Researchers at the University of California, Davis, have developed a proof-of-concept sensor that may usher in a new era for millimeter wave radars. Millimeter wave radars send fast-moving electro­magnetic waves to targets to analyze their movement, position and speed from the waves bounced back. The benefits of millimeter waves are their natural sensi­tivity to small-scale movements and their ability to focus on and sense data from micro­scopic objects. The new sensor uses an innovative millimeter wave radar design to detect tiny vibra­tions and changes in a target’s position with ultra high precision making it better or on par with the world’s most accurate sensors. Yet unlike its peers, this one is the size of a sesame seed, is cheap to produce and features a long battery life.

Omeed Momeni and his lab in the department of electrical and computer engineering led the effort. It is part of an ongoing project funded by the Foundation for Food & Agri­culture Research& to develop a low-cost sensor capable of tracking the water status of individual plants. This new radar is the necessary stepping­stone that proves it is possible. Millimeter waves, ranging from 30 to 300 gigahertz, enable fast communi­cation networks, such as 5G, and is desirable for its short-range sensing capa­bilities. But they can be tough to work with due to high power consumption and limited performance of semi­conductors at these frequencies.

The primary issue the team faced throughout its first year working on the sensor was homing in on the desired source. There was so much noise that, when the researchers attempted to pick up the delicate signal of a small leaf thinning, their sensors were drowned out. “It seemed really impossible because the noise levels that we were looking at were required to be so low that almost no signal source could actually handle it,” said Momeni. At one point, they weren’t sure if they could overcome the challenge, with his team noting they would need to build a radar chip that was 10 times more powerful and accurate than the current state-of-the-art design – something that seemed dependent upon techno­logical advance­ments that might be years into the future.

Hao Wang, an electrical engi­neering doctoral student in Momeni’s High-Speed Integrated Systems Lab had a moment of inspiration to bypass the techno­logical restraints while meeting with Momeni one day: Why not cancel out the noise with itself? That would theoretically solve the issue their sensors were facing, and Wang was finishing up a chip design for his disser­tation to do just that. “This was not out of thin air, a brand-new concept,” said Wang. “This was based on what we [in Momeni’s lab] have accumulated from research throughout the years – and then you innovate more.” The lab worked quickly to assemble a proto­type to test Wang’s idea. It worked on their first try. 

The proto­type succeeded because it allowed them to handle the volume of noise their sensor received like a simple arithmetic problem. They subtracted the unnecessary noise while maintaining the sensi­tivity of their measurement and the integrity of their data. With this technique, the millimeter wave sensor could detect all the information it needed without becoming drowned out by noise. This innovation powered the sensor’s high accuracy rates.

Wang’s chip is also simple to produce and features a unique design that greatly improves the energy effi­ciency of the millimeter wave sensor. These additional advance­ments may solve two of the most signi­ficant issues facing millimeter wave sensors: high energy consump­tion and limited performance of semi­conductor transistors in terms of noise, gain and output power. As the team continues to refine and iterate on their design, they are excited for researchers to experiment with it. Outside of their project, they think it has promise for detecting the structural integrity of buildings and improving virtual reality but believe it has far more potential than they even realize. (Source: UC Davis)

Reference: H. Wang et al.: A Highly Accurate and Sensitive mmWave Displacement-Sensing Doppler Radar With a Quadrature-Less Edge-Driven Phase Demodulator, IEEE J. Solid-State Circ. 58, 3266704 (2023); DOI: 10.1109/JSSC.2023.3266704

Link: High-Speed Integrated Systems Lab, Dept. of Electrical and Computer Engineering, University of California at Davis, Davis, USA