Towards Deployable Battery-Free Networked Systems

Abstract

The ecological impact of today’s battery-powered Internet of Things (IoT) is troubling. Technology advancements that reduce the reliance on batteries could blunt the environmental impact of the projected billions of IoT devices. With the emergence of low-cost, small, and high-performance microcontrollers, along with more efficient micro-energy harvesting devices that can harness the power of sunlight, motion, and heat a new revolution in computing has come. That is, IoT devices are increasingly leaving their batteries behind and are relying only on ambient power from sunlight, motion, thermal gradients, and other modalities to power their operation. Unfortunately, harvested energy can fluctuate greatly and is hard to predict, leading to intermittent operation. Intermittently-powered devices form a new class of low-power devices that can guarantee correct and forward-progressing computation despite these frequent power interrupts.

Despite the inconvenience of intermittent operation, the benefit of using intermittently-powered devices instead of ‘classical’ battery-based ones is threefold. The removal of batteries creates a more environmentally-friendly device, harvesting energy from ambient sources is sustainable and removing the battery can potentially lead towards perpetual operation—as long as there is an ambient energy source, battery-free devices will continue operating.

Challenges of battery-free devices however, still include basic features that are foundational to IoT devices. Interaction with battery-free devices has so far remained largely unexplored although reactive and screen-oriented systems are a significant part of today’s and future Internet of Things. Common tools used during development, such as debuggers and testing frameworks, are practically non-existent for intermittent devices. Even basic concepts such as keeping track of time need to be carefully considered on intermittently-powered devices. Finally, wireless networking of intermittently-powered devices is severely limited to only backscatter or one directional communication.

This dissertation addresses the challenges mentioned above by developing and deploying mechanisms that enable connected and fully interactive applications on battery-free devices. These mechanisms alleviate key challenges that hinder actual adoption and infrastructure-less deployment of these battery-free devices.