There is an urban legend which I can actually vouch for as actual fact. At the BBC Droitwich transmitting station in Worcestershire, England, is a 400-kW (ERP) AM transmitter with its carrier set at a very accurate 200 kHz. During WWII, the transmitter was the main source of information for embattled Europe - reaching, as it did, to the South of France and deep into Germany, and carrying coded messages for the underground. The 50+ acre site houses the two transmitter buildings (the second for a MW transmitter with separate mast), the huge multiple-conductor T-aerial, and grass -- lots of grass.
The BBC rented out the site to a local farmer.
One day this guy was talking with his mates in a local pub and a BBC employee heard him boast that he never paid for his lighting. A couple of days later he got a visit from a policeman and a senior BBC manager. It was absolutely true. With the light switches turned off, every fluorescent in his cottage glowed brightly. He was not charged with any offence; he certainly wasn't "stealing electricity" (which is the quaint way someone in the UK is charged for using a public phone without payment, in the days you could tap a number using the handset cradle switch); he was doing what any radio amateur would have done years ago to check operations with a glowing open-circuit neon lamp.
If you've ever driven to a high-power radio station (any band, any type of modulation) you will have found that in the last few hundred meters the transmitters completely take over your car radio. In most cases, it does have to be turned on, but I have heard the effect once when the radio was turned off. What is happening is that you have entered the direct magnetic field of the station (which is carrying the same modulation as the radiated signals).
So, we know that RF magnetic fields can transfer energy and there are ways of making it quite directive. A small village in the South of France is powered by the magnetic component of an RF signal from the top of a cliff above the village: about a 150m path.
And there have been many other experiments conducted over the years, primarily in France, Japan and the USA. Many more of those experiments are out of the public eye, and the last open discussion I have seen was nearly a decade ago in, "Status of international experimentation in wireless power transmission" by G E Maryniak, published in Fuels and Energy Abstracts (Elsevier), Volume 37, Number 6, November 1996, pp 442 - 442(1). Much of the work in progress is for space-based systems, and there are, of course, ongoing potential weapon discussions.
It was therefore rather a surprise to read a headline about RF power transmission being rediscovered by an Assistant Professor at MIT, Marin Soljacic, who is presenting a paper on the subject at the American Institute of Physics meeting in San Francisco later this week.
The good Assistant Professor wants, he says, to use the "part of the electromagnetic field that is non-radiative (sic)." Wow, what a scientific breakthrough -- it would make Tesla roll in his grave with anger! And let me tell you that I would not be in the same room as a device that was, as he hopes is possible, producing enough energy to recharge my laptop.
On the other side of the planet, in Australia, there is talk of finding some magic frequency that somehow does not harm life, and Dr. Geoff Anstis (UofT, Sydney) worries about the analogy with mobile phone health concerns. He feels that decades of use would have to pass before you might "be happy that there isn't a significant problem."
I will happily go along with that attitude. And it's one of the reasons why there won't be a cell phone under the tree this Christmas for my 12-year old -- even if every other child in her class has one. That kind of peer pressure does not work on this Dad.
But, after all these years, it is good to see MIT following up on the Broadcast Power episode, "The Positive Negative Man" from The Avengers where, after removing the baddies, Emma and Steed got stuck to one another on his oil-belching Bentley. "We're inseparable." That's magnetic power for you.
