General description & Context

The rise of wireless interconnected devices, for instance in the framework of the Internet of Things (“IoT”), shows unprecedented promising outcomes in the framework of the communication society (smart cities, digital society…). At the dawn of the advent of IoT and 5G, where forecasts predict more than 75 billion of connected devices worldwide by 2025 ([1]), representing between $4 trillion to $11 trillion in economic value ([2]), unique opportunities appear for instance in terms of global communication, sensing and monitoring for structural, goods and person safety (buildings, transportations…) or gathering information from numerous environments to achieve better life quality as well as sustainable development. Progresses in these fields however raise, in addition to ethical questioning, numerous technical issues (data processing…) especially, at the device level:

• Acoustic Wave filters selectivity, wideband capabilities and power consumption: fast and reliable telecommunication as well as combined communication media (4/5G, Wi-Fi, Bluetooth…), require very wide frequency spectrum, that nowadays cannot be achieved by the same circuit (for example a phone requires tens to hundreds of filters - [3] -, several for each antenna), raising integration issues. Besides, the cost of such filters is high due to the need of fine tuning. Last but not least, using many components to perform similar functions yields significant power demands. While the consumption of a single device is limited (a few 100’s of mW), the high number of such systems yields a total power consumption with emission of ~730 million tons of CO₂ ([4]), comparable to air transportation ([5]). In the framework of sustainable development, reducing power consumption of each device is of considerable priority. Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) filters, able to work at >1 GHz, show a constantly increasing market size, with prediction up to 20.5 billion US$ in 2025 ([6]). Making them able to adapt their frequency selectivity would open new routes for integration and power savings, while preserving high data rate and reliability.
• Power supply reliability and shortage risk: an attractive aspect of IoT is ubiquity, ranging from massive infrastructures to small animal tracking for example. Wide spreading of these systems requires continuous and reliable energy sources. While primary batteries are commonly used to this end, they are not adapted in many cases. The current major limitation of battery is no longer their initial energy, but their intrinsic leakage and self-discharge that consume energy without effectively using it. This prevents the development of left-behind devices (e.g., wireless sensors) in remote or confined locations, which is even more critical when considering relatively harsh environments. For example, Li-Ion batteries exposed to a 60° C temperature loose more than half of their energy within one year ([7]). Small-scale (millimeters to centimeters) energy harvesting has been proposed as a viable alternative for such systems, with typical power densities up to a few mW.cm^-3 matching well power requirements of targeted applications (wireless sensors and sensor networks). Energy harvesting principles consist in taking advantage of energy sources surrounding the device (solar, mechanical, thermal…) and convert them into electricity, bringing energy in a safe, reliable, and endless way while addressing CO₂ emission issue. Vibrations offer wide and reliable availability, and associated conversion materials show good integration potential and high-power densities.

Going beyond the comfort zone for exploiting unimagined potentials

To address such challenges, FIESTA proposes an innovative approach using stress-induced transitions in ferroelectrics. These materials present attractive properties such as good electromechanical coupling, good power density, high integrability and easy control, as well as secondary benefits such as resilience to electromagnetic perturbation (contrary to ferromagnetic ones). While they have mostly been used considering linear behavior, FIESTA proposes to go beyond this comfort zone, taking advantage of intrinsic nonlinearities in such materials embedded in a global system to obtain acoustic filters providing frequency band hopping as well as energy harvesters with power densities beyond the state of the art (a decade is expected), both developed in parallel but sharing many common aspects (low required stress for phase transition, piezoelectric behavior in both phases, high fatigue life…). In the framework of FIESTA, the project is mainly constructed around a common material (KTN) that allows realistically reachable stress-induced transition for both applications, with extension to polymers for energy harvesting. Because of the strong link between stress and temperature at the structural level, researches and developed technologies will be also adaptable to thermal excitation. In terms of energy harvesting for instance, this enables realistic multifunctional harvesters efficiently converting energy from both mechanical and thermal sources.

Going transdisciplinary by a global approach / Degrade parts for global optimization

Proposing new insights and devices requires merging disciplines and promoting transdisciplinarity to transcend outcomes, yielding a competence of the sum greater than the sum of competence. FIESTA embraces all aspects combining material science, physics, mechanical and electrical engineering and, last but not least, the interfaces between them. This will ultimately allow globally optimized researches and applications, while combinations of independently optimized blocks yield sub-optimal global systems due to numerous bidirectional interactions at various scales. An example in FIESTA is to optimize the material properties to ensure reachable stress-induced transitions by using elaboration methods with low cost and upscaling possibilities. What is usually considered as a limitation will therefore be taken in advantage to propose innovative solutions for the two applicative targets of the project, both sharing the unique characteristics of a single material (KTN) in the form of film or bulk shape. Furthermore, with this transdisciplinary approach multiscale nonlinearities also arise, combining intrinsic material ones with those generated from the electrical interfaces.

Nonetheless, in addition to common transversal aspects, FIESTA will also bring significant advances in each field. It is expected that material tailoring will unveil the mechanisms behind phase transitions induced by temperature and uniaxial/biaxial stress and related nonlinearities of physical properties, as well as parameters (compositions, elaboration procedure…) to control this effect. On the mechanical side, new structures generating high stress from realistic excitations will be developed.

Going to genuine science with links to societal stakes

One key philosophy behind FIESTA is also to strongly link fundamental research with societal needs while keeping a genuine scientific questioning. More particularly, the principles of the project aims at starting from the scientific conceptualization of socio-economic challenges to translate them into scientific issues, that are then thoroughly and scientifically analyzed to bring solutions to the original issue (Figure 3) thanks to the transdisciplinary approach.

References