In order to provide a serious alternative to chemical batteries for the energy supply of isolated sensors, bistable generators have been enthusiastically highlighted in recent years for their ability to harvest vibration energy on a wider frequency range compared to linear generators. Nevertheless, these bistable harvesters are generally characterized through a frequency sweep which does not reveal all the steady-state behaviors they can reach and therefore their full energy harvesting potential. Among such behaviors, subharmonic motions are hidden by this classical characterization and therefore had not received a lot of attention. This study proposes an original complete analytical analysis of subharmonic orbits for energy harvesting to predict their contribution to the global bandwidth of bistable generators. In addition, a new criterion, referred as stability robustness, is introduced to estimate the sensitivity of those behaviors to disturbances of different levels, allowing to finely and accurately estimate suitable behaviors for energy harvesting purposes in realistic conditions (behaviors easy to reach and maintain in time). Experimental results conducted with a buckled beams based electromagnetic generator confirm the pertinence of this criterion showing good agreement with the analytical predictions. Subharmonic behaviors finally appears, both theoretically and experimentally, to be of significant interest, as exploiting them leads to a 180% increase of the global operating frequency range of the considered bistable energy harvester, for which more than 100 µW are generated on a 70 Hz bandwidth at 0.5 g.

In the aim of giving an alternative to chemical batteries for energy supply of wireless autonomous devices, the present work focuses on ambient vibration energy harvesting using harvesters taking benefit of energy stored in an oscillating mass subjected to acceleration. More particularly, the attention is put on nonlinear bistable harvesters which offer a wider bandwidth than linear ones. However, due to their nonlinearities, these bistable harvesters exhibit different coexisting behaviors (orbits) on their operating frequency range. Only some of them are interesting for energy harvesting because of their high amplitude of oscillations inducing high energy levels (high orbits). Nevertheless, those high orbits are coexisting with low orbits (i.e., low harvestable energy) on a major portion of their frequency range and thus are not automatically reached. This work hence introduce new strategies to experience orbit jumps from low to high orbits playing with different parameters of the bistable harvester. Preliminary analyses based on energy considerations demonstrates that the most technically achievable strategy, adopted for the experimental analysis, is the orbit jump with fast modifications of its buckling level. More particularly, the bistable harvester is first quickly over-buckled at a particular instant and then quickly released to its initial buckling level when the mass reaches a maximum of displacement (in order to maximize the potential energy brought to the mass). Two elements of this strategy were adjustable: the amplitude of the buckling level variation and the instant at which this change starts. Experimental results show that choosing a good combination of those two elements leads to a high probability to jump from low to high orbits on the whole frequency range concerned by high orbits (from 70% chance to 100% chance to jump). Thanks to this orbit jump technique, the high orbits can be ensured for the considered bistable harvester on a continuous wide frequency range of 50 Hz (from 20 Hz to 70 Hz) on which the mean harvested power varies from 20 µW to 500 µW. Finally, it is shown that the energy consumed to ensure the orbit jump can be recovered within 2 seconds.

Recent research on primary battery alternatives for supplying autonomous wireless devices has recently highlighted the advantages of nonlinear oscillators' dynamics and more particularly bistable oscillators' behavior for ambient vibration harvesting. The key property of bistable oscillators compared to linear ones is their enhanced operational frequency bandwidth under harmonic excitation, potentially leading to a better adaptation to the environment. However, the classical frequency response characterization of such devices does not reveal all the possible dynamic behaviors offered by bistable oscillators. Thus, subharmonic motions are experimentally investigated in this letter, and their energy harvesting potential as well as their ability to enhance the bistable generator bandwidth is evaluated. The results obtained with a generator integrating buckled beams for the bistability feature show that, in addition to the commonly considered harmonic behavior, subharmonics allow widening of the useful operating frequency band of the bistable microgenerator by 180% compared to the sole exploitation of the first harmonic motion.

This study focuses on vibration energy harvesting with piezoelectric bistable inertial generators in order to provide an alternative or a support to chemical batteries in the power supply of isolated wireless sensors (leading to a better autonomy of these devices). The objective of the present work is to provide guidelines to optimize this kind of generator through the investigation of the influence of different parameters (load resistance, mass, stiffness, buckling level) on its frequency response. These guidelines will be obtained exploiting a new analytical model for piezoelectric bistable harvesters which will be constructed based on a recent model introduced for electromagnetic bistable harvesters. This model includes the study of subharmonic behaviors which can be used to enhance the global bandwidth of the harvester as well as a stability robustness criterion which allows a better prediction of experimental observations. The new model will be validated by experimental data and finally exploited to provide guidelines for piezoelectric bistable harvester optimization.

The present work focuses on vibration energy harvesting to replace chemical batteries as power supplies in wireless autonomous sensors. More particularly, this article deals with nonlinear inertial oscillators and more precisely bistable harvesters, which offer a wide bandwidth compared to linear structures. These harvesters require AC-DC electronic interface to be able to supply wireless sensors or small intermediate storage elements (used to smooth the power demand). However, few studies have investigated the influence of AC-DC circuits on bistable harvesters. This work therefore focuses on developing the first analytical model able to predict the frequency response of a bistable harvester coupled to one of these interfaces: the SECE circuit (Synchronized Electric Charge Extraction). This mathematical model includes subharmonic behaviors, stability analyses to small disturbances and the analyses of the stability robustness of high orbits characterizing their capability to handle external disturbances in real conditions without falling on a low orbit. The model is then validated experimentally with a buckled beam bistable harvester with piezoelectric conversion. The latter shows that the use of SECE circuit leads to multiply the mean extracted power from 1.3 to 2.2 compared to a direct connection to the load. The reachable frequency range is nevertheless divided by 1.5.

In order to scavenge the energy of ambient vibrations, bistable vibration energy harvesters constitute a promising solution due to their large frequency bandwidth. Because of their complex dynamics, simple models that easily explain and predict the behavior of such harvesters are missing from the literature. To tackle this issue, this paper derives simple analytical closed-form models of the characteristics of bistable energy harvesters (e.g., power-frequency response, displacement response, cut-off frequency of the interwell motion) by mean of truncated harmonic balance methods. Measurements on a bistable piezoelectric energy harvester illustrate that the proposed analytical models allow the prediction of the mechanical displacement and harvested power, with a relative error below 10%. From these models, the influences of various parameters such as the inertial mass, the acceleration amplitude, the electromechanical coupling, and the resistive load, are derived, analyzed and discussed. The proposed models and analysis give an intuitive understanding of the dynamics of bistable vibration energy harvesters, and can be exploited for their design and optimization.

This paper presents a model suited for the design of mechanically bistable beams used in Piezoelectric EnergyHarvesters (PEHs). The proposed model accounts for the bending and compression of post-buckled beams used in the PEH. The effect of the beam's geometry on the generated power and frequency bandwidth is evaluated with a performance criterion. It is concluded that a low beam compression stiffness can have a negative impact on the performance of the PEH and that the bending stiffness solely implies a prestress on the piezoelectric transducer.

Solid rotor induction motors (SRIMs) are asynchronous motors suited for high speed applications. This work presents an experimental case study where standard loss segregation procedures for induction motors are performed with a two-phase smooth solid rotor induction motor in order to verify their applicability. Even though the machine is supposed to operate at high frequency, the tests are performed at reduced frequency and voltage in order to avoid the effects of time harmonics. An adjustment in the separation of losses is proposed to contemplate the effects of the high no-load slip, and the behavior of the stray losses under high per-unit slip is analyzed in a load test. The test results are finally extrapolated for the rated condition.