Scientists develop impossible millimeter-wave sensor with vast potential

Scientists at the University of California, Davis, have created a proof-of-concept sensor that could usher in a new era for millimeter-wave radar. In fact, they call his design a mission impossible made possible.

Millimeter wave radars use fast electromagnetic waves, targeting objects to determine their movement, position and speed based on the reflection of these waves. What sets millimeter waves apart is their acute sensitivity to minute movements and their ability to collect data on extremely small objects.

The new sensor uses an innovative millimeter-wave radar design to detect vibrations a thousand times smaller and changes in a target’s position a hundred times smaller than a strand of human hair, making it better than or comparable to sensors the most precise in the world. Yet unlike its peers, this one is the size of a sesame seed, inexpensive to produce, and has long battery life.

Professor Omeed Momenian and his laboratory in the Department of Electrical and Computer Engineering led this effort. It’s part of an ongoing project funded by the Foundation for Food and Agriculture Research, or FFAR, to develop a low-cost sensor that can track the water status of individual plants. This new radar is the springboard needed to prove that it is possible. The work was recently published in the journal IEEE Journal of Solid State Circuits.

The millimeter wave challenge

Millimeter wave is the electromagnetic frequency between microwave and infrared, ranging from 30 to 300 gigahertz. It enables fast communications networks, such as 5G, and is desirable for its short-range sensing capabilities. But it may be difficult to work with due to the high power consumption and limited performance of semiconductors at these frequencies.

The main problem the team faced during its first year of work on the sensor was finding the desired source. There was so much noise that when researchers tried to pick up the delicate signal of a small lightening of leaves, their sensors were drowned out.

It really seemed impossible because the noise levels we were studying had to be so low that almost no signal source could actually handle them, Momeni said.

At one point, they weren’t sure they could meet the challenge, with his team noting that they would need to build a radar chip 10 times more powerful and precise than the current state-of-the-art design, which seemed to depend on technological advances which could occur in the years to come.

Tuning to a different frequency

Sometimes you just need to have an idea that approaches the problem from another angle. Enter Hao Wang, an electrical engineering doctoral student at MomenisHigh-Speed ​​Integrated Systems Lab, who worked on the sensor project before graduating in 2021.

Wang had a moment of inspiration to circumvent technological constraints during a meeting with Momeni one day: why not cancel out the noise with himself? This would theoretically solve the problem facing their sensors, and Wang was finishing designing a chip for his thesis to do just that.

It’s not a brand new concept, Wang said. This was based on what we [in Momenis lab] accumulated through research over the years and then you innovate further.

The lab worked quickly to assemble a prototype to test Wang’s idea. It worked on their first try.

The prototype was successful because it allowed them to treat the volume of noise received by their sensor as a simple arithmetic problem. They subtracted unnecessary noise while maintaining the sensitivity of their measurements and the integrity of their data.

Using this technique, the millimeter wave sensor could detect all the information it needed without being drowned out by noise. This innovation has taken sensors to a high level precision rates.

Wang’s chip is also simple to produce and features a unique design that significantly improves the power efficiency of the millimeter-wave sensor. These additional advances could address two of the most significant problems facing millimeter-wave sensors: high power consumption and limited performance of solid-state transistors in terms of noise, gain, and output power.

As the team continues to refine and iterate on their design, they’re excited for researchers to experiment with it. Outside of their FFAR project, they believe it shows promise for detecting the structural integrity of buildings and enhancing virtual reality, but believe it has much greater potential than they realize.

Reference: A Highly Precise and Sensitive Millimeter-Wave Displacement-Sensing Doppler Radar with a Quadrature-Free Edge-Driven Phase Demodulator by Hao Wang, Hamidreza Afzal, and Omeed Momeni, April 25, 2023, IEEE Journal of Solid State Circuits.
DOI: 10.1109/JSSC.2023.3266704

The study was funded by the Foundation for Food and Agricultural Research.