TU Chemnitz: surround sound out of light, roll-printed speaker paper


If the Institute of Print and Media Technology at Chemnitz University of Technology in Germany has its way, many speakers of the future will not only be as thin as paper, but will also have an impressive sound. This is a reality already in the laboratories of the Chemnitz researchers, who developed the multiple award-winning "T-Book" back in 2015 – a large-format illustrated book equipped with printed electronics. If you turn a page, it begins to sound through a speaker invisibly located inside the sheet of paper. "The T-Book was and is a milestone in the development of printed electronics, but the development continues," says Prof Dr Arved C. Hübler, under whose leadership this technology trend, which is becoming increasingly important worldwide, has been driven forward for more than 20 years.

Five years ago, the sonorous paper loudspeakers from Chemnitz were still manufactured in a semi-automatic single-sheet production process. In this process, normal paper or foils are printed with two layers of a conductive organic polymer as electrodes. Between them is a piezoelectric layer as the active element, which causes the paper or film to vibrate. Loud and clear sound is produced by the displacement of air. Both sides of the loudspeaker paper can be printed in colour. Since this was only possible in single sheets in limited formats, the efficiency of this relatively slow manufacturing process is very low. Therefore, researchers at the Institute of Print and Media Technology have been looking for a new way since May 2017 – towards cost-effective mass production.

The goal of their latest project, "roll-printed speaker paper" (T-Paper in short), was therefore to convert sheet production into roll production. "Researchers from the fields of print media technology, chemistry, physics, acoustics, electrical engineering and economics, coming from six nations, developed a continuous, highly productive and safe roll production of loudspeaker webs," reports project leader Georg C. Schmidt. Not only did they use the roll-to-roll (R2R) printing process, but they also developed inline technologies for other process steps, such as the lamination of functional layers. "In this way, electronics can be embedded in the paper – invisibly and protected," says Hübler. In addition, inline polarisation of the piezoelectric polymer layers has been achieved for the first time and complete inline process monitoring of the printed functional layers is possible. The final project results were published in the renowned journal "Advanced Materials" in January 2021.

The potential of loudspeaker paper was extended to other areas of application in the T-Paper project. For example, metre-long loudspeaker installations can now be manufactured in web form or as a circle ("T-RING"). "In our T-RING prototype, an almost four-metre-long track with 56 individual loudspeakers was connected into seven segments and formed into a circle, making a 360° surround sound installation possible," says Schmidt. The loudspeaker track, including printed circuitry, weighs only 150 grammes and consists of 90 percent conventional paper that can be printed in colour on both sides. "This means that low-cost infotainment solutions are now possible in museums, at trade fairs and in the advertising industry, for example. In public buildings, for example, very homogeneous sound reinforcement of long distances such as corridors is possible. But the process technology itself could also become interesting in other areas, for example in the production of inline measuring systems for Industry 4.0," the project manager says.

The "T-Paper" project was funded by the Federal Ministry of Education and Research with €1.37M from 2017 to 2020 as part of the funding measure "Validation of the technological and societal innovation potential of scientific research - VIP+".

Caption: Varvara Bachul from the Institute of Print and Media Technology at Chemnitz University of Technology analyses the sound generated inside the T-RING (photo: TU Chemnitz)

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