Each of us comes with a built-in generator. Now Americanc scientist Michael McAlpine has developed a material that will allow us to turn our bodies into miniature power plants.
Michael McAlpine holds a little piece of film in his hand. It’s flexible and looks like a laminated chip, not much bigger than his thumbnail. If it weren’t clasped between the fingers of this proudly beaming young chemist at Princeton University, you might mistake it for a scrap of packaging and throw it away by accident. But this small square of silicone might be a step toward a greener and more energy-efficient future. With this discovery, Michael McAlpine aims to harvest energy where it is generated every day but dissipates unused: right in the human body.
“The average American consumes about 2,000 calories a day,” says McAlpine, a professor of mechanical and aerospace engineering, “and that energy is then released as mechanical energy in the form of movement.” Every time we walk, run to catch a bus or simply draw a breath, we generate energy. The human body is a miniature power plant, producing 70 watts per step and one watt per breath. Instead of lugging around batteries for our cell phones and MP3 players, we could use the energy our bodies produce to listen to music, make phone calls and check our e-mails while we’re out and about. And it gets better: If implanted in a person’s body, the silicone in McAlpine’s hand could power a pacemaker. That would be a huge boon for patients, who currently have to undergo surgery every four to five years to replace the device’s battery.
This vision was the springboard for McAlpine’s research, diverting him from his previous work in flexible electronics. “How can you convert mechanical energy into electric energy?” was the question this scientist with a PhD in chemistry asked himself when he started as an assistant professor for mechanical and aerospace engineering at Princeton three years ago. Piezoelectric materials were the logical answer. “Piezos,” as they’re affectionately referred to in the field, are materials that switch their electric polarization when flexed or compressed. Even if you’ve never heard of them, you’ve seen them in action: They can be found in quartz watches, guitar pickups and even disposable lighters. When you press the piezo in a lighter, it generates electric current. The spark created when that energy is released ignites the gas flame. The most familiar piezos are crystals like quartz and ceramics, and they’re definitely not new. Way back in 1880, the brothers Jacques and Pierre Curie discovered that mechanically applying pressure to tourmaline crystals generated a charge on the surface. “None of the components in our material is new,” says McAlpine. “If you look at it that way, all this could have been discovered 20 years ago.”
What is new is the way people are using them. Like all crystals and ceramics, piezos are usually hard and breakable. But an implant designed to convert the motion of the chest when breathing into electricity or the sole of a shoe that’s supposed to turn our steps into power has to be flexible. McAlpine took the most efficient of all piezoelectric materials, PZT (lead zirconate titanate), and cut it into nanoribbons. They are just one one-hundredth of a millimeter wide and make the hard material flexible. In the next step, the PZT nanoribbons are transferred onto silicone. To show how that works, McAlpine takes a lump of the Silly Putty we all used to play with as kids and drops it onto a newspaper. The ink is imprinted on the putty — and in exactly the same way, the PZT is imprinted on the silicone. Then it’s laminated with another layer of silicone.
“Piezorubber unites the best of both worlds,” its innovator elaborates.
“It combines the biocompatibility of silicone — which, of course, is used for cosmetic implants — with the energy-generating capacity of a piezo. And you can bend it like a piece of rubber.” A little piezorubber element implanted in a patient’s chest or embedded in the sole of a shoe could harness the energy of our movements and use it to power devices that now require batteries.
It’s one of “The 50 Best Inventions of 2010” according to Time magazine, and the scientific journal Technology Review distinguished Michael McAlpine’s work last year with its TR35 Award for innovators under 35. The young assistant professor is gratified by so much acclaim, particularly as it means he will now be able to attract the best students to his team. But high achievement is nothing new to this son of a lawyer from Connecticut. In middle school, Michael was driven to the high school for math courses. Anything else would have underchallenged him. He doesn’t attribute his success to his mathematical talent alone, though. “Today it takes more to be a good scientist than being good at math; you have to be a good communicator, too,” says the 33-year-old McAlpine, adding, “and you have to be unconventional. I inherited a mathematical mindset from my mother and ‘swimming against the current’ from my father. He is kind of a rebel, his back is covered with tattoos and he was a salesman for ladies’ lingerie.”
Will McAlpine’s discovery make generating power as easy as taking a walk? Not quite. Piezorubber won’t create enough juice to supply shopping malls or whole towns. “If they lined the floors of a shopping mall, shoppers’ footsteps could generate enough electricity to power a ‘sale’ sign in a store,” McAlpine guesses. But if piezorubber helps free us from always having to charge our mobile devices at a wall outlet, that’s still a big improvement. It could save a great deal of energy, and not just because we are using more and more portable gadgets, but because their chargers are often left plugged in around the clock. Most of the power they eat up is wasted. Germany’s Federal Environment Agency has estimated that standby/off-mode losses in that country amount to at least four billion euros each year. And in the U.S., chargers for iPods, laptops and the like make up about five percent of electricity bills.
Now McAlpine’s team is working on the efficiency of piezorubber. Its capacity depends on the volume of the material. A thumbnailsized piece could power a pace- maker, and one the size of the sole of your shoe could charge a cell phone — but other dimensions are possible. “Just think how much energy a dance floor full of people generates,” raves McAlpine. “That energy is produced anyway, all you have to do is harvest it!”
Dorothea Sundergeld (copy) & Elias Hassos (photos)
One of the 50 best inventions in 2010: In the Princeton University laboratory Michael Mc Alpine develops implants that can transfer kinetic energy to electricity.
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