June 8, 2007 at 8:36 PM ET
Andre Kurs' credit cards still work. So do the gizmos that he carries around with him. And the last time he checked, his head hasn't exploded.
That answers some of the questions that have popped up in the wake of this week's revelations from Kurs and his colleagues at the Massachusetts Institute of Technology about a new scheme for transferring electric power without wires. But there are plenty more questions yet to be answered: Is the method now known as "WiTricity" really, truly safe over the long term? Can it compete with other strategies to generate, transmit and store electrical power? How long until I never have to plug in my laptop again?
Right now, none of those questions is easy to answer. Kurs, a physicist at MIT, said the research group has patents pending on the technology and is just beginning to look into how it might be commercialized.
In one sense, the researchers are going where many scientists have gone before: Most famously, Nikola Tesla tried to set up a power-beaming tower a century ago, but was never able to get it up and running. One company, Splashpower, already offers a wireless recharging system, although you have to set your specially equipped gizmos right on a pad to fill them up with juice.
In another sense, the MIT technology - which depends on coupled magnetic resonators to send power more efficiently than can be done through inductance alone - pushes the envelope beyond what Tesla had in mind.
This week's reports indicated that the WiTricity transmission system had a power efficiency of about 40 percent over a distance of 7.5 feet. Kurs pointed out, however, that the efficiency rose past 50 percent if the distance was reduced to just below 7 feet - and that at closer distances, efficiencies of up to 70 percent were achieved. "That's competitive with rechargeable batteries," Kurs said.
The health issue will take a longer time to resolve. "Without a proper study, which includes effects of long-term exposures, it is inappropriate to make claims of safety for this," Frank Shellock, an expert on the issues surrounding magnetic resonance imaging, told me in an e-mail.
In response, Kurs told me that "the fields involved are much weaker than the fields that are involved in MRI." He pointed out that the emissions were well within IEEE's internationally accepted standards.
That's not to say that Kurs and his colleagues take the health questions lightly.
"We're not experts in physiology," Kurs said. "We agree that this is something that needs to be examined carefully. But even if it turns out that 1 mHz or 10 mHz is dangerous for infants, we can still tailor the system to work around that."
Over the past few days, Kurs has truly had to deal with questions about whether getting too close to the electromagnetic coils would make your head explode, or whether they could erase the data on a credit card's magnetic strip. He said his head and his credit cards were all safe, even though he was nearly touching the coils during the MIT experiments.
"There were no effects," Kurs told me. "Nothing funny happened, my hair didn't stand up. ... I had my credit cards. They were in my front pocket, which is a few inches away from the equipment."
For another perspective, I turned to Kelly Classic, media relations liaison for the Health Physics Society and a medical health physicist at the Mayo Clinic. Here's her e-mailed response:
"This idea is very interesting and fun. I know that I personally would like to have this available, especially for my laptop.
"I reviewed the materials and also sent them to one of our non-ionizing radiation specialists (his name is Ken Foster, but he preferred that conversations be between you and me) and here are some of our general thoughts (Ken also just wrote a paper on WiFi hazards, and his information sheet on this is on our Web site.)
"First, when we’re talking about health effects, it boils down to how much of the energy is absorbed in our tissue and is it enough to cause damage (by heating or another mechanism). So, most times when we’re talking about radiofrequency radiation (electric and magnetic fields), we talk in terms of a Specific Absorption or Specific Absorption Rate (SA or SAR). It’s a bit like ionizing radiation when we say you can be exposed to X rays, but how much was absorbed? It is the amount that is absorbed that is of interest for biological effects.
"From what we know, It doesn’t appear that human health effects would be an issue from the low-frequency field (10 MHz or 1 MHz) being discussed. These fields do not interact strongly with the human body and, according to their measurements, all of the fields (electric, magnetic, etc.) produced are below international safety limits for that type of field.
"They mention that in one of their experiments there was no interference with other devices (like a cell phone). This might need to be investigated a bit more, especially with respect to use in a medical setting. We’d want to know whether the field could cause an erratic response in some medical devices (i.e. pacemakers, EEG units). More recent reports about cell phones and Wi-Fi in medical settings indicate that they are not an issue in a medical setting, but this is a different frequency and it would be prudent to do some checking before its widespread use.
"The authors have a statement - 'The experimental setup radiates roughly 5 watts when transmitting 60 watts over a distance of more than seven feet ... this is equivalent to the power radiated by a few cell phones' - that is quite misleading, though we understand they are trying to relate this to a device with which we are familiar. But the application they are discussing, WiTricity, is a 'near-field' application, and talking about radiated power is meaningless in this context. These coils are not 'radiating' fields to the extent that someone standing at a larger distance is affected, and the number has no connection with the energy transfer. The comparison with cell phones is also misleading. The potential for biological effects is not even thought to be similar when comparing 10 MHz to the 850 or 1950 MHz of cell phones.
"There is also a misleading section when the authors talk about transferring 60 watts into the light bulb. It's really not clear how much energy was transmitted, but it was enough to power a 60-watt light bulb, and the energy transmitted to do that would not need to be much (essentially meaning that there isn’t that much energy 'freely roaming' between the transmitter coil and the receiving coil, which is also reassuring from a health effects standpoint)."
When I ran these remarks past Kurs, he responded thusly by e-mail:
"Concerning the power radiated: Devices containing alternating currents generally radiate, and ours certainly does. As Ms. Classic points out, this radiation occurs in the far field and is not relevant to health issues of humans standing close to the device. We mentioned the power radiated not because of its relation to health, but because it is considered as power lost in our scheme, and due to concerns about pollution of the electromagnetic spectrum. Note also that the 5 watts cited can be considerably reduced, as we point out in the article.
"About the amount of power transferred, we properly calibrated our experiment to make sure that the light-bulb was indeed being fed 60 watts."
You'd think this week's news would be heartening to any gadget geek. But our own gadget guru, Gary Krakow, isn't impressed just yet. In addition to the health issue and the efficiency issue, Krakow brought up a bigger philosophical point - which I'm sure Chris Eldridge and some of our other Cosmic Log regulars would share. Here's some of what Krakow had to say:
"The future of electricity is that our homes – and cars (Prius, etc.) will generate electricity for our own, personal use. ...
"My weekend home is cooled/heated by a heat pump – now 20 years old. I pay something like 40 percent of what a normal 'all-electric' house pays for air conditioning and heat. Just kick that idea 'up a notch' – put a small windmill (etc.) in your neighborhood for 20 to 30 homes – and you no longer need high-tension power lines.
"Those high-tension lines produce huge magnetic fields. How about the MIT guys standing under those to light their bulbs? They can also see what those fields do to the grass beneath the wires. ..."
So what do you think? Feel free to chime in on our discussion board or in the comments section below.