There’s a whole lot of energy out there that’s just kind of hanging around. The brakes on cars and trains turn momentum into heat, for example, which we now have systems for recapturing and recycling. But there are many more examples of wasted “ambient” energy that we don’t recapture. Even regular old walking around as bipedal animals is an inefficient process; the energy we expend in a single stride is greater than it would be given a perfectly efficient process.
Such is life, but nowadays we’re surrounded by devices that don’t require all that much power to operate. A couple of volts goes a long way. A newly developed nanogenerator, described this week in the journal Nano Energy, puts that into perspective, offering a means of converting the energy expended in a standard touchscreen swipe into sufficient power to light up a touchscreen.
The nanogenerator in question is what’s known as a biocompatible ferroelectret nanogenerator, or FENG—a paper-thin sheet of layered materials including silver, polyimide, and a sort of giant charged molecule known as polypropylene ferroelectret. The layers of the FENG are loaded up with charged ions, which results in a construction that, when compressed, produces electrical energy.
The high-level picture is that the FENG winds up with really huge dipoles—magnetic poles of opposite charge—existing on its different layers, which then change in relation to each other as the material is deformed under pressure. This change results in differences in electrical potential, which is what gives us useful electrical energy.
So, we hear about self-powered devices kind of a lot. What makes this one interesting is that it’s a new kind of device. That is, a FENG is not piezoelectric (electricity via squishing crystals) or triboelectric (electricity via certain kinds of friction).
The paper describes some advantages: “their simple fabrication allows for encapsulated low-cost devices. In view of the environment, health, and safety, the fabrication of encapsulated FENG avoids the use of harmful elements (e.g. lead) or toxic materials (e.g. carbon nanotubes), making it more attractive for biocompatible and perhaps even implantable applications.”
The device also has the neat property of becoming more powerful when folded. In a statement, lead investigator Nelson Sepulveda explains: “Each time you fold it you are increasing exponentially the amount of voltage you are creating. You can start with a large device, but when you fold it once, and again, and again, it’s now much smaller and has more energy. Now it may be small enough to put in a specially made heel of your shoe so it creates power each time your heel strikes the ground.”
Sepulveda and co.’s current task is in developing technology that would allow for the transmission of energy generated by said heel strike into devices like headsets.