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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 has resulted in
the need for significantly higher power to operate the electronics. This issue has been further complicated due to the
stagnate 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.
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