Electricity and electrical power is a crucial technology underpinning nearly all aspects of modern life. The whole planet is strung with copper wires to move electricity around so it can be used for myriad purposes. And we use huge numbers of batteries to temporarily store electrical power for portable devices where it is impractical or inconvenient to have a power cord.
Preferably, batteries need periodic recharging – simply discarding used batteries and replacing them is very wasteful. We are all very familiar with periodically plugging our mobile phones, tablet and laptop computers, cordless power tools and other equipment into power sockets to recharge them. As they become more popular, we are also starting to get accustomed to plugging in our electric cars and other vehicles. All this plugging and unplugging can be quite inconvenient, and luckily the technology exists to avoid it.
Humanity’s understanding of electricity evolved over centuries, and Faraday and Henry independently discovered and experimentally quantified electromagnetic induction in the 1830’s. A wire carrying an electric current creates a magnetic field around the wire. If a second wire is placed near the first one, the magnetic field induces a current in the second wire, even when they are not in contact. This effect is amplified if the wires are coiled and if a permanent magnet is present. This effect gives us a way of passing an electric current between two points wirelessly, but it only works over relatively short distances.
The electromagnetic effect has been known about and used for many years. Electrical interference – “snow” on TV screens, radio static and so on – arises from undesired induced couplings between wires. Many power transformers also rely on electromagnetic induction for their operation, as do many electrical isolation safety switches. Electric motors also rely on the electromagnetic effect, and could not exist without it. Electrical engineers and others are always concerned about electromagnetic interference and when laying out the routes and locations of wiring, motors, transformers and other electrical devices in buildings and vehicles and other equipment.
We are also starting to see inductive recharging in devices for convenience. My electric toothbrush, for example, sits in a stand and is inductively recharged without me having to plug it in. By contrast, my electric shaver has to be plugged into its stand – I find it much easier to pick up and use my toothbrush than my shaver.
The Wireless Power Consortium (wirelesspowerconsortium.com) has developed the Qi (pronounced “Chee”) standard for inductively recharging devices. A recharging pad contains the primary induction loop – the power “transmitter” – and the complaint device contains the secondary loop – the power “receiver”. Simply placing a complaint device on the pad initiates recharging, which continues until the device is full, or it is removed from the pad. The low power Qi specification can transmit 5W up to 40mm, which is enough to recharge a mobile phone or tablet computer. The medium power Qi specification can transmit up to 120W.
Several new mobile phones and tablet computers like the Google Nexus 7 Tablet are advertised as being Qi compliant, and so putting them on any Qi recharging pad will recharge them. “Qi hotspots” are also starting to be seen in cafes, airports and other public places. I also expect to start seeing them in schools and on people’s desks soon.
Life would be much easier for me, if I could simply put my phone and tablet computer down on my desk to recharge them while I am working. I look forward to seeing Qi hotspots all round Macau in the future, and hopefully relatively soon.