Numerical and experimental investigations of piezoelectric energy harvesters

Thien Hoang (1) , Maxime Bavencoffe (2) , Guillaume Férin (1) , Franck Levassort (2) , Claire Bantignies (1) , An Nguyen-Dinh (1) , Marc Lethiecq (2) , Guylaine Poulin-Vittrant (2)

1 Vermon S.A.
2 GREMAN - UMR 7347 - GREMAN (matériaux, microélectronique, acoustique et nanotechnologies)

In order to supply low consumption electronic devices, wasted mechanical energy available in our environment can be converted into useful electrical energy by piezoelectric harvesters. The two common structures used for vibration energy harvesting are a cantilever-based unimorph or bimorph. The unimorph is constituted of one PZT layer bonded on an elastic one, and the bimorph is made of two PZT layers separated with an inner elastic shim material. Further deepening the comprehension of these mechanical energy harvesters will facilitate their design. Moreover, it is commonly known that material properties of piezoelectric thin films differ from bulk ones [1]. This can be a significant source of error for the device simulation, using analytical models or finite element (FE) models. Numerical models are powerful tools and require an accurate set of material properties of the PZT layer. For this purpose, an original method has been introduced [2], requiring only the electrical impedance measurement of the PZT layer in free-free mechanical boundary conditions: the effective values of the electrical, mechanical and piezoelectric tensors are identified using successively a one-dimensional analytical model and a three-dimensional (3D) FE model of the electrical impedance. The pursued goal is to build a 3D FE model for the design of our harvesters. Firstly, the set of electromechanical properties of the PZT layer, taking into account mechanical and dielectric losses, is identified thanks to an original method [2], based solely on the electrical impedance characterization in free-free boundary conditions. But since the PZT layer is bonded on the elastic shim material, and the final devices are clamped at one end, the influence of the modification of the mechanical boundary conditions has to be determined. For this purpose, a 14μm thick layer of brass has been bonded onto a 150μm thick of PZT to form a 164μm thick unimorph structure. In the same way, another PZT layer has been added to the unimorph structure to constitute a 314μm thick bimorph structure. For each structure, a numerical study based on the FE method has been carried out. In particular, a frequency domain study has been performed on a 3D FE model in clamped-free mechanical boundary conditions to calculate the electrical response of the considered sample in the frequency range of 60Hz-145Hz. The electrical impedance of the sample has been measured on the same frequency range using an impedance analyzer (HIOKI IM3570, Koizumi, Ueda, Nagano, Japan) and compared to the numerical results. The electrical impedance of the samples has been computed and compared with the experiment. The discrepancy between modelling and experimental results is less than 4% in frequency and 16% in impedance magnitude. This demonstrates the accuracy of our model to predict the electrical behavior of piezoelectric cantilevers in clamped-free mechanical boundary conditions. The next step of this work is to model the vibrational behavior of our clamped devices and estimate their electrical output performances (generated voltage, current and power as a function of the resistive load) when the clamped end of the harvester is submitted to a vibration, with the purpose of mechanical energy harvesting.

Domaines: Micro et nanotechnologies/Microélectronique; Energie électrique

Thien Hoang, Maxime Bavencoffe, Guillaume Férin, Franck Levassort, Claire Bantignies, et al.. Numerical and experimental investigations of piezoelectric energy harvesters. Electroceramics for End users X Conference (PIEZO2019), Jan 2019, Spindleruv Mlyn, Czech Republic. ⟨hal-02390824⟩