PhD Defense of Namanu PANAYANTHATTA

Keywords:
Nanotechnology,nanogenerators,AFM characterization,electrical characterization,Nanosystems,piezoelectric

Résumé :
The overall aim of this PhD work is the investigation of the harvest of power from ambient vibrations at relatively low frequencies < 500 Hz using lead free piezoelectric materials in order to power low power sensors or actuators that are used in the “Internet of things” IOT networks. The rapid growth of communication and information Technology (IT), along with the progress in the semiconductor industry in recent times, has generated growing interest in the field of IoT. The IOT concept comprises of “Smart Structures” with autonomous self-powered sensors, actuators and associated low-power electronics circuits that is spread across a network of wireless sensor nodes (WSNs) that can sense and share data among one another and the master unit. In order to make it fully autonomous it is very important that they are powered independently and therefore it is challenging to replace the depleted energy in the batteries. In this situation, the use of ubiquitous ambient mechanical vibrations to generate electricity for powering the WSNs is a promising choice.
Among the various transduction mechanisms to convert vibrational energy to electric energy, piezoelectric transduction has drawn considerable attention because of its simplicity in structure, high energy density and good compatibility with micro/nano fabrication techniques. However, the mostly used high performing piezoelectric ceramics such as Lead Zirconate Titanate (PZT) contains lead which is hazardous. Recently, the European Union has also implemented the Restriction of Hazardous Substances legislation, that has set a strict standard restricting the use of lead-based piezoelectric materials in future electronic devices. This thesis will therefore investigate about novel lead-free materials as a potential candidate for high performance energy harvesting devices. This thesis begins with the basic introduction to the energy harvesting at microscale to power IOT nodes, followed by the chapter on piezoelectric materials and the extraction of their basic properties in order to develop devices. In the next chapter, fabrication and characterization of lead free piezoelectric energy harvester is described, followed by the application of such devices in real time sensing. The thesis focusses on the investigation of lead-free piezoelectric materials such as Sodium Potassium Niobate, Lithium Tantalate and Lithium Niobate as a potential candidate for energy harvesting applications. A brief discussion on processing and deposition of these piezoelectric materials to function as energy harvesting devices is also presented. Various techniques that have been used to characterize the electromechanical piezoelectric properties, morphologies such as Atomic Force Microscopy are typical examples of those techniques. The extracted electromechanical properties are compared with the state of the art in the literature. The fabrication and characterization of a lead free microgenerator based on lead free Lithium Niobate wafer is described. Also, the voltage conditioning circuit for ensuring controlled and stable DC output is discussed. An efficient architecture for the maximum power transfer (MPPT) from the piezoelectric harvester to load is proposed. The piezoelectric harvester demonstrated excellent ability in sensing and energy harvesting. The piezoelectric Harvester was demonstrated to power an Energy Autonomous Wireless Vibration Sensor EAWVS vibration sensor, that could be used for condition monitoring in automobile, heavy machineries, motors and so on. The EAWVS provides the added flexibility, that allows the measurement readout remotely and wirelessly by exploiting the Bluetooth Low Energy BLE communication and transmitting beacons at a remote BS with the sensor reading based on the easy-to-implement time-domain readout by measuring the advertising time Tadv. Finally, a brief summary into future prospective is discussed.

Jury members :

• Edwige BANO, PROFESSOR OF UNIVERSITIES, Grenoble INP : Supervisor
• Daniel ALQUIER, PROFESSOR OF UNIVERSITIES, University of Tours :  Reviewer
• Alain GIANI, PROFESSOR OF UNIVERSITIES,University of Montpellier : Reviewer
• Skandar BASROUR, PROFESSOR OF UNIVERSITIES, University of Grenoble Alpes : Examiner