Alternative Geometries for Increasing Power Density in Vibration Energy Scavenging for Wireless Sensor Networks

Vibration energy scavenging with piezoelectric material can currently generate up to 300 microwatts per cubic centimeter, making it a viable method of powering low-power electronics. Given the growing interest in small-scale devices, particularly wireless sensor networks, concerns over how to indefinitely power them have become extremely relevant. Current limiting factors in the field of piezoelectric vibration energy scavenging include: coupling coefficients, strain distribution, and frequency matching. This paper addresses each of these three factors with a novel design and a corresponding analysis of its performance. For example, the power output of a cantilevered rectangular piezoelectric beam is limited by its uneven strain distribution under load. A prototype scavenger using a harmonically matched trapezoidal geometry solves this problem by evening the strain distribution throughout the beam, increasing by 30% the output power per unit volume. Another design is created which softens the frequency response of the generator, relaxing the constraint of frequency matching. The paper concludes that each of the three challenges to vibration energy scavenging can be met through creativity in mechanism design, making higher power densities possible and broader applications more feasible.