In order to facilitate the deployment of sensors in urban infrastructures in a smart and sustainable city perspective, it is necessary to deploy low cost communicating systems that are energy autonomous, reliable, and if possible compact and based on low polluting materials. In this thesis, we propose to study a new concept of electromechanical capacitive sensors with complete energy autonomy, both for measurement and data transmission, thanks to the combined action of the triboelectric effect and the electrostatic breakdown of air. Two applications will be targeted, the monitoring of suspended structures (e.g. bridges or buildings) based on the variation of their frequency of resonance, and the monitoring of road pavement based on their in-plane or out-of-plane deformation.

Triboelectric energy generators are electrostatic transducers which are self-polarized when two suitable materials are brought into contact [Zha18]. They have the particularity of allowing the generation of voltages of several hundred volts, sometimes in a single mechanical actuation. This high voltage, if applied to the terminals of a "switch" consisting of two conductors separated by a gap of a few microns, can be the cause of the "breakdown" of the ambient dielectric (here the air) if the limits of the Paschen law are reached. Consequently, an electromagnetic wave is generated by this micro-plasma according to the principle of the Hertz experiment [Jou89].

The thesis will consist in implementing conversion of energy from the mechanical domain into electromagnetic waves while encoding the measured data from a capacitive sensor in the transmitted signal. Thus, it will be possible to free the transmitter system from any electronics except for a few diodes and capacitors, which will greatly reduce the overall power consumption. Although it has been demonstrated that such a transmission system with a triboelectric energy generator with a surface area of less than one cm2 can emit an electrical pulse that can be sensed at a distance of more than ten meters [Wang21], the exact mode of transmission and the means of influencing its characteristics are still largely misunderstood.

The proposed approach is to add the capacitive sensor in the transmission loop in order to make the frequency modulation dependent on other mechanical parameters to be measured. These mechanical parameters vary the geometry of the sensors and therefore its capacitance value. This results in a modulation of the frequency, and/or the amplitude and/or the periodicity of the transmitted signal, which can provide information about the dynamic mechanical phenomenon that has caused the modification of the geometry of this additional transducer. For example, it is possible to measure locally, in time and space, an acceleration on a mechanical structure. This acceleration is a response to the mechanical excitation of the structure. When done at distributed localizations across the structure, these acceleration data can be used to infer the structure’s mechanical health. To carry out such distributed measurements, the transmission loop also needs to be tuned so as to allow discriminating between multiple emitting devices.

In a first part, the candidate will design and fabricate the capacitive sensors for the measurement of dynamic mechanical quantities from a civil engineering structure or from the roadway under the effect of a passing vehicle. These sensors will be made using MEMS technologies for miniaturization goals. Realistic mechanical stimuli for in-lab experiments will be provided by Navier (bridge and building applications) and EASE (5G road applications) laboratories, both from Uni Gustave Eiffel. These two collaborations will also allow experiments in real environments.

A second part of the thesis will consist in optimizing the propagation distance by studying the antenna system initially constituted by the micro-plasma switch at the emission and a simple loop antenna at the reception. The candidate will study the possibility of integrating the micro-plasma switch into an antenna and/or a reflector plane in order to improve the directivity of the system.

For a low cost and "natural" approach, the triboelectric energy generators will use cellulose film-based active layers provided by a collaborative research team from the Mid Sweden University. To increase in efficiency, a second active layer of opposite polarity will be added, thanks to a long-term partnership with the team of Prof. S.-W. Kim's from the Sungkyunkwan University (South Korea) which is a world reference for triboelectric materials. The micro-plasma switches could be also MEMS components from the clean rooms of UGE/ESIEE Paris [Zha20] or simple electrical wires.

This thesis will take place at ESYCOM lab (Armine Karami, Jean-Marc Laheurte, Philippe Basset) which has more than 15 years of history in electrostatic kinetic energy harvesting with a focus on triboelectricity in recent years, and more than 20 years of history in antenna design. In addition, collaborations inside Univ Gustave Eiffel will take place with Navier lab (Michaël Peigney) for the bridge and building applications and with EASE lab (Malal Kane) for road-related applications. This thesis includes a long (several months) stay at SKKU and a possible short (a few weeks) stay at Mid Sweden University.

[Zha18] 10.1016/j.nanoen.2018.06.038
[Zhan20] 10.1038/s41467-020-17019-5
[Jou89] 10.1051/jphystap:018890080011601
[Wan21] 10.1126/sciadv.abi6751

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