CU professor Zoya Popovic helps develop innovative thermometer

BOULDER — To develop a noninvasive internal thermometer, University of Colorado professor Zoya Popovic had to combine several disciplines and bring together medicine with electromagnetics, radio frequencies and algorithms, plus attract several investors to provide the funding.

Popovic, distinguished professor of electrical, computer and energy engineering at CU Boulder and a CU professor since 1990, and her team of doctoral students developed a small wearable non-invasive and purely passive sensor that can measure temperature several centimeters below the skin. The sensor can be used for situations such as  inflammation, tumors, brain tissue after an injury or stroke, and possibly lung temperature for symptoms associated with COVID-19.

“You need to know a lot of different things, so that’s why it’s not been solved. There is nothing out there that can do this that can measure internal body temperature,” said Popovic, who holds a PhD in electrical engineering from California Institute of Technology in Pasadena, which she earned in 1990, and a bachelor’s degree in the same field from the University of Belgrade, Serbia, Yugoslavia, which she earned in 1985. “I’ve talked to a lot of doctors. They’ve convinced me that this is worth putting time into.”

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Popovic pitched her innovation among 14 university science, engineering and bioscience innovators in November 2020 during the Lab Venture Challenge, hosted by Venture Partners at CU Boulder to fund projects that have commercial potential and can be turned into business ventures, while also being scientifically supported. Twelve grants were awarded, and Popovic and her business partner, Jim Pollock, received one of them for the top amount of $125,000.

Pollock, an entrepreneur with an electrical engineering degree from Massachusetts Institute of Technology, created a company, LumenAstra, in November 2020 specifically to bring the project to fruition, and serves as its chief executive officer, while Popovic is chief technical officer. With his company, he was able to license a patent from the university and obtain sole rights — the patent had been issued in December 2019.

“The venture funding will help with first steps,” Popovic said. “The company is just beginning, but we already are getting some funds to develop the technology, from agencies interested in developing and commercializing the technology.”

Popovic didn’t originally set out to develop an internal thermometer, working primarily for the past 15-plus years with her graduate research students on high-efficiency radio transmitters for cellular and satellite communications, as well as radar and heating. She graduated more than 60 doctoral students, each with a different project within the fields of radio engineering and applied electromagnetics. She typically writes a proposal for a problem that needs to be solved, obtains funding from the government — such as the National Aeronautics and Space Administration, Department of Defense, Department of Energy, National Science Foundation and National Institute of Standards and Technology — large companies, small businesses and foundations, and hires graduate students or post-doctoral fellows to conduct the research, which often becomes their dissertation topic. Her average amount of funding per year has been about $1.5 million over the past few decades.

“It’s effectively like running a small company but organized differently,” Popovic said.

Popovic originally worked on making cell phone tower transmitters more efficient and, because she understands radio frequencies, was contacted about a problem with soldiers overheating under heavy training or in extreme climates. She made a prototype thermometer, came up with some theories and published a paper — and then she got excited about the prospects of the project in terms of its many possible applications to help people. She figured out how to measure internal body temperature using natural emission of tissues in the lower microwave frequency range that can penetrate the skin (the wavelength is larger and about the same size of that for a cell phone frequency) to about 5 centimeters deep.

Popovic’s device works in the quiet radio band used by radio astronomers, where the interference is low and transmission isn’t allowed.

“We can use this band because it gives us penetration and can measure through most tissues,” Popovic said.

The device consists of a probe antenna connected to a sensitive receiver. The signal at the output of the receiver is processed using algorithms to differentiate the tissue layers and their temperatures.

“My goal is to estimate the temperature of the tissue layers under the skin. One measurement is the total of all the tissues,” Popovic said. “You have to do math to determine the temperature of each layer. To do that, you need to know electromagnetics.”

Popovic wrote a proposal to the National Science Foundation and received funding for her research from 2014 to 2017. She hired two graduate students to prove the principle, develop the device and take measurements on tissue phantoms.

Recently, Popovic wrote another proposal and received three more years of funding from NSF for a new PhD student to work on this topic for his dissertation. In addition, the receiver was improved further and designed on a chip, which will help with commercialization, allowing for testing on humans and making the product cost-effective and wearable, Popovic said.

Popovic gets involved in projects like the internal thermometer to be able to work closely with her students.

“I mostly enjoy working with students, with young people,” Popovic said. “I know they’re smart, and I turn them into experts and everyone wants to hire them. … I like the teaching, but most of all, I like to work individually with students.”

Rob Streeter, a PhD electrical engineering candidate in his second year, is part of the research team for the internal thermometer. Before deciding on a school, he scheduled time to meet with some of the professors at CU Boulder

“Zoya was wildly intelligent but very energetic and had the coolest project,” Streeter said, adding that he liked the mix of disciplines it included. “What makes Zoya a great professor is her ability to identify what her students are passionate about and make it work as a project. She has incredible energy to devote to her students.”

Philip Zurek, a PhD electrical engineering candidate in his fifth year, likes how Popovic “cares really deeply about her students,” he said.

“That’s what drives everything she does. She’s willing to put in plenty of time to help students reach their potential,” Zurek said, adding that Popovic is available before and after class and extends her office hours. “It shows in the quality of students who come out under her professorship and what they end up achieving in their careers.”

The students, once they graduate, do not have trouble finding a job and instead have trouble choosing which one to take, Zurek said.

“They know Zoya is able to produce knowledgeable students, so that has never been a problem for anybody,” Zurek said.

Popovic was named a distinguished professor in 2010 and Lockheed Martin Endowed Chair in 2017. She developed five undergraduate and graduate electromagnetics and microwave laboratory courses and coauthored “Introductory Electromagnetics,” published in 2000, for a junior-level electrical and computer engineering course.