Expanding the Data Highway

Electrical engineer explores next-gen transistors and alternative frequencies to streamline future network activity

By Derrick Bang

DAVIS, Calif.; July 10, 2015 – Omeed Momeni was a childhood tinkerer, forever soldering transistors, resistors and capacitors onto circuit boards. He still remembers the moment of elation, after building an FM radio transmitter and receiver that actually worked.

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Omeed Momeni, assistant professor in the UC Davis Department of Electrical and Computer Engineering.

By the time he entered high school, Momeni’s interest had migrated to computers, particularly after his father, a civil engineer, bought one for the family.

“I was fascinated,” laughs Momeni, an assistant professor in the UC Davis Department of Electrical and Computer Engineering. “I wanted to know what was going on inside that box; how did it makes graphics and do all those other things, with transistors and a circuit board?

“If you look at a car engine, you can see things move, and you can get an idea of how it works. But there’s nothing to ‘see’ inside a computer.”

Momeni’s mounting interest soon became a lifetime career; he completed his undergraduate work in electrical engineering at Iran’s Isfahan University of Technology, and then set his sights on the United States. (Although he grew up in Iran, Momeni was born in the U.S., where he and his family remained until he was 5, while his father completed his PhD work at Kansas State University.)

“I always wanted to return to the United States, because everybody knows that it’s the best place for higher education and top research,” Momeni insists. “The world’s best research, in many fields, takes place right here.”

He spent a few months at Arizona State University, then switched to USC to finish his master’s degree. “The move to USC came about because I also got a job as an engineer at NASA’s Jet Propulsion Lab in Pasadena. I designed L-band transceivers for synthetic aperture radars, and high-power amplifiers for mass spectrometer applications.

“But that work didn’t relate much to my desired research field, so after I completed my master’s, I accepted an offer to join Professor Ehsan Afshari, at Cornell’s School of Electrical and Computer Engineering. I was his first PhD student, and I helped start his research lab.”

Momeni has very fond memories of his PhD work, which he completed in 2011.

“Those four years were the happiest time that I’ve ever spent during my career. When you’re a student, you’re responsible solely for doing your research; you don’t have to worry about anything else … and that’s a working environment that you’ll never get back again!

“A PhD is a time of your life when you can fully apply yourself to something you want to do, because you like it, and because it’s truly significant: something that you’ll later be able to look back on and say, I did the best I could, something I’m proud of.”

Momeni clearly embraced that level of dedication; he won 2011’s Best PhD Thesis Award from Cornell’s Department of Electrical and Computer Engineering.

Several offers arrived after he finished his doctorate, but Momeni knew where he wanted to be. Momeni joined the faculty at UC Davis in 2012.

“UC Davis was at the top of my list, because its ECE department is famous and well-respected in the circuits field. Lots of faculty members work on different branches of circuits, which is ideal, if you wish to start your research in the same field.

“And we have a high-frequency lab — the Davis Millimeter-Wave Research Center — that’s unique in the country. It has equipment that most universities can’t even dream of!”

“Consider smart phones: We download and upload, and there’s a certain speed related to such activities, perhaps 50 megabits per second. Individual phones communicate with neighboring towers at different frequencies between 800 MHz and 2.5 gigahertz (GHz). The data communication speed is related to that frequency range and the bandwidth they can occupy. All smart phones operate at that frequency range, so it’s extremely congested.

“With the upcoming arrival of 5G and even 6G networks, the necessary goal is to increase the data rate, which means we need to increase the frequency. But the transistors used on these small chips cannot handle higher frequencies as well, so our challenge is figuring out how to incorporate the transistors in a circuit so that the system can handle higher frequencies. Right now, we’re looking at frequencies of 30, 60 and 90 GHz, and even 200-700 GHz.

“And we want to put all these capabilities onto small silicon chips, in order to produce hand-held devices for communication, imaging, sensing and spectroscopy. This also opens all sorts of other possibilities, such as disease detection via devices that would analyze a person’s exhaled breath.”

The inherent problem is that the physical characteristics of the transistors themselves have hit a wall. Today’s transistors are so small that their dimensions are comparable to the size of silicon atoms; fundamentally, then, the transistors can’t get any smaller.

UC Davis Prof. Omeed Momeni

Omeed Momeni, assistant professor in the UC Davis Department of Electrical and Computer Engineering.

“That’s the challenge,” Momeni agrees. “We’re trying to come up with new ways of using the same silicon transistors: new systems, at new frequencies, that nobody has thought possible.”

Momeni’s efforts already have attracted the attention of the National Science Foundation’s Division of Electrical, Communications and Cyber Systems, which in January awarded him a five-year CAREER grant of $500,000.

“For the grant, we’re tackling the problem of integrating systems on a single chip, because as the frequency goes higher, the signal loss increases. Transmitters need antenna arrays to boost radiated signal power, which in turn require phase shifters, to ‘tune’ the direction of the beam … but phase shifters at higher frequencies are extremely lossy.

“We’ve proposed a system that will bypass phase-shifters, and will exploit other signal properties — specifically, traveling- and standing-wave properties — to do the same thing as a phase-shifter, but with significantly lower loss. That’ll make it possible for higher and higher frequencies to radiate with much better efficiency and superior performance.”

Although devoted both to his research and teaching, Momeni also believes strongly in outreach. He’s deeply involved with the UC LEADS (Leadership Excellence through Advanced Degrees) Program and the MacNair Scholars Program, both of which encourage under-represented students to enroll in post-graduate research.

“Such students could perhaps become the first people in their families to earn a PhD,” Momeni explains, “which makes them excellent role models for their extended relations and friends. I had an undergraduate from UC Santa Cruz here last summer, and we worked together, and it went really well. When he graduates later this year, I know he’ll continue on toward a master’s degree.”

Aside from his one-on-one interactions with students, Momeni has served on panels for both UC LEADS and MacNair, and also worked as an event judge and in other capacities.

“It’s essential work. You don’t get paid for it — nor would I expect to — but it’s food for the soul.

“It makes you feel like you’ve given back, and done something important for the surrounding community.”