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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 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.

LiNbO3 has been little studied for the piezoelectric energy harvesting applications. Although it is a cheap piezoelectric material without lead and toxic elements, it beneficiates of technological maturity in single crystal fabrication for optical and acoustic applications. In this Letter, we propose to investigate a (YXlt)/128°/90° LiNbO3 cut as it offers a transverse piezoelectric coupling of k23 = 0.49, which is comparable to that of commonly used PZT ceramics. A flexible beam of 65 mm length and a tip mass made of a LiNbO3 thick film bonded on silicon were studied under 0.1 g sinusoidal acceleration. The beam presented an open-circuit resonance frequency of 105.9 Hz and a displacement up to 1.5 mm. In the frame of a single degree of freedom lumped model with a rectifying bridge, the electromechanical coupling of the device (km2), the figure of merit km2Q, and the normalized average power density were compared to both Pb-based and Pb-free current devices. The generated power density by our device was 965 μW/cm2/g2, which is among the highest reported values compared to both Pb- and Pb-free vibrational harvesting devices.

Summary This paper addresses the design optimization process of an energy harvesting device for scavenging energy from an e-gadget, utilizing its ”rocking” motion. The plucking mechanism inspired by the frequency up-conversion technique provides initial displacement exciting piezoelectric beams and increases the total number of excitations multiple times. The harvester is designed in conjunction with the multidimensional surrogate optimization algorithm to maximize the device’s performance considering the geometrical features of the concept and the constrained operating environment. The established numerical model is validated first using a set of experimental data. The obtained numerical results demonstrate that the developed 10.2″ size device produces 55 mJ in half-period when inclined at 45°, which is equivalent to generating 0.3 W. Considering that an iPad of the same size consumes around 3 W, the proposed energy harvester is capable of extending its battery life by 10%., Graphical abstract, Highlights • The paper provides a novel design of an energy harvesting device for e-gadgets • Surrogate optimization is carried for global maximization of the device’s performance • The concept is validated using analytical, numerical, and experimental approaches • Power generation can reach up to 0.3 W when a 10.2" tablet is considered at 45°, Engineering; Mechanical engineering; Energy Systems ; Materials science; Energy materials

International audience; Lead-free lithium niobate (LiNbO

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.

Single-crystalline LiNbO3 films were studied as a pyro- and piezo-electric transducer for energy harvesting applications. Two types of devices: piezoelectric cantilever (PiEH) and pyroelectric chip (ThEH) were microfabricated. Different types of characterization were done, starting from a comparison of finite element method (FEM) simulated eigen-frequencies of cantilever beam and optical vibrometer measurements. According to electrical characterization, resonance frequencies of two cantilevers with different thickness were 1.26 kHz and 485 Hz with generated spontaneous power of 14 μW and 4 μW at 275-300 kΩ, respectively. Finally thermal characterization of pyroelectric samples showed voltage amplitudes ranging from 1 to 2.5mV in the temperature range of 50-200 °C.

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.