Development of numerical tools for the simulation of ultrasonic nondestructive inspection.
The CEA LIST develops the CIVA software platform (http://www-civa.cea.fr), in position of global leader for the simulation and expertise of non-destructive testing (ultrasonic and electromagnetic methods, radiography, X tomography). In the context of extending and improving capabilities of the CIVA platform, the post-doc fellow will contribute to the development of numerical methods for the ultrasonic testing (UT) simulation module.
The semi-analytical models of CIVA are based on physical simplifying hypotheses for the propagation of the ultrasonic beam and its interaction with defects. These methods provide efficient computational performances with accurate results in a wide range of realistic applications. However, configurations for which these models are not valid. The so called “numerical models” including finite element method (FEM), finite difference method (FDM) or boundary element method (BEM) enable to deal with these configurations without any simplifying hypotheses. However, the computation time is prohibitive in an industrial context, especially for 3D applications. The approach adopted in the CIVA platform consists in hybridizing semi analytical models with numerical ones in order to benefit of both the numerical efficiency of the former and the capability of simulating complex phenomena of the later.
The tasks associated to the post include the development of numerical methods themselves, in collaboration with academic partners, the integration in CIVA of a meshing solution enabling the data formatting for the numerical solving and specific developments for the coupling with semi analytical methods. Multi-boxes solutions, enabling for example the optimization of configurations with several defects or a coupling around the source and the defect, will be studied.
Compensation methods (for magnetic perturbation) for shape capture via orientation sensors
Our laboratory works for several years on shape capture (curves, surfaces) in static and moving positions, via inertial sensors - e.g. accelerometers ans magnetometers - able to provide information about their own orientation. In fact, in real conditions, sensors do not exactly provide their orientation, the measure is disturbed with external contributions (own motion acceleration, vibrations, magnetic perturbations). This work consists in analysing these disturbances, proposing preprocessing to clean data to obtain "denoised" tangential information to allow the reconstruction of these curves and surfaces.
First, we study the case of the reconstruction of a metallic pipe: we want to reconstruct a curve with magnetic sensors disturbed (the surface reconstruction will be explored afterwards). This work consists in finding the best methods allowing to extract the needed information from these "noised" signals (data fusion, source separation, model of perturbations, adding a new sensor modality,... are domains to explore). In this goal, a bibliographic study will be done firstly by the Post Doc student, then he will have to implement the different methods found, and test the performances with real signals acquired with our system of shape capture in a disturbed environment.
Porous layer integration for advanced temporary substrates
Double transfer of thin single crystalline processed layer can be very interesting for all technologies that require front and back side engineering of the silicon active film. With the increase of the electronical system complexity, this alternative technology can offer new opportunities to miniaturize the semiconductor devices. To fulfill such requirements, a recent alternative technology was developed at the CEA-LETI, based on the use of porous silicon substrates [1]. This new technology will be of a great interest for 3D integration, back-side imager but also MEMS or photovoltaics applications. This technology should now be validated at a larger scale, and we need to focus on all involved mechanisms such as the porous silicon layer rupture.
In a first place, the applicant should comprehend the specification of porous materials in thin film configuration, including elaboration steps and distinctive properties of transferred porous layers. Subsequently he/she may need to interact with Leti’s technological experts to determine process improvements to be implemented to reach pre-established specifications of desired prototypes. In order to evaluate and recommend appropriate materials and equipments, he/she may need to extensively focus on the behaviour of porous material under specific stress conditions such as chemical, thermal or mechanical solicitations. The purpose is to ensure compliance to Smart Cut or Smart stacking technologies that involve amongst others processes molecular bonding technology.
Later, the effort should be focused on the development of a specific technology to induce the mechanical separation inside the buried porous silicon layer. One line of approach would be to trigger the mechanical separation by ultrasound solicitation. Understanding the mechanisms of the splitting and characterising the resulting structures are part of the expected work to be completed in this project.
[1] A-S.Stragier et al., JECS,158 (5) H595-H599 (2011)
New acoustical transducer inspired by the middle ear for source localization
The external and middle ears can be seen as a whole system able to convert the acoustical energy from the free field to a semi-confined media dedicated to an efficient transduction of the signals of interest. Among species this configuration is highly dependent on the environment and the usage. The work will focus on the simulation by the finite element method using the COMSOL software of the acoustical coupling of a vibrating membrane placed at the interface between an acoustic wave guide and a semi-confined network of cavities. Methods developed to study the design of microphones are well suited. In particular the methods that help study the impact of a non planar shape of the back of the cavity just behind the vibrating membrane. It will be asked to demonstrate how these configuration help creating optimized set-up condition. In a second phase, design rules inspired by anatomical specificities will be extracted. The optimisation of three parameters is of main interest : directionality, sensitivity to a larger range of input signals and spectral responses within a narrow or large frequency band. In the meanwhile a lumped model based on the acoustic-mechanic-electrical analogy of the complete system will be done on the basis of a preliminary study demonstrating the interest in using a system-level simulation tool (ASYGN) to reproduce the performance of the organ on one side and the artificial transducers inspired from the organ on the other side.
