Sixth-generation, or 6G, cellular networks are the next step in wireless communication, and electromagnetic terahertz waves are seen as crucial to its development. However, terahertz waves, with their higher frequency and shorter wavelength, are subject to greater interference from electromagnetic noise, making clear and secure transmission a challenge. Researchers from the University of Tokyo, as part of a multi-institution team, have now created an electromagnetic wave absorber for waves between 0.1–1 terahertz (THz). This greatly expands the range of the terahertz frequency which could be commercially used in the future. The ultrathin film is inexpensive, environmentally friendly and can be used outdoors, as it is resistant to heat, water, light and organic solvents.

If you have access to a 5G network, you’ll probably have noticed a dramatic difference compared to the more widely available 4G. Its low latency (the time it takes for a signal to bounce from its source to a receiver and back) means lower lag times, which is great for gamers, while download speeds of up to 20 gigabits per second (compared to 0.1 gigabits per second) and potentially 1,000 times greater data capacity opens up opportunities for smart homes and smart cities. But this isn’t the end of the road for wireless cellular technology, and developers have already been looking toward the next step – 6G.

Terahertz waves are predicted to serve as carriers for the upcoming sixth-generation networks. Recent reports on tests with terahertz waves showed data transmission speeds of up to 240 gigabits per second. However, the challenge is not only to further improve speed, latency and data capacity, but to also prevent interference and reduce noise to ensure a secure and clear signal. That’s where electromagnetic wave absorbers come in. They can inhibit the transmission or reflection of electromagnetic waves and when placed on the covers of transmitters and antennas, help to enhance communication precision.

Now, a team including researchers at the University of Tokyo and Japanese chemical and iron-based alloy manufacturer Nippon Denko Co., Ltd., has developed the world’s thinnest electromagnetic wave absorber, capable of absorbing waves in the 0.1–1 THz range. To date, only absorbers for waves below 0.3 THz have been made commercially available, but a frequency range beyond this is anticipated to be used for large-capacity 5G and 6G.

“This frequency range is expected to be used for various applications including wireless communications, noncontact vital monitoring systems, quality-inspection scanning systems via tomographic imaging, and security sensing for detecting hazardous materials,” said Professor Shin-ichi Ohkoshi from the Graduate School of Science.

Composed of an electrically conductive metal oxide called lambda-trititanium-pentoxide (λ-Ti₃O₅), insulated within a titanium dioxide (TiO₂) coating, the absorber is made entirely of titanium and oxygen. The absorber is made in powder form, which can be turned into an ultrathin film through compression molding and then applied to surfaces as needed.

“Our strategy was to combine an electrically conductive material with an insulating material. When a terahertz wave passes through, its alternating electric field induces scattering of the electric current generated inside of the conductive material, which causes energy loss and results in the dissipation of electromagnetic energy,” explained Ohkoshi. “This dissipation of interfering waves enables the suppression of noise, i.e., unwanted waves, resulting in a clear signal.”

As the film is only 48 micrometers, or microns, thick (an average human hair is around 100 micrometers) and titanium is a highly abundant element, the absorber is economical for mass production and can be used even inside compact devices. It is also resistant to heat, water, light and organic solvents, and so can be used in outdoor environments and can even withstand harsh conditions.

“The higher frequency range above 0.3 THz remains an unexplored area in materials science and I have been eager to contribute to its development,” said Ohkoshi. “Our next step is to further develop the terahertz absorber and work toward its practical application, so that we can contribute to a more sustainable, eco-friendly, superfast wireless future.”