Abstract
Wearable devices promise to reduce strain on the healthcare system and to improve quality of life for users. However, adoption in healthcare settings is limited due in part to the need for constant battery maintenance; which leads to reduced adherence, more complex operation and missing sections of data. Energy harvesting can reduce the reliance on batteries, but the harvesting potential varies substantially depending on where the harvester is placed. Few previous studies investigating placement have considered the foot as a harvesting site, despite the significant interest in smart-shoes and the intrinsic social discreteness of wearable devices at the foot. We investigate the amount of power that can be harvested from four sites on the human body (wrist, hip, ankle and foot), with 12 participants walking on a treadmill. We analyse the differences in the frequency spectrum at each of these sites and perform a sweep of inertial energy harvester parameters to identify the optimal parameters for each site on the body. By considering both performing the harvesting at the foot, and the frequency distribution of the input spectrum present for the first time, we identify that harvesting at the foot provides multiple benefits: more power is available in total; greater physical size is available (compared to the wrist); lower $Q$ harvesters can provide better broadband response; and the foot is the least sensitive location for changes in frequency of walking rate. For harvesters sized at 100 mm, we find that there is 4.2, 6.4 and 25.7 times more power at the hip, ankle and foot respectively compared to the wrist. Foot based sensors thus provide a promising approach towards future fully battery-free wearable devices, motivating future work to investigate the sensing modalities that are feasible at the foot.
Highlights
A key limitation of wearable devices is limited battery life [1]–[3], with devices often requiring recharging daily or every few days
Previous estimates have shown that lower body locations are more energy-dense for energy harvesting in an absolute sense [26], [27], to our knowledge no studies have compared the actual energy harvested from the foot with other locations on the body. (Some studies have used the ankle as a proxy for the foot, which we demonstrate is not valid.) previous works have not given a detailed investigation into how the frequency content of the collected waveforms differ at each site of the body and how this affects the optimum harvester parameters and harvester output
HARVESTER MODEL In this work we focus on inertial kinetic energy harvesters, the energy output from which can be modelled with a massspring-damper system, as shown in Figure 1, based upon the model presented by Büren et al [26]
Summary
A key limitation of wearable devices is limited battery life [1]–[3], with devices often requiring recharging daily or every few days. This frequency increases for more complex devices that offer either greater sensing modalities, sampling rate or access to the raw data. In many target groups where wearables could offer the largest benefit, such as the elderly and those with cognitive impairments, sensing needs to be fully automated and completely unobtrusive to the end-user [4]. Devices would be completely energy-autonomous allowing people to use them in a fit-and-forget fashion where there is no need for battery maintenance. The power consumption of recent commercial devices is a long way from realising this, necessitating improved batteries or approaches such as energy harvesting to be investigated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
