A 10-fold increase in the ability to harvest mechanical and thermal energy over standard piezoelectric composites may be possible using a piezoelectric ceramic foam supported by a flexible polymer support, according to Penn State researchers.
In the search for ways to harvest small amounts of energy to run mobile electronic devices or sensors for health monitoring, researchers typically add hard ceramic nanoparticles or nanowires to a soft, flexible polymer support. The polymer provides the flexibility, while the piezo nanoparticles convert the mechanical energy into electrical voltage. But these materials are relatively inefficient, because upon mechanical loading the mechanical energy is largely absorbed by the bulk of the polymer, with a very small fraction transferred to the piezo nanoparticles. While adding more ceramic would increase the energy efficiency, it comes with the tradeoff of less flexibility.
"The hard ceramics in the soft polymer is like stones in water," said Qing Wang, professor of materials science and engineering, Penn State. "You can slap the surface of the water, but little force is transferred to the stones. We call that strain-transfer capability."
Almost three decades ago, the late Penn State materials scientist Bob Newnham came up with the concept that the connectivity of the piezo filler determined the efficiency of the piezoelectric effect. A three-dimensional material would be more efficient than what he classified as zero-dimensional nanoparticles, one-dimensional nanowires or two-dimensional films, because the mechanical energy would be transported directly through the three-dimensional material instead of dissipating into the polymer matrix.
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