Smart Textiles and Intelligent Textiles
Smart textiles are textiles that can sense and react to environmental conditions or stimuli from mechanical, thermal, chemical, electrical, or magnetic sources. Smart textiles may combine fabrics with glass, ceramics, metal, or carbon to produce lightweight hybrids with incredible properties. Sophisticated finishes, such as silicone coatings and holographic laminates, transform color, texture, and even form.
Electronic Embedded Smart Textiles
Today, the interaction of human individuals with electronic devices demands specific user skills. In this context, the concept of smart clothes promises greater user-friendliness and more efficient services cost level of important microelectronic functions is sufficiently low 5, and enabling key technologies are mature enough to exploit this vision. An interconnect and packaging technology is demonstrated using a polyester narrow fabric with several warp threads replaced by copper wires which are coated with silver and polyester. Six of those parallel conductive warp threads from one lead. For the electrical connections, the coating of the wires and the surrounding textile material is removed by laser treatment forming holes.
Electronic circuits built entirely out of textiles to distribute data and power have been devised by researchers at MIT, USA. They can perform touch sensing, and use passive components sewn from conductive yarns as well as conventional electronic components. This creates interactive electronic devices such as musical keyboards and graphic input surfaces. One day entire computers may be made from textile articles that people prefer to wear. And these electronic circuits are a modest beginning in that direction.
The first conductive fabric tried was silk organza which contains two types of fibers. On the warp is a plain silk thread while running in the other direction on the weft is a silk thread wrapped in thin copper foil. This metallic yarn is prepared just like cloth-core telephone wire and is highly conductive.
The silk fiber core has high tensile strength and can withstand high temperatures. This allows the yarn to be sewn or embroidered with industrial machinery. The spacing between these fibers also permits them to be taken care of individually, so a strip of this fabric can function like a ribbon cable. Circuits fabricated on organza only need to be protected from folding contact with themselves, which can be accomplished by coating, supporting or backing the fabric with an insulating layer which can also be cloth. There are also conductive yarns manufactured specifically for producing filters for the processing of fine powders.
These yarns have conductive and cloth fibers interspersed throughout. Varying the ratio of the two constituent fibers leads to differences in resistivity. These fibers can be sewn to create conductive traces and resistive elements. While some components such as resistors, capacitors, and coils can be sewn out of fabric, there is still a need to attach other components to the fabric. This can be done by soldering directly onto the metallic yarn. Surface mount LEDs, crystals, piezo transducers, and other surface mount components with pads spaced more than 0.100 inches apart are easy to solder into the fabric.
Once components are attached, their connections to the metallic yarn may need to be mechanically strengthened. This can be achieved with acrylic or another flexible coating. Components with ordinary leads can be sewn directly into circuits on fabric, and specially shaped feet could be developed to facilitate this process. Gripper snaps make excellent connectors between the fabric and electronics. Since the snap pierces the yarn it creates a surprisingly robust electrical contact. It also provides a good surface to solder to. In this way, subsystems can be easily snapped into clothing or removed for washing.
Wearable electronic circuit
Several circuits have been built on and with fabric to date, including busses to connect various digital devices, microcontroller systems that sense proximity and touch, and all-fabric keyboards and touchpads. Building systems in this way is easy because components can be soldered directly onto the conductive yarn.
The addressability of conductors in the fabric makes it a good material for prototyping and it can simply be cut where signals lines are to terminate. Keyboards can also be made in a single layer of fabric using capacitive sensing [Baxter97], where an array of embroidered or silk-screened electrodes make up the points of contact. This is shown in the figure. A finger’s contact with an electrode can be sensed by measuring the increase in the electrode’s total capacitance.
It is worth noting that this can be done with a single bidirectional digital I/O pin per electrode, and a leakage resistor sewed in highly resistive yarn. Capacitive sensing arrays can also be used to tell how well a piece of clothing fits the wearer because the signal varies with pressure.
The keypad is flexible, durable, and responsive to touch. A printed circuit board supports the components necessary to do capacitive sensing and output keypress events as a serial data stream.
