Institut FEMTO-ST
  • Besançon, France
Recent publications
In this paper, the design of large-scale quasi-periodic Vibration Energy Harvesters (VEH) is optimized to enhance the harvested power of an electromagnetic mode localized structure. This work aims to optimize the output power by employing the energy localization phenomenon in a large-scale periodic configuration by introducing the minimum number of perturbations. The harvested power, number, and location of perturbations are among the objectives that need to be optimized. A genetic-based mixed-integer optimization algorithm is used to meet the objective functions within a constraint on the system kinetic energy. Numerical simulations for quasi-periodic systems with 20 and 100 Degrees of Freedom (DOF) are performed. It is shown that the ratio of harvested power increases as the number of perturbations rises and it exceeds 80% of the total output power by perturbing almost one-third of the total DOFs. The proposed methodology is a decision-making aid to provide an optimal design in a generalized quasi-periodic VEH in order to reduce the number of harvesting transducers while providing a significantly high amount of harvested power.
Background : Caveolae are invaginated plasma membrane domains of 50-100 nm in diameter involved in many important physiological functions in cells. They are composed of different proteins, including the membrane-embedded caveolins and the peripheric cavins. Caveolin-1 has already been expressed in various expression systems ( E. coli, insect cells, Toxoplasma gondii, cell-free system), generating intracellular caveolin-enriched vesicles in E. coli , insect cells and T. gondii . These systems helped to understand the protein insertion within the membrane and its oligomerization. There is still need for fundamental insights into the formation of specific domains on membrane, deformation of a biological membrane driven by caveolin-1, the organization of a caveolar coat, and the requirement of specific lipids and proteins during the process. The aim of this study was to test whether the heterologously expressed caveolin-1β was able to induce the formation of intracellular vesicles within a Gram ⁺ bacterium, Lactococcus lactis , since it displays a specific lipid composition different from E. coli and appears to emerge as a good alternative to E. coli for efficient overexpression of various membrane proteins. Results: Recombinant bacteria transformed with the plasmid pNZ-HTC coding for the canine isoform of caveolin-1β has been shown to produce caveolin-1β, under its functional oligomeric form, at a high expression level unexpected for an eukaryotic membrane protein. Electron microscopy revealed several intracellular vesicles from 30 to 60 nm, a size comparable to E. coli h-caveolae, beneath the plasma membrane of the overexpressing bacteria, showing that caveolin-1β is sufficient to induce membrane vesiculation. Immunolabelling studies showed antibodies on such neo-formed intracellular vesicles, but none on plasma membrane. Density gradient fractionation allowed the correlation between detection of oligomers on Western blotting and appearance of vesicles measurable by DLS, showing the requirement of caveolin-1β oligomerization for vesicle formation. Conclusion: These caveolin-1β enriched intracellular neo-formed vesicles might be useful for potential co-expression of membrane proteins of pharmaceutical interest for their simplified functional characterization.
Actuation of micro-robots in relation to the field of programmable matter has been the aim of most researches working on the topic. Most studies have concentrated on the ability of these robot modules to latch with one another and to be able to move around each other to form the desired configuration. These mostly have been based on Modular Self re-configurable Robots (MSR) which use mechanical, magnetic or pneumatic method in their manoeuvres. However, these have been faced by the challenges of miniaturization, power consumption and power transfer between modules. Electrostatic actuation has attracted more interest in recent works due to the ability to scale down the modules and to use the configuration for power transfer and communication. In this work, we propose to use electrostatic chuck principle to actuate modules having a cylinder form. Instead of using one array of electrodes, two columns of electrodes array, positive and negative, are considered to increase the force generated by the chuck effect. An array of electrodes prototype has been fabricated using lithography process for validating the actuation. A sufficient force and torque are generated for latching and making the cylinder rolling respectively, thus validating and showing the potential of electrostatic actuation for miniaturized programmable matter application.
This paper deals with the modeling and control problem of a Hydraulically Amplified Self-healing Electrostatic (HASEL) actuator based on the port-Hamiltonian framework. A nonlinear spring-damper system is used to approximate the mechanical deformation of the actuator due to the motion of the fluid while a nonlinear capacitance is used to approximate the electric behavior of the system. The actuator position control strategy is investigated based on the Interconnection Damping Assignment-Passivity Based Control (IDA-PBC) method, with further Integral Actions (IA) added to cope with load uncertainties. The proposed model and control laws are validated on an experimental benchmark. The experimental tests demonstrate that the proposed model is accurate up to 94% of fitness. The controllers allow assigning the actuator position with ramp and sinusoidal references with the relative error less than 5%. At last, the robustness of the proposed IDA-PBC controller with IA has been shown with the experimental result for the unknown load disturbance rejection.
