A Self-Powered Insole for Human Motion Recognition

Abstract

Biomechanical energy harvesting is a feasible solution for powering wearable sensors by directly driving electronics or acting as wearable self-powered sensors. A wearable insole that not only can harvest energy from foot pressure during walking but also can serve as a self-powered human motion recognition sensor is reported. The insole is designed as a sandwich structure consisting of two wavy silica gel film separated by a flexible piezoelectric foil stave, which has higher performance compared with conventional piezoelectric harvesters with cantilever structure. The energy harvesting insole is capable of driving some common electronics by scavenging energy from human walking. Moreover, it can be used to recognize human motion as the waveforms it generates change when people are in different locomotion modes. It is demonstrated that different types of human motion such as walking and running are clearly classified by the insole without any external power source. This work not only expands the applications of piezoelectric energy harvesters for wearable power supplies and self-powered sensors, but also provides possible approaches for wearable self-powered human motion monitoring that is of great importance in many fields such as rehabilitation and sports science.

Sensing, Computing, and Communications for Energy Harvesting IoTs: A Survey

“…Packet counting [74] Counting error ranges from 4% to 20% on flat surfaces Using piezoelectric energy harvester inside shoes, Han et al [67] conducted an experiment with three subjects performing six different activities -normal walking, strolling, brisk walking, jogging, ascending stairs, and descending stairs. By simply using the relationships between peak values, time length, and slopes of transducer AC waveforms, they were able to classify these six activities with over 90% accuracy.…”

Design Considerations for Self-Powered Wearable Wireless Multimodal Vigilant Sensing Systems

“…One example of this is seen in the wearable insole designed by the authors in [13]. As previously discussed, this insole uses piezoelectric films to generate voltage waveforms that can be used to perform motion monitoring.…”

“…For example, the authors in [12] appear to view that a system is wearable if it can be easily attached to the body and does not impede the wearer's movements, while the authors in [13] appear to view that a system is wearable if it is integrated into an article of clothing regardless of whether or not the intended measurements can be easily obtained. The authors in [14], however, appear to have a much more strict definition of wearable and view that a system is wearable if it does not burden the user in any capacity -both in wearing the system and extracting data from it.…”

“…For example, if an accelerometer must be placed on the user's ankle and the intended energy to be harvested is solar, then it may not be practical to move the solar cells closer to the ankle since they would harvest much less energy. So instead, it could be better to use piezoelectric energy harvesting since that harvester could be more easily integrated into a shoe like in [13]. Finally, ECG electrodes are more difficult to match to an energy harvesting location since they are not compact and require specific placement on the body.…”

“…In [13], the authors present a system that is designed to recognize different forms of human motion such as normal walking, strolling, brisk walking, jogging, and ascending or descending stairs. To achieve this goal, they designed a wearable insole based on piezoelectric films.…”