While some wireless devices are powered by batteries, either rechargeable or single-use throwaways, others need to be physically connected to a power source. Even rechargeable batteries like those in cell phones and laptop computers need to be plugged in at some point to recharge them.
This need to connect wireless devices to a power source, either continuously or for an occasional recharge, limits these devices from achieving real wireless status.
Cutting the Cord
Eliminating the power cord has long been the dream of many inventors and innovators. Although a few "proximity chargers" are available today that effectively eliminate the cord between the device and the charger, they still require the device to be in close physical contact (more on this later).Imagine if everything that we now plug into electrical outlets (also referred to as "convenience outlets") could get their power from a wireless source while we use it! Batteries in cell phones and portable computers would be continually recharged. Appliances and equipment normally tethered by a power cord would become truly portable, receiving power from nearby wireless transmitters.
As unbelievable as this sounds, we're very close to realizing true wireless power.
Early Attempts
Wireless power transmission is not a new idea. In fact, Nikola Tesla, one of the first pioneers in wireless power technology during the late 19th and early 20th centuries, demonstrated that wireless power transmission was possible.Tesla's last attempt at wireless power transmission on a global scale was the New York based Wardenclyffe Tower. Unfortunately, Tesla's funding ran out before he completed the project, and the tower was dismantled in 1917.
After Wardenclyffe, Tesla did very little work with wireless power distribution. Although others such as Hidetsugu Yagi tried to reintroduce wireless power transmission, there was little advancement until the 1960s when William C. Brown began experimenting with power transmission using microwave technology.
21st Century Wireless Power
Today, wireless energy transmission technologies of various types continue to be developed in theory and in practice. One type requires very close proximity to the source. Another can transmit power over several meters, and others can span many miles. There's even a technology that seemingly plucks energy from the air.One example of existing wireless power technology is the cordless toothbrush that recharges its battery using inductive coupling without a direct electrical connection. In this example of close proximity wireless power, the battery inside the toothbrush is recharged by a magnetic field generated by the charging base using current from an electrical outlet. When the toothbrush is placed in the base, the base's magnetic field induces an electric current in the toothbrush and recharges the battery.
Nascent products from WildCharge, Powermat, and others charge cell phones and other devices just by laying them on a charging mat. Although these products use close proximity inductive power transmission to recharge the devices, they still have at least one power cord.
Continuing Development
Marin Soljačić, an MIT professor, is leading a team to develop near-field wireless power transmission using a technology called strongly coupled magnetic resonance (what's this?). This technology relies on a transmitter and receiver that are "in tune" with each other to transfer energy over several meters. Soljačić founded WiTricity to develop this technology, which he says is safe for people and animals.The Intel Wireless Resonant Energy Link (WREL) project is building on the MIT research. According to an article in The Register, Intel used their WREL technology to power light bulbs, audio speakers, and even a netbook computer over a one meter distance. Intel is working to improve WREL efficiency and to scale down the large prototype to a size more practical for laptops and cellphones.
The ZigBee Alliance is promoting a technology that harvests energy from many sources (such as ambient radio waves) in the surrounding environment. Although energy harvesting is not a wireless power transmission technology in the strictest sense, it does convert ambient energy to electrical power and provides for energy independence in certain applications.
Not Too Distant Future
Despite the smattering of close proximity wireless chargers, near-field wireless power technologies have done little more than energize light bulbs over the past 100 years, researchers are confident that practical near-field wireless power products will be available to consumers in the next five years. And certainly within the next two decades, near-field wireless power should be commonplace.Eventually, wireless power transmitters will be embedded within the walls, ceilings and floors of homes, offices and other buildings. We would never have to find a "convenience" outlet to plug in lighting, appliances and electronic equipment – just set them down anywhere in a room and they instantly have power.
Your cell phone and other portable devices will automatically recharge themselves just by walking into a room with them. You'll be able to easily move lamps and TVs anywhere in your home or even outside. And you won't have to worry about forgetting to plug in your electric-powered car. Just pull it in the garage and it'll start recharging automatically.
Now that's convenience.
References:
1. "The Transmission of Electrical Energy Without Wires" by Nikola Tesla. Electrical World, March 5, 1904 (http://www.tfcbooks.com/tesla/1904-03-05.htm).
2. "Intel's Wireless Power Play" by Kate Greene. Technology Review, Massachusetts Institute of Technology (http://www.technologyreview.com/energy/22906/).
3. "Wireless Transmission of Electricity" from PESWiki.com, Pure Energy Systems Wiki (http://peswiki.com/index.php/Directory:Wireless_Transmission_of_Electricity)
By Harry Hiles, HBH Technology LLC — 2 July 2009
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