New train glazing for good thermal insulation and mobile reception

From left to right: Jérémy Fleury (PhD student), Azad Kalamian (trainee), Andreas Schüler (MER, group leader), Luc Burnier (group engineer)

From left to right: Jérémy Fleury (PhD student), Azad Kalamian (trainee), Andreas Schüler (MER, group leader), Luc Burnier (group engineer)

Thanks to the support of the enable program, researchers at EPFL are developing a new generation of glazing in collaboration with industrial partners. What makes them special? They have excellent energy efficiency and let through the latest generation of waves used in mobile telecommunications.

For almost two decades, trains have been equipped with insulating glass in order to reduce energy losses. "These double-glazed windows contain a conductive metal coating that prevents either overheating by near-infrared solar radiation and/or heat loss by thermal radiation," explains Andreas Schüler of the Nanotechnology Group for Solar Energy Conversion at EPFL (of the Solar Energy and Building Physics Laboratory LESO-PB). "This thin metal layer therefore makes it possible to control the interior temperature of train cars and save heating and/or cooling energy."

Insulating glass, but impervious to waves

However, the glazing does have one drawback: it strongly attenuates telecommunication waves. "In addition to the metal envelope of modern railcars, this makes the trains completely opaque to mobile phone signals," says Schüler.

About ten years ago, railways and mobile network companies found a solution to signal blocking in the form of signal amplifiers (commonly known as "repeaters"). Placed inside each rail car, these devices pick up and amplify the signal emitted by the telecommunication antennas placed along the rails. Although repeaters are effective, they have several disadvantages such as a limited life span (between 4 and 8 years, compared to about 30 years for a wagon), high cost (CHF 15,000) and additional power consumption (up to 700 watts).

A first solution developed at EPFL in 2016

This finding prompted Andreas Schüler and his colleagues to develop a new type of glazing in 2016 that is both energy efficient and transparent to the microwaves used in mobile telecommunications. How? "By modifying the metal layer with a specific laser treatment. Thus, the glazing can let the waves through," says Schüler. The technology has won several awards and the windows have been installed in 34 regional trains operated by the Swiss transport company BLS.

New glass compatible with the latest telecommunication technologies

The rapid evolution of mobile communication generations and, above all, the growth in data traffic have led to the use of a new communication technology called MIMO (see definition in box). The MIMO technology is already used in 4G LTE (0.8, 1.8 and 2.6 GHz) and is of utmost importance for the implementation and coverage of the Swiss 5G (3.5 − 3.8 GHz). The antennas used in this technology are crossed and the electromagnetic waves now have two distinct polarization directions, with horizontal and vertical components.

"Swisscom approached us in 2019 to express interest in an energy-saving glazing specially adapted to MIMO technology in order to increase data throughput rates without further expensive renewal of the signal boosters," says Schüler. This triggered a collaboration between Swisscom, SBB, LESO-PB (EPFL) and the company Flachglas on the MIMO friendly window project, which was developed as part of a 6-month internship with the support of the enable program offered by the Technology Transfer Office of EPFL.

"The innovative double glazing developed initially in 2016 has been developed further and adapted to MIMO technology," explains Héloïse Delaporte, who has just completed her internship at the LESO-PB of EPFL. The first prototype, manufactured in collaboration with Flachglas, has been tested and the feasibility has been proven. "We are now in the final stages of optimization and hope to have the final prototype by the end of the year," adds Schüler. "At the same time, a patent has been filed on behalf of EPFL and Swisscom”.

Great potential for buildings
In the long term, the LESO-PB team expects its glazing to have a considerable impact in the building industry. In particular, tests carried out since 2018 in the SolAce unit of EMPA's NEST experimental building in Dübendorf (more information).

Project budget (enable support)
Internship: CHF 17,215
Prototyping: CHF 15,000

About enable:
enable is the technology acceleration program of EPFL. One of the missions of EPFL is to encourage the transfer of research results to products and services through licensing. To this end, enable provides funding and expertise to refine and advance early-stage technology to make a step further towards the market.“We select projects with significant commercial potential and provide financial support and domain expertise to fuel translational research, proof-of-concept, and technological development. We simultaneously build relationships with industry, generating partnerships and licensing opportunities”, explains Eric Meurville, Technology Acceleration Manager at the EPFL Technology Transfer Office. Every year, around 15 EPFL technologies are supported by enable.