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Over the past four decades, energy microsources based on piezoelectric energy harvesting have been intensively studied for applications in autonomous sensor systems. The research is triggered by the request for replacing standard lead-based piezoelectric ceramics with environmentally friendly lead-free materials and potential deployment of energy-harvesting microsystems in internet of things, internet of health, ‘place and leave’ sensors in infrastructures and agriculture monitoring. Moreover, futher system miniaturization and co-integration of functions are required in line with a desired possibility to increase the harvested power density per material volume. Thus, further research efforts are necessary to develop more sustainable materials/systems with high-performance. This paper gives a comprehensive overview on the processing and functional testing the lead-free bulk materials and thin films and discusses their potential in the applications in the stress- and strain-driven piezoelectric energy harvesting. This includes the methodology of estimation of the substrate clamping and orientation/texture effects in the thin films, and identification of orientations offering high figure of merit. The ability to control film orientation of different lead-free materials is reviewed and the expected piezoelectric performances are compared with the ones reported in literature.

In this work we consider dimples as a possible passive boundary layer control strategy in order to improve the wind turbine blades performance. Due to the complexity of the phenomenon, Large–Eddy Simulation (LES) is here used to analyze the flow field induced by dimples on the NACA 642–014A laminar airfoil operating at Re = 1.75 ⋅ 10 5 . We have selected a laminar airfoil since this kind of airfoils has been considered as successful solution for modern utility–scale wind turbines. Experimental measurements were also carried out at the Environmental Wind Tunnel of the “Universita Politecnica delle Marche” for the sake of validation of our numerical investigations. LES results provided a good agreement with experimental data. It has been shown that dimples application can produce a reduction of the boundary layer separation; additionally, in all the considered cases, dimples reduce the pressure drag coefficient with a consequent increase of the viscous drag coefficient.

The huge number of electronic devices called the Internet of Things requires miniaturized, autonomous and ecologically sustainable power sources. A viable way to power these devices is by converting mechanical energy into electrical through electro-active materials. The most promising and widely used electro-active materials for mechanical energy harvesting are piezoelectric materials, where the main one used are toxic or not biocompatible. In this work, we focus our attention on biocompatible and sustainable piezoelectric materials for energy harvesting. The aim of this work is to facilitate and expedite the effort of selecting the best piezoelectric material for a specific mechanical energy harvesting application by comprehensively reviewing and presenting the latest progress in the field. We also identify and discuss the characteristic property of each material for each class to which the material belong to, in terms of piezoelectric constants and achievable power.

International audience; Wireless sensor nodes (WSNs) are the fundamental part of an Internet of Things (IoT) system for detecting and transmitting data to a master node for processing. Several research studies reveal that one of the disadvantages of conventional, battery-powered WSNs, however, is that they typically require periodic maintenance. This paper aims to contribute to existing research studies on this issue by exploring a new energy-autonomous and battery-free WSN concept for monitor vibrations. The node is self-powered from the conversion of ambient mechanical vibration energy into electrical energy through a piezoelectric transducer implemented with lead-free lithium niobate piezoelectric material to also explore solutions that go towards a greener and more sustainable IoT. Instead of implementing any particular sensors, the vibration measurement system exploits the proportionality between the mechanical power generated by a piezoelectric transducer and the time taken to store it as electrical energy in a capacitor. This helps reduce the component count with respect to conventional WSNs, as well as energy consumption and production costs, while optimizing the overall node size and weight. The readout is therefore a function of the time it takes for the energy storage capacitor to charge between two constant voltage levels. The result of this work is a system that includes a specially designed lead-free piezoelectric vibrational transducer and a battery-less sensor platform with Bluetooth low energy (BLE) connectivity. The system can harvest energy in the acceleration range [0.5 g–1.2 g] and measure vibrations with a limit of detection (LoD) of 0.6 g.

In this paper, we present integrated lead-free energy converters based on a suitable MEMS fabrication process with an embedded layer of LiNbO3. The fabrication technology has been developed to realize micromachined self-generating transducers to convert kinetic energy into electrical energy. The process proposed presents several interesting features with the possibility of realizing smaller scale devices, integrated systems, miniaturized mechanical and electromechanical sensors, and transducers with an active layer used as the main conversion element. When the system is fabricated in the typical cantilever configuration, it can produce a peak-to-peak open-circuit output voltage of 0.208 V, due to flexural deformation, and a power density of 1.9 nW·mm−3·g−2 at resonance, with values of acceleration and frequency of 2.4 g and 4096 Hz, respectively. The electromechanical transduction capability is exploited for sensing and power generation/energy harvesting applications. Theoretical considerations, simulations, numerical analyses, and experiments are presented to show the proposed LiNbO3-based MEMS fabrication process suitability. This paper presents substantial contributions to the state-of-the-art, proposing an integral solution regarding the design, modelling, simulation, realization, and characterization of a novel transducer.