ZEL: Net-Zero-Energy Lifelogging System using Heterogeneous Energy Harvesters

TL;DR

ZEL is a wearable lifelogging system that achieves near-perpetual operation by utilizing heterogeneous energy harvesters and efficient switching, enabling accurate activity recognition without battery replacement.

Contribution

This work introduces ZEL, the first net-zero-energy lifelogging system using heterogeneous energy harvesters and a lightweight wearable device for long-term activity monitoring.

Findings

Achieved 87.2% person-dependent activity recognition accuracy.

Achieved 93.1% static/dynamic activity recognition accuracy.

System demonstrated 99.6% zero-energy operation rate.

Abstract

We present ZEL, the first net-zero-energy lifelogging system that allows office workers to collect semi-permanent records of when, where, and what activities they perform on company premises. ZEL achieves high accuracy lifelogging by using heterogeneous energy harvesters with different characteristics. The system is based on a 192-gram nametag-shaped wearable device worn by each employee that is equipped with two comparators to enable seamless switching between system states, thereby minimizing the battery usage and enabling net-zero-energy, semi-permanent data collection. To demonstrate the effectiveness of our system, we conducted data collection experiments with 11 participants in a practical environment and found that the person-dependent (PD) model achieves an 8-place recognition accuracy level of 87.2% (weighted F-measure) and a static/dynamic activities recognition accuracy level of 93.1% (weighted F-measure). Additional testing confirmed the practical long-term operability of the system and showed it could achieve a zero-energy operation rate of 99.6% i.e., net-zero-energy operation.