Integrated antenna arrays for 60 GHz high-data rate communications
This post-doctoral offer is in support of our work program on the design of millimetre-wave antennas for high data rate communication systems in the 57-66 GHz frequency band. The realization of smart devices in this frequency band with a high level of integration and a low cost is a challenge accessible today thanks to the recent microelectronic technologies as well as other silicon technologies such as assembly, packaging or micromachining. Some applications in the consumer electronics domain are clearly identified and expected to result in product in a very short term.
After a series of project completed these last years on the design of single antennas built and validated on different technologies, such as silicon or ceramic, the future projects will focus on the demonstration of antenna arrays with electronic beamsteering for long range applications. Several demonstrators will be realized in collaboration with our partners developing the integrated circuits and fabrication/assembly technologies in order to obtain a fully functional system.
Metamaterials : design of an integrated high-impedance surface at 60 GHz, transposition and potentialities at 60 THz
Invisibility cloaking, sub-wavelength, thin antenna substrates, absorbers, etc., metamaterial structures have open many perspectives, some of them seeming futuristic while other being very practical given the current ste of the art in the domains of materials, microtechnologies and integrated optics.
this post-doctoral work will focus on the study of high-impedance surfaces and the possibility of transposition of these designs between very different frequency bands (6 GHz, 60 GHz, 60 THz) corresponding to a wide range of technologies and applications.
After a thorough bibliographic study of the current state of the art, the developments will include the design of high-impedance surfaces at the three frequency bands cited above and an experimental demonstration at 6 GHz and possibly at 60 GHz.
Deployment of distributed consensus protocols on blockchains with Smart Contract
The aim is to implement various distributed consensus protocols on both public and private blockchain platforms supporting Smart Contracts technology. The techniques based on Proof-of-Stake and token management will be analyzed and their level of security will be evaluated in terms of energy consumption and quality of the distribution of the trust in the system. The techniques to verify the transactions of the blockchain Ethereum will be implemented, as well as other algorithms, lighter and that consume less energy, dedicated to "private" blockchains where users are authenticated. The platform Hyperledger will be used to test the various distributed consensus protocols. New algorithms will be proposed and the solutions will be deployed for applications in the field of the Internet of Things.
Nano-silicon based negative composite electrode for lithium-ion batteries
With the aim of improving the battery type lithium-ion batteries, many works are devoted to research of new materials for the manufacturing of high-capacity electrodes. Silicon is an attractive material as an element of negative electrode instead of graphitic carbon with its high capacity that can theoretically reach almost 3579 mAh/g (Li15Si4, ten times more than the graphite (372 mAh / g, LiC6) . However, one major problem that has prevented the development of such electrodes is the high coefficient of volumetric expansion of silicon which leads to rapid degradation of the material (cracked, spraying the electrode ,....) and its performance. In this context, the work of post-doc will be to explore the electrochemical performance of negative electrodes prepared from silicon nanoparticles synthesized by laser pyrolysis CEA. The work will be to incorporate nanoparticles in a negative composite electrode and test its performance. The understanding work will be focused on the dual influence of nanostructuration of silicon particles and of the composition / implementation of the composite electrode on the performance. Thus, this work will be located at the junction of two CEA laboratory specialists from both key points of the study (Synthesis in Saclay, development and characterization of batteries in Grenoble).
Nanoimprint process development on flexible substrate for electronic and optical applications
This subject aims to develop specific nanoimprint processes for various materials and to apply them to the realization of various components on plastic film. Several themes will be addressed through different materials, on the substrate itself or on a more or less thin layer deposited on a flexible plastic film. An incomplete list of these materials is presented below. They correspond to various potential applications. In the field of electronics, printing processes of dielectric materials will be studied. Particular substrates are also pressed for the creation of OTFT. In the field of optics, the structuring of several conducting polymers with special optical properties is considered for various applications. Some of these polymers belong to the family of PEDOT used also in the field of photovoltaics. The multilayer structure of polymers will be explored for the realization of 3D structures.
Finally, the ability to print polymer films loaded nanoparticles will also analyzed.