[wordup] Piezoelectric Shoe Energy

[Adam Shand]

and they keep saying there's an energy crisis ... yeesh, they just aren't
looking in the right places. :)

URL: http://www.computer.org/micro/homepage/may_june/shenck/
Via: http://slashdot.org/article.pl?sid=01/06/22/1838251&mode=flat

Energy Scavenging with Shoe-Mounted
Piezoelectrics
Nathan S. Shenck
Joseph A. Paradiso

MIT Media Laboratory, Responsive Environments Group

Decreasing size and power requirements of wearable microelectronics make
it possible to replace batteries with systems that capture energy from the
user?s environment. Unobtrusive devices developed at the MIT Media Lab
scavenge electricity from the forces exerted on a shoe during walking: a
flexible piezoelectric foil stave to harness sole-bending energy and a
reinforced PZT dimorph to capture heel-strike energy.

Consumer reliance on wearable electronic devices has grown significantly
in the past decade. With increasing use come demands for decreased size
and enhanced capabilities, necessitating new ways to supply electric
energy to these devices.  Until now, chemical-cell batteries have been
sufficient, but replacing them is a costly nuisance, and this solution
will become less practical as demands evolve. Another approach is a
centralized, body-worn power pack, with multiple distribution lines, but
such a system will be cumbersome and impractical as the user wears more
devices.

Fortunately, as power requirements drop for body-worn devices, a third
approach, which eliminates the power wiring problem, is emerging:
developing and storing electric energy at the devices themselves by
scavenging waste energy from human activities. For example, the average
person spends a significant part of the day on foot, dissipating abundant
energy into the insole of a shoe. Harnessed unobtrusively, this wasted
energy could be used in a variety of low-power applications, such as
pagers, health monitors, self-powered emergency receivers, radio frequency
identification (RFID) tags, and emergency beacons or locators. If wiring
devices to the generator proves impractical for some applications, a
battery could be trickle-charged at the shoe and manually moved into the
devices.

Studies at the MIT Media Laboratory have explored the feasibility of
harnessing waste energy from a variety of body sources. Thad Starner?s
benchmark conceptual investigation in 1995 analyzed various human
activities and found that the heel strike during walking is the most
plentiful and readily tapped source of waste energy.1 Starner estimated
that 67 watts of power are available in the heel movement of an average
(68 kg) person walking at a brisk pace (two steps per second with the foot
moving 5 cm vertically). Admittedly, scavenging most of that energy
unobtrusively would be impossible. But even a small percentage of it (up
to a sizable fraction of a watt),2 removed imperceptibly, would provide
enough power to operate many of the body-worn systems on the market today.

A second MIT Media Lab study3 and independent work at other institutions
(for example, Antaki et al.4) supported this conclusion and proposed a
system of embedded piezoelectric materials and miniature control
electronics. The researchers observed that a shoe or boot having a
relatively large volume of space available in the sole and the heel
platform would make an ideal test bed for exploring body-energy
harvesting.

In the years since these studies, researchers have further explored
parasitic power harvesting in shoes. In particular, at the MIT Media Lab,
we have implemented a demonstration of shoe power at work and developed
new ways to efficiently condition raw, low-frequency piezoelectric shoe
signals into a continuous, reliable energy source. Other approaches use
rigid piezoelectric materials driven at resonance to achieve higher power
levels. In contrast, we have concentrated on embedding simple mechanical
structures and flexible piezoelectric materials into the shoe, resulting
in minimal impact on the shoe?s design or feel.

See web site for the rest ...