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Conventional energy harvester typically consists of a cantilevered composite piezoelectric beam which has a proof mass at its free end while its fixed end is mounted on a vibrating base structure. The resulting relative motion between the proof mass and the base structure produces a mechanical strain in the piezoelectric elements which is converted into electrical power by virtue of the direct piezoelectric effect. In this paper, the harvester is provided with a dynamic magnifier consisting of a spring-mass system which is placed between the fixed end of the piezoelectric beam and the vibrating base structure. The main function of the dynamic magnifier, as the name implies, is to magnify the strain experienced by the piezoelectric elements in order to amplify the electrical power output of the harvester. With proper selection of the design parameters of the magnifier, the harvested power can be significantly enhanced and the effective bandwidth of the harvester can be improved. The theory governing the operation of this class of cantilevered piezoelectric energy harvesters with dynamic magnifier (CPEHDM) is developed using the finite element method. Numerical examples are presented to illustrate the merits of the CPEHDM in comparison with the conventional piezoelectric energy harvesters (CPEH). The obtained results demonstrate the feasibility of the CPEHDM as a simple and effective means for enhancing the magnitude and spectral characteristics of CPEH.

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An energy harvester operating in the thickness-mode (TMH) or longitudinal-mode (LMH) consists of a piezoelectric element which is sandwiched between a proof mass and a base. The piezo-element is poled along a direction perpendicular to the electrodes. When the base is subjected to a sinusoidal excitation, along the poling direction, a relative motion is generated between the proof mass and the base producing mechanical strain in the piezoelectric element. The resulting strain is converted into electrical power by virtue of the direct piezoelectric effect. In this study, a shear-mode harvester (SMH) is considered as a viable alternative to the TMH and LMH to enhance the harvested output power. The enhancement is generated by capitalizing on the fact that the strain constant of the piezoelectric in shear is much higher than those due to thickness or longitudinal deflections. To achieve such an enhancement, the piezoelectric element is poled along a direction parallel to its electrodes and is sandwiched between a proof mass and oscillating base in a design similar to that of the TMH and the LMH. Sinusoidal excitation of the base, along the poling direction, makes the piezo-element experience mechanical shear strain which when converted into electrical power produces outputs that are larger than those of the TMH and the LMH. The theory governing the operation of this class of SMH is developed for simple resistive electrical loads. Numerical examples are presented to illustrate the optimal performance characteristics of the SMH in comparison with the TMH and LMH. The effect of the piezo-element material, excitation frequency and electrical load on the harvested power is presented. The obtained results demonstrate the feasibility of the SMH as a simple and effective means for enhancing the power output characteristics of conventional TMH and LMH.

Energy dissipation in polymeric composite metamaterials requires special mathematical models owing to the viscoelastic nature of their constituents, namely, the polymeric matrix, bonding agent, and local resonators. Unlike traditional composites, polymeric metamaterials are a class of hybrid composites which can distinctly be tailored for damping to achieve superior noise, vibration, and harshness (NVH) properties with no trade-offs in strength and while maintaining a high stiffness to mass ratio. The objective of this paper is to investigate viscoelastic metadamping in one-dimensional (1D) multi-bandgap polymeric composite metamaterials by combining the linear hereditary theory of viscoelasticity with the Floquet-Bloch theory of wave propagation in infinite elastic media. Important distinctions between metamaterial and phononic unit cell models are explained based on the free wave approach with wavenumber-eliminated damping-frequency band structures. The developed model enables viscoelastic metadamping to be investigated by varying two independent relaxation parameters describing the viscoelasticity level in the host structure and the integrated resonators. The dispersion mechanics within high damping regimes as well as the effects of boundary conditions on the damped response are discussed in detail. Finally, the results are generalized for composite metamaterials with multiple resonators.