MP-HAR: A Novel Motion-Powered Real-Time Human Activity Recognition System
Zijie Chen, Li Teng, Lan Xu, Jingyi Yu, Junrui Liang
Abstract
With the rapid advance of the Internet of Things (IoT), more and more wearable devices are being developed for real-time monitoring. Most of these existing monitors are powered by chemical batteries. Replacing and disposing batteries for an exponentially increasing number of IoT nodes prohibitively results in labor-intensive maintenance. It is also environmentally unfriendly. Gls EH, reclaiming the wasted ambient energy, is a promising technology for battery-free IoT. This article presents a novel motion-powered real-time human activity recognition (HAR) system called motion-powered HAR system (MP-HAR), where the harvester works as both an energy source and sensor. MP-HAR emphasizes low-power as well as low-cost characteristics, encompassing four necessary units: 1) energy transduction unit (ETU); 2) energy management unit (EMU); 3) energy user unit (EUU); and 4) edge computing unit (ECU). In particular, the unique intermittent operation based on the reconfigurable on/off threshold voltages given by the well-rounded energy-aware circuit has been discussed in detail. The balance between energy supply and information demand in MP-HAR has been achieved by using a handy design. Utilizing the unique correspondence between human arm swing frequency and harvested energy, the information flows with energy inside the system. By knowing the interval between transmitted packets, MP-HAR has realized HAR in real time. Moreover, an all-in-one prototype has been fabricated to validate the performance of the proposed system. Lab and field tests have demonstrated that MP-HAR can reliably recognize different human activities, such as standing, walking, jogging, and running. As a cyber-electro-mechanical co-design, MP-HAR has brought a promising solution for pervasive HAR and ubiquitous IoT.