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Docomo and AGC use Metasurface Lens to Guide Millimeter Waves (mmWaves) Indoors

We wrote about Futuristic Glass Antenna by NTT Docomo and AGC back in 2019. It's good to see the partnership continue with this new announcement about use of metasurface lens to enhance radio signal reception indoors. 

Metamaterials is one of the focus areas of 6G as highlighted here. Samsung's 6G Vision whitepaper explains it as follows:

A metamaterial is usually constructed by arranging multiple tunable elements (PIN diodes, varactor diodes, etc.) in repeating patterns, at scales that are smaller than the wavelengths. Its precise shape, geometry, size, orientation, and arrangement enable smart properties capable of manipulating electromagnetic waves, e.g., blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials. In addition, each element constituting a metamaterial can be controlled independently to achieve desirable characteristics of the electromagnetic waves such as the direction of propagation and reflection.

Metasurface lens as a phase shifting structure is applied to the signal radiated from an antenna array. It can adjust a beam direction by applying DC bias to its constituting elements. The metasurface lens has potential to help sharpen a beam shape.

NTT Docomo and AGC announced that they have developed a prototype technology that efficiently guides 28-GHz 5G radio signals received from outdoors to specific locations indoors using a film-like metasurface lens that attaches to window surfaces. DOCOMO and AGC also conducted what is believed to be world's first successful trial to direct 28-GHz signals passing through a window to specific locations indoors as well as raise the strength of the signals. The press release says: 

Newly emerging 5G networks as well as 6G networks of the future are expected to use high-frequency radio waves, such as 28 GHz. Although high-frequency signals enable the realization of advanced communication standards, they are subject to high attenuation over long distances and their high directivity resulting in low diffraction (or weak bending around objects) generally limits their range to within the line of sight of the transmitting base station. Consequently, it is difficult for high-frequency radio waves to penetrate windows, and even if they do they are attenuated to the point of not being able to propagate sufficiently to establish wireless communication links indoors.

The new metasurface lens is made with an artificially engineered material featuring a large number of sub-wavelength unit cells arranged periodically on a two-dimensional surface. Elements arranged in various shapes on the metasurface substrate can be attached to a glass window to direct radio signals to specific points ("focal points") indoors. It is believed that radio waves from an outdoor base station could be received on a window's broad surface and then efficiently propagated to specific focal points inside a building with the help of repeaters and reflectors.

The metasurface lens material is a transparent film that can cover virtually the entire inside surface of a window. The material has no effect on LTE and sub-6 band radio waves, so it can be used to improve indoor reception of 28 GHz radio signals without affecting the performance of legacy wireless frequencies.

The trial confirmed that the metasurface lens improves the power level of 28 GHz radio signals received at indoor focal points. The trial also confirmed the ability to control focal-point position as well as the ability to switch from single to dual focal points.

In addition, DOCOMO and AGC verified that structural design technology can be deployed to enable metasurface lenses to allow high-frequency radio signals to penetrate glass that has been coated for heat insulation.

DOCOMO and AGC have been developing transparent metasurface technology for use in solutions that not only improve access to high-frequency radio signals but also are aesthetically acceptable. The new metasurface lens incorporates DOCOMO's metasurface design technology and AGC's design and microfabrication technologies.

I am hoping to see a lot more of these, tunable to different frequencies in the future as we move on to even higher frequencies and Tera hertz frequencies. I am hoping a video with demo will be available soon.

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