Many emerging high-volume sensing applications are, by necessity, wireless. Thus, each sensing and communication node must contain its own power source or be able to harvest its own power. Example applications include smart buildings and homes, wearable health and wellness sensors (i.e. mobile health), structural health monitoring, smart transportation environments, biomedical implants and much more. Today, almost all wireless sensors use batteries as their sole power source. In some cases this is not limiting. In other applications, where recharging batteries is a nuisance or expensive, energy harvesting is clearly beneficial. In other applications, regular battery replacement is impossible and thus energy harvesting is critical. This presentation will focus specifically on wearables and harvesting energy from human body motion to power them.
There are two fundamental challenges with harvesting energy from human: very low frequency excitation and multi-directional excitation. Because of the low frequency excitation, linear (as opposed to rotational) energy harvesters are usually displacement limited. Rotational architectures exist (i.e. self-powered watches) but their power production is exceptionally low, much too low for current and envisioned wearables. We have developed models to predict the maximum possible power that could be generated from regular human motions given realistic size constraints. In this presentation I will discuss the implications of these models for product design and demonstrate that much more power is available than is produced by existing products. We have developed a series of prototypes to enhance the power output using both electromagnetic and piezoelectric transducers. These prototypes perform significantly better than the current state of the art, but are still well below the theoretical limit. Thus, there is still much room for improvement and innovation.
Shad Roundy is the director of the Integrated Self-Powered Sensing lab at the University of Utah which focuses on energy harvesting, wireless power transfer, and more generally applications of ubiquitous wireless sensing. Shad received his PhD in Mechanical Engineering from the University of California, Berkeley in 2003. From there he moved to the Australian National University where he was a senior lecturer in the Systems Engineering Department. He spent the next several years working with startup companies LV Sensors and EcoHarvester developing MEMS pressure sensors, accelerometers, gyroscopes, and energy harvesting devices. In 2012, he re-entered academia joining the mechanical engineering faculty at the University of Utah. Dr. Roundy is the recipient of the National Science Foundation CAREER Award, DoE Integrated Manufacturing Fellowship, the Intel Noyce Fellowship, and was named by MIT’s Technology Review as one of the world’s top 100 young innovators for 2004.