Senior thesis lights the way to promising new sensor technology

Written by
Scott Lyon
Nov. 4, 2019

Undergraduate researchers in electrical engineering have innovated on a new hybrid imaging technology, with potential applications in biomedical sensing, laboratory imaging and short-distance wireless communication.

Alumnus TJ Smith, first author on a paper outlining the team's findings, presented the work at the 2019 IEEE European Solid-State Circuits Conference in Krakow, Poland in September. He was joined by his co-authors and former undergraduate collaborators Anna Broome and Dan Stanley, both of whom are now graduate students at Stanford University. All three researchers graduated from Princeton in 2018.

"The session chairs were surprised that the paper came out of an undergraduate senior thesis," said Kaushik Sengupta, associate professor of electrical engineering and the students' co-adviser. "More so because it was the highest rated paper in the subcommittee." The paper was invited for a journal submission in IEEE Solid-State Circuits Letters.

The team created a system that emits and senses electromagnetic radiation at elusive frequencies between microwaves and infrared light. Because of their ability to effectively "see through" thin layers of material, these terahertz frequencies have wide potential for applications across astronomy, health, security and drug delivery, but engineers have struggled to develop viable solid-state sources for these frequencies.

Smith, Broome and Stanley side-stepped the issue by bringing together solid-state CMOS sensors, typically used with visible and infrared light, and quantum cascade lasers, which tend to operate in the mid-infrared to low-terahertz part of the spectrum. By creating an interface for the two technologies, the team showed that the hybrid system can effectively sense frequencies up to 3.5 terahertz, squarely in the range known as the "terahertz gap." The work also demonstrated how future researchers could leverage a similar system to sense frequencies up to 10 terahertz.

The conference presentation extended a collaboration that began as three senior thesis projects. Gerard Wysocki, associate professor of electrical engineering, also co-advised the project.