Material property manipulation of photopolymer vibration energy harvesters

The inefficiency in converting naturally occurring vibration frequencies (sub- 100 Hz) to electrical energy continues to be a major obstacle for miniaturized vibration energy harvesters. In a recent work, we addressed this issue by introducing photopolymer-based designs, using projection microstereolithography, which exhibited 61 Hz resonant frequencies due to low elastic moduli and low flexural rigidity using a three-dimensional, helical coil design. In this paper, we extend upon those findings to report on a post-process technique which uses ultraviolet exposure time to manipulate the material properties of photopolymer-based vibration energy harvesters. The results show with 1-3 minutes of post-exposure, an effective elastic modulus variation from 399-904 MPa and a parasitic damping change from 0.0595-0.0986 kgs _-1 . Likewise, resonant frequency shifts of 53.5-80.5 Hz and power output increase from 56.5 to 120.4 μW (when excited at a constant acceleration of 6.06±0.06 ms _-2 ) are achieved, without geometry changes and using the same photopolymer material.