Textination Newsline

Researchers at Fraunhofer have developed an ultra-compact near-infrared spectrometer suitable for recognizing and analyzing textiles. Mixed fabrics can also be reliably identified through the combination of imaging, special AI (artificial intelligence) algorithms and spectroscopy. The technology could be used to optimize recycling old clothing, so old apparel could be sorted according to type. A highly miniaturized version of the system can even fit into a smartphone. This could lead to a host of new applications for end-users in everyday life — from checking clothes when out shopping to detecting counterfeits.

Infrared spectrometers are powerful measuring instruments when it comes to non-destructive analysis of organic materials. The Fraunhofer Institute for Photonic Microsystems IPMS in Dresden has recently developed a spectral analyzer system that recognizes and analyzes textile fabrics. The system can also reliably recognize mixed fabrics. Possible applications range from checking fabrics when out shopping to cleaning garments correctly, and even sustainable, sorted recycling. The spectrometer is so tiny, it can be integrated into a smartphone.

Researchers at Fraunhofer rely on near-infrared (NIR) spectroscopy to achieve the required reliability and accuracy when identifying textiles. The system works for wavelengths between 950 and 1900 nanometers, which is close to the visible spectrum. Advantages of near-infrared technology include being easy to use and having a wide range of applications. “We combine NIR spectroscopy with imaging and AI to achieve higher accuracy when recognizing and analyzing objects,” explains Dr. Heinrich Grüger, research scientist in the Sensoric Micromodules department at Fraunhofer IPMS.

How textile analysis works
Firstly, a conventional camera module captures an image of the garment. The AI selects a specific point from the fabric’s image data to be examined by the spectral analyzer module. Light reflected from the fabric is captured by the spectrometer module. There, it passes through an entrance slit, is transformed into parallel light beams using a collimating mirror and projected onto a grating using a scanning mirror. Depending on the angle of incidence and exit, the grating splits the light beams into different wavelengths. Light reflected from the grating is directed by the scanner mirror to a detector which captures the light as an electrical signal. An A/D converter then digitizes these signals, which are subsequently analyzed in the signal processor. The resulting spectrometric profile for the textile fabric reveals which fibers it is made from by comparing to a reference database.“ The optical resolution is 10 nanometers. This high resolution means the NIR spectrometer can also use AI to identify mixed fabrics such as items of clothing made from polyester and cotton,” says Grüger. Measuring just 10 mm × 10 mm and being 6.5 mm thick, the system is so compact it could easily be integrated into a standard smartphone.

Recycling old clothing
Grüger sees an important application for the AI-controlled spectrometer when it comes to recycling. According to the Federal Statistical Office of Germany, approximately 176,200 tons of textile and clothing waste was collected from private homes in Germany in 2021. NIR spectroscopy could improve recycling efficiency and reduce the mountain of old clothing. This would enable companies that recycle old clothing to sort it more efficiently and faster. Textiles that are still in one piece, for instance, go to the second-hand trade. Damaged textiles are sorted for recycling, and the fibers they are made from, such as linen, silk, cotton or lyocell, can be reused. Severely soiled textiles would be incinerated or processed into insulation mats, for example. Spectroscopic identifies and sorts textiles more accurately and much faster than a human can.

If NIR spectroscopy was to be integrated into a smartphone, end-users might also benefit from the Fraunhofer institute’s technology. When buying clothes, a quick check with a smartphone reveals whether that expensive silk scarf is genuinely made from silk, or whether that exclusive dress from the fashion label is not instead a counterfeit, exposed through an alternative mix of fabrics. And should the label with the cleaning instructions no longer be legible, the smartphone has a textile scanner to identify the fabric and so determine the appropriate wash cycle.

