Researchers Zap Microwave Interference

Nov. 18, 2003 -- Have you ever noticed how sometimes your kitchen microwave oven zaps more than last night's leftovers?

In some homes where wireless technology — cordless phones, Wi-Fi wireless computer networks, and cell phones — rule, the common kitchen appliance can be a noisy nuisance.

That's because microwave ovens emit high-energy radio waves that are roughly in the same or nearby frequencies used by those wireless systems.

Microwave oven makers traditionally try to mitigate the problem by adding internal shielding — basically, metal cages to trap microwave emissions that might cause interference.

But researchers at the University of Michigan in Ann Arbor may have stumbled upon a simple, more elegant solution.

Magnetically Managing Microwaves

Professor Ron Gilgenbach, along with professor Yue Ying Lau and graduate student Bogdan Neculaes, had been researching how to make better magnetrons — the devices that create microwave energy in ovens and, more importantly, radar systems.

With support from the U.S. Air Force Office of Scientific Research, the team had hoped their study would help create more efficient radar systems for the military.

"We were studying the noise of magnetrons which affects accuracy of radar [systems]," says Gilgenbach, a professor of nuclear energy and radiological sciences. "Any improvements would allow soldiers to detect smaller missiles and incoming weapons at greater distances."

And killing the "noise" — the random radio waves along the 2.4 gigahertz frequency — turned out to be a fairly simple trick, according to the work of Gilgenbach's team.

The Univ. of Michigan team discovered that by placing ordinary magnets in a specific pattern along the magnetron, they could sharpen or focus the microwaves into a single, exact frequency.

Not Radars, But Radar Ranges?

The researchers admit that they will need to study further how this may be incorporated into more efficient radar detection systems. But Gilgenbach and others note that the biggest impact of the technology may be on the consumer side.

"The invention at the University of Michigan is significant," says Jim Benham, president of L-3 Electron Devices which makes microwave devices for commercial and military applications in San Carlos, Calif.

And while L-3 will help the University scientist test the technology for military and commercial radar systems, Benham says that "None of those are huge marketplaces."

However, "The opportunity exists in the commercial microwave oven world to use this [technology]," says Benham. "I know from personal experience that microwave oven makers are very interested in any technology that puts out less interference with cordless phones."

And what makes the university's technique even more compelling for eventual commercial use: It can be easily added to current magnetron production without a lot of cost.

An Aid for Future Wireless Kitchens

And the prospect for less noisy home microwaves could have some big payoffs — in the near future.

For now, typical microwave ovens doesn't pose too much of a problem for wireless computer networks, says Dennis Eaton, chairman of the Wi-Fi Alliance, an industry group that certifies the popular wireless standard.

"Browsing the Internet, e-mail, or most of the things we do today with a wireless network of computers — those are sporadic communications," says Eaton. "If you drop a packet of data due to interference, it gets recovered."

But the new microwave technology could really be helpful as home networks are used for more than just surfing the Web for data.

For example, more home entertainment devices are adding Wi-Fi capabilies, allowing digital audio and video to be shared between rooms wirelessly. And such entertaining uses will require wireless networks that are far faster and much less tolerant of interference.

"If you're watching digital video wirelessly and a data packet drops, you're going to notice picture degradation," says Eaton. "That's when things like interference from microwave ovens and cordless phones become real apparent."

And with more computer companies and consumer electronics makers adding wirelessly capabilities into their product, research from Gilgenbach and his team could soon find a new place to call home.

The team's research work has been published in a recent edition of Applied Physics Letters, a publication of the American Institute of Physics.