Researchers Win $3.5 Million to Improve Wireless

A Georgia Institute of Technology research team has received a $3.5 million grant to use tiny, power-saving analog chips to develop portable communications technology capable of scanning a broad range of radio-frequency (RF) bands for open channels.
The resulting analog spectral processors (ASP), to be developed at the Georgia Electronic Design Center (GEDC), would have a range of uses, from aiding battlefield communication to enabling cellular phones to find less-crowded frequencies.

ASP technology is related to the “cognitive radio” (CR) concept, which involves utilizing less-busy frequencies for optimal cell-phone and radio performance.

Farrokh Ayazi, a GEDC researcher who is co-director of the Center for MEMS and Microsystems Technology (CMMT), is principal investigator on the project. The project, led by BAE Systems Inc, has received $11 million from DARPA, of which $3.5 million will go to Georgia Tech over three years. Purdue University is also on the BAE Systems team.

“The project’s goal is basically to create a small, low-power handheld device that combines a spectrum analyzer and a truly powerful communication device,” said Ayazi, who is an associate professor in the Georgia Tech School of Electrical and Computer Engineering (ECE). “The spectrum analyzer would scan the frequency spectrum all the way from 20 MHz to 6 GHz to find empty spots—channels that are receiving less use.”

This extensive range would allow ASPs to be useful in a range of applications, Ayazi said. Such a wide-band spectral processor would help soldiers switch channels quickly to avoid enemy jamming measures at military-use frequencies, while also enhancing military and civilian communications at other frequencies.
"Prof. Ayazi’s award continues to establish the GEDC as a world leader in the development of technologies for cognitive radio applications,” said Joy Laskar, GEDC’s director and the Schlumberger Chair in Microelectronics in the School of Electrical and Computer Engineering. “The GEDC is a major player in the IEEE 802.22 CR standard, and this award will look to provide critical enabling analog-technology blocks that should impact both the DoD and commercial markets.”

Two other DARPA-funded teams are also working on spectral processors. A Rockwell-led team includes the University of San Diego, Stanford and Cornell University, while Honeywell is leading a team includes the University of California Berkeley and the University of Pennsylvania.

Central to the BAE Systems/Georgia Tech/Purdue effort will be extensive use of analog micro- and nano-mechanical circuits, rather than digital circuits, in designing spectral processors. In the analog domain, chips and other devices work by moving between signal levels in a continuous fashion, while digital chips and devices move between separate and discontinuous levels and do not recognize the transition between levels.

Micromechanical circuits have a number of advantages over electronic digital chips. They typically use far less power and run cooler than digital circuits, and are also smaller, offer much better communications quality, and are relatively inexpensive to manufacture.

“What we’re proposing is to solve the cognitive-radio problem in the analog domain rather than the digital domain, with virtually no added power,” Ayazi said.

To develop analog spectral processors, the Georgia Tech team will use micro-electromechanical systems (MEMS), which are tiny analog machines that operate at the microscale – one millionth of a meter.

To scan and move swiftly between far-flung frequencies, the researchers will use MEMS technology in constructing arrays of micro-mechanical resonators, also known as bulk acoustic-wave (BAW) resonators. These devices play a role in finding and holding a radio-frequency signal.

In constructing extensive arrays of signal-seeking BAW resonators, researchers must choose between two approaches. One is to use resonators to create an array of many fixed filters—each tuned to a specific frequency—that will cover the entire spectrum. The other approach involves tunable filters that can move back and forth to some degree between frequencies. Ayazi said that further research will determine the optimal approach.

The structural material of choice for acoustic-wave resonators will be nano-crystalline diamond, micro-machined to reach frequencies of up to 10 GHz.

Researchers will also use silver, the highest-conductivity metal, in micro-machining the analog arrays. Silver will aid in achieving high-quality inductors and capacitors, the components that aid tuning to a specific frequency.

“This is a very exciting challenge, and it also involves a lot of advancement in the packaging technology for MEMS,” Ayazi said. “These ultra-small micro-mechanical components must be free to move, so the packaging is totally different than the traditional integrated circuit.”

He explained that the packaging material -– the substance that holds and protects the ASPs –- cannot come into contact with the vibrating structures of the micro-mechanical resonators. Working at microscale, researchers must create a small cavity on top of the electronics to achieve a hermetic environment that will seal out damaging moisture.

A key to ASP packaging will be advanced organic materials that possess low signal-loss properties and are strong and semi-hermetic. Working with Prof. Paul Kohl of Georgia Tech’s School of Chemical and Biomolecular Engineering, Ayazi will use specially-tailored polymers to develop an effective package for the filter arrays.

“The combination of all these elements will eventually produce an array of highly improved tunable filters,” Ayazi said. “We are basically looking for orders of magnitude improvement in performance, size and cost. The ultimate goal is to integrate ASP’s with high-speed electronics on a single chip and bring unprecedented capabilities to the wireless world.”