New Technology Reveals Objects Hidden Around Corners

Even though the figure in red lies hidden, out of the direct line of sight of the figure in green, radiation naturally emitted by the concealed figure at submillimeter wavelengths betrays its presence. At these long wavelengths, many types of walls act as partial mirrors, reflecting the light into view of the green figure. Courtesy of NIST

By Catherine Dorrough

A researcher at the National Institute of Standards and Technology (NIST) and his colleagues have developed a new way to see images hidden outside of the observer’s line of sight. Although still in the early stages of development, the technology could have future applications in police surveillance and search and rescue operations. Other potential use cases include improving robotic vision and enhancing the safety and accuracy of self-driving cars, according to a press release from NIST.

While there are other methods for imaging objects behind obstructions, most of them rely on reflections of either visible or infrared light. However, these methods present technical challenges that require the use of sophisticated algorithms and significant computing time to render even a semi-sharp image. Additionally, the light could alert a person that they are under surveillance.

Other methods that don’t require a light source rely instead on analyzing shadows cast by hidden objects or detecting heat via infrared radiation. However, these methods yield limited results. “A good algorithm and lots of computer power might extract an image, but not a very good one,” said NIST physicist Erich Grossman in the NIST press release.

The setup for the experiment at Erich Grossman’s home, where the hidden object (Grossman himself) sat just behind an occluding, or concealing, wall, out of direct view of detectors. “Wall under test” connotes the various types of walls, including ceramic tile and plywood, that the team examined to determine which were best at reflecting submillimeter radiation. Courtesy of E. Grossman/NIST

Grossman and his collaborators at the University of Minnesota Twin Cities in Minneapolis have instead developed a technique that uses “submillimeter” radiation. The submillimeter range of the light spectrum lies just beyond microwave radiation and is naturally emitted by people and objects. Using curved mirrors to focus the invisible light, the researchers demonstrated that they could render images of objects hidden behind walls in 20 minutes. With a larger array of detectors and transistors, Grossman said, the method should be able to image hidden objects in real time.

“What’s cool about this method is its simplicity,” Grossman said in the press release. “There’s no quantum mechanics, no relativity, there’s nothing cryogenic or anything fancy – just transistors and a basic computer and mirrors.” The entire apparatus is small enough to fit in a backpack.

The release goes on to say: “With NIST facilities closed during the peak of the COVID-19 pandemic, Grossman used his own home — converting the bedroom of his daughter, who had left for college, into a makeshift laboratory. Grossman himself was the body hidden behind a wall.”

The work was supported by NIST and the Defense Advanced Research Projects Agency (DARPA), and was presented on July 12 at the annual Imaging and Applied Optics Congress in Vancouver, Canada.