Exactly how does the Palm Pre's charger work?

Having a completely sealed toothbrush means that you don't want to even have an opening for the charger any water that gets in may not exactly give you a shock, but it can fry the circuits. It is because of this that many electric toothbrushes rely on what is called inductive coupling to charge the battery without any physical contact.

But what is inductive coupling? Wikipedia says that, in electrical engineering, two conductors are referred to as inductively coupled when they are configured such that change in current flow through one wire induces a voltage across the ends of the other wire.

How it works

Before we proceed, remember the cross talk that you get when on the phone sometimes? You know, when you are talking to your friend and you can hear two other people complete strangers also talking? This is also called inductive coupling, though this is called unnecessary inductive coupling because this tends to irritate you.

But the principle is the same in both cases voltage in one circuit induces voltage in another circuit. In the case of cross talk, it irritates; in the case of the Palm Pre, it charges the battery. Simple, right?

Old hat

While it may seem new to us if we buy the Pre or an electrical toothbrush, the thought behind this is almost 190 years old. The seeds of this type of technology were sown in 1820 when Andru00e9-Marie Ampu00e8re described what is today known to all of us as Ampere's law, which shows that electric current produces a magnetic field.

Later, in 1894, Nikola Tesla wirelessly lit up vacuum tubes by means of the electrodynamic resonance effects. In 20008, Intel reproduced Tesla's implementation by wirelessly powering a light bulb with 75 per cent efficiency.

As Sherlock Holmes said A Study in Scarlet, "There is nothing new under the sun. It has all been done before."

Leave that on my desk
Pre users will not be the only ones to use a charger that doesn't need wires. A furniture company called Herman Miller, which is based in Michigan, has a plan to use their furniture to support inductive coupling. So, you may soon just leave your cell phone from any manufacturer on your table and get it charged.

QUICK TAKE
>>Palm's Pre uses a charger called Touchstone
>>It charges the Pre without using any wires
>>Though it may seem new, this technology has been around for almost 190 years

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