Radar has been around for nearly a century. Radar is a simple and elegant element of humanity’s technological toolbox: you put out radio waves, a receiver picks up their reflections, and you examine the waves to figure out where and how far away things are.
Designers can now develop complex radar systems that employ many receivers. When a single device, such as your smartphone, pings numerous receivers, it can be triangulated with amazing accuracy.
Researchers at the National Institute of Standards and Technology (NIST) in the United States have developed a new radar scanning system that employs the opposite setup, with a single receiver and several transmitters. Even when things are buried behind walls or traveling at supersonic speeds, this new radio arrangement can provide real-time photos and video.
The technique could make it easier for first responders to locate individuals in smoke-filled burning buildings or follow debris racing through space. The findings were published in the journal Nature Communications.
Although microwaves are what bounce around to warm your meal, NIST’s method relies on microwaves—the waves themselves, not the equipment. Microwaves are the radio wave family’s shortest members. Their wavelengths range from the thickness of a coin to the size of a school ruler. Microwaves are already employed in radar; for example, equipment that tracks a car’s speed on the road often relies on them.
Microwave wavelengths can be shortened ten thousand times from the shortest microwave wavelengths to produce visible light. All of these are part of the electromagnetic spectrum, and aside from wavelengths, there isn’t much of a distinction between them.
When it comes to producing images, however, microwaves offer some benefits over light. “I can’t see through those walls,” says Fabio da Silva, one of the NIST experts who spearheaded the endeavor. “The wavelengths that the human eye is sensitive to don’t permeate such objects very well.” “However, you should be able to ‘see’ past the barriers if you go to longer wavelengths, such as in the microwave regime.”
That’s why your router can reach anyplace in your house, and your phone can pick up a signal underground—microwaves that can pass through walls and floors connect them to the internet. That means the new method developed by the researchers can penetrate even relatively solid materials like drywall and concrete. It will also be unaffected by bad weather, such as thick clouds and rain.
Traditional radar, on the other hand, isn’t very excellent at producing detailed images quickly. “To get an image, [radar systems] normally have to scan their illumination patterns, which slows down the imaging process,” says Mohammadreza Imani, a microwave imaging expert and professor at Arizona State University who was not involved in the NIST study.
The researchers at NIST intended to create a system that could get around this limitation. The NIST team drew inspiration from new gadgets known as “single-pixel cameras,” which are, in essence, cameras without lenses. They put out the light and measure how long it takes for the light to return using ultra-fast and ultra-sensitive detectors. You can make photos rapidly and efficiently if you can get a system that processes data swiftly.
Another important component of the researchers’ approach is “light-in-flight,” which is based on how waves bounce off objects to reach their receivers. “You employ the idea that light bounces off other objects and these objects then illuminate other objects as a result of many bounces,” da Silva explains.
Aside from imagery, 3D rendering software frequently uses light-in-flight to create more realistic visuals. It was modified by NIST researchers to work with their microwaves.
The ability to merge all of these notions into a viable scanning system was a major challenge for da Silva and his colleagues. As a result, they resorted to GPS, which locates you by calculating your position about several satellites. Da Silva and his colleagues employed numerous microwave sources and a single receiver, tying everything together with computer algorithms.
The result is a system that can scan an area the size of an above-average dwelling in microseconds and then locate items as small as 1 millimeter. The researchers also believe that the system can be used for applications comparable to radar’s original purpose: tracking hypersonic objects that travel at speeds greater than five times that of sound. Explosions or space debris, for example, are becoming a greater concern as Earth’s orbit becomes increasingly clogged with human-made garbage.
“The system detailed in this paper can discern between first- and second-scattering events, in addition to delivering quick imaging over a vast scene,” explains Imani. To put it another way, it can detect not just a bounce, but also the bounce after a bounce. “The second-scattering events can be used to picture through and around obstacles.”
The team’s findings are based on NIST laboratory demonstrations. Since then, da Silva has left NIST for a business called Wavsens, where he aims to continue developing the technology and eventually put it on the market for widespread usage.
“In the next couple of months, we anticipate to have something like a prototype test done,” he says. “Then, perhaps, within the next year, we will have something that can be deployed or tested in real-world applications.”
Other researchers hope to develop microwave security scanners that are speedier, less intrusive, and far smaller than the enormous pneumatic tube devices seen at airports. Microwave imagers also serve as the foundation for self-driving vehicles. Imani claims that small microwave cameras could potentially find their way inside your phone.
“It may also be used merely for fun,” Imani explains, “for example, to evaluate [the] fitting of a shoe without any detrimental effect.” It’s similar to old X-ray shoe fitters, but without the radiation.