Metamaterials signal Wi-Fi boost
Scientists in Canada have created metamaterials with unique reflective properties in the radiowave regime that could enable more wireless data to be transmitted over a single frequency, opening the door for a new generation of wireless communications.
Professor George Eleftheriades and Postdoctoral Fellow Sajjad Taravati, at the University of Toronto, have uncovered a new property – ‘full-duplex non-reciprocity’. They have done so by creating a metasurface in printed-circuit board technology as chains of repeating unit cells, each about 20mm in size and made from copper patch antennae integrated with silicon semiconductor devices.
‘In everyday experience,’ says Eleftheriades, ‘a microwave emitted from a tower reaches its intended terminal point, like a modem, and then goes back to the telecommunication station. 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, therefore, features 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.
Current full-duplex receivers, on the other hand, used for military radar, are unsuitable for consumer applications because they are made of bulky and expensive structures that comprise ferrite materials and biasing magnets to manipulate the reflective beam.
‘We propose a completely different mechanism. No magnets or ferrites. Everything is done using printed circuit boards and silicon electronic components such as transistors,’ says Elefthreriades.
According to the research, published in Nature Communications, the proposed mechanism would make it far easier to achieve full-duplex functionality. The silicon transistors embedded in the unit cells at the microscopic level exhibit unique characteristics, enabling the team to spatially separate the forward and backward paths in one frequency. This full-duplex architecture means that the mobile phone user can talk and listen on the same channel at the same time.
Significantly, the microwaves reflect off the new metasurface in an unusual way, exhibiting a property known as non-reciprocity.
‘When you’re driving and look in the rear-view mirror, you see the driver behind you. That driver can also see you because the light bounces off the mirror and follows the same path backwards,’ says Eleftheriades. ‘What’s unusual about the non-reciprocity 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.’
The study of non-reciprocal metamaterials has been a ‘hot’ research area, but has focused primarily on time modulation, says Eleftheriades. ‘Here…the metasurface we made combines several functionalities which make it quite unique: 1) the angle of reflectance is not necessarily equal to the angle of incidence – the former angle can be controlled which allows beam re-direction; 2) the reflected signal is actively amplified with respect to the incident signal; 3) most remarkably, the forward and backward paths are not identical as in conventional mirrors (non-reciprocity).’
Eleftheriades says the new metamaterial’s additional capability to steer the reflective beam could be used to enhance wireless communication in an office through its integration into a building’s interior and/or exterior walls.
In doing so, the directive beam can follow the mobile phone user’s movements, creating a dedicated communication channel, improving the quality of service and throughput as a result. Also, when the line of sight between the two callers is broken, the reflector in the wall would enable a beam deflection to re-establish the link.
Montreal-based start-up, LATYS Intelligence, which was co-founded by University alumnus Gursimran Singh Sethi, plans to take the team’s proof-of-concept and develop commercial applications for the Internet of Things and for adoption in 5G/6G wireless networks.
‘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.
One of the short-term goals is to customise the technology at different frequency ranges, such as at millimetre-wave frequencies. Over the long-term, the metamaterials’ ability to non-reciprocally steer and amplify incoming beams could also be useful for medical imaging, solar panels and nascent cloaking technology.
