Energy harvesting from a backpack instrumented with piezoelectric shoulder straps

Abstract

Over the past few decades the use of portable and wearable electronics has grown steadily. These devices are becoming increasingly more powerful. However, the gains that have been made in the device performance have resulted in the need for significantly higher power to operate the electronics. This issue has been further complicated due to the stagnant growth of battery technology over the past decade. In order to increase the life of these electronics, researchers have begun investigating methods of generating energy from ambient sources such that the life of the electronics can be prolonged. Recent developments in the field have led to the design of a number of mechanisms that can be used to generate electrical energy, from a variety of sources including thermal, solar, strain, inertia, etc. Many of these energy sources are available for use with humans, but their use must be carefully considered such that parasitic effects that could disrupt the user’s gait or endurance are avoided. These issues have arisen from previous attempts to integrate power harvesting mechanisms into a shoe such that the energy released during a heal strike could be harvested. This study develops a novel energy harvesting backpack that can generate electrical energy from the differential forces between the wearer and the pack. The goal of this system is to make the energy harvesting device transparent to the wearer such that his or her endurance and dexterity is not compromised. This will be accomplished by replacing the traditional strap of the backpack with one made of the piezoelectric polymer polyvinylidene fluoride (PVDF). Piezoelectric materials have a structure such that an applied electrical potential results in a mechanical strain. Conversely, an applied stress results in the generation of an electrical charge, which makes the material useful for power harvesting applications. PVDF is highly flexible and has a high strength, allowing it to effectively act as the load bearing member. In order to preserve the performance of the backpack and user, the design of the pack will be held as close to existing systems as possible. This paper develops a theoretical model of the piezoelectric strap and uses experimental testing to identify its performance in this application.

Vibration Energy Harvesting: Machinery Vibration, Human Movement and Flow Induced Vibration

“…Energy harvesting from a backpack with piezoelectric strips was reported by Granstrom et al (2007). The traditional strap of the backpack was replaced by one made of PVDF.…”

Continuous production of piezoelectric PVDF fibre for e-textile applications

“…One of the attempts to generate energy from human walking by Shenck et al [6] by embedding a combination of piezoelectric PVDF and Lead Zirconate Titanate (PZT) structures in the shoe was successful to power a low energy electronic device. Another attempt to harvest energy from human body motion was by Granstrom et al [8] where these researchers embedded piezoelectric PVDF films into the straps of a backpack. Li et al [2] and Vatansever et al [9] demonstrated that piezoelectric PVDF can be used to generate a continuous power of the order of 100 µW using wind energy at moderate wind speeds.…”

Alternative Resources for Renewable Energy: Piezoelectric and Photovoltaic Smart Structures

“…Granstrom et al [38] developed a theoretical model of an energy harvesting backpack that can generate electrical energy from flexible piezoelectric PVDF films integrated into the straps. It was found that 45.6mW of power could be generated from a complete backpack with two piezoelectric straps with an efficiency of more than 13%.…”