A continuum mechanics framework is used herein to model the strains induced in a micromechanical structure by surface phenomena such as adsorption. The resulting picture significantly differs from those of a liquid under surface tension. Considering a solid isotropic elastic material, it is shown that a sphere undergoes a non uniform deformation under surface adsorption. The direction of the surface’s displacement is additionally shown to depend on both the material and the sphere’s radius. It is also shown that modeling surface effects with an elastic membrane surrounding a Cauchy elastic material, the elastic energy is usually misestimated. The reported results also reveal that the overall response of a mechanical structure to surface adsorption strongly depends, at a given scaling, of the higher-grade elastic behavior of the material.
Robotics and autonomous systems are reshaping the world, changing healthcare, food production and biodiversity management. While they will play a fundamental role in delivering the UN Sustainable Development Goals, associated opportunities and threats are yet to be considered systematically. We report on a horizon scan evaluating robotics and autonomous systems impact on all Sustainable Development Goals, involving 102 experts from around the world. Robotics and autonomous systems are likely to transform how the Sustainable Development Goals are achieved, through replacing and supporting human activities, fostering innovation, enhancing remote access and improving monitoring. Emerging threats relate to reinforcing inequalities, exacerbating environmental change, diverting resources from tried-and-tested solutions and reducing freedom and privacy through inadequate governance. Although predicting future impacts of robotics and autonomous systems on the Sustainable Development Goals is difficult, thoroughly examining technological developments early is essential to prevent unintended detrimental consequences. Additionally, robotics and autonomous systems should be considered explicitly when developing future iterations of the Sustainable Development Goals to avoid reversing progress or exacerbating inequalities.
This paper presents recent advances on two dimensional length-extension mode (2D-LEM) quartz resonators providing high quality (Q) factor on resonances at a few MHz. The resonators have been collectively manufactured using one or two steps quartz deep reactive-ion etching (DRIE) processes. These resonators combine the intrinsic qualities of quartz in comparison to silicon (i.e. high Q factor, low temperature sensitivity and piezoelectricity) and the advantages of microelectromechanical systems (MEMS) resonators: small dimensions, low power consumption and collective processes. Samples vibrating at frequencies f of 2.2, 3 and 4.5 MHz have shown promising results with very high Q factor. Q factor as high as 180,000 for fundamental mode vibrating at 2.2 MHz and 89,000 for harmonic mode at 8.9 MHz were measured which lead to quality factor and resonance frequency products (Q·f) figure of merit near 1012 Hz at the state of the art for 2D-LEM quartz resonators and the higher Q factor measured for DRIE made quartz resonators. Two designs, several dimensions and two processes have been investigated. Two main limiting damping mechanisms were identified and one of them is strongly linked to the technological limits of the etching process.
The retrieval of an observed object’s pose is an essential computer vision problem. The challenge arises in many different fields, among them robotics control, contactless metrology, or augmented reality. When the observed object shrinks from the macroscopic scale to the microscopic, pose estimation is further complicated by the weaker perspective of imaging macroscale lenses down to the quasi-orthographic projection inherent to microscope objectives. This paper tackles this issue of microscale pose estimation in two complementary steps that rely on the use of planar periodic targets. We first consider the orthographic projection case as a means of presenting the theory of the method and showing how the pose of periodic patterns can be directly retrieved from the Fourier frequency spectrum of a given image. We then address the perspective case with long focal lengths, in which the full six-degrees of freedom (6-DOF) pose can be retrieved without ambiguities by following the same theoretical background. In addition to theoretically justifying pose retrieval via Fourier analysis of acquired images, this paper demonstrates the method’s actual performance. Both simulations and experimentation are conducted to validate the method and confirm an experimental resolution lower than 1 / 1000 th of a pixel for translations. For orientation measurement, resolutions below 1 μ rad. for in-plane orientation, and below 100 μ rad. for off-axis orientations can be achieved. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Langatate (LGT) crystals of La3Ga5.5Ta0·5O14 composition of diameter 50 mm were grown from the melt by Czochralski technique. Using (1–2 wt %) Ga2O3 excess in the starting charge and growing crystal in mixture argon (0.1–1%O2) gas atmosphere are a good condition to crystallize LGT under stationary stable regime. The LGT crystals grown along Z-axis exhibit strong faceting. The grown crystals were exempt of inclusions, cracks and secondary phases. The presence of oxygen in the growth chamber is necessary to limit gallium oxide evaporation and strongly affect the crystals coloration and the transmission spectra in the range (200–500 nm). The electrical resistivity is sensitive to the oxygen content in the growth environment.
