Three-dimensional vibration energy harvester using a spiral piezoelectric element

We have developed a three-dimensional (3-D) molding process for the production of piezoelectric ceramic elements by using a master polymer mold produced by microstereolithography. In this method, ceramic slurry is injected into a 3-D polymeric mold via a centrifugal casting process. The polymeric master mold is thermally decomposed so that complex 3-D piezoelectric ceramic elements can be produced. To demonstrate the fabrication of 3-D piezoelectric ceramic elements, we produced a spiral piezoelectric element that can convert multidirectional loads into a voltage. We confirmed that a prototype of the spiral piezoelectric element could generate a voltage by applying a load in both parallel and lateral directions in relation to the helical axis. The power output of 123 pW was obtained by applying the maximum load of 2.8N at 2 Hz along the helical axis. In addition, to improve the performance of power generation, we utilized a two-step sintering process to obtain dense piezoelectric elements. As a result, we obtained a sintering body with relative density of 92.8 % that is higher than that of a conventional sintered body. Piezoelectric constant d₃₁ of the sintered body attained to -40.0 pC/N that is better than that of a conventional sintered body. The 3-D ceramic molding process is capable to produce a highly efficient 3-D piezoelectric energy harvester that can scavenge multidirectional vibration energy to generate electrical energy by optimizing its 3-D shape.