tested for acoustic emission sensing through a pencil lead break test. In spite of a low signal-to-noise ratio, acoustic events are clearly detected. The multi-frequency aspect and the large bandwidth capability of the CMUTs are hence demonstrated and highlight the adaptability of the sensor to its environment.

International audience; In order to overcome mode aliasing limitation in linear mode-localized sensors, we demonstrate in this letter both theoreticallyandexperimentallyhowtotunetheelectrostaticnonlinearityandexceedtheultimatesensitivityreachable in the linear regime. A mass sensor composed of two coupled micro-cantilevers with different lengths is considered and the results show that the sensitivity can be significantly enhanced up to 67 %. By performing experiments on the fabricated device and depositing the mass perturbation with a focused ion beam, the same phenomenon has been observed. These promising results open the way towards ultrasensitive multimodal microsensors with functionalized nonlinearities.

International audience; This paper presents a compliant monolithic multistable actuator which is able to switch its moving part between several stable positions linearly in one dimensional direction. The number of stable positions can be increased by extending the range of displacement of the moving part. The transition in each step of displacement is made to the nearest stable position in the direction of motion. Upward and downward steps are made by a specific sequence of moving, using a bistable module, opening and closing two internal clamps which are actuated by U-shaped electrothermal actuator using three subsystems. The principle and the design of each subsystem in the discrete acruator, fabrication process and experimental results are presented. The fabricated prototypes of the discrete actuator showed a proper functioning. The mean achieved displacement is 120.67±0.08 µm over 12 upward steps with a mean step of 10.06 µm, which is very close to the designed performance.

International audience; This paper focuses on the dynamic characterization of an electrothermal actuator devoted to discrete MEMS positioning. Based on U-shape structure, such actuator has been employed in several MEMS applications where fine and repeatable positioning is required. The studied electrothermal actuator here is microfabricated on a doped SOI substrate and its dynamic response, during heating and cooling cycles, is recorded using precise and high-speed camera. To explain its dynamic behavior, FEM simulations, using Comsol multiphysics software facility, are carried out. The result of this numerical analysis shows a strong relationship between the temperature distribution and the displacement provided by the actuator. Finally, the influence of the dynamic behavior on the control of the actuator is discussed using experimental characterizations of its displacements under several voltage pulses with different frequencies.

International audience; Capacitive micromachined ultrasonic transducers (CMUTs) are microelectromechanical systems used for the generation of ultrasounds. The fundamental element of the transducer is a clamped thin metallized membrane that vibrates under voltage variations. To control such oscillations and to optimize its dynamic response it is necessary to know the modal parameters of the membrane such as resonance frequency, damping and stiffness coefficients. The purpose of this work is to identify these parameters using only the time data obtained from the membrane center displacement. Dynamic measurements are conducted in time domain and we use two methods to identify the modal parameters: a subspace method based on an innovation model of the state-space representation and the continuous wavelet transform method based on the use of the ridge of the wavelet transform of the displacement. Experimental results are presented showing the effectiveness of these two procedures in modal parameter identification.

This paper focuses on a fabrication process for CMUTs using anodic bonding of a silicon on insulator wafer on a glass wafer. This technology makes possible the fabrication of large membranes and can extend the frequency range of CMUTs to lower frequencies of operation. Silicon membranes having radii of 50, 70, 100 and 150 μm and a 1.5 μm thickness are fabricated and electromechanically characterized. Resonant frequencies from 0.6 to 2.3 MHz and an electromechanical coupling coefficient around 58% are reported. The discrepancies between experimental and theoretical values of the first resonance frequency can be explained by a combined effect of a tensile residual stress (between 90 and 110 MPa) in the membranes and experimental boundary conditions that can be modeled by a torsional stiffness of 2.10−7 N.m.rad–1 instead of a perfectly clamped ring.

