FIVE years ago, when the World Trade Centre fell, a shockwave rolled around the world. It ruined many lives and sank a few companies. But who would have known that it would hit Sir Trevor Baylis' business so hard?
Sir Trevor, a British inventor best known for the wind-up radio, was developing a shoe that would charge your mobile phone battery as you walked. The shoe had a slot for the battery and captured some of the energy discharged in the average human step, roughly eight watts (about eight joules), and used it to charge a phone over thousands of strides.
Sir Trevor even walked 160 kilometres across the Namibian desert to raise money for the idea. But it collapsed along with the twin towers.
"After 9/11, anyone wearing electric shoes would look like a bomber. That's what you have to watch with any electric kit that you carry nowadays," he muses.
Richard Reid, who tried to blow up a plane by carrying explosives in his heels - which made customs officials particularly nervous about footwear - has a lot to answer for.
The idea of harvesting otherwise wasted energy isn't new, but it's beginning to gain appeal. Researchers are hoping to reap energy from people and are also planning to use the vibrations from motors and even passing trains to generate power.
Converting vibrations into a tiny charge may be enough to power a wireless sensor, or thousands of footsteps could power lights and audio systems.
Piezoelectricity has been the biggest hope for energy harvesters.
Discovered in 1880, piezoelectric crystals emit a charge when subjected to sudden mechanical stress.
When you press the button on an electric lighter or the ignition switch on your gas oven, a piezocrystal is probably causing the spark.
In 1996, Massachusetts Institute of Technology Media Lab doctoral student Thad Starner wrote a paper about "the potential for energy harvesting".
Using a piezoelectric shoe insert that flexed with each step, or a flywheel system connected to a small spring in the back of the shoe, five to eight joules could be recovered from each foot-fall, he said. Other options for harvesting human energy included finger motion (a 90-words-per-minute typist can generate 19 milliwatts). Dr Starner believed that by using footfall energy alone, he could power a small wearable computer.
Building a low-powered wearable computer in the lab is one thing, but commercialising wearable computing and wearable power would involve a huge design and user testing effort. Besides, such a computing technology hasn't captured the public imagination yet. People don't want to walk around looking like one of the Borg from Star Trek.
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