Recent IoT emerging systems and applications require processing over encrypted data to preserve confidentiality. However, designing efficient Homomorphic Encryption (HE) algorithm to respond better to real-time requirements of IoT applications and tiny IoT devices is primordial. Unfortunately, existing homomorphic asymmetric schemes do not provide the efficiency implementation. While, on the other hand, homomorphic symmetric approaches suffer from a low level of security. In this paper, an efficient flexible additive homomorphic symmetric cipher scheme is proposed and it is called “ACiS”. Moreover, ACiS is based on the dynamic key approach to reach a high level of security, where different cryptographic primitives are used for different sessions. In addition, it can achieve a good performance and robustness against confidentiality attacks. It is based on a simple round function that should be iterated for nr iterations and nr>1. Furthermore, the proposed solution is analyzed and evaluated in terms of security and performance levels. Experimental results prove that the proposed solution reaches a good balance between performance and security level compared to the Paillier cipher scheme (a well-known asymmetric additive HE scheme).
Existing copper-coated carbon fibers used in wire scanners to measure the transverse beam profile in the accelerators at CERN are approaching material limits. A new instrument design has showed that the main limitation now comes from the centerpiece of the instrument: the wire. Large amplitude vibrations increase the risk of failure during scans. New required specifications concerning the beam measurements for the Future Circular Collider (FCC) project cannot be met. Fortunately, the commercial development of long microscopic yarns made of spun carbon nanotubes has paved the way for possible alternatives. The objective of this study is to determine if those Carbon NanoTube Yarns (CNTY) could replace the current carbon fibers (CF) for beam instrumentation, and if so, to determine the best configuration in terms of diameters and mounting system. To do so, we have made extensive testing and microscopy on CNT yarns with diameters of 10, 20 and 30 μm, with two different mounting systems, the Paper Frame conditioning (PF) or partial Copper-Coated conditioning (CC). A Weibull approach was used to extrapolate our results to the real length of the wires used in operational instruments. This study shows that considering the Weibull criteria, the best configuration to increase the accuracy of the beam profile measurement is to use a not copper-coated 20 μm diameter CNTY.
Flexoelectricity is an electromechanical coupling phenomenon, that can generate noticeable electric polarization in dielectric materials for nanoscale strain gradients. It is gaining an increasing attention because of its potential applications, and the fact that experimental results were initially an order of magnitude higher than initial theoretical predictions. This stimulated intense experimental and theoretical researches to investigate flexoelectric coefficients in dielectric materials such as two-dimensional materials. In this work, we concentrate on the calculation of the flexoelectric coefficients of 2D-MoS 2 thanks to a model using self-consistently determined charges and dipoles on the atoms. More specifically, we study the importance of two contributions which were neglected/omitted in previous papers using this model, namely the charge term in the total polarization and the conservation of electric charge through a Lagrange multiplier. Our calculations demonstrate that the results for flexoelectric coefficient computed with this improved definition of polarization agree better with experimental measurements, provided consistent definitions for signs are used. Additionally, we show how two physical contributions with opposite signs compete to give net values of flexoelectric coefficients that can be either positive of negative depending on their relative importance, and give net values for the case of MoS 2 .
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379 members
Maria-Pilar Bernal
  • Department of Optics
Marie-Ange Manier
  • Département Informatique des Systèmes Complexes (DISC) / Université de Technologie de Belfort-Montbéliard
Vincent Laude
  • Department of Micro Nano Sciences and Systems (MN2S)
Vincent Humblot
  • Department of Micro Nano Sciences and Systems (MN2S)
Aleksandr Oseev
  • Department of Micro Nano Sciences and Systems (MN2S)
15B Avenue des Montboucons, 25030, Besançon, France
Head of institution
Laurent Larger
+33 (0)3 63 08 24 00