Magnetic resonance power transfer may be one step closer according to a report carried by the BBC, and has been brought forward by Physics Prof. Marin Soljacic at MIT. WiTricity is a company founded by Soljacic and a number of his fellow researchers that aim to bring this technology to the market place.
The up spin is that small items such as cell phones, computers and other electronics, even televisions, may be recharged without the use of cables and perhaps doing away with batteries or at least making them smaller. In lab experiments they were able to transmit power to a 60W bulb using a magnetic resonance field generated over two meters away with 40% efficiency – which was an impressive feat. However, being 40% efficient is very poor compared to almost zero losses by just plugging the item directly into the mains, so any loss in efficiency is a less positive outcome thing, especially if your power generation uses greenhouse gas loaded fossil fuels.
In terms of health, their published reports say that their magnetic fields generate only 0.0001T (Tesla) and magnetic fields of up to 1T (ten thousand times bigger) have been used on humans in magnetic resonance imaging machines. The Earth’s magnetic field strength is 30-60 microTesla (0.00003T to 0.00006T), so their machine has a magnetic field strength about 3.3 more than this when it provides a ‘few Watts’ of power transfer according to one of their papers (Efficient Wireless Non-Radiative Mid-range Energy Transfer).
In another paper (Effect of Using Capacitively-loaded Loops and Lowering the Operating Frequency on Field Strengths and Power Levels), they calculated the field strength 20cms from the transmitter and determined at 1MHz the efficiency was 60% and levels were within IEEE standards. When the transmitter and receiver were not aligned, the efficiency was reduced.
Taking a look at a World Health Organization (WHO) fact sheet, it seems that the WHO proposes that people should not be exposed continuously to levels exceeding 40mT (0.04T, 400 times bigger than the number quoted in the science paper) or 0.5mT (0.0005T, 5 times bigger than the number quoted) if you have implanted electronic devices such as a pacemaker. The WHO information also states, “It is not possible to determine whether there are any long-term health consequences even from exposure in the millitesla range because, to date, there are no well-conducted epidemiological or long-term animal studies”. The WHO also says that people moving within a higher strength magnetic field could experience nausea. However, there could also be sensitive people who are likely to be affected at much lower levels than an “average” individual.
If you are a highly sensitive person or have a pacemaker, you maybe should consider sticking to recharging your electronic toys with the old fashioned method of sticking the plug in the wall and maybe WiTricity should conduct more tests with a wider cross section of people (not animals) – ranging from “average” to highly sensitive.
Trevor Williams is a University of Victoria Mechanical Engineering PhD candidate specialising in renewable energy, power grid modelling and plug-in hybrid electric vehicles. He has a bachelors in Aeronautical Engineering, a Masters in Management Science and over 23 years international experience in the space industry, having worked on Earth observation and telecommunications satellites. He is the author of the Eco-Geek blog.
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