Researchers overcome barrier to shrinking wireless devices

James Bond-style technologies such as cell phones the size of earpieces and invisible sensors that detect toxins are closer to reality. U-M researchers have figured out how to build smaller wireless systems while still retaining the range and power efficiency of larger systems.

One obstacle to further shrinking small wireless devices has been the difficulty in fitting all the components onto one chip, but researchers have built a tiny silicon-compatible antenna and frequency resonator to do just that.

The antenna and resonator are two of the most problematic "off-chip" components in wireless systems, requiring large amounts of space off the chip, thus limiting how small a device can be built.

Until now, small antennae weren't power efficient and resonators were not accurate, says Kamal Sarabandi, director of the radiation laboratory department in electrical engineering and computer science (EECS). His research group developed the antenna.

The technology is being created for use in environmental sensors but could be applied to cell phones, laptops and other wireless devices, says Michael Flynn, head of the wireless interface group.

"We could have cell phones almost the size of an earpiece," Flynn says. "You could have sensor nodes that are almost invisible; you could just sprinkle them around."

Rather than use a traditional wire antenna, researchers built a slot antenna. Instead of a metal wire, the entire plane in a slot antenna is covered with metal, leaving only a slot or groove bare. Wire surrounds the groove so it is much more effective at radiating electromagnetic waves in a small antenna, Sarabandi says. Because of the shape, the wireless system does not need a network to match the antenna frequency to the rest of the electronic device.

Intel is interested in using the technology in laptop computers, so Sarabandi's group has been talking with the company about a possible collaboration.

The second component U-M scientists have replaced is the quartz frequency resonator, which allows a wireless device to focus on a specific signal and ignore others. The work was done by EECS associate professor Clark Nguyen's group.

Instead of quartz, scientists used MEMS-based technology to build the resonator so it can be fitted onto the chip. It functions similarly to the way the rim of a wine glass thrums when flicked by a finger. The wine-glass rim design helps retain the purity of the signal.

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