Electronic or e-yarns are a natural development within e-textiles as the sector strives toward greater miniaturization, flexibility and a more seamless integration of electronics and textiles. What has started to emerge in a relatively short time is the added value and novelty that it can bring to both smart materials and to yarn development.
Here we look at two growing areas of development. The first relates to haptics, with capabilities ranging from tactile data gloves to vibration-sensing. The second sector focuses on the dual market drivers of product security and transparency. In each case, the use of electronic or e-yarns is offering more flexible, smaller and user-friendly alternatives to existing electronics.
Sensing yarns with haptic capabilities are being used to provide functionality while maximizing dexterity. This is particularly important in the design of smart gloves with two recent examples of innovation in this field coming from researchers in Germany and the U.K.
The German Institutes of Textile and Fiber Research (DITF) Denkendorf has developed flat-knit data gloves where a knitted sensor yarn is integrated during the manufacturing process to produce a completely knitted work glove. The advantage of using a textile sensor is increased elasticity, breathability, drape and flexibility leading to better wearer comfort and usability over longer periods of time.
Part of the issue with more traditional, flexible foil-based sensors is the need for additional process steps and overall cost. The integration of sensors as part of the knitting process offers significant improvements as the textile goes from being the carrier or substrate for the sensor to being the sensor.
In terms of performance, the knitted sensor more easily adapts around the wearer’s hand, reducing the problem of slippage with the skin and the signal noise that this can generate. The multi-layered knitted glove uses polyester as a base layer. To create the force sensor, a silver-coated polyamide (PA) yarn is used for the electrodes, and polymer yarns filled with carbon black are used for the functional layers with the piezoresistive properties.
To protect the sensors from moisture and dust, the final glove is dip-coated with a protective flexible layer such as rubber. It is expected that this will be particularly useful in the workplace, where it is important to know how long an object is held or pressed, with the possibility of locating sensors very precisely in the fingertips or palm area. The DITF have filed the technology as a patent for “Knit product and process for its preparation.”
The Advanced Textiles Researcher Group at Nottingham Trent University are also addressing a glove-focused workplace issue, one caused by overexposure to hand-transmitted vibrations (HTV’s). A 1983 study by the U.S. National Institute for Occupational Safety and Health (NIOSH) estimated that 1.2 million workers in the U.S. were affected.
“Vibrating hand tools can cause vibration syndrome, a condition also known as vibration white finger and as Raynaud’s phenomenon of occupational origin. Vibration syndrome has adverse circulatory and neural effects in the fingers; the signs and symptoms include numbness, pain, and blanching (turning pale and ashen),” the study reported.
Research into the efficacy of anti-vibration gloves funded by NIOSH and the Health and Safety Executive (HSE) published in 2016 advised that anti-vibration gloves cannot be relied on to fully provide the wearer with a sufficient and consistent level of protection. The researchers at Nottingham Trent University are now developing vibration-sensing electronic yarns that can be used in the monitoring of hand-transmitted vibrations. The use of a sensing yarn allows for the tracking to take place closer to the entry point to the body (palm and index finger) without causing discomfort or interfering with the worker’s ability to use the power tool correctly.
The yarn is comprised of small-scale triaxial accelerometers soldered onto fine copper wires, then embedded in the core of the yarn. The yarn is given an outer fibrous covering that consolidates the structure and allows for further processing as well as providing for a positive tactile quality for wearer comfort.
The level of vibration damping achieved is further impacted by the textile structures, and research is currently underway into knit-braids and braids. The researchers have reached proof-of-concept stage and are confident from results achieved that it can contribute to an improved understanding, and therefore the mitigation of, HTV in the workplace.
Transparency and security
The problem of yarn and fabric transparency has been highlighted by Crispin Argento, former executive director of the Organic Cotton Accelerator (OCA), who in a recent New York Times interview estimated that up to four-fifths of organic cotton grown in India is conventional cotton, with several industry insiders claiming that certification fraud is widespread in the country.
The demand for transparency and security from product counterfeiting extends beyond apparel into the whole advanced textiles sector. The verification process is becoming both more transparent and discrete, with new developments in yarn technology that allow for the information to be literally embedded in the fabric structure.
At the University of Wollongong in Australia, researchers are developing a method for signalling the provenance of garments using radio frequency watermarks with two levels of authentication utilized. These are designed to be easy to use by legitimate vendors, but extremely difficult to forge or to hack because the watermark is embedded and based on the radiation signature of electroactive materials.
In tandem with this technology, garment or product manufacturers can use RFID verification on the garment. Without the authentication of both the fabric and garment the process will be incomplete and untrusted. The researchers argue that a dual process addresses the reality that fabric and final product are likely manufactured in different facilities, so this system provides the consumer with a higher level of authenticity.
The RF watermark is based on a conductive silver-coated nylon yarn with additional research underway into the use of conductive polymers, carbon nanotubes (CNT), CNT/spandex and graphene yarns. The results so far are promising as textile antenna because of their mechanical similarity to conventional fibers and yarns.
Challenges remain before commercialization is possible. The danger of damage during laundering, as well as just general use, means that some protection of the yarn is needed. The researchers are proposing encapsulation of the yarn using two types of silicone to prevent damage.
FibreTrace®, based in Singapore, says that its mission is “to ensure every member of the textile supply chain has the ability to take direct accountability to reduce the environmental impact of the global industry.” They are doing this through the provision of real-time verification across the whole supply chain, backed up by primary impact data, as well as verification of the fiber content and its quality.
The company’s technology has been patented as a “Photon marker system for fiber material.” The technology uses rare earth ceramic pigment luminescent nano-particle photon markers that are mixed within a cellulose slurry before being extruded to form trace fiber strands. These are then processed into slivers that are blended with a base fiber or multiple fibers.
According to the patent, the number and proportion of different photon markers and their concentration levels within the yarn, thread, cloth, fabric, textile or garment generate specific photonic response signatures when examined under a spectrophotometer reader. Data signatures can be assigned to provide verification of provenance, base fiber identification, base fiber concentration, the manufacturer and other specified data throughout the manufacturing and supply chain to the finished product.
FiberTrace has just launched partnerships with Acatel advanced vertical finishing mill, and with the Suedwolle Group to provide verified, audited and real-time traceability for their patented luxury Escorial fiber.
Each of the above examples provides evidence that e-yarns are being developed to provide solutions to real-world problems, whether in workplace health or in combating counterfeit products. What is also clear is the importance of the fabric structure—and the entire product value chain—in realizing these outcomes.
Dr. Marie O’Mahony is an industry consultant, author and academic. She is the author of several books on advanced and smart textiles published by Thames and Hudson, and is a visiting professor at the Royal College of Art (RCA), London.