Low-frequency, broadband vibration energy harvester using coupled oscillators and frequency up-conversion by mechanical stoppers

Abstract

The frequencies of ambient vibrations are often low (below 30 Hz). A broadband (3 dB bandwidth is larger than 10 Hz at an acceleration amplitude of 9.81 m s−2) vibration based energy harvester is proposed for transducing mechanical energy at such low frequencies into electrical energy. The mechanical setup converts low frequency mechanical vibrations into high frequency resonance oscillations of the transducer. This conversion is done by mechanical impacts on two mechanical stoppers. The originality of the presented design is that both low-frequency and high-frequency oscillators are permanently mechanically coupled. In the equivalent mechanical circuit, this coupling is achieved by connecting the ends of the stiff spring to both seismic masses, whereas one seismic mass (collison member) is also attached to the soft spring used as the constitutive element of a low-frequency oscillator. Further, both mechanical oscillators are not realized as conventional cantilever beams. In particular, the high frequency oscillator with the natural frequency of 340 Hz is a disc-shaped diaphragm with attached piezoelectric elements and a seismic mass. It is shown that it is possible to convert mechanical vibrations with acceleration amplitude of 9.81 m s−2 in the region between approximately 7 and 25 Hz into electrical power larger than 0.1 mW with the maximum value of 0.8 mW. A simplified mathematical model based on piecewise linear coupled oscillators shows good agreement with experimental results. The ways to enhance the performance of the harvester and improve agreement with experiments are discussed.

Low-frequency and broadband vibration energy harvester driven by mechanical impact based on layer-separated piezoelectric beam

“…Yuan et al [29] focused on the semi-analytical approach based on the harmonic balance method to predict steady-state responses of nonlinear piezoelectric vibration energy harvester, which consists of an oscillator of two magnetic beams. Dechant et al [30] studied a new kind of low-frequency broadband VEH coupled with two mechanical stoppers, which significantly improves the vibration-to-electricity conversion efficiency by 40%-81%. Two-degree-of-freedom piecewise-linear PVEH was also studied by Liu et al [31] and Zhao et al [32] , which demonstrates good harvesting performance.…”

Important considerations in optimising the structural aspect of a SDOF electromagnetic vibration energy harvester

“…Substituting Eqs. (6), (7) and (8) into equation 5and differentiating it with respect of time results in an expression describing the transverse velocity of the beam under first mode vibration.…”

“…Despite being a main issue, it is actually difficult to optimise the frequency bandwidth of a harvester as the definition of an 'optimum' frequency bandwidth is vague and maximising the bandwidth would generally take a large toll on the power output. Hence, most studies would focus on methods to improve the frequency bandwidth instead of optimising it [7][8][9]. In contrast, many studies have been conducted to optimise the power output of a vibration energy harvester.…”

Nonlinear dynamics and triboelectric energy harvesting from a three-degree-of-freedom vibro-impact oscillator

“…Vibro-impact is often used in PEH systems since impact improves harvesting efficiency through frequency up-conversion [23][24][25][26], which helps cope with the frequency incompatibility between the ambient vibration and the harvester [23]. The vibro-impact in PEH systems usually happens between flexible beams and relatively rigid stoppers.…”