Structural instabilities: from energy harvesting to tunable structures

Intriguing morphologies and surface patterns in nature at different scales from wrinkles on skins of mammalians, plants, and fruits to crumpled membranes of blood cells have inspired a big body of research in soft matter instabilities. In this project, we extend the application of soft matter instabilities to kinetic energy harvesting and tunable structures.

Conventional vibratory energy harvesters usually suffer from narrow bandwidth and are very inefficient at small scale for low frequency harvesting. Furthermore, they suffer from inherent low power densities (e.g. only a small area near the clamped end of a large cantilever-type energy harvester is used to induce large strains and voltages in a piezoelectric energy harvester). Here, to improve the harvesting effectiveness and increase the power densities, we propose to exploit surface instability or in general instability in layered composites, e.g. wrinkling, where intriguing morphological patterns with large strain are formed under compressive loads. The induced large strains which are independent of the excitation frequency and exist throughout the whole structure, are exploited to give rise to large strains in an attached piezoelectric layer to generate charge and, hence energy. 

Now if we design and fabricate the composite such that it is initially close to the instability point, we can induce the wrinkling by applying a small voltage (with the right polarity) to the piezo layers. This process is revesible as such instabilities are elastic. This way we can control the instability, and hence, extend the application of the aforementioned idea from energy harvesting to a whole new level of tunable material/structures with a myriad of applications


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