We use radar to spot aircraft and thunderstorms, but what if it could be used for smaller-scale things?
A team of researchers from the University of Sydney have figured out a way to collect radar data with resolutions of centimetres. They say their invention could (among other things) be used to monitor breathing and movement in hospitals, instead of uncomfortable physical straps or privacy-invading cameras.
“The important parameters that matter when you build a radar system are going to be the frequency of the radar, and the bandwidth over which the radar signal is,” explains Professor Benajmin Eggleton, director of the Nano Institute at Sydney Uni.
Radar works by sending out a radio wave, and recording when it bounces off an object and returns to the source. The difference in time between pulse and return can be used to figure out how far away the object is.
This is how air traffic controllers manage incoming flights, and military forces track craft in the air and at sea.
“For that traditional application, the frequency is relatively low – like 500 megahertz. Because all you need to know is: is it a big plane or a small plane?” says Eggleton.
But at higher frequencies, radar could return more information.
“If you can increase the frequency of the radar and go to higher frequencies – tens of gigahertz, 40 gigahertz, for example, you can then increase the bandwidth of the signal,” explains Eggleton.
“Now that radar has very high spatial resolution. So not only can you see the location with incredible precision, but you will actually map out the shape of the object with incredible precision.”
High bandwidth radar is not a new concept – but up until now, it’s mostly been impractical.
“The bottleneck with these high bandwidth radar systems is that you need general waveform generators, and signal processing that you typically do with electronics, and that’s very hard,” says Eggleton. These devices become very expensive, very quickly.
But the researchers have sidestepped this issue with photonics – the physics of light waves.
“We use a photonic trick, basically, to generate this high bandwidth radar without requiring any high-speed electronics,” says Eggleton. “And that’s the magic.”
The researchers’ “photonic radar” can see things with a resolution of 1.3 centimetres.
Eggleton says they’ve used this radar to examine a hand-held drone, as a proof of concept. “We can actually see the blades of a drone moving around,” he says.
But the team believe the implications for healthcare are more interesting.
“We think the really important applications here are around human movement and monitoring vital signs, for example, remotely,” says Eggleton.
“The energy of the radar’s so low that there’s no possibility of radiation damage. So you can actually see the breathing of a human because it will see the moving back and forward on the chest. But at the same time, the resolution is not good enough to see the person[’s face] so you don’t get caught up in privacy issues.
“Remote sensors that avoid privacy issues, that can monitor multiple people simultaneously and their vital signs, is the sweet spot where we think this radar technology will have impact.”
As well as being more comfortable than physical straps, this technique could be particularly useful for burn victims and babies – both groups are difficult to attach monitors to.
But while safe for patients, the system could potentially interfere with other telecommunications signals. Fortunately, there’s a simple way to avoid that.
“We’d have to choose frequencies that don’t overlap,” says Eggleton.
“The nice thing about our approach is that it’s agile […] we can configure it to any frequency range. And we would choose frequencies that don’t interact with 4G or 5G, for example.”
Next, the researchers are hoping to test their radar on cane toads, because their heavy breathing makes them good proxies for humans. Unfortunately, animal ethics approval is slowing them down – not because of the danger posed to the toads (there is none), but because of the complications involved in transporting, storing, and handling the toads.
“Getting a cane toad into a lab is an incredibly complicated procedure – which is ironic given cane toads are regarded as a nuisance,” says Eggleton. “Animal ethics is very serious.”
A paper describing the research has been published in Laser & Photonics Reviews.