Kyle Schurman
Feb 15, 2012

Passing power through thin air: WiTricity charges phones and cars without wires

The idea of being able to pass electricity through the air dates back to the 1890s and the famous electrical engineer and inventor Nikola Tesla, who proposed an idea of transmitting electrical energy without wires across the entire world. Although this idea currently has had some application in things like virtual lightning rods, the process of truly carrying electricity without wires through the air to power an everyday device, such as a radio or computer, hasn’t been realized.

However, we have seen some types of wireless power emerging in recent years, led by the idea of inductive charging of batteries. A new product from Witricity promises to continue to push the idea of inductive charging farther along, increasing the distance across which the electricity can travel. The company derives its name from the term used to describe this new charging technology -- 'WiTricity' -- a word similar in appearance to the term 'WiFi.'

Real-world uses of inductive charging were initially developed at MIT several years ago, and the Witricity technology would further enhance that work. Witricity expects to release products later this year that will charge personal electronics across an open space. Within a few years, you could see similar products that may be powerful enough to charge the large batteries in an electric car without the need to plug in.

Currently, the inductive charging products are limited to those that work over a really short distance, such as electronic toothbrushes, or that require physical contact between the battery of the device and a charging pad. By extending the distance over which this technology would work, Witricity could quickly gain control of this potentially burgeoning market.

Think about it. Having the ability to charge devices without the need to plug into an outlet would be one of the greatest steps forward for easier and better usage of the large collection of personal electronics devices most of us have accumulated.

The idea of being able to set your smartphone, iPod, tablet, game controller, and other devices near a charging zone and have them automatically charge -- without having to go through the hassle of seeking out the right cord -- is very appealing. You could set your purse or briefcase near the charging zone at 6 p.m. and not think about them until the next morning, when your devices would be fully charged again.

To make inductive charging work, the system passes electricity through a coil, which generates a magnetic field. The receiving coil is able to draw power from that magnetic field, as long as it is close enough to be inside the magnetic field. Witricity is able to extend the distance over which its products can transmit the power by better tuning the sending and receiving coils, creating a larger magnetic field.

Witricity also has developed hardware called repeaters that can extend the distance of the magnetic field, similar to how you might use repeaters with your WiFi home network to extend the reach of a single wireless router throughout your house.

The biggest hurdle to seeing widespread use of inductive charging comes in making sure that all electronic devices have the needed hardware to use the technology. Witricity and other companies have the ideas, but they have to convince the product manufacturers to include the needed components. For example, with cell phones, Witricity wants the manufacturers to place a cover on the phone that would allow inductive charging to take place. Other components for this technology might have to be built into the devices or batteries themselves, which could raise the cost of the products.

Manufacturers of these devices can be leery of adding hardware and driving up the costs of their products for a technology that’s really still in its infancy stage. Some manufacturers may want to see the idea of inductive charging gain more widespread use before embracing it, which leads to the “chicken or the egg” problem: Without having the technology built into the devices, the technology can’t gain more widespread use. It’s going to require a few manufacturers taking a chance, hoping to reap the benefits of being an early adopter, to really get ideas like Witricity’s off the ground.

Other companies are working on similar technologies. Apple has considered placing a coil inside a desktop computer monitor to provide power wirelessly to a keyboard and mouse. Oak Ridge and Stanford researchers have received a federal grant that could allow electric buses to charge their batteries wirelessly as they idle at stoplights, through the use of coils embedded in the road.

All of these ideas would help us keep the numerous batteries that we use every day fully charged, regardless of whether we remember to plug them in at night. For the forgetful among us, these real-world applications of Tesla’s century-old idea could provide the productivity we all crave without the need to ever curse a dead battery again.