How Does Wireless Charging Work – And Is It Actually Safe?

You can charge a mobile phone wirelessly now: but why is plugging and unplugging a cable actually more dangerous?

James Hunt

In 1899, the inventor Nikola Tesla began performing the first successful experiments on wireless power transfer. His initial success led him to believe that one day power would be transmitted around the planet without the need for cables. It took over 100 years, but his dream of wire-free power transmission did eventually get realised – though perhaps not with the scale and methods he envisioned.

Wireless charging is becoming increasingly popular in devices like phones and tablets, which combine a need for long battery life with low weight requirements. Conventional battery technology is straining against its own limits, which means most of us must head back to the wall for a top-up at least once a day. Faced with this, the only option manufacturers have is to make the charging process as pain-free as possible. In theory, wireless power makes recharging your phone as seamless as putting it down.

But how does it actually work? And, perhaps more importantly, how safe is it?UntitledModern wireless power draws on the same principle that Tesla investigated over a century ago: induction.

In 1887 Tesla became one of the first people to develop a usable induction motor (one of his originals is on display in the Science Museum in London) and the principle of electromagnetic induction – using an electromagnetic field to transfer power between two objects – is what forms the basis of all modern wireless charging, as well as things like contactless payment, cooking hobs and wireless speakers.

In a practical sense, induction works very simply: first, you feed power to a base unit or charging station which contains an induction coil. This powered coil will create an electromagnetic field around itself, and when a second induction coil gets near enough, the power will automatically be transferred to it and converted back into an electrical current. By installing the second coil inside another device, you can wirelessly supply power which can then be used to activate the device (in the cased of low-power RFID chips, for example) or charge its batteries.

Most induction chargers only operate over a short distance, however, and while physical contact between a device and its base unit isn’t necessary for induction to work, the fields generated are so weak that it’s usually the only way to get close enough.

As for safety, there’s really nothing to worry about. The average induction charger creates a field no more dangerous than radio waves, and isn’t strong enough to have any effect on the human body. If anything, plugging and unplugging a cable is more dangerous because there’s a minute chance it could fray and shock you. By contrast, induction hardware can be safely encased in thick plastic and still work. This is why electric toothbrushes have long used induction to charge: the units can remain sealed and waterproof.

If you’re wondering why induction charging hasn’t taken over the world, there are a few good reasons.

For a start, it’s not very good. Most wireless chargers operate at about 40% efficiency, where a decent cable can provide double that amount. Low efficiency means it loses energy to heat, so devices charge slower, which results in a higher power bill when compared to physical cables. It’s also more complex and therefore more expensive to manufacture.

The big issue is practicality, though. You can easily use your phone while it’s plugged into a charger, but under modern implementations the wireless base station must remain very close to the device to charge it.

But things are changing.

Returning to Tesla’s original experiments, an effect called Resonance Induction Coupling allowed the inventor to safely transmit power over several metres, and was the cause of his optimism about long-distance power transfer. Perhaps the most popular wireless charging standard, Qi, has recently been updated to allow a version of this to be implemented in compatible devices. The result is that the charging range has increased to a princely four centimetres.

It might not sound like much, but it’s a definite start. In the future, wall-sized charge stations might be able to transmit power to multiple devices in multiple rooms without requiring any specific positioning or proximity. You’d charge your phone simply by being in the house. It may have taken over a century to get to this point, but we’re closer than ever to wireless power transfer becoming commonplace. It’s what Tesla would’ve wanted. Source: Http://

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