Wireless Cities are Coming: Get Ready to Ditch Your Power Cords
Here’s a bold prediction for you: very soon, we’ll live in a wireless world. This is where you’re probably thinking, “Hold your sweet-smartphonin’-butt there mister.... We already live in a wireless world.” One could argue—given our network of mobile phone, towers, and satellites—that we’ve now effectively transitioned enough of our communications infrastructure away from the wire that we can deem ourselves “wireless." However, in fact, we are not a wireless world. One significant tether still remains: the mighty power cord.
Our global system of satellites, antennas, and batteries allow us to take our mobile tools on the road and exchange information wirelessly for impressive lengths of time. Sooner or later however, every indulgent reprieve we take from the world’s largest tangle is met with insistent indicator lights, panicked beeping, and a cacophony of calls to plug something in.
Now, imagine a world without power cords—no phone cords; no flatscreen tv cords running down your wall; no more tripping over your laptop’s power cord on the way to the bathroom in between episodes of Lost Girl. This is the (very-near) future—all your power-hungry electronic devices will run with no wires...nor batteries.
Wireless transfer of energy has been the elusive dream of many aspirational electrical engineers and foot-tangle-ensnared cubicle-workers for decades. And, thanks to a discovery made by a group of enterprising individuals at MIT in 2007...it’s here.
Okay...well, truth be told...it’s been here since long before 2007. In fact, wireless energy transfer—in the broadest sense—has been here since the dawn of time (sunlight, lightning, electromagnetic waves, etc.) But, the ability to harness and use wireless energy transfer to direct electricity was first demonstrated in 1891 by Nikola Tesla, a Serbian-born electrical engineer and scientist. Perhaps his greatest invention—in a long line of great inventions—was the Tesla Coil, a device which he used to beam energy across great distances, but which we use today to play the theme songs from 1980s video games.
Despite Tesla’s early advances, his work—though exciting—did not lead to widespread wireless power. The need for wireless energy transfer was not urgent—and therefore the public will—did not yet exist. For over a century, wireless power remained a novelty.
However, after being awakened for the sixth night in a month by a beeping cell phone begging for power, MIT professor Marin Soljacic decided that wireless energy transfer was no longer a novelty, it had graduated to necessity. He gathered a team and got to work retooling Tesla’s experiments for the 21st century.
The goal of Soljacic and his team was simple: to create a wireless energy system that could power a room full of electronics using one base station and several receivers. As wireless energy transfer can happen in a number of ways, there are different approaches one could take to solve this problem:
- Microwaves (the electromagnetic waves, not the oven) are cheap and available, but require line-of-sight between the power source and the electronic device. Also, they fry people's brains.
- Laserbeams—another form of electromagnetic waves—could also be used as a form of wireless energy transfer. But, as anyone who has seen the early Val Kilmer classic, Real Genius, knows—lasers can take the head off a stone statue with surprising aplomb.
Soljacic and his team needed to find a form of wireless energy transfer that was entirely safe and could navigate the halls and corners of a modern home. Therefore, they focused their attention on magnets—or, more specifically magnetically-coupled resonators.
A magnet (or magnetic field) is created when an electric current is passed through a coil of wire. Conversely, an electric current is created when a coil of wire is passed through a magnetic field. Harnessing this phenomenon, it is possible to transfer energy wirelessly by creating a powerful magnetic field using a base station of coiled wire connected to a wall socket, and a receiver made of a coiled wire connected to an electronic device. When the receiver is moved within range of the magnetic field created by the base station, its coiled wire would become electrified and power the attached device.
The problem with this rather basic method is that the base station’s magnetic field would spray in all directions, all the time—making the system power-hungry and highly-inefficient.
So Soljacic and his team decided they needed a way to “pair” the base station and the receivers so that the energy transfer was targeted and efficient. They explored "resonance."
Resonance is a natural phenomenon that occurs in all objects—wood, glass, Coke cans, the human body, etc. Based on the weight, density, flexibility, shape, size, and every other factor contributing to the physical makeup of an object, that object will oscillate with greater amplitude at some frequencies than others.
For example, if you were to place three empty wine glasses next to your stereo’s speaker, they may or may not vibrate depending on the frequency of the sound waves being emitted. At low frequencies—as would result from your early ‘90s gangsta rap tape—the glasses, due to the fact that glass is a dense, rigid material, would not vibrate in sync with the music. The material would “fend off” the vibrations from the music.
However, swap out your gangsta rap for your favorite “only-when-no-one-is-around” opera tape—with its ear-piercing mezzo-soprano high notes, and you’ve got yourself a science party. The high-frequency sound waves penetrate the wine glass by shaking the tightly-packed molecules in the material at a frequency at which they can move about. The glass absorbs the energy from the sound waves with stunning efficiency at this frequency and your wine glasses shatter. (Sorry!)
Now, place three MORE wine glasses in front of the speaker. Fill each with a different amount of water. The addition of water changes the wine glass’s natural oscillation frequency. So, if you were to blast the opera from the speakers again, the glasses would shatter at different times as the notes reached a glass’s specific resonant frequency. The speaker's energy and the individual wine glasses "pair" (or resonate) at different frequencies.
Electromagnetic waves—like those created in the system’s base station—work just like sound waves. And magnets—like any other objects—are subject to the phenomenon of resonance. This means that by tuning the magnet in the base station and the magnet in the receiver to resonate at the same frequency, the MIT team was able to create an electrical charge in specifically-tuned receivers, and no charge in others—effectively targeting energy transfer (in open rooms and around corners) and making all other objects in the house—even other magnets—unaffected.
The implications for this breakthrough are immeasurable. Not only does this technology offer us the ability to cast away our power cords, but it also means that one day we’ll be able to cast aside our hugely expensive, inefficient, and polluting batteries as well. Any device within range of a identically-tuned base station—in your living room, in a coffee shop, in the car, in an airplane, etc.—would draw power from that base station.
For more information, see WiTricity.com.
This month, challenge a neighbor to GOOD's energy smackdown. Find a neighbor with a household of roughly the same square footage and see who can trim their power bill the most. Throughout February, we'll share ideas and resources for shrinking your household carbon footprint, so join the conversation at good.is/energy.
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