A multi-layered polydimethylsiloxane structure for application in low-excitation, broadband and low frequency energy harvesting

Vibrational kinetic energy is a promising energy source that can be harvested due to its abundance in daily life, especially from human motion. This low frequency vibration poses a challenge in achieving a small device that is practical and wearable. Further, the effective energy harvesting of a linear structure is very limited to a narrow range of frequencies around the resonance. These two limitations call for the development of wide bandwidth energy harvesters that can work at a wider low frequency range. Using low Young's modulus material is a common technique to achieve a low resonant frequency energy harvester. Nonlinear bistability is a potential solution for bandwidth broadening. In this paper, a broadband low frequency vibrational energy harvester using multi-layered soft polydimethylsiloxane (PDMS) will be presented. First, a multi-layered PDMS structure was created by sandwiching a thicker PDMS with two thinner pre-stressed PDMS films. After releasing the prestresses, the multi-layered PDMS structure can settle into two cylindrical configurations. An analytical model that can predict the shapes of this multi-layered structure has been developed using classical lamination theory along with Rayleigh-Ritz approximation technique. Through this model, PDMS shapes can be easily predicted by changing various parameters such as the ratio of side length to thickness, prestrain levels, and Young's modulus. A multi-layered PDMS structure has been further proposed to be used as a bistable energy harvester. The soft PDMS allows working frequencies of lower than 15 Hz. The dynamic response of this harvester under small input excitation shows a softening spring system, before the strong nonlinear 'snap through' effect occurs. This softening spring system is able to broaden the bandwidth of the energy harvesting device.