A piezoelectric transducer that can harvest electricity from mechanical energy along all three vibrational axes with high-energy transduction efficiency has been developed at the University of Michigan. Most extant micro- and meso-scale inertial energy harvesters operate along a single vibrational axis. However, the ability to harvest electrical energy from vibrations applied along any spatial direction can improve the power output and extend the practical applications of inertial harvesters. Single-transducer three-axis energy harvester’s designs are only available today for electrostatic and electromagnetic resonators and demonstrate very limited power density. And till date, only two-axis piezoelectric inertial harvesters have been reported. In addition to the limited number of operational axes, the architectures used in these devices often require manual assembly of three-dimensional structures, thereby preventing further device miniaturization. A naïve method of achieving operation along all three axes is to align three individual harvesters along the three different axes within a single package. However, this method decreases the total power density and increases the overall cost due to larger device size.
The multi-axis piezoelectric transducer developed at the University of Michigan leverages a new type of piezoelectric transduction scheme. The device consists of a central motion platform, which is symmetrically carried by multiple piezoelectric beams connected to an anchor frame. The top surfaces of the piezoelectric beams are covered by partitioned transduction electrodes, which enable energy transduction from both angular and linear motions in both in-plane and out-of-plane directions. The cross-section of the beams can be formed from either a single block of a piezoelectric material layer, a unimorph structure (a stack of a piezoelectric and a non-piezoelectric material layers), or a bimorph structure (a stack of two or more piezoelectric layers). When operated as an energy harvester or a motion sensor, the device provides signal transduction capability from both linear and angular motions in all three dimensions in a single unit. And since a single device replaces multiple single-axis devices, significant savings in device footprint and fabrication costs can be realized. In addition, the device can be used simultaneously for vibration sensing, energy harvesting, and excitation of the transducer to increase harvesting efficiency.
- Inertial energy harvesting for wireless sensor nodes, wearable electronics, and portable electronics
- High efficiency
- Low area
- Reduced fabrication costs