The wireless frequencies we use to send and receive data are becoming increasingly congested. Indeed, with an ever-increasing number of IoT (Internet of Things) devices in our home – from smart speakers and cameras, to doorbells and lights – we’re gradually running out of bandwidth to use.
But this could all be about to change, now scientists have shown that an altogether different range of frequencies – terahertz – could soon play a significant role in the future of wireless technology.
Terahertz are about 100 times higher in frequency than the microwaves used by Bluetooth and Wi-Fi devices. As such, they have shorter wavelengths and a higher bandwidth capacity for data transmission. However, their shorter wavelength also means they cannot pass through objects like typical wireless carrier waves. For this reason, it’s always been thought that they’d be redundant in domestic applications, where there’s rarely a clear line of sight between a router and its connected wireless devices.
However, researchers from Brown University, whose work is published in APL Photonics, from AIP Publishing, have demonstrated the feasibility of using terahertz carrier waves for data transmission in a diverse range of environments, including “non-line-of-sight” applications.
Daniel Mittleman, who led the study, and his group of researchers placed a receiver around various indoor and outdoor objects, and when a terahertz signal was pointed directly at the receiver, it was easily detected. Where line-of-sight was not possible, the signal could also be bounced off objects in order to achieve detection. Indeed, in one particular experiment, the signal was reflected off two distinct sections of a wall (see diagram) before eventually being detected by a receiver.
Left: A diagram of the terahertz wireless link that incorporates two bounces off walls, so that there is no line-of-sight path from the transmitter to the receiver. Right: A close-up photo of the transmitter rig used in the experiments. Credit: Dan Mittelman
“We’re not the first group to study the feasibility of THz wireless links, either indoors or outdoors, but there have been few comprehensive studies,” explained Mittleman. Many researchers in the field have believed that links that rely on indirect, or non-line-of-sight pathways, are impossible. “Our work shows that this isn’t necessarily the case,” he said
Despite Mittelman’s discovery, I wondered how these type of carrier waves might ever practically be implemented in a domestic environment, considering they’re so easily blocked by physical objects like walls, doors, people and even pets.
“I don’t think anybody is picturing that it would be used in the way we now use 4G networks, which operate at much lower frequencies (where penetration through walls is feasible), Mittelman told Alphr. “At these high frequencies above 100GHz, walls are opaque, so you would never plan to distribute signals through walls.
“Instead, one should picture that terahertz signals would be distributed in a room in a local area network, where there are no walls to block signals. You could link that LAN to the outside world via optical fibre, or via 4G or 5G wireless signals… Of course, that whole idea falls down if the LAN links are so fragile that they can be blocked every time somebody walks by. So the possibility of using non-line-of-sight links in a room is quite important.”
The discovery that terahertz can be reflected, then, could be the difference between the technology working and not working in a domestic setting, because it’d allow you to use walls and even the ceiling to bounce signals and minimise the risk of them being interrupted.
“As an illustrative example, you might imagine that a high-definition TV broadcast signal could be delivered to your home by fibre optics, and then linked from the fibre terminal to a nearby TV by a terahertz wireless signal,” Mittelman continued.
Are terahertz waves safe?
Because of their higher frequency, terahertz waves carry more photon energy than microwaves, which has led to questions about their safety. However, at the powers used in wireless devices, Mittelman believes they’re perfectly safe.
“There is no more reason to believe that there are any safety concerns with terahertz radiation than there are with the microwave radiation from your cell phone,” he tells me. “In fact, one can argue that terahertz should be safer than microwaves at comparable exposure levels, because the penetration depth into living tissue is smaller at higher frequencies.”
“As far as anybody knows, the interaction of terahertz signals with aqueous media (i.e., living tissue) is no different than the interaction of microwaves with the same media – enough power causes heating, and enough heating can be bad. If you base your conclusions on the best available data right now, then that’s all there is to worry about.”
When could we see this new technology rolled out?
To be honest, I’m still a little skeptical about the prospect of seeing this new wireless technology in our own homes anytime soon, but Mittelman is more optimistic.
“We are on the verge of seeing a new generation of wireless technology rolled out in the western hemisphere (5G will be coming in the next year or two),” he tells me. The history of wireless technologies has taught us that the capacity of a new wireless generation lasts for about eight years before it becomes saturated, and needs to be replaced or supplemented. That was the timescale for 3G and 4G, and it’s likely to also be the case for 5G.”
“I guess we’ll be pretty happy with the brand new 5G technologies for a while, but then the demand will grow and grow, and we’ll start to feel the need for something that might be called 6G, in about ten years from now. I believe that we need to do the necessary fundamental research now, in order to make that future possible when we need it. I hope that’s what happens, anyway.”