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Window Glass Used as a Lens for Radio Waves for the First Time in the World
Efficiently directs outside EHF radio frequencies indoors
Expectations for future technology beyond 5G and 6G
Successful proving test carried out by Docomo and AGC


NTT Docomo and AGC successfully developed a prototype metasurface lens, using metasurface technology, to efficiently direct outdoor EHF radio waves (28 Ghz band) indoors in preparation for the further advancement of 5G (5G Evolution) and 6G mobile communications protocols. The two companies used the prototype successfully for the first time in the world, at the Docomo R&D Center in Yokosuka, Kanagawa on December 18 of last year, to increase reception indoors by focusing the EHF radio waves passing through the window glass on a specific location in the room. The metasurface lens they developed was viewed from February 4 through February 7 at the “docomo Open House 2021” event held online by NTT Docomo.

The extremely high frequency (EHF) radio waves planned for use in 5G Evolution and 6G are more directional and can suffer from attenuation more easily when compared to the current LTE and sub-6 band radio waves. As a result, the radio waves emitted from outdoor cell towers becomes attenuated when it reaches building windows and enters the buildings in a weakened state without adequately spreading. This has made it difficult to establish communication areas inside buildings using outdoor cell towers.

In response, elements on the metasurface of the metasurface lens designed this time for the 28 Ghz band are given several different shapes and carefully arrayed so that the EHF radio waves that pass through the glass will be focused on a specific location in the room.

In other words, the weak radio waves spread across the window surface are increased in strength by focusing them. If a tool to improve coverage is then placed there, such as a repeater or reflector, the interior of the building can be included within the area covered by the outdoor cell tower.

Furthermore, the metasurface lens itself is designed to take the form of a film which can be affixed to a window from the inside, making it easy to pull the radio waves from the cell tower inside the room, while having no effect on existing LTE or sub-6 bands, allowing the EHF coverage to be improved while still operating other bands.

The team was able to confirm during the test that the reception indoors was increased by focusing the EHF radio waves passing through the window glass using the metasurface lens. Also, control of the focal point of the technology was tested, and the ability to switch between single focal point and bifocal points was verified. This was tested in anticipation of such applications as placing multiple repeaters or reflectors indoors, or the need to track mobile devices.

Furthermore, the test showed that by combining the metasurface lens with glass designed to pass electromagnetic radiation without losing its insulation properties, such glass can still allow the increased receptivity of EHF radio waves indoors due to technology by AGC involving glass structures conducive to electromagnetic wave transmission.

This article has been translated by JST with permission from The Science News Ltd.( Unauthorized reproduction of the article and photographs is prohibited.

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