Wireless recharging with WiTricity

In the on-going war against cables, it looks like it could soon be curtains for the power cables of all kind of mobile devices thanks to WiTricity. The WiTricity company was founded to market the concept of wireless electricity, developed at the Massachusetts Institute of Technology. The concept is simple: just place your device near a charging station and it'll recharge itself without even having to be plugged in.

The idea in itself is nothing new, as transmitting electricity with no physical channel was one of Tesla's major projects about a hundred years ago. However, transmitting a decent and efficient output is a different question entirely, not to mention doing so without creating any kind of troublesome electrical fields.

Back in 2005, a team of researchers at MIT looked into transmitting energy via magnetic resonance. They built a system based on two copper coils. One coil was connected to an AC power supply, creating a resonant source, and the other coil served as a resonant capture device, and was in turn connected to a 60-watt light bulb. It's the same basic principle as a transformer or an induction charger, but resonance makes the system more effective and increases the distance of transmission, which was previously all-but limited to the diameter of the coils. In the demonstration, the two coils had a 60 cm diameter and were placed about two metres apart.


After the initial discovery, the WiTricity company was created to slowly work on improving the system. One major field of development was the installation of several receivers, as a system only allowing one wireless connection at a time wouldn't be much use to anyone.

More receivers

More recent work has led researchers to a major breakthrough, as they found the system efficiency increased with the number of receivers. The resonance of several receivers with a given transmitter created a more effective, more powerful system and improved energy transfer. During the experiments, when two devices with an individual transfer efficiency of 20% were used simultaneously, the total efficiency rose to 30%. In other words, each received less energy, but less energy was lost overall.

So in an average living room containing several electronic devices (lamps, computer, TV, hi-fi, etc.), energy loss could be greatly reduced and the system could become even more efficient. However, correctly hooking up several devices at once wasn't as straight forward as it seemed. Plus, for devices that never really move from their position next to the plug socket, it's difficult to see how wireless power could be better than a good old cable.

In other words, wireless electricity would be mostly useful for mobile devices, particularly computers, consoles, mobile phones, games controllers or even electric cars. It's aimed at any battery-powered device that we have to plug in and recharge each time we get home. Thanks to this system, such devices could be powered or recharged automatically, with no cable connection required, as soon as they're in the same room as a wireless electricity source.

Note that WiTricity has nothing to do with the Airnergy system presented by RCA at the last CES, which could recharge a battery by tapping into Wi-Fi networks. Airnergy transmits power via electromagnetic radiation, which currently presents more potential health issues than the WiTricity system's magnetic field. Apparently, the latter is much 'safer', as the interactions between magnetic fields and living beings are minimal. Plus, objects outside of the resonant frequency capture hardly any of the energy transmitted.

A question of size?

It remains to be seen whether it will really be possible to install WiTricity receivers in all mobile devices. For the moment, the smallest receivers presented are still too large to fit neatly into a mobile phone. The transmitters are less problematic, as one per room will generally suffice and they can be easily concealed under a table, for example.

It's also worth asking whether the system will really be efficient enough to prevent it becoming a new way of wasting power. Then again, even if the efficiency isn't top notch, it'll surely still be less damaging for the environment than disposable batteries ...

For the moment though, we'll just have to keep plugging our devices in when they run out, and continue investigating other potential power sources for mobile technology. For example, although it's not perfect, Samsung's Blue Earth offers an interesting way of keeping your phone powered up while you're on the move.


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