Power for the wireless world
By Sean Mc Kernan | Nov 18 2008
Is copper to be relegated to the saucepan? Wireless technology takes the next step, explains Sean McKernan.Remember when there was no Sky TV, and in order to record a TV programme we had to set up an old fashioned video recorder? This necessitated us to navigate our way behind the TV into a tangled world of cables and power cords to find the right ones and hook them up. And as in most houses, there were probably an insufficient number of sockets for all of the appliances present; some devices had to be unplugged so that the correct ones could be plugged in.In the process of removing unwanted plugs, important devices can be turned off too. Which in my case, turned out to be the computer I was typing this article upon. So (for the second time) I started to write on the newly emerging field of wireless electricity transmission or WiTricity.Wireless electricity is not a new concept but has been an idea since the early 20th century. It was never considered a serious initiative until now. We use many electronic devices: mobile phones, laptops, mp3 players... (the list goes on) and each has a separate cable. With insufficient sockets in most houses the idea of wireless electricity becomes an ever more attractive prospect in the modern world.With the runaway success of wireless broadband freeing computers from the shackles of cables, researchers at the Massachusetts Institute of Technology (MIT) have set about creating a technique allowing wireless transmission of electricity over a two metre distance. They have achieved this using a process called electromagnetic induction, coupled with a natural phenomenon known as resonance.For those without a background in physics, electromagnetic induction is the process in which an electrified coil of wire creates a magnetic field. This releases energy into the close surrounding space. If another wire coil is within a certain distance, energy is absorbed by the wire, creating an electric current without any connection between the two objects.This phenomenon was discovered by Michael Faraday in 1891 and has been used ever since in electric transformers, such as those used in phone and laptop chargers. But it may now have a new incarnation.Though electromagnetic induction is a straightforward form of energy transfer, it typically has a very low efficiency. Much of the energy is lost in all directions, and the second coil picks up a mere fraction.Therefore, until recently it has been unsuitable for long-range use. Scientists at MIT have pioneered a new idea, resonance, to drastically increase its efficiency.Imagine a room full of beer bottles with different amounts of liquid in each of them. If an opera singer sung a high-pitched note, the sound-energy would be transferred to the glasses but only a few might shatter.Each of the beer bottles vibrate differently under the frequency of the note because of the various levels of liquid in each. There are only a few bottles whose liquid level, or reception frequency, will match the notes so closely that the vibration will cause it to shatter. In this case, the energy transfer between the opera note and the beer bottle is maximal – this is known as resonance.The same idea is used in WiTricity as both of the wire coils have the same frequency (several million hertz) allowing the coils to ‘couple’ and therefore only allow energy to be transferred between the two coils. This increases the efficiency of energy transfer over one million times compared to electromagnetic induction alone.This form of energy transmission could be used to power all forms of devices in a close proximity, including mobile phones, laptops and television. The coil of wire needed to power the device would only be a few centimetres in diameter and very light allowing unfettered access to electricity inside a home.As with many groundbreaking technologies, there are still numerous drawbacks to this method of power. At the moment, the most serious concern surrounds the health implications of such a device. Theoretically energy should only be transmitted between objects with the same frequency as the emitting coil - several million vibrations per second.But in real-world conditions small amounts of energy could be transmitted to the body, causing genetic damage and possibly resulting in cancer. Currently extensive research is being carried out to ascertain if this can occur.Another major drawback is the inefficiency in power transmission. Even when resonance is being utilised, the general efficiency of this technology is still approximately 40 per cent – too low to be economically feasible. If one were to implement such devices, electricity uses would more than double.The current electricity system is more than 90 per cent efficient, and in a world with dwindling energy resources efficiency will remain the most important factor in evaluating new technologies. MIT scientists have demonstrated that over very short distances the efficiency can be made much higher, however this under highly controlled circumstances.Still, there is hope that there may be some way of utilising this technology in the future. With its introduction, phone chargers and long copper wires would become a thing of a past. And just as we wonder how those in the far past dealt without electricity, so too will we wonder how annoying it must have been to be tripping over wires in the library.