Japanese mobile operator NTT DOCOMO, working in collaboration with the global glass manufacturer AGC Inc., has successfully conducted what is believed to be the world's first trial of a prototype transparent dynamic metasurface using 28 GHz 5G radio signals.
The new metasurface achieves dynamic manipulation of radio-wave reflection and penetration in a highly transparent package suitable for unobtrusive use in the windows of buildings and vehicles as well as on billboards.
The metasurface, an artificially engineered material, comprises a large number of sub-wavelength unit cells placed in a periodic arrangement on a two-dimensional surface covered with a glass substrate.
Prototype of transparent dynamic metasurface
AGC manufactured the optically transparent metasurface using microfabrication techniques, based on a theoretical model proposed and designed by DOCOMO.
Moving the glass substrate slightly enables dynamic control of radio waves in three modes: full penetration of incident radio waves, partial reflection of incident radio waves and full reflection of all radio waves.
Compared to conventional methods using semiconductors, this new design offers two advantages: it allows dynamic control while maintaining transparency of the window and it facilitates enlargement of the substrate.
The metasurface can manipulate radio waves in accordance with the specific installation environment, particularly in locations not suited to the installation of base stations, such as built-up areas or in indoor areas where reception needs to be blocked selectively, such as in high-security areas.
Also, the transparent substrate does not interfere aesthetically or physically with the surrounding environment or people's line of sight, making it ideal for use within buildings and on vehicles or billboards, for example.
The new technology deployed in the activation of the transparent metasurface also works with frequencies higher than those used for 5G.
Going forward, in addition to incorporating the technology in methods for efficiently and flexibly establishing 5G access areas, DOCOMO will further research and develop the technology for use with newer wireless communication systems.
Putting the prototype into trial
In the trial, radio waves were beamed perpendicularly to measure penetration in two modes: full penetration, where the metasurface substrate and movable transparent substrate were attached to each other, and full reflection, where the metasurface substrate and movable transparent substrate were separated by more than 200 micrometres.
Tests of both modes at 28 GHz produced successful results. Radio waves passed through the substrate in penetration mode and were blocked in reflection mode, in both cases without attenuation. The distance between the two substrates was manually controlled in the current test, but in future tests, a piezoelectric actuator will be used to switch between penetration and reflection modes at high speed.
Previously, DOCOMO began studying the use of metamaterial reflect-array technology to freely manipulate the direction and beam shape of reflected radio waves, a necessity for the highly linear high-frequency bands of 5G and later-generation mobile networks. However, each metamaterial reflect-array must be designed for its specific installation location. Furthermore, radio waves cannot reach the back of a reflect-array and the antenna itself can block views of the area's surroundings.
The prototype transparent dynamic metasurface will be presented during DOCOMO Open House 2020, which will take place in the Tokyo Big Sight exhibition complex in Tokyo on January 23 to 24, 2020.
