My childhood bicycle included a small generator that was turned by the front wheel to power the head and taillights — an effective early form of “personal” power generation. Because passing cars could only see me while the bike was moving, I also attached reflectors to the front and rear fenders. This all happened long before modern reflective tapes and their seemingly electronic glow.
Fast forward a few decades. I once visited a company that made lighted clothing. The firm wove optical fibers in the cloth and connected them to concealed, battery-powered light sources hooked to a programmable microchip. This arrangement generated all manner of animated pictures and crawling words on the backs, fronts, and sleeves of denim jackets — considered quite cool among the younger set and anyone wishing to be a walking billboard.
These developments led to today’s wide array of elaborate lighted clothing that uses LEDs, light fibers, and electroluminescent wires. Sport-team mascots wearing lighted costumes entertain fans, while clothing designers fashion decorated evening dresses and even underwear — with lights. More-serious applications include lighted clothing that keeps joggers and bicyclists safe and uses the small amount of electricity generated from their leg and arm movements.
As lighting gets more efficient, it becomes easier to illuminate products using personal power generation. In fact, a number of clever devices have been developed that work based on piezoelectric effects or coil motion in a permanent-magnet field. For example, piezoelectric elements in shoe soles can capture the impact energy from walking. The average power output of such devices has been measured at 6 W for a 155-lb person. Output jumps an order of magnitude larger when the person starts jogging.
Another example involves a backpack containing a spring-loaded frame that converts the up-and-down motion of walking into electricity via an induction coil or mechanical link to a generator. The 2 to 3-in. amplitude of normal walking can generate up to 7 W — enough to operate an MP3, GPS, and cell phone simultaneously. Of course, both the walking shoe and backpack generate oscillatory output that must be conditioned to provide the necessary dc current. And a battery to store excess energy for use during nonactive periods is a must.
Other applications include autonomous operation of medical-assist devices such as pumps for implanted organs and drug delivery, which require about 5 W for operation. Foot soldiers could also use these energy sources to power communication, health monitoring, and personal environmental-control devices.
Attaching light receivers instead of emitters to clothing fosters even more innovation. For example, attaching photoreceptors to optical fibers in clothing lets lasers on weapons detect combatants during war games. A recent MIT innovation uses optical fibers with semiconductor layers and embedded electrodes, interwoven with the fibers of conventional cloth, to serve as a distributed camera lens. The “wearable camera,” energized by the user’s movement, assembles images from each source point into a complete digital image. No more need for phototaking cell phones — you just snap images with your parka.
— Howard A. Kuhn
Kuhn is R&D Director of The Ex One Co. and is responsible for developing and implementing direct digital manufacturing and tooling technologies. Kuhn is also an Adjunct Professor at the Univ. of Pittsburgh School of Engineering, where he teaches engineering entrepreneurship and is involved in the digital manufacturing of scaffolds for regenerative medicine.
Edited by Leslie Gordon