Sensor structures with fine or coarse pored surfaces can be manufactured as fusible foils. (Photo: Fraunhofer ISC)
Smart textiles and especially electronic textiles (e-textiles) with their sensory and actuatory functions offer a wide range of applications in medical technology, sports, furniture, vehicles and transport safety. The Center Smart Materials (CeSMa) of the Fraunhofer Institute of Silicate Research ISC in Würzburg/Germany is developing silicone-based elastomer sensors which, due to their chemical, thermal and mechanical robustness, are very well suited for use in technical textiles.
By adding electrically conductive components, the silicone can be produced as a stretchable conductive foil, usable e.g. as flexible heating element. If alternating layers of conductive and insulating silicone are laminated together, stretchable capacitors are created that can be used to measure strain and pressure. Depending on the intended use, the design and softness of the sensors can be adjusted. This allows tailor-made sensitivity and characteristics of the sensors according to the required properties.
The silicone used is skin-friendly, washable, robust and very flexible. Sensors made of this silicone withstand even extreme strains and very frequent use without losing their essential qualities.
In a current project, CeSMa has further developed its intelligent sensors so they can be applied to textiles by printing techniques or ordinary ironing.
The elastomer sensors can be applied permanently to polyester and cotton with a conventional iron in a short time (about 1 minute) even at low temperatures of 80°C. Since the method allows an individual placement of sensor structures, it is especially suitable for smaller batch sizes. In addition, the structures are manufactured separately as ironing films, so that in theory any sensor patterns and various functions can be combined. Currently, work is being carried out different surface structures, ranging from super-smooth to very coarse pored. The sensors can be ironed on almost all textiles and, therefore, are not only intended for original equipment, but above all for the retrofitting of textiles. Thus, use in private households is also possible.
With direct textile printing processes, large-area sensor structures can be imprinted on the desired material in the shortest possible time. The process can be easily integrated into the further processing of the textiles. Very large quantities or mass production are possible. Compared to ironing the printing process is technically more complex, but due to the high number of units that can be implemented it is cheaper and thus particularly interesting for larger manufacturers of textiles.
Heating surfaces and pressure or strain sensors can be ironed on or printed. They can be connected with commercially available cables or with elastic conductive structures. This results in textile-integrated sensor systems that can be used to control functions (actuators, light signals, data processing).
Since the sensors convert mechanical strain into electrical signals, they are also suitable for measuring signals from the human body, i.e. breathing, movement or muscle contraction.
In the field of health care or sports, sensory clothing can be used to monitor proper movement or posture. Using sensor functions, therapeutic exercises could be done and reviewed at home without having a therapist present.
In the area of gaming and in machine control, a glove with the possibility of non-contact gesture control can replace the joystick. For the world of experience of virtual reality (VR), this feature could be particularly interesting in order to eliminate hardware that interrupts the direct experience. Using the principle of gesture control, robots and machines can be controlled remotely or components in the VR world can be manipulated.
In terms of occupational safety and the optimization of manual production processes, workplace ergonomics are becoming increasingly important. In production, when it comes to physically demanding work, sensors can supportively control whether strains are too great or when a posture is disadvantageous. Integrated in seating, sensors can give a warning when an unhealthy posture could lead to health problems.
Fusible and printable elastomer sensors offer interesting new possibilities to implement sensory functionalities in textiles cost-effectively and individually.