International audience; Our work deals with the study of the dynamic characteristics of a single circular CMUT transducer under squeeze film damping effect. A simplified analytical approach is developed for parallel plate approximation for the electromechanical behavior and the squeeze film damping. Analytically calculated results demonstrates, that trends of resonant frequency with bias voltage are defined by the ratio of air spring constant to mechanical spring constant. At the same time FEM multiphysics model is built to define the influence of membrane flexibility and venting boundary conditions to the dimensionless viscous and elastic damping forces. FEM study shows the presence of viscous loss in the sealed air-filled cavity and the insensitivity of squeeze film damping forces to the type of lateral venting boundary conditions in high squeeze number region which is typical for CMUT operation. Finally, theexperimental dynamic characterization is conducted on CMUT with 67 μm – 167 μm radii fabricated utilizing an anodic bondingtechnology. Experimental data are in a good agreement with the results of multiphysics FEM calculation, which take into accountbias voltage, initial plate deflection, radiation loss and squeeze film damping.

International audience; The paper focuses on a MEMS mass detection sensor using mode localization and electrostatic actuation to counterbalance the manufacturing defects. The sensor is composed of two cantilevers with different lengths, connected together with a weak mechanical spring. A DC voltage is applied on the shortest beam so that the system is balanced when no mass is added, allowing the manufacturing defects to be compensated.Harmonic simulations were carried out using COMSOL Multiphysics®. It shows for example that for 100μm/90μm long, 20μm width and 2μm thick cantilevers, a DC voltage of 60.4V is necessary to balance the system. In these conditions and with a quality factor of 1500, a 17.5pg added mass will create a relative change of 22% in the modal amplitude of the first mode of the longest cantilever while the relative shift in the resonant frequency is only 0.24%.

International audience; This paper describes numerical and experimental characterization of capacitive micromachined ultrasonic transducers (CMUTs) for ultrasound transmission. Simulations based on a finite elements method to model the electromechanical behaviour of CMUTs and to determine the dimensions of elementary cells are presented. In particular, we analyse how the collapse voltage and the capacitanceare affected by different parameters of a circular cell and by different bias voltages. The fill factor is defined as the ratio of the top electrode radius to the membrane radius and we study the influence of the fill factor in the performances of CMUTs. The fabrication process of a CMUT uses anodic bonding of a SOI wafer on a borosilicate glass substrate and we compare experimental results with numericalresults in terms of eigenfrequencies, bandwidth, quality factor and capacitance for non-metallized and metallized membranes.

In this paper, we develop original analytical electro-thermal and thermo-mechanical models for the U-shaped electro-thermal actuator. The dynamics of the temperature distribution and displacement are obtained as a direct relationship between the system's dimensions, material properties and electrical input. The electro-thermal model provides an exact solution of the hybrid partial differential equations that describe the electro-thermal behaviour for each of the actuator's three connected arms. The solution is obtained using a new calculation method that allows the representation of an integrable function by a hybrid infinite sum of sine and cosine functions. The displacement at the actuator's tip is then calculated using a quasi-static model based on the superposition and virtual works principles. The obtained temperature and displacement solutions are then discussed and compared with finite element method simulations via ANSYS® and experimental results. Comparisons showed good agreement making the proposed modelling a reliable alternative which paves the way for improving the design and optimising the dimensions of U-shaped micro-actuators.

International audience; A multiphysics model for capacitive micromachined ultrasonic transducers (CMUTs) is developed taking into account the main sources of nonlinearities in the case of circular plates. The equation of motion is reduced to an asymmetric Duffing equation which is solved using the harmonic balance method coupled with the asymptotic numerical method. Multiple-valued solutions, indicating the occurrence of jump phenomena, are observed numerically and confirmed experimentally on measured frequency responses of micro-machined CMUTs based on anodic bonding of a SOI wafer on a glass wafer. This purely numerical approach allows designers to control the resonator bifurcationtopology by tuning the design parameters and thus gives the possibility of driving the CMUT beyond its critical amplitude. As a consequence, the CMUT performances can be enhanced in terms of bandwidth and generated acoustic power.

The dynamic behavior of a U-shaped electrothermal actuator is investigated in this paper based on experimental findings and FEM simulations. Few previous works are found in the literature that have addressed the dynamic response of U-shaped actuators. A lack of data on the transient displacement of the actuator in the heating and cooling cycles is noted. Experiments are made in order to characterize the dynamic response of the actuator. The actuators are micro-fabricated on doped SOI wafers and the displacement is recorded with a high speed camera. FEM simulations are in good agreement with the experimental findings. Simulations and experiments show that the shape of displacement follows evolution of the temperature distribution inside the actuator. The influence of the dynamic behavior on the control of the actuator is finally discussed.

