Compact spinning technology makes thermal images brighter

As today’s cutting-edge research field, observing heat is becoming increasingly hot.

Researchers at Purdue University have combined the power of advanced surfaces (including metamaterials) with thermal imaging algorithms to create a technology that could open new frontiers in machine vision and autonomous systems.

Previously, such advanced surfaces were used for imaging techniques in the visible spectrum. However, the use of these cutting-edge technologies for infrared thermal imaging has so far been little explored.

“The robustness and simplicity of the device greatly improves its practicality in real-world applications.” –Xueji Wang, Purdue University

The Purdue team calls their device “Spinning MetaCam,” and it not only helps classify materials, but also opens new possibilities for security, thermography, medical imaging, and remote sensing technologies. We are reporting that there is a possibility.

To potentially make these applications possible, the Purdue team is applying a field of materials science called metasurfaces. Metasurfaces are structured electromagnetic nanoscale surfaces designed to act like water taps, filtering and directing light.

Unlike traditional materials that naturally bend, reflect, or absorb light, metasurfaces are fitted with subwavelength-scale structures that manipulate the intensity, spectrum, and polarization of light. For Spinning MetaCam, the researchers tailored the metasurface as a series of gold structures with adjustable orientation on a wheel of zinc selenide wafers.

“Our system leverages a specially designed metasurface with state-of-the-art computational algorithms,” said Xueji Wang, a postdoctoral fellow in electrical and computer engineering at Purdue University. . “By stacking and rotating these metasurfaces, we decompose thermal light into its spectral…components.”

Wang added that the researchers used a standard thermal sensor in the device. Their essential innovations are on both sides: before the light hits the sensor, and afterward in how they process the data the sensor generates.

But the key to their method involves a rotating metasurface, with rotational manipulation allowing the imaging system to maximize the most relevant spectral and thermal information sent to the sensor, Wang said. points out. This approach is superior to traditional infrared filters made from traditional non-rotating materials, Wang added.

The rotational motion is achieved with a standard rotor, increasing robustness compared to the delicate mirror movements required in interferometers. “The device’s robustness and simplicity greatly improve its practicality in real-world applications,” he said.

Application for rotating MetaCam

According to Wang, Spinning MetaCam has several advantages compared to traditional thermal imaging. The compact design, measuring approximately 10cm x 10cm x 10cm, stands in stark contrast to the bulky nature of traditional spectral thermal imagers. Because of Spinning MetaCam’s portable and versatile configuration, it could potentially be used in search and rescue operations, industrial sites, airport security, military and border security, and more, Wang said.

“Traditional spectral thermal imagers are often bulky benchtop systems that rely on large filter wheels and interferometers, making them unsuitable for portable devices,” Wang says.

This group of cameras, which use long-wavelength infrared (LWIR), could potentially detect hidden objects and materials, perhaps for security or military purposes. And its sensitivity to tiny temperature differences offers another opportunity for developers to use it, perhaps in medical settings, Wang said.

The potential of this technology in autonomous navigation is also noteworthy. Of course, lidar, radar, and sonar are all widely used or at least being considered as self-driving technologies. But Metacam represents the latest development in another imaging modality, which researchers last year called heat-assisted detection and ranging, or HADAR. As the authors of the 2023 paper note, HADAR does not necessarily require illumination, which could make it a particularly useful modality for night-time and low-light applications.

Wang said the next steps for the technology include manufacturing challenges, acknowledging the need for nanofabrication and specialized infrared materials. All of this represents the complexity of current pipelines, but at the same time the larger field of meta-optics is rapidly evolving, Wang says.

“The next steps will focus on improving spectral resolution, transmission efficiency, and speed of image capture and processing,” Wang said.

The goal is to overcome the camera’s current limitations regarding hot objects, he added. “We aim to extend this to room-temperature imaging using techniques such as improved materials, metasurface designs, and anti-reflection coatings,” Wang says.

The researchers published their findings this month in the journal Optica.