High-Frequency Telecoms Takes Several Steps Closer to Commercialisation

January 25, 2023

Written by Alex Lawrence

During the past few months, there has been a flurry of related news in material science which could have an impact on the development of 6G wireless communications. This article brings together a variety of what may well turn out to be complementary discoveries supporting widespread communications over high-frequency spectrum.

Starting with antennas, a Chinese team published their work developing a metasurface capable of creating a highly directional beam at high frequencies, while simultaneously self-filtering to reduce sideband interference. The work was led by Professor Chan Chi-hou, Acting Provost and Chair Professor of Electronic Engineering in the Department of Electrical Engineering at City University of Hong Kong (CityU).

The metasurface would effectively act as an antenna, unlike Reconfigurable Intelligent Surfaces (RIS) which are designed to reflect or enhance signals received from other antennas.

Sideband interference is a problem faced by what the paper describes as “traditional” metasurfaces. Frequencies above and below the signal can be created accidentally and interfere with the main signal. However, the team points to the waveguides built into the metasurface as a method to prevent this interference while also creating some very focussed directionality in the signal output.

Professor Chan commented that the metasurface would be able to support functions that have been proposed for 6G. It, could, according to the professor, “scan and duplicate an image that is similar to a real person, so that mobile phone users can talk with each other with 3D hologram imaging. It also performs better against eavesdropping than the conventional transmitter architecture.”

Changing mmWave economics

Meanwhile, at the UK’s University of Sheffield, researchers have been able to 3D print mmWave antennas using silver nanoparticles. Their performance is comparable to the traditional etched antennas. This might not sound like a breakthrough as mmWave is not new, but the cost to manufacture is a small percentage of the etching process. This has two ramifications.

Firstly, it means that antennas can be made much more accessible. With a dramatically lower cost to produce, mmWave communications can find its way into a wide variety of devices for both receiving and broadcasting. The antennas will still cost a few pounds to produce but this compares to a few hundred previously.

While this is not low enough to fit within the bill of materials for smaller IoT sensors, it wouldn’t be out of place in low-end electronics or even to use for tracking location and condition monitoring of hand-held power tools – something useful in the home, but much more so in campuses and factories. This would also support more pervasive device to device communications and mesh networking at high data rates.  

Secondly, it means that the calculations of ROI for deploying mmWave improve. Even though established telecoms providers may struggle, community mmWave along the same lines as community Wi-Fi may become an option, providing inexpensive 5G to areas which would otherwise not have such access. Moreover, the 3D printed antennas were tested effectively at up to 48GHz. While this may not be in the sub-THz bands talked about as the innovation for 6G, mmWave may be  a credible 6G mid-band.

From generating high-frequency waves, we come to an announcement from South Korea’s Institute of Material Science (KIMS) about absorbing them. A team there has developed the first continuous manufacturing process for epsilon iron oxide, one of few materials that can absorb electromagnetic waves in the 30-200GHz spectrum. Currently, shielding for mmWave devices and antennas is difficult to do, with the result being that only a handful of companies have been able to support it; and none of them use epsilon iron oxide, which is a highly coercive magnetic material with uses elsewhere such as in electric motors.

Again, this is another element that may be involved in reducing the cost to produce devices communicating at mmWave frequencies by enabling mass production of important components. The team at KIMS is currently reported to be discussing technology transfer of the process with several organisations globally as well as aiming to extend their research into the THz band. 

Photonic Wave Generation

Meanwhile, Swiss researchers at EPFL and ETH Zurich have announced their development of a thin-film photonic chip that can generate finely tailored frequency waves in the 300GHz – 30THz range.

The chip uses photons rather than electrons, which is a valuable element in the development of photonic networks. Today’s networks are a combination of photonic, principally sending light signals through fibre optic cables, and electronic for the junctions, routers, and other devices.

The emerging field of photonics faces different challenges from the better-understood electronics arena, but the use of all-photonic networks aims to reduce the latency and energy wastage of networks that today switch many times between electrons and photons. Projects like NTT’s IOWN are outstanding projects in this direction today.

Within the circuit, light is converted into Terahertz frequencies using microscopic antennas within a lithium niobate film, which can tailor the frequency, amplitude, length and phase of signals. The light used as an input is interoperable with lasers used in telecoms already, so that the commercialisation of such photonic chips will be telecoms-compatible.

“Generating waves at very high frequencies is extremely challenging, and there are very few techniques that can generate them with unique patterns,” said Cristina Benea-Chelmus, project lead and Assistant Professor of Microengineering at EPFL’s School of Engineering. “We are now able to engineer the exact temporal shape of terahertz waves – to say essentially, ‘I want a waveform that looks like this.’”

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