Energy harvesting from a multifrequency response of a tuned bending–torsion system

We investigate the benefits of tuning the frequencies of an energy harvester to extract more energy from a base excitation that comprises three frequency components. The energy harvester is composed of a unimorph cantilever beam with asymmetric tip masses. By adjusting the asymmetry of the tip masses, we can tune this beam–mass structure to harvest energy from multifrequency components of a base excitation. We model the beam using the Euler–Bernoulli beam theory and use the first three global mode shapes of the harvester in a Galerkin procedure to derive a reduced-order model describing its response. We derive an exact analytical solution for the tip deflection, twisting angle, voltage output, and harvested electrical power. Using this solution, we investigate the advantages of harvesting energy from a response that contains multifrequencies in comparison to a response that contains a single frequency by tuning only the fundamental frequency. The advantages of this bending–torsion energy harvester and the effect of its tuning are investigated for different short- and open-circuit configurations. The results show that, through a proper tuning of this bending–torsion harvester, the harvested power can be increased significantly and it can be made to cover a wide range of electrical load resistances.