Functional Electronic Screen Printing –
Electroluminescent Smart Fabric Watch
Marc De Vos, Dr Russel Torah, Prof Steve Beeby and Dr John TudorSmart Textiles Salon6th June 2013
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Overview• Motivation for screen printed smart fabrics.
• Introduce functional electronic screen printing on fabrics.
• Printed smart fabric watch design.
• Printing process for electroluminescent watch.
• Demonstration video.
• Conclusions and further work.
• Examples of other screen printed smart fabrics.
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Motivation for a printed watch• Digital watches are typically flexible straps with rigid displays.
• Key Advantages of a printed smart fabric watch:
–Increased comfort and flexibility through all fabric design.
–Washable – greater sporting applications.
–Can be easily integrated into other garments, furniture or curtains.
• The technology can be used to demonstrate electroluminescent applications for visual displays.
• Could be used alongside standard artwork for advertising displays.
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Functional Electronic Screen Printing on Fabrics• Screen printing requires a screen, squeegee and a printable paste.
• Key advantage: Any pattern can be printed, not restricted to warp and weft directions.
• Key advantage: Printed on top of the fabric so the fabric properties next to the skin are not affected.
• Key advantage: Roll to roll process so can be printed as part of the fabric manufacturing process.
• It can be used to deposit standard materials such as conductors, resistors and dielectrics.
• We have also developed more exotic printable materials such as piezoelectric, piezoresistive, thermochromic, sacrificial and electroluminescent.
• Typical print thickness after drying is between 5 and 50µm depending on the materials.
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Printed smart fabric watch design• Electroluminescence requires an electric field to be
applied across a phosphor layer using.
• A capacitor sandwich structure is used with a semi-transparent top electrode layer to allow light emission.
• The layers are printed directly on to the fabric with no further processing required.
• Initial design is large to prove the concept. The design principle can be scaled up or down depending on application.
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Printing process for EL watch on fabric
• 6 individually printed and cured layers for the EL watch:
– Interface layer: reduces surface roughness of the fabric.
– Bottom electrode layer: provides the ground plane.
– Dielectric layer: allows for a greater lamp brightness and reduced chance of short circuits.
– Phosphor layer: provides the light producing layer, the phosphor emits light under the influence of an electric field.
– Top/bus electrode layer: provides connection to the top electrode of the capacitor structure.
– Semi-transparent electrode layer: provides an even distribution of charge across the phosphor layer for improved light distribution.
Electrical characteristics• Input voltage of 2.7-5.5v, 3v used for testing.
• If a standard “button cell” battery used, estimated lifetime of ~12 hours continuous use.
• Lifetime could be significantly improved through use of touch sensors to turn display on/off.
• Average resistance over a track of ~12 Ω – dependent on length and flexing.
• Average resistance across top semi-transparent electrode of ~10 kΩ/cm.
• Could implement a swipe feature to turn on.
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Demonstration video
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Photos of printed EL watch display prototype
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Conclusions and further work• World’s first all screen printed EL watch display on fabric.
• Can be printed on most fabrics.
• First prototype stage demonstrated, future devices will be smaller and with more multi-layered PCB approach.
• Integration of electronics possible into smaller packages on to fabric or as a detachable flexible circuit board.
• Additional functions such as a swipe across the touch pads to turn on the display.
• Smaller display and shorter wires would further increase the battery lifetime.
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Examples of other UoS printed smart fabrics
Acknowledgments• University of Southampton – Electronics and
Computer Science – www.ecs.soton.ac.uk
• Smart Fabric Inks Ltd – www.fabinks.com
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