Imagine walking into a room and all your electronic devices start charging instantaneously, without you having to fumble through numerous wires to find the correct one to plug into your devices. Sounds like something from a futuristic sci-fi movie? Well, this future is not too far off, thanks to a newly invented technology – Witricity.
Witricity, short for “wireless electricity” is a technology invented by physicists at MIT to allow wireless energy transfer over large distances. Current wireless charging methods employ induction plates on which you can place your devices such as handphones. As we learn in Electromagnetic Induction, a changing magnetic field induces a current in a nearby conducting wire. As such, the induction charging plate consists of a primary coil that generates a changing magnetic field. This oscillating field is then picked up a secondary coil in the device to be charged, which in turn induces a current to charge the device.
However, one major drawback of this method is that the device must be in close proximity to the induction plate, practically rendering the device immobile while it is being charged. One might wonder, what if we increase the strength of the magnetic field? Indeed, increasing the magnetic field might be a plausible solution, except that too strong a magnetic field can disable magnetic devices such as credit cards and hard disks!
How then can we send large magnetic fields through distances such that only the device(s) of interest pick up these magnetic fields? Fortunately, oscillations provide us with the answer. One might have seen a video where an opera singer is able to shatter a distant wine glass simply through her voice.
To understand this effect, we first have to appreciate that all objects have a natural frequency – the frequency that the object will vibrate at when given a disturbance. To find the natural frequency of the wine glass, we can simply tap it with a spoon and let it vibrate. When an external oscillator (in this case the opera singer) emits a wave that is of the same frequency as that of the natural frequency of the object (wine glass), resonance occurs. Maximum energy is then transferred from the external oscillator to the object.
Similarly, Witricity makes use of this phenomena. The devices to be charged have a high natural frequency that is matched by the frequency at which the magnetic field oscillates. This way, the magnetic field would be picked up only by the devices to be charged.
Image courtesy WiTricity via the IDTechEx Energy Harvesting Conference
By using resonant transfer, efficiency is increased. Furthermore, since there is no radiation produced, this wireless method of charging is safe to humans as well! One particular useful application of this wireless charging method is in pacemakers. Modern pacemakers used to regulate heartbeats require their batteries to be replaced every 7 to 8 years, meaning the patient has to undergo surgery. With Witricity, pacemakers can be charged while they are still in the patients’ bodies!