UC Davis Infrared Sensor Opens New Possibilities for Medicine and Industry

Infrared, or IR, sensors do more than detect heat energy. They help spot wildfires, monitor air pollution and detect signs of disease. However, many of the most advanced IR sensors must operate at sub-zero temperatures, adding cost and complexity to the systems that rely on them. 

In a new study published in Nature Communications, researchers at the University of California, Davis, detail a cutting-edge IR sensor they created that works at room temperature. The work was led by electrical and computer engineering professors J. Sebastian Gomez-Diaz and William Putnam. 

“With this technology, we overcome the need to operate IR sensors at very low temperatures,” Gomez-Diaz said. “We open a new avenue for achieving high responsivity that was not possible before.”  

Good Vibrations 

The new infrared sensor relies on micro-electrical-mechanical systems, or MEMS. MEMS are tiny devices, about the size of a grain of sand, that feature electrical and moving parts to fulfill a specific function.  

Traditional IR sensors use photodetectors, which convert light into electricity. Photodetectors struggle with picking up unwanted signals from the environment, which is why advanced sensors must operate at freezing temperatures, where there is less noise. 

Instead of photodetectors, Gomez-Diaz’s team uses an IR sensor with a MEMS device. The device features a membrane that vibrates when exposed to light. Different levels of light intensity cause the membrane to vibrate at slightly different frequencies.  

To measure and interpret these changes, his team uses radio frequencies and reflectometry, a technique that captures how much incoming energy is reflected.  

The team sends a radio wave to the sensor and analyzes how it is sent back. They can also use radio waves to tune the device to a specific operating point where even small changes in light create huge changes in the reflected signal. Gomez-Diaz calls this operating point “critical coupling.” 

“By taking advantage of this interrogation method at critical coupling, we revealed that the sensing performance of MEMS is much, much higher than we ever expected,” he said.  

The combination of a membrane-based design and radio frequencies to increase performance allows the IR sensor to be responsive enough to detect weak signals, even in room temperature environments.  

While researchers have explored IR sensors that combine radio frequencies and MEMS before, previous approaches never achieved such a high level of performance as with the UC Davis team’s vibrating membrane, explained Gomez-Diaz.  

Finding the Right Tune 

Since the team can use radio waves to tune how responsive the sensor is, this makes the sensor very adaptable. 

The device can be adjusted to detect IR signals as low as 740 picowatts, which would be like hearing a distant whisper at a loud concert. At the other end of the spectrum, the device can detect signals as powerful as 100 microwatts. That would be like hearing someone shout through a microphone at that same concert.  

“We can adapt to the environment or to the signals we are trying to detect in a dynamic way, and that is very difficult to achieve with other technologies,” Gomez-Diaz said.  

The tunability of the devices comes with some costs. For one, when the device is made more responsive to weak signals, it cannot detect powerful signals. The use of MEMS also makes the device slower than IR sensors using photodetectors. 

A Signal of Things to Come 

The initial drive for Gomez-Diaz to make a next-generation IR sensor that works at room temperature came from a research roadblock. 

For the past few years, he has been working with Associate Professor of Biomedical Engineering Randy Carney on a project to detect cancer from biofluids. The idea is to create a small device that can capture the molecular fingerprints of cancer from a saliva or blood sample. However, the team couldn’t progress the research because the IR sensors they needed didn’t exist yet. 

“We tried to do cancer sensing with the technology that was available, and then we realized the detectors were not good enough,” he said. “We needed to push the technology, and now we have found a new operating regime that is much better.”  

While Gomez-Diaz will use the new IR sensor to advance the cancer project, he believes the sensors show immense potential. For example, the fact that they can operate at room temperature may open the door to better environmental sensors and even next-level consumer electronics. 

“We are making a specific implementation, but the idea is very general and can be applied to many other devices,” he said. 

The research was supported by the Department of Defense – Army, the National Institutes of Health and the National Science Foundation.