 results in a significant decrease in the mechanical energy available for harvesting. When optimized, the proposed design could allow a device to use much less piezoelectric material than a standard design, and still harvest the same amount of energy.
“The main contribution of this work is to demonstrate that taking energy from the storage stage and transferring it to the source, although it seems counter-productive because of the losses in the transfer mechanism, can lead to outstanding performance in terms of power output,” Lallart told PhysOrg.com. “In particular, performing these operations in a pulsed fashion (i.e., providing initial energy to the active material) makes the technique easy to implement. One of the most remarkable things about this technique is its ability to bypass the power limit of all other techniques when considering the damping effect induced by the scavenging process (constant force magnitude case).”
As the scientists explained, most previous methods for energy conversion enhancement have been “unidirectional,” meaning they don’t take advantage of using the energy generated from the device itself as input energy. The few previous methods that were “bidirectional” like the current design, using output energy for input energy, required constant driving of the device, resulting in a complex implementation and requiring a significant amount of energy for driving the system, which made them barely realistic.
In contrast, the fact that the new method only requires quick pulses allows for an easier implementation and greatly reduces the driving energy. The energy extraction and injection processes are so much quicker than the device’s vibration time period that they can be considered instantaneous. For these reasons, the scientists predict that this approach could improve the amount of energy harvested by two, three, or four times compared with other methods aiming at increasing the power output, even at low energy extraction efficiencies.
“The main motivations in energy harvesting research are explained by the growth of small-scale, low-power electronic devices, as well as the limitations of primary batteries that raise maintenance issues because of their limited lifespan and environmental problems due to their complex recycling process,” Lallart said. “Although the viability of self-powered systems has already been demonstrated, the functions of such devices are still limited by the available energy. Hence, the aim of research on energy harvesting is twofold. First, increasing the power output of microgenerators allows for implementing more functions in the self-powered device. Second, improvements in the conversion abilities of active materials would permit a significant reduction of the amount of material required to harvest a given amount of energy, allowing for the disposal of small-scale, embeddable devices.”
More information: Mickaël Lallart and Daniel Guyomar. “Piezoelectric conversion and energy harvesting enhancement by initial energy injection.” Applied Physics Letters 97, 014104 (2010). DOI: 10.1063/1.3462304
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