International audience; A computational multiphysics model for an electrically actuated clamped circular plate is developed. The Galerkin approach is used in order to transform the continuous model into a system having finite degrees of freedom. The discretized system is solved using the harmonic balance method (HBM) coupled with the asymptotic numerical method (ANM). The effects of the electrostatic excitation on the CMUT frequency responses are investigated for two set of design parameters. This model is an effective tool for MEMS designers to enhance the performances of CMUTs in term of generated acoustic power.

The following work investigates output mechanical power limits of electrostatic micromotors using stator/rotor contact interactions. Loading characteristics of micrometer size motors monolithically coupled with elastic polysilicon torque sensors are measured through an high-frequency complementary metal oxide semiconductor (CMOS) camera combined with a specific image processing software. Short duration video sequences recorded during the rotor braking are analyzed by tracking of a target pixel attached to the tested devices. Output mechanical power limits are measured through electrostatic probing on the wafer level within a few milliseconds. Experiments point out an unusual mechanical power per mass unit which is as high as 100 W/gr, considering driving frequencies on the order of 100 kHz.

International audience; In medical ultrasound imaging, mostly piezoelectric crystals are used as ultrasonic transducers. Capacitive micromachined ultrasonic transducers (CMUTs) introduced around 1994 have been shown to be a good alternative to conventional piezoelectric transducers in various aspects, such as sensitivity, transduction efficiency or bandwidth. This paper focuses on a fabrication process for CMUTs using anodic bonding of a silicon on insulator wafer on a glass wafer. The processing steps are described leading to a good control of the mechanical response of the membrane. This technology makes possible the fabrication of large membranes and can extend the frequency range of CMUTs to lower frequencies of operation. Silicon membranes having radii of 50, 70, 100 and 150 µm and a 1.5 µm thickness are fabricated and electromechanically characterized using an auto-balanced bridge impedance analyzer. Resonant frequencies from 0.6 to 2.3 MHz and an electromechanical coupling coefficient around 55% are reported. The effects of residual stress in the membranes and uncontrolled clamping conditions are clearly responsible for the discrepancies between experimental and theoretical values of the first resonance frequency. The residual stress in the membranes is determined to be between 90 and 110 MPa. The actual boundary conditions are between the clamped condition and the simply supported condition and can be modeled with a torsional stiffness of 2.10−7 Nm rad-1 in the numerical model.

Computer chips and other electronics have been getting faster and cheaper for a long time. But, often overlooked, they are also getting smaller and therefore allowing wearable high-technology to be developed on the near future. Current miniaturization and integration trends will result in the need to assemble ever-smaller systems and to handle smaller and smaller chips and other components that will be too small for humans to manipulate and assemble. As a consequence, the automation infrastructure of the future electronics assembly industry will have to scale with the technology, using fully and entirely automated micromachines such as manipulators and intelligent conveyance systems. The paper investigates, consequently, rapid and accurate positioning systems that will allow very small chips and components to be conveyed and automatically sorted. High-density arrays of silicon-based electrostatic actuators particularly are analyzed, according to their ability to move parts locally with high speed and sub-micrometer positioning accuracy. Actuator densities as high as 1000 actuators/mm are investigated, therefore allowing micrometer silicon based components to be manipulated. Lower densities involving larger actuation cells are also investigated in order to move millimeter size components on a few cm square motive surface. Very first design steps toward future smart surfaces are finally discussed. The paper shows how arrayed silicon based sensors, that can be easily distributed along with arrayed actuators, may provide tactile information from the external world, therefore allowing intelligent conveyance systems to be realized on the near future.

International audience; A mechanical stop mechanism is developed in order to compensate MEMS fabrication tolerances in discrete positioning. The mechanical stop mechanism is designed to be implemented on SOI wafers using a common DRIE etching process. The various fabrication tolerances obtained due to the etching process are presented and discussed in the paper. The principle and design of the mechanism are then presented. Finally, experiments on microfabricated positioning prototypes show accurate steps unaffected by the fabrication tolerances.

