# Energy Harvesting from Ankle Flexion During Gait Using Flexible CdS and PVDF Sensors

## TL;DR

This study explores harvesting energy from ankle movements during walking using flexible sensors made of PVDF and CdS.

## Contribution

The novel contribution is the fabrication and testing of a CdS thin film for energy harvesting from ankle flexion during gait.

## Key findings

- The CdS film achieved a d33 coefficient of 1.4928 nm/V, showing high electrical energy generation from strain.
- Ankle flexion generated over 700% more energy than heel strike when using CdS sensors.
- The talocrural joint produced 11.359 μJ with PVDF and 0.854 μJ with CdS during gait tests.

## Abstract

In this work, energy was harvested from ankle flexion during gait. For this, two piezoelectric thin films were tested: PVDF and CdS. The PVDF film was a commercial option, and the CdS film was fabricated in our laboratory. Deposition of the CdS film is also reported in this work. Energy harvested during gait from heel strike and ankle flexion was compared. Tests were performed with 10 healthy volunteers walking on a treadmill at 1.2–1.5 km/h. The volunteers wore a sock with piezoelectric films incorporated in the heel and ankle joint (talocrural joint). Tests were performed first with the PVDF film and then with the CdS film. The CdS thin film obtained a d33 coefficient of 1.4928 nm/V, indicating high electrical energy generated from strain-stress. The talocrural joint generated the most energy: 11.359 μJ for the PVDF film and 0.854 μJ for the CdS film. Although the CdS film generated less energy than the commercial option, it was shown that harvesting energy from ankle flexion increased the energy harvested by more than 700% during gait compared to the energy harvested from heel-to-ground impact.