Dear Colleagues

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Why should you read this short note below about transferring power wirelessly? Well; like it or not, it is definitely a method that will be used extensively in the future. So, another useful concept to consider in your next design and to add to your engineering toolbox. Maybe not today, but very soon.

Transferring Power Wirelessly

Nikola Tesla – a famous electrical engineer working over a hundred years ago, had a dream of transferring power wirelessly using Tesla coils. He believed in wireless power passionately. Well before the world was wired – and well before the trillions of dollars of investment in copper cabling infrastructure that we see around us now. Over a hundred years ago, no one dreamed of stringing power lines throughout the world. Tesla thought of installing wireless power everywhere rather than clumsy copper cables. Now, I have some doubts about whether his dream will be realized in terms of long distance transfer of power. But for short distances? Well, a brilliant idea whose time has definitely come. At present, we are tethered to the wall, by a deluge of power cables. So the last few metres from the wall to the appliance needs to be bridged – and soon. I am always aghast at the mishmash of cables tying our varied electrical devices to the power cables. Wireless data communications has made a massive difference to the data side. But we need some action on the power front for short distance transfer of power for the last few metres.

The principle of the short distance transfer of power is based on the (inevitable) oscillating electric current running through a coil. The magnetic field is then coupled to another resonant coil (separated by free space). Induction works well over short distance. Resonance is the key. Think of the opera singer breaking a wine glass with her singing at precisely the right frequency or note. The term for this technology is based on stuff we knew from the eighteenth century, which is called highly coupled magnetic resonance. This operates well up to 2.5 metres. Power can be delivered through walls and multiple devices can be operating at the same time. These resonators can be conveniently put in walls and ceilings in a home or office. One can then simply recharge one’s phone and computer without any power contact, which is similar to the principle of the toothbrush induction charger but over far greater distances of a few meters.  Remember we are not “sending electricity through the air” as such but relying on magnetic coupling. Only another resonant coil in the vicinity can capture the energy. Hence this is considered pretty safe as only a magnetic field is used. Human beings appear like free space to a magnetic field and the intensity of the magnetic fields are the same as that of the earth. At the end of the day, this is both safe and convenient.

Another interesting application of power through the air is harnessing TV and radio signals which also have considerable power. A TV station broadcasts at over a megawatt. A radio or TV signal is detected through an antenna and then rectified to provide a small DC current which can power a device. This has been demonstrated by Intel and the University of Washington. I still remember the days of crystal radio where one could listen to one’s favourite station and not use any power. A reasonable distance away from a TV tower you can supply up to 100 microwatts. TV towers are always there. Power requirements of smallest devices are now minimal. One only needs 20mW to keep a mobile phone going in standby mode. Many consumer electronic devices which power down can use this energy to keep going with a small reptilian brain still ticking along keeping an eye on things (such as a clock). There is so much energy in the environment to harness.

I must confess to some slight nagging doubts about the impact of all this wireless transmission – data and power on our health. But so far, no real evidence has emerged apart from some disquieting evidence of cancer with excessive use of mobile phones. But this is an issue we need to keep a weather eye on.

As we all know - in the world today, we do need energy and even more convenient transmission of it wirelessly, is appealing. As the famous poet, William Blake, wryly observed:

Energy is eternal delight.

Good installation practice for Programmable Logic Controllers

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Yours in engineering learning

Steve