Electrical interfaces for piezoelectric mechanical energy harvesting devices

The recovery of small-scale ambient mechanical energy (power of the order of a few tens of microwatts to a few milliwatts) is of growing interest in a wide variety of application areas: industry, transport (goods, people, energy), the medical field, the general public, etc. This interest is linked to the development of a wide variety of autonomous electronic devices, most of which are powered by rechargeable batteries or cells. This interest is linked to the development of a wide variety of autonomous electronic devices, most of which are powered by rechargeable batteries. Mechanical energy is present in most environments, in different forms and with different characteristics. Capturing and converting this ambient mechanical energy into electricity can extend battery life, space out battery recharging, and in some cases even eliminate the need for energy storage.

Several technologies for converting mechanical energy into electricity can be considered for this type of application. The most conventional are based on the principles of magnetodynamic, piezoelectric and electrostatic transduction. This article focuses specifically on piezoelectric transduction, which offers numerous advantages for small-scale energy recovery from ambient mechanical vibrations: simple implementation, compactness, high energy density, high efficiency over a wide frequency range. However, the development of compact, efficient energy recovery systems using piezoelectric transducers requires suitable interface circuits. From an electrical point of view, a piezoelectric transducer does not behave like an ideal voltage or current generator, but like a generator with an internal impedance whose modulus and phase vary quite widely. In addition, the amplitude of the electrical quantities generated by the piezoelectric effect depends on ambient vibrations, and can also vary widely. For all these reasons, optimal extraction of the electrical energy generated by piezoelectric transduction requires suitable interface circuits and specific control principles, which are outlined in this article.

Despite high conversion efficiency, the electromechanical coupling of a piezoelectric energy recovery device can be relatively weak, depending on the materials used and the mechanical structure implemented. In this case, specific interface circuits are proposed to significantly increase the level of electrical power recovered. From an energy point of view, the effect of these circuits can be likened either to an improvement in the electromechanical transduction properties of the piezoelectric device, or to better control of energy exchanges (including the reactive part). In the case of piezoelectric resonators with strong electromechanical coupling, some of these interface circuits optimize power while offering...