No abstract

Bistable vibration energy harvesters are attracting more and more interest because of their capability to scavenge energy over a large frequency band. The bistable effect is usually based on magnetic interaction or buckled beams. This paper presents a novel architecture based on amplified piezoelectric structures. This buckled spring–mass architecture allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric materials as efficiently as possible. Modeling and design are performed and a normalized expression of the harvester behavior is given. Chirp and band-limited noise excitations are used to evaluate the proposed harvester’s performances. Simulation and experimental results are in good agreement. A method of using a spectrum plot for investigating the interwell motion is presented. The effect of the electric load impedance matching strategy is also studied. Results and comparisons with the literature show that the proposed device combines a large bandwidth and a high power density.

This article presents a novel nonlinear energy extraction technique for piezoelectric vibration energy harvesting. The proposed approach is an improvement of the previous technique, “synchronous electric charge extraction,” which is the first that optimizes the harvested power whatever the connected load. The new approach is then named as “optimized synchronous electric charge extraction.” Compared with synchronous electric charge extraction, the conversion effectiveness is enhanced while simplifying the electronic circuitry and the switch control strategy. The analytical expression of the harvested powers is derived for a classical electromechanical structure. Finally, theoretical predictions confirmed by experimental results show that optimized synchronous electric charge extraction increases the harvested power for a very large range of load resistance, which is a favorable characteristic for wideband vibration energy harvesting.

This article presents a self-powered interface circuit for the optimized synchronous electric charge extraction technique applied to piezoelectric vibration energy harvesting. A peak detector circuit is developed to detect the maximum and minimum vibration displacements and drive the electronic switches synchronously. This approach does not require additional piezoelectric elements to power the electronic interface itself for which a detailed analysis and a simple model are proposed to give a better understanding on the working principle. Finally, the influence of the switching phase lag and the peak detector power consumption on the harvested power is studied. Experimental studies are conducted and successfully compared with the theoretical approach.

Vibration energy harvesters based on piezoelectric resonators are promising for powering Wireless Sensors Nodes (WSNs). Yet, any mismatch between the resonant frequency of traditional harvesters and the vibration frequency can drastically decrease the scavenged power and make them ineffective. Electrical techniques able to tune the resonant frequency of piezoelectric harvesters has been proposed as a solution and opens up new perspectives. To be fully competitive, this approach requires energy harvesters with very strong global electromechanical coupling coefficients k² (>10%), whose design remains a challenge today. This work reports on a method to design strongly coupled piezoelectric cantilevers thanks to an analytical approach based on the Rayleigh-Ritz method and a two degrees-of-freedom model, which considers the proof mass inertia effects. Through an expression of the coupling coefficient, we provide design guidelines, which are experimentally validated. We show that a long proof mass is a very effective configuration to maximize the global electromechanical coupling coefficient and consequently the frequency bandwidth of the system. Three proposed prototypes exhibit some of the strongest squared global electromechanical coupling coefficients k² of the state-of-the-art of piezoelectric harvesters (16.6% for the PMN-PT cantilever, 11.3% and 16.4% for the narrow and wide PZT-5A cantilevers respectively) and demonstrate a wide bandwidth behavior (10.1%, 7.8% and 11.3% of the central frequency respectively). Using a strongly coupled prototype based on PZT-5A leveraged by a dedicated integrated circuit, we experimentally show that it can harvest enough power (more than 100µW) to supply a WSN over a frequency bandwidth as large as 21%.