Strongly coupled piezoelectric cantilevers for broadband vibration energy harvesting

Abstract

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%.

Comparison of Metal-Based PZT and PMN–PT Energy Harvesters Fabricated by Aerosol Deposition Method

“…Table 5 shows a comparison of the output performance of the recently reported PZT- and PMN–PT-based energy harvesters on a metal substrate. Although the fabrication technology of the proposed PMN–PT film is not well-developed, the energy density is better than that reported previously [ 19 , 44 , 45 , 46 , 47 ]. We expect the output performance of the PMN–PT-based energy harvester can be improved by optimizing the fabrication process, including the deposition parameters, poling condition, and annealing profile.…”

Non-linear losses study in strongly coupled piezoelectric device for broadband energy harvesting

“…The model introduced here is derived from the two degree of freedom linear model that we presented in [12], focusing on the first resonant mode. The Hamilton principle and the Rayleigh method are used to determine the equation of motion and the equation of current.…”

“…The Hamilton principle and the Rayleigh method are used to determine the equation of motion and the equation of current. Unlike the model in [12], nonlinear terms are introduced in the enthalpy expression to consider the mechanical softening and piezoelectric coefficient nonlinearity. Moreover,…”

“…In order for this approach to be effective, it is necessary to employ piezoelectric harvesters with very strong global electromechanical coupling coefficients ² ( 2 > 10 %). Proposals for the design of such harvesters have therefore recently been made in the literature [12,13] and offer promising perspectives for broadband vibration energy harvesting. Nevertheless, the presence of nonlinear dielectric losses in the piezoelectric materials have been shown to considerably reduce the harvested power when strongly coupled materials are used [14].…”

Modeling the Piezoelectric Cantilever Resonator with Different Width Layers

“…The piezoelectric cantilever is one of the most important structures for micro-electro-mechanical system (MEMS) application and it has been used in atomic force microscopes, chemical sensors and biosensors, radio frequency (RF) switches, photon detectors, micromirrors, and energy harvesters [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. Tip displacement and resonance frequency are two important characters of the piezoelectric cantilever, especially when setting the height of the cantilever in the RF switch [ 8 ] and tuning the resonance frequency of the energy harvester that matches the ambient vibrating frequency for improving the power efficiency [ 4 ].…”