Abstract
system to date has served all of the needs of wearable
computing—light weight, minimum effort, high power
generation, convenient power delivery, and good power
regulation. We believe that our approach has the potential
to solve these problems for a class of wearable devices by
placing both the generator and powered electronics in a
location where considerable energy is easily available,
namely the shoe.
As the power requirements for microelectronics continue
decreasing, environmental energy sources can begin to
replace batteries in certain wearable subsystems. In this
spirit, this paper examines three different devices that can be
built into a shoe, (where excess energy is readily harvested)
and used for generating electrical power "parasitically" while
walking. Two of these are piezoelectric in nature: a
unimorph strip made from piezoceramic composite material
and a stave made from a multilayer laminate of PVDF foil.
The third is a shoe-mounted rotary magnetic generator. Test
results are given for these systems, their relative merits and
compromises are discussed, and suggestions are proposed for
improvements and potential applications in wearable
systems. As a self-powered application example, a system
had been built around the piezoelectric shoes that
periodically broadcasts a digital RFID as the bearer walks.
In previous studies [5], it has been calculated that up to
67 Watts of power are available from heel strikes during a
brisk walk (68 kg person, 2 steps/sec, heel moving 5 cm).
This level of power extraction from walking would certainly
interfere greatly with one's gait. Our philosophy, in
contrast, has been to try to generate power entirely
parasitically, that is through mechanisms that capture and
make use of energy normally dissipated wastefully into the
environment. There is much less energy of this type than
available through deliberate means of harvesting human
power (e.g. through a hand crank or foot pedal), but it is our
goal to unobtrusively collect energy for low-power
applications. We have approached this problem by using
the energy from the weight transfer during a step to perform
useful work.
1: Introduction
As wearable electronic devices evolve and proliferate,
there will be a growing need for more power delivery to
distributed points around the human body. Today, much of
that storage is provided by batteries and power delivery is
via wires. The current approach to power distribution is
clearly becoming problematic -- as more appliances are
carried, we are forced to either use more small batteries that
require replacement everywhere or run wires through our
clothing to supply appliances from a central power source.
Both are undesirable. A better solution is clearly to
generate power where it is being used, bypassing the storage
and distribution problem altogether. As power requirements
drop for most wearable devices, it is no longer infeasible to
harvest a useful amount of energy "parasitically" from a
normal range of human activity.
2: Background Information
The context in which we place our generator is that of a
sport sneaker. This type of shoe differs from ordinary shoes
in one important feature—its energy dissipating sole.
While walking in ordinary "hard" shoes, the foot is rapidly
decelerated from its relatively high downward speed to zero
velocity relative to the ground—an action that requires the
application of relatively large and sudden forces to the foot.
Barring shock absorption in the feet, this can be simply
modeled as a sudden step in velocity; the force applied to the
foot to achieve this deceleration is an impulse

Download full report
http://citeseerx.ist.psu.edu/viewdoc/dow...1&type=pdf