International audience; In this paper, we investigate the effect of high modes of buckling on the mechanical behavior of a pre-shaped curved beam. In a first stage, the presented modeling develops further the snapping forces solution and bistability conditions in order to include high modes of buckling. In a second stage, we develop the analytical solution of the stresses inside the beam during deflection between the two sides of buckling. The buckling with or without mechanical conditions on antisymmetric modes, the force characteristics, bistability conditions and stresses are described in this paper based on mathematical approach in order to provide a clear physical understanding of the curved beam behaviorand its design parameters. The accurate knowledge of the design parameters is important in order to achieve the best integration of the curved beam in a complete microstructure. The analytical results are compared with and without considering high modes of bucklingand have shown to be in excellent agreement with FEM simulations. The results show the importance of the high modes in calculating stresses and snapping forces.

The paper presents a macroscopic description for the simulation of the two way shape memory effect (TWSME) of shape memory alloys (SMA), and is an extension of a previous work dealing with the global thermomechanical behavior of SMA. The model is set in the framework of the thermodynamics of irreversible processes. Two internal variables are taken into account : the volume fraction of self-accommodating (pure thermal effect) and oriented (stress-induced) product phase. A term dedicated to the modeling of the trained SMA is added to the specific free energy derived for the non-trained SMA. This term φ ed , depends on the thermomechanical procedure of training submitted to the sample. In the present case, it accounts for the stress tensor σ ed applied during thermal cycling. The parameters of the model have been identified for a Cu–Zn–Al SMA, and the simulated results show good agreement with experiments.

A new generation of electrostatic micro-motors is investigated using cooperation of arrayed direct-drive actuators. Electrostatic scratch-drive actuators (SDA), which combine active frictional contact mechanisms with electrostatic actuation, are particularly analyzed. Active polysilicon sheets of 2*3 mm2 that integrate up to several thousands of electrostatic scratch drive actuators are fabricated by silicon surface micro-machining process. Each elementary actuator provides its contribution according to the driving force superposition principle, with internal forces as high as 105uN are available from this sheet. According to their natural flexibility, active polysilicon sheets can be coated onto large surfaces. A new generation of self-assembled tubular electrostatic micromotors is developed using this concept. A prototype of a cylindrical micromotor, whose external diameter and length are 1 mm and 2 mm, respectively, has been realized through the insertion of a flexible active polysilicon sheet at the rotor/motor- frame interface. After final assembling, the sheet has to be jammed onto the chassis, in order to allow the rotor to be moved with respect to the motor frame. Thus, the sheet must be in close contact with both the rotor and the motor frame, whatever the gap, which separates the two macroscopic parts. The problem related to the micro/macro world interfacing is solved during the design of sheet in allowing an out-of- plane motion of SDA in order to provide a self gap compensation, whatever both the thermal expansion effects and the macroscopic machining tolerances. The expected driving characteristics show the interest of both cooperative arrayed microactuators and direct drive frictional mechanisms.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Rapid positioning devices having nanometer accuracy are being used in the production of semiconductors. Micro- mechanical-oscillators made by silicon surface micromachining are expected to suit with such devices, according to their direct-drive capabilities. This communication investigates a first generation of microconveyers using high density arrays of micro- mechanical-oscillators. Densities as high as 1000 actuators/mm2 have been already achieved, therefore allowing shape recognition using tactile information on the near future. Thus, depending on the overall size of the conveyance system, millimeter size moving parts having different shapes are expected to be selected, and then independently distributed onto intelligent surfaces. The proposed conveyance system have been fabricated using a multi layer silicon surface micromachining process. Basically, electrodes are deposited onto a silicon substrate, in order to selectively address each elementary actuation cell. Each elementary cell is mechanically connected to a 1.2 micrometers thick polysilicon sheet frame which is deposited above distributed electrodes. The oscillators are activated by electrostatic force. The operating mechanism that is investigated in the communication is as follow: out-of-plane displacements of the frame are synchronized with the motion of mechanical oscillators, in order to allow the declutching mechanism which is needed to convey the moving part. The very first presented here allow us to expect a nanometer positioning resolution in open loop-control.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Capabilities of future direct-drive electrostatic actuators are investigated through the mechanical characterization of annular-type polysilicon micromotors. Contact interactions are provided at the stator/rotor interface in order to allow high integrated speed reduction to be performed. The driving torque is therefore considerably amplified, as a consequence of the torque/speed duality. Direct torque measurements are performed through a self-adjustable torque sensor that is integrated in the polysilicon rotor. The first experimental results presented here give rise to the expectations of numerous direct drive applications down to the micrometer scale.

