An Energy Logger for Kinetic-Powered Wrist-Wearable Systems

Abstract

Kinetic energy harvesting is a promising technology towards the development of alternative battery-charging schemes or even self-powered wearable devices that obtain their power supply from human motion. Although there are many developments with schemes that leverage piezoelectric materials and human motion to power devices especially from footsteps, some other body locations like the wrist still need assessment with piezoelectric generators to evaluate their potential of limitations. In this work, we present the results of logging the energy transference from a wrist-worn piezoelectric harvester to a battery in a wearable device. This system is the continuation of our previous work where we implemented the harvester with a resistive load previously tuned to obtain maximum power and assessed the energy harvested during physical activities. Now, we replace the linear load with a charge controller and a Li-ion battery in the same wearable set-up. These new conditions are not optimal for the piezoelectric generator but present a more realistic environment for the kinetic harvester and allows a more precise study of the feasibility of a self-powered system. Tests show that five minutes of activities that involve arm motion can provide between 1.75 mJ and 2.98 mJ of energy, which can represent between 3.6 seconds and 6.2 seconds of additional battery duration. Hence, these results provide an insight of the limitations and challenges remaining in the piezoelectric-based kinetic harvesting field for wearable devices.

Recent Advances in Wearable Sensing Technologies

“…Use of piezoelectric devices to extract energy from human movements [68] or mechanical waves such as wind or ultrasound to recharge a battery or to power a device [69] Implantable medical devices [69], wrist wearables [70] Thermoelectric generators…”

Development of Piezoelectric Elastomers and Their Applications in Soft Devices

“…[29] Despite the advantages of piezoelectric materials, it is often challenging to find a single material that can combine flexibility and high piezoelectric properties [30,31] in traditional piezoelectric materials. To enable piezoelectric materials to withstand high strain and make them suitable for wearable devices, [32][33][34][35] human skin, [36,37] and other fields, [38,39] stretchable and flexible piezoelectric elastomers have been developed in the past decade. Presently, most of these piezoelectric elastomers are prepared based on piezoelectric ceramics or polymers as fillers, which are then added into an elastomer matrix to form a piezoelectric elastomer composite.…”