The circuit board makes contact with the electrodes at the circular pads only at the bottom of the electrode pattern. In a test application, 50 denim jackets were embroidered in this pattern. Some of these jackets are equipped with miniature MIDI synthesizers controlled by the keypad.
The responsiveness of the keyboard to touch and timing were found by several users to be excellent. These researchers have tried to combine conventional sewing and electronics techniques with a novel class of materials to create interactive digital devices. All of the input devices can be made by seamstresses or clothing factories, entirely from fabric. These textile-based sensors, buttons, and switches are easy to scale in size. They also can conform to any desired shape, which is a great advantage over most existing, delicate touch sensors that must remain flat to work at all. Subsystems can be connected together using ordinary textile snaps and fasteners. Finally, they can be washed like regular clothes when subjected to dirt.
Smart Textiles in Fashion
These are intelligent textiles which change color (because the dye applied on the surface change color) with change in temperature. Chromic materials are the general term referring to materials which radiate the colour, erase the colour or just change it because of its induction caused by the external stimuli, such as light, heat, electricity, solvent, pressure.
The color change is especially due to application of thermo chromic dyes whose color changes at particular temperature. 2 types of thermo chromic systems that have been successfully applied to textiles may be recognized, the liquid crystal type and the molecular rearrangement type. In both the cases, the dye is entrapped in microcapsules, applied to garment fabric like a pigment in a resin binder.
The most important types of liquid crystals for the thermo chromic systems are the so called cholesteric types, where adjacent molecules are so arranged that they form helices. Themochromism results from selective reflection of light by the liquid crystal. The wavelength of the light reflected is governed by the refractive index of the liquid crystal and by the pitch of the helical arrangement of its molecules. Since the length of the pitch varies with temperature, the wavelength of the reflected light is also altered, and a color change results.
An alternative way of inducing thermo chromism is by means of a rearrangement of the molecular structure of a dye as a result of a change in temperature. The most common types of dye which exhibit thermo chromism through molecular rearrangement are the Spiro lactones, although other types have also been identified.
A colorless dye precursor is microencapsulated and is solid at lower temperatures. On heating, the system becomes colored or loses color at the melting point of the mixture. The reverse change occurs at this temperature if the mixture is then cooled. However, although thermo chromism and molecular rearrangement in dyes has aroused a degree of commercial interest, the overall mechanism underlying the changes in color is far from clear cut and is still very much open to speculation7.
A temperature sensitive fabric with trade name SWAY was manufactured by introducing microcapsules, diameter 3-4mm to enclose heat sensitive dyes, which are resin coated homogeneous over fabric surface. The microcapsules were made of glass and contained the dyestuff, the chromophore agent (electron acceptor) and color neutralizers (alcohol etc.) which reacted and exhibited color/no color according to environmental temperature. SWAY had 4 basic colors and 64 combined colors. It could reversibly change color at temperature greater than 5◦C and could be operated from -40◦C to 80◦C.
Danial Cooper has designed a jacket that is useful for protecting the wearer from pollution. The front panels are made of nylon fabric embedded with nitrogen oxide, sulfur dioxide and ozone monitors. When there is pollution, the fabric changes its color from blue to orange16.
Musical jacket turns an ordinary jacket into a wearable musical instrument. Musical jacket allows the wearer to play notes, chords, rhythms, and accompaniment using any instrument available in the general music scheme. It integrates fabric keypad, a sequencer, synthesizer, amplifying speakers, conductive organza, and batteries to power these subsystems.
The smart suit consists of global mobile system for communication, functional architecture for navigation, and electrically heated fabric panels for heating. The sensor system consists of a heart rate sensor, three position and movement sensors, ten temperature sensors, an electrical conductivity sensor and two impair detecting sensors.
The implementations and synchronization requires a user interface (UI), a central processing unit (CPU) and a power source. Each main module, excluding the sensors and the user interface is set into the supporting vests. This smart suit allows easy, fast, and cost efficient group communication. A cellular telephone, loudspeaker