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Piezoelectric resonators

PYTHEAS

9th March 2023

Vibration control and piezoelectric resonators

A year ago, we introduced PYTHEAS Technology’s first PhD thesis. We can now tell you more about Floriane Peyrouse’s research within the scope of her thesis: “Robust piezoelectric resonators: application to low-frequency vibration control and energy harvesting”.

This thesis deals with vibration control, and more precisely with the design of vibration absorbers. If you’re not familiar with the subject, we invite you to read our article describing piezoelectric resonators and PYTHEAS Technology’s work.

PYTHEAS Technology is invested in the optimization of piezoelectric absorbers and several technological challenges have been identified.

Potential optimizations of piezoelectric resonators

Reduction of the operating frequency to 10Hz

Several potential applications led us to explore the reduction of the natural frequency of piezoelectric resonators, and by doing so their optimal operating frequency. The application using VIV (Vortex Induced Vibration) to generate power has for instance been studied by PYTHEAS Technology. This device could extract energy from slow marine currents to produce electricity. When a cylinder is positioned perpendicularly to the current, under the action of the vortices generated downstream, a thrust force is applied on the cylinder and induces its oscillation. PYTHEAS Technology develops a generator which exploits this phenomenon by placing a grid of cylinders under the sea and using piezoelectric resonators to convert their oscillatory energy into electricity. This technology has been developed during the PyVIV and PyCHARGE projects. The VIV phenomenon’s frequency approximates 10 Hertz, which motivates the research to reduce the operating frequency of piezoelectric resonators.

Frequency robustness

The main objective of the thesis is to improve the robustness of piezoelectric resonators. Conventional resonators are designed for a specific frequency. Their performances will be degraded if this frequency has been incorrectly estimated or if it evolves with time. The development of a robust absorber is thus necessary to remain efficient in a larger frequency range. Two methodologies can be considered: designing a device with an adaptable frequency to manually adjust its value by modifying its parameters, or designing a high-performance device with a large frequency bandwidth.

Floriane’s feedback on the first year of thesis

During the elaboration of the subject, it was decided to implement a non-linear mechanism in the resonator.

Nonlinear vibration absorbers, also called Nonlinear Energy Sinks (NES), are characterized by a nonlinear stiffness. The absorber’s movement is no longer proportional to the exerted force. The relation at play can for example be cubic: F=k₁.x+k₃.x³. With this phenomenon, the NES can automatically synchronize with the structure’s oscillations. Designing piezoelectric resonators with a nonlinear stiffness would allow us to obtain performances similar to a NES and to increase their frequency robustness. Non-linear piezoelectric resonators could operate at the structures’ natural frequency even if it evolves. The thesis’ technical objective is to establish the different design rules for piezoelectric NES.

Because of this nonlinearity, NES are sensitive to the amplitude of the solicitation, i.e. to the applied strength magnitude, and should be correctly designed according to this amplitude level. Damping appears as a critical parameter which needs to be perfectly adjusted, however mechanical damping is sparsely predictable and adjustable. By adding piezoelectric elements and a shunt, it would be possible to modify the behavior of the system. Electrical components affect the mechanical components’ dynamics and vice versa thanks to the electromechanical conversion at play. Adding a resistor inside the shunt would induce an electric damping. The total damping value could then equal the optimal value by adjusting the resistor value.

The first months of the thesis were dedicated to the assimilation of the analytical methodologies used to study NES. Performance indicators were defined to compare their responses with conventional TMDs. Different optimization methods based on these indicators are currently under study to determine the resonators’ optimal factors. These results will then be used to design a prototype.

Here is what we can reveal about our progress with this thesis about piezoelectric resonators. Floriane is continuing her research and tests and we hope to be able to share more results soon.

Until then, if you’re interested in this subject and would like to discuss it with us, do not hesitate to contact us by email (contact@pytheas-technology.com), or to write directly to Floriane (floriane.peyrouse@pytheas-technology.com).