Most of us take for granted the fact that wireless signals act like a fine mist—they drift through walls, bounce off sofas, and eventually find our phones.

For 4G and early 5G, this "good enough" approach was fine. But as we push toward 6G, the way signals behave starts to change. In later 5G and in 6G, higher-frequency waves act less like mist and more like beams of light. They travel in straight lines and are easily blocked; for these signals, a standard window is less of a gateway and more of a bottleneck. If you aren't standing in the direct line of sight, you're in a dead zone.

NTT’s latest research asks: what if the window could stop being a problem and actually help?

Bending Radio Waves

Think of sunlight. Normally, it just pours through glass at whatever angle it arrives. Now imagine if that glass could catch the light and consciously bend it into the dark corners of the room. NTT has developed a way to do exactly that, only instead of light, it works with the invisible radio waves we rely on for everything.

The solution it’s come up with is a transmissive metasurface—a paper-thin, engineered layer that acts like a smart lens for radio waves. Instead of just letting signals pass through, NTT’s new surface can steer, focus, or even split them. Imagine a signal hitting a window and being instantly redirected to a laptop in a far corner, or split into three separate beams for different devices.

It’s not a new concept, but until now making it thin and fast enough for the real world has been the sticking point. That’s where liquid crystals—the same stuff in your TV screen—come in. By applying a tiny electric field, these crystals can change how they handle waves in real time, allowing the window to adjust signals.

So far, there’s been a major limitation: to work with high-frequency 6G, liquid crystal layers had to be thick, which made them slow to react and difficult to manufacture. NTT has finally broken that link.

World-Leading Liquid Crystal

By rethinking the internal structure of the surface, researchers have created the world’s thinnest liquid crystal layer for the application. They’ve managed to concentrate the electric field so efficiently that the layer is just 3.5 micrometers thick. Not sure how impressive that is? For comparison, a human hair is roughly 20 times as thick.

Above and beyond being a technical win, these smart windows can be built using existing large-scale factory lines, making them much more practical to produce for real-world buildings.

The window’s surface is made up of tiny repeating elements, a bit like pixels on a screen. Each one is extremely small, about one-eighth of the wavelength of the signal it controls. Because there are so many of these “radio pixels,” the system can shape signals very precisely—instead of just sending a wave in one direction, it can split and guide it into several paths at once, aiming each one where it’s needed. That level of control is hard to achieve with traditional array antennas.

From Microwave To Sub-Terahertz

Another useful feature is that it isn’t tied to just one type of signal. The same design can work across a wide range of frequencies, from microwaves up to sub-terahertz bands, and it can handle signals in different orientations, both horizontal and vertical. That makes it much more practical for real-world mobile networks, where conditions are rarely neat or predictable.

In lab tests at 115 GHz, NTT researchers were able to show how a single incoming signal could be reshaped into multiple directed beams. In effect, the window stops being a passive surface and starts acting more like a guide, pulling signals inside and directing them toward specific devices.

Beyond just faster downloads, the tech could be used in areas such as radar and environmental sensing. While it’s still in the research phase, the philosophy behind it is elegant. Instead of trying to force 6G signals to act like old radio waves, we’re teaching our buildings to help them along.

A window is no longer just a piece of glass; it’s got the potential to be an active part of how signals move through a building.

Innovating a Sustainable Future for People and Planet

For further information, please see this link:
https://group.ntt/jp/newsrelease/2026/03/27/260327a.html (Japanese)

If you have any questions on the content of this article, please contact:

Public Relations
NTT Science and Core Technology Laboratory Group
https://tools.group.ntt/en/news/contact/index.php

Daniel O'Connor

Daniel O'Connor joined the NTT Group in 1999 when he began work as the Public Relations Manager of NTT Europe. While in London, he liaised with the local press, created the company's intranet site, wrote technical copy for industry magazines and managed exhibition stands from initial design to finished displays.

Later seconded to the headquarters of NTT Communications in Tokyo, he contributed to the company's first-ever winning of global telecoms awards and the digitalisation of internal company information exchange.

Since 2015 Daniel has created content for the Group's Global Leadership Institute, the One NTT Network and is currently working with NTT R&D teams to grow public understanding of the cutting-edge research undertaken by the NTT Group.