Smart metasurfaces promise to double wireless network capacity
This newly realized property, called “full-duplex nonreciprocity,” say the researchers, could double the capacity of existing wireless networks.
“This is happening,” says George Eleftheriades, a professor in the Edward S. Rogers Sr. department of electrical and computer engineering in the Faculty of Applied Science & Engineering. “Within the next three to five years this technology will be adopted.”
Metamaterials are synthetic structures composed of building blocks that are smaller than the wavelengths they are designed to manipulate. The material used by the researchers is composed of repeating unit cells about 20 millimeters in size. These appear to form one homogenous object – a metasurface – for larger electromagnetic waves such as microwaves, which are used to carry cell phone signals and reflect off the metasurface exhibiting a property known as nonreciprocity.
An example to illustrate this using light is a car’s rear-view mirror, say the researchers.
“When you’re driving and look in the rear-view mirror, you see the driver behind you,” says Eleftheriades. “That driver can also see you because light bounces off the mirror and follows the same path backwards. What’s unusual about nonreciprocity is that the incident angle and the reflected angle are not equal. To be specific, the backward path for the wave is different. Basically, you can see someone, but you cannot be seen.”
In addition, metasurfaces can be used to steer and amplify incoming beams, which is useful in many applications, from medical imaging and solar panels to satellite communications and even nascent cloaking technology. By adding the capability to steer the reflective beam, new intelligent metasurfaces could make a significant mark on wireless communication, say the researchers.
“In everyday experience, a microwave emitted from a tower reaches its intended terminal point, like a modem, and then goes back to the telecommunication station,” says Eleftheriades. “That’s why when you have a conversation on your cellphone, you do not talk and listen on the same channel. If you did, the signals would interfere and you wouldn’t be able to separate your own voice from the voice of your partner.”
Today’s 5G networks feature only “half-duplex” links – essentially, the 5G signal uses slightly different frequencies, or the same frequency but at a slightly different time, to avoid interference. The time delay is imperceptible to the user.
By contrast, the full-duplex architecture developed by the researchers means that one can talk and listen on the same channel at the same time. Unlike other metamaterial technology, say the researchers, it spatially separates the forward and backward paths within the one frequency – doubling the system capacity.
While full-duplex functionality exists in a limited capacity in military-grade radars, it’s currently unsuitable for consumer applications such as mobile devices. For example, current full-duplex transceivers are made of bulky and expensive structures comprising ferrite materials and biasing magnets to manipulate the beam.
“We propose a completely different mechanism,” says Elefthreriades. “No magnets or ferrites. Everything is done using printed circuit boards and silicon electronic components such as transistors.”
The broad applicability of these intelligent metasurfaces is exciting, say the researchers. The intellectual property for their proof of concept was recently transferred to the Montreal-based startup LATYS Intelligence Inc., which was co-founded by U of T Engineering alumnus Gursimran Singh Sethi.
“Tunable, asymmetric radiation beams in both the reception and transmission states have incredible potential to address some of the most pressing and major challenges in the wireless communication industry,” says Sethi. “By spatially decoupling the receive and transmit paths, we can create ‘true full-duplex systems’ that can support bidirectional communication at the same time and the same frequency.
“This will allow LATYS products and prototypes to gain an edge over competition and much traction,” says Sethi, “especially in radio-hostile environments such as industrial automation, IIoT [Industrial Internet of Things] and 5G applications.”
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