Dr. Lawrence Rome's "Suspended-Load Backpack" has clearly struck a nerve on the web, with links to it popping up all over the place. One aspect of the story that's unusual is that Rome is a biologist, not a product designer or engineer, and he published his discussion of the concept in Science. For Rome, the backpack is as relevant to the study of biomechanics as it is to figuring out new forms of energy production. I won't belabor you with the details of the backpack and how it works; National Geographic does a terrific job of filling that role. Instead, I'd like to speculate for a moment about the bigger picture.
We've become accustomed to idea of embedding solid-state electronics into various materials, making it possible for airplane wings to report otherwise invisible damage, walls to become solar panels, and objects of all sorts to be able to report their location and condition with cheap RFID tags. But all of these, while they may make the materials "smart" in some way, remain intrinsically passive systems. What happens when motion and pressure are added to the mix?
The Suspended Load Backpack, when thought of in the abstract, is an example of a system able to derive utility from otherwise wasted kinetic energy. It's not difficult to extrapolate from the backpack to other kinds of motion-based energy generation, such as the potential power in vehicle shock absorbers. This would be of some value to hybrid-electric cars. If the weight and motion of a backpack can generate seven watts of power, how much more could come from the weight and motion of a car? Would it match, or even exceed, the power input from solar panels?
And kinetic energy doesn't just mean power generation. Piezoelectric crystals turn physical pressure into electromagnetic output, and one might imagine that this is another way to make electricity. But as Dawn noted a few days ago in her piece on piezoelectric signaling, embedding piezoelectric crystals into the soles of shoes to generate energy from walking didn't actually produce much power (something mentioned by Rome in his Science article, in a comparison between the 20 milliwatt output of the shoes vs. the up-to-7.4 watt output of his backpack). Pressure into power wasn't much of a useful trick; instead, it turns out that the ability of piezoelectric crystals to turn pressure into electromagnetism is better as a method of sending short-range wireless signals. Dawn talks about one of the real-world applications of this process, a wireless light switch, but (again), what else can it do? Could we, for example, take advantage of this capability for environmental sensors?
Both the energy-generating backpack and the wireless, zero-energy light switch are very interesting and cool applications; both have the potential for widespread use. But for me, the greatest value they could have would be as harbingers of new technological families, or as catalysts for new ways of thinking about how we can best take advantage of our material surroundings. How else can motion and pressure be used to build a better environment?
