Magazine March 2013

All the latest information from the textile world

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Just an imageStructure of a solar cell with textile front electrode

Smart Fabrics from Switzerland – Welcome to Sefar

Fabric electrodes for flexible solar cells

Just an imageTransparent front electrode on fabric base

Just an imageFurther example of a smart fabric

The Sefar Group has a worldwide presence, with subsidiaries in 21 countries and agencies in a further 75 countries. The Smart Fabrics Group was founded seven years ago as part of the Sefar AG. Typical projects are currently located in the solar power, sensor system and heating sectors. A few of these Smart Fabrics projects and technologies are presented below.

In recent years, for example, Sefar has developed a transparent front electrode on a fabric base for flexible solar cells. The synthetic fabric is coated on one side with a gas-tight, transparent layer ; it offers transmittance of over 85 percent, and can be processed using the roll-to-roll method. The conductivity in the fabric is created by means of woven-in metal wires (R < 1 Ω/sq).

Conventional solar technologies are based on materials like ITO, TCO, CNT or nanowires. These materials are either brittle, expensive, UV-unstable, or poor conductors.

Currently the electrode has been optimized for so-called dye solar cells (DSCs). However it can also be utilized for further optoelectronic applications such as conventional solar cells, OLEDs, electroluminescent lamps, or displays.

PowerSense fabrics

Just an imageLeakage sensor tape

Under the title of PowerSense, Sefar offers applications that use fabrics to measure sizes and parameters. The majority of the fabrics developed are customized ones.

Tape for leakage detection

To detect leaks in pipelines, a section of fabric has been developed with fine longitudinal wires at close intervals. In combination with a transfer adhesive this creates a kind of "tape" that is wound around the tube of the pipeline. If leakage occurs, the fine wire is cut by the material escaping under high pressure. This can be established simply by measuring the electrical resistance.

Just an imageKnitted fabric with meander-shaped, embedded wire and edge reinforcement

Break-in detection, temperature measurement – knitted and woven fabrics with outstanding potential

Just an imageCargo container with fabric attached

Just an imageFlat temperature sensor for the EU project PROSPIE

Just an imageFlow-speed measurement using filter fabric

Knitted fabrics to detect break-ins

For a joint project with Tamper-Proof Global Systems Corporation (TPGS), Sefar developed a knitted fabric with a meander-shaped, embedded infinite metal wire. The fine wire is closely integrated above the knit width of 1.20 m.

The aim of this application is to detect break-ins in cargo containers. Here, all six sides within the container are covered with the fabric. The individual knitted fabric sections are electrically connected to an electronic monitoring system, and are also coated with an additional protective layer.
As soon as the thin metal wire in one of the sections is broken, an alarm sounds.

Fabrics for temperature measurement

Another textile sensor was invented and built for the EU project "PROSPIE". Here it was important that the average surface temperature could be recorded without creating heat build-up. The open fabric of the textile temperature sensor from Sefar fulfilled this requirement.

Filter fabric with flow speed sensor

The flow velocity of a fluid can be measured according to the principle of Constant Temperature Anemometry (CTA). Here the fluid flows through filter fabric containing two spatially separated wire structures. One structure is warmed up to a few Kelvin higher than the fluid temperature, and the other structure measures the actual fluid temperature. The temperature of the heated structure is kept constant by an electronic control – independent of the fluid flow. The voltage required corresponds to the fluid speed. In this way, the fluid flow can be recorded across the entire cross section of the pipe.

Just an imageStretch sensor in yarn form

Stretch sensor yarn

Just an imageMeasuring curve of the stretch sensor

Stretch measurement is an important element for recording mechanical processes in fabrics and plastic components. Sefar has developed a special sensor yarn for this purpose. In contrast to stretch sensors, which are based on changes in conductivity in coated yarns, the Sefar yarn only displays minimal hysteresis behavior. The measuring curve shows a few loaded/unloaded cycles with a short pause in between. The stretch in each cycle amounts to 1.5 percent – a typical value for dynamic strain in fabrics.

Sefar sets standards

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Over the past few years, Sefar has developed an extensive technology portfolio for Smart Fabrics on the basis of electrically conductive fabrics. These fabrics are often used in industry as intermediate products. For example, the flexible, textile character of the fabric and its open knit enable 3D deformation and integration into injection-molded parts.

Fabrics for functional integration are unique. Entirely new applications would be impossible without them. Furthermore, the use of Sefar fabrics can radically simplify existing production processes.

Sefar – contact data:

Hinterbissausstrasse 12
CH-9410 Heiden

Tel: +41 (0) 71 898 5700
Fax: +41 (0) 71 898 5721

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Groz-Beckert – Partner to Leading Fabric Producers

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Sefar purchases the weaving accessories it needs for processing sensitive warp yarns from Groz-Beckert. For the highest weaving densities, 12-row warp stop motions are used. Carbon-fiber reinforced hybrid heald frames from Groz-Beckert enable Sefar to weave at widths of up to 430 cm without intermediate struts getting in the way. For the finest monofilaments, the Swiss company uses healds and drop wires from Groz-Beckert.

Do you have any questions you'd like to ask about weaving accessories or weaving preparation? If so, Groz-Beckert looks forward to a discussion with you!