This paper investigates millimeter scale electrostatic motors designed through a new "bottom-up design approach." Active polysilicon sheets involving thousands of elementary scratch drive actuators are analyzed, according to the driving force superposition capabilities of distributed electrostatic actuators. Driving forces as high as 1 00,000 pIN are reported in this paper, using 6 mm2 polysilicon sheets that integrate up to 1430 elementary scratch drive actuators. The mechanical power transmission from the sheet to the external load is also investigated. Because of structural height limitations, active polysilicon sheets do not allow significant driving forces to be transmitted to the external world. Therefore, original architectures, such as tubular electrostatic motors, are proposed using the insertion of a flexible polysilicon stator within the gap of a macroscopic cylindrical joint. An original self-assembling method is used in order to develop a first generation of millimeter scale electrostatic actuators. Expected performances that are evaluated from the in situ sheet characterization (i.e., from characterization onto the silicon wafer) point out the relevance of the bottom-up design methodology proposed in this paper. For the first time, visible effects up to the human scale are conceivable from silicon-based electrostatic motors that will allow innumerable actuation applications to be performed in the near future.

This paper is devoted to the design, the fabrication and the characterization of a new generation of direct-drive silicon based electrostatic micromotors. The following work points out the main torque limitations that occur in the design of conventional electrostatic actuators using electrostatic field interactions. Stator/rotor contact interactions are then considered, in order to provide larger external torque. Distributed motion systems are also investigated, because of significant driving forces that are expected through cooperative arrayed microactuators. According to this analysis, annular-type micromotors having a (500 Atm external diameter are proposed. The motor actuation involves stator/rotor contact interactions by using a flexible polysilicon rotor which combines arrayed elementary bending actuators. Moreover, the rotor integrates a self-adjusted torque sensor that allows the driving torque to be directly measured. Experimental characteristics point out the relevance of the proposed design rules. Unusual driving torque, one thousand times higher than ones obtained using conventional electrostatic wobble motors, have been already measured. Rotation speed ranging from 0.001 up to 750 rpm is also reported, according to the driving voltage frequency which was tuned from 1 Hz up to 500 kHz.

In this study, we investigate new-generation high-torque/low-speed electrostatic micromotors as well as original on-chip testing methods for the mechanical characterization of silicon-based microactuators. Torque/speed characteristics of micrometer-size electrostatic actuators are measured for the first time using real-time elastic braking video analysis of polysilicon rotors that are monolithically coupled with elastic mechanical sensors. Loading characteristics measured through on-chip electrostatic probing indicate the potentialities of emerging actuator design methodologies involving frictional stator/rotor contact interactions on the micrometer scale.

Polysilicon deposited by low pressure chemical vapor deposition is the most widely used structural material for surface-micromachined microelectromechanical systems. Thus, investigations are still needed in order to identify polysilicon mechanical characteristics as a function of the deposition conditions. The following work focuses on new micrometer size monolithic test cells combining polysilicon tensile specimens and ultra-high driving force electrostatic actuators fabricated from a common process flow. The proposed approach allows intrinsic material properties such as polysilicon tensile fracture to be measured through electrostatic probing, using on-chip micrometer size uniaxial tensile test cells.

A new generation of electrostatic micromotors is investigated using cooperation of arrayed direct-drive actuators. Electrostatic scratch-drive actuators (SDAs), which combine active frictional contact mechanisms with electrostatic actuation are particularly analyzed. A prototype of a cylindrical micromotor, whose external diameter and length are, respectively, 1 mm and 2 mm, has been realized through the insertion of a flexible active polysilicon sheet at the rotor/motor-frame interface. The sheet, which acts as a stator, is fabricated by the surface micromachining process and then released automatically from the silicon wafer. One thousand four hundred thirty actuators are integrated on a 6 mm2 polysilicon sheet surface, leading to high-driving-torque characteristics.

International audience; This article deals with the optimization of the main element of a digital microrobot, which is a bistable module. the bistable module consists of curved beams and electrothermal actuators. A design study of the curved beam and the electrothermal actuator is presented in order to achievethe limits in line with miniaturization. Finally, An optimization for the dimensions is proposed respect to microfabrication and elastic limits.