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PhD : selection by topics

Engineering science >> Electromagnetism - Electrical engineering
4 proposition(s).

DC-DC Power Converter at micro-Watt and millimeter scales

Département Architectures Conception et Logiciels Embarqués (LIST-LETI)

01-09-2019

SL-DRT-19-0314

antoni.quelel@cea.fr

The aim of the PhD is to develop compact (mm3) power supplies with high efficiency at low power delivery (nW to µW).

Compact and ultra-wideband antenna arrays in Ka-band

Département Systèmes

Laboratoire Antennes, Propagation, Couplage Inductif

01-09-2019

SL-DRT-19-0386

loic.marnat@cea.fr

Millimeter-wave communication (e.g. 5G) or radar (e.g. automobile) systems require directive antennas to compensate for transmission losses and ultra-wideband antennas to ensure, depending on the targeted application, a high data rate or a fine resolution. Agility of radiation pattern is thus a key point. Array antennas offer undeniable advantages and come with a tradeoff between the number of radiating elements and the number of active circuit to achieve the performance required in terms of beam focalization and radiated power (for a form factor defined by the targeted system). However, classical design rules associated to typical array elements arrangement can be show stopper for the antenna integration in some applications and typically lead to limited operating band and scanning range. The aim of the thesis is to get rid of these limitations and to design a seamless compact phased array antenna while ensuring outstanding performance in terms of band of operation and scanning capabilities. To do so, studies will focus on tightly coupled miniature elements put in an array fashion. Four main steps will be needed to understand and model such compact array antennas: - State of the art on tightly coupled and ultra-wideband antenna arrays, - Theoretical study describing the coupled elements behavior and the law governing the coupling between them in dense arrays, - Design if a compact array based on miniature and ultra-wideband coupled elements. Technology compatible with seamless and low cost solutions will be preferred. - Active Ka-band prototype will be realized and measured. The thesis will lead to a compact active millimeter-wave phased array prototype competitive as compared to actual state of the art. These studies will pave the way to the use of phased array in applications with complex and compact environments such as 5G terminal and access point or automotive radars and even for advanced satellite antennas.

Tunable Metasurface

Département Systèmes

Laboratoire Antennes, Propagation, Couplage Inductif

01-06-2019

SL-DRT-19-0406

jean-francois.pintos@cea.fr

Metamaterials have been studied by the scientific community for several years with a particular focus on 2D or 3D meta shapes. In the antenna field, these structured materials have been mainly used as magnetic surfaces, filtering surfaces for surface waves or the antenna itself. The main disadvantage of these materials is its narrow band behaviour. Recent research has shown that it is possible to modify the response of metasurfaces by adding a film sensitive to a control voltage to the patterns or by arranging the active components between them. More recently, CEA Leti has developed a new approach, through a thesis, to modify the performance of a metasurface, by inserting control devices on its rear surface as well as on the feeder. The proposal, made here, is in line with the continuity of this work, initiated within the LAPCI laboratory, with a specific development around massively tunable metasurfaces. Indeed, it has been demonstrated that the metasurface/feeder pair should be jointly designed/optimized when the metasurface and/or feeder were compact or even miniature. The purpose of this thesis is to study this interaction through the notion of load impedance and to realize a final demonstrator of a reconfigurable metasurface of several hundred active elements. The main interest is to consider the use of ultra-compact adjustable metamaterials in order to miniaturize the size of an antenna placed near a reflecting plane. The second major point concerns the possibility of frequency-dependent control of the complete device (by nature very narrow band) over a frequency band of several tens of percent. During this thesis, the candidate will develop the theoretical modeling of the proposed device and validate the expected performances through 2D and/or 3D electromagnetic simulation campaigns. He/she will be in charge of having the selected demonstrators carried out and will carry out measurements of the devices in the test facilities of CEA-Leti and/or CNES (anechoic chamber). The candidate will be integrated into the Antenna, Propagation and Inductive Coupling Laboratory in Grenoble. He/she will be part of the research team (permanent, doctoral and non-permanent) and will be supervised by a research engineer from the laboratory. The candidate will be required to present his or her work at national and international conferences and symposiums.

Detection and location of faults in a multiconductor transmission line

Département Architectures Conception et Logiciels Embarqués (LIST-LETI)

Laboratoire Fiabilité et Intégration Capteur

01-09-2019

SL-DRT-19-0758

moussa.kafal@cea.fr

The proper functioning of a distribution network depends on the ability to quickly detect the occurrence of faults, such as discharges, short circuits or the penetration of moisture in the cables. If the nature of these defects depends on the application context, the techniques used to detect them depend essentially on the ability to request a cable with test signals, and to monitor the appearance of response signals that would testify to the existence of a modification in the cables. While this approach is clear in the case of standard cables consisting of two conductors, the case of Multiconductor cables remains more complex to deal with. Indeed, applying test signals to a pair of conductors typically causes parasitic excitation of nearby conductors, because of the electromagnetic coupling that connects them. This phenomenon can considerably complicate the interpretation of the results of a test, by creating an ambiguity in the identification of the faulty driver, because several drivers can couple with those actually under test. In this thesis, the coupling will be considered as an opportunity, because it allows to probe a larger number of drivers at the same time. The intrinsic ambiguity of such a proposition can be removed by repeating the tests on several pairs of conductors. It then seems interesting to define optimum choice strategies of drivers to test to cover the largest number of neighboring drivers, without testing all possible combinations. In this sense, this proposal is parsimonious, introducing the concept of effective test surface covered from a pair of conductors. A promising decision strategy for identifying a failing driver is provided by Bayesian tree and graph-based approaches. These tools make it possible to cross the information obtained in order to identify an explanatory model, here the faulty driver. Among the advantages of this approach we can count on their ability to integrate qualitative information, such as the typology of the defect, and to provide a result formulated in terms of probabilities associated with each possible scenario, thus qualifying the interpretation of results and to assess their reliability, unlike purely numerical methods. It will then be necessary to carry out a preparatory work, making it possible to evaluate the probability a priori of observing parasitic signals from a fault on a neighboring conductor. This work will be based on the study of line theory and will provide the link between the physical aspects of Multiconductor propagation and the observables considered during the tests.

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