Food check and dermatology
Researchers at Fraunhofer IPMS can even envisage applications beyond the textile industry. Smartphones fitted with spectrometers might be used to provide information about the quality of groceries such as fruit and vegetables when out shopping. The technology might conceivably also be used to examine skin. A quick scan with the cell phone spectrometer could identify particularly dry or greasy patches. Perhaps applications in medical diagnostics might even be conceivable — examining patches of skin where a melanoma is suspected, for example — but this would need professional involvement too.

Imagine a truck tarp that can harvest the energy of sunlight!
With the help of new textile-based solar cells developed by Fraunhofer researchers, semitrailers could soon be producing the electricity needed to power cooling systems or other onboard equipment. In short, textile-based solar cells could soon be adding a whole new dimension to photovoltaics, complementing the use of conventional silicon-based solar cells. Solar panels on building roofs are a common enough sight today – as are large-scale solar parks. In the future, we may well see other surfaces being exploited for photovoltaic generation. Truck tarps, for example, could be used to produce the electricity consumed by the driver when underway or parked up for the night, or to power electronic systems used to locate trailers in shipping terminals. Similarly, conventional building facades could be covered with photovoltaic textiles in place of concrete render. Or the blinds used to provide shade in buildings with glass facades could be used to create hundreds of square meters of additional surface for producing power.

Glass-fiber fabric as a solar-cell substrate
At the heart of such visions are pliable, textile-based solar cells developed at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in collaboration with the Fraunhofer Institute for Electronic Nano Systems ENAS, Sächsisches Textilforschungsinstitut e.V and industrial partners erfal GmbH & Co. KG, PONGS Technical Textiles GmbH, Paul Rauschert GmbH & Co. KG and GILLES PLANEN GmbH. “There are a number of processes that enable solar cells to be incorporated in coatings applied to textiles,” explains Dr. Lars Rebenklau, group manager for system integration and electronic packaging at Fraunhofer IKTS. In other words, the substrate for the solar cells is a woven fabric rather than the glass or silicon conventionally used. “That might sound easy, but the machines in the textile industry are designed to handle huge rolls of fabric – five or six meters wide and up to 1000 meters in length,” explains Dr. Jonas Sundqvist, group manager for thin-film technology at Fraunhofer IKTS. “And during the coating process, the textiles have to withstand temperatures of around 200 °Celsius. Other factors play a key role too: the fabric must meet fire regulations, have a high tensile strength and be cheap to produce. “The consortium therefore opted for a glass-fiber fabric, which fulfills all of these specifications,” Rebenklau says.

An emphasis on standard processes
Researchers also faced the challenge of how to apply the wafer-thin layers that make up a solar cell – the bottom electrode, the photovoltaic layer and the top electrode – to the fabric. These layers are between one and ten microns in thickness. By comparison, the surface of the fabric is like a mountain range. The solution was first to apply a layer that levels out the peaks and troughs on the surface of the fabric. For this purpose, researchers opted for a standard process from the textile industry: transfer printing, which is also used to rubberize fabrics. All the other processes have been adapted in such a way that they can be easily incorporated in standard production methods used in the textile industry. For example, the two electrodes – which are made of electrically conductive polyester – and the photovoltaic layer are applied by means of the common roll-to-roll method. The solar cells are also laminated with an additional protective layer in order to make them more robust.

Fabric-based solar cells ready for market launch in around five years
The research team has already produced an initial prototype. “This has demonstrated the basic functionality of our textile-based solar cells,” Rebenklau says. “Right now, they have an efficiency of between 0.1 and 0.3 percent.” In a follow-up project, he and the team are seeking to push this over the five percent mark, at which point the textile-based solar cells would prove commercially viable. Silicon-based solar cells are significantly more efficient, at between ten and 20 percent. However, this new form of solar cell is not intended to replace the conventional type, merely offer an alternative for specific applications. In the coming months, the team will be investigating ways of enhancing the service life of the fabric-based solar cells. If all goes according to plan, the first textile-based solar cells could be ready for commercialization in around five years. This would fulfill the original goal of the PhotoTex project: to provide new stimulus for Germany’s textile industry and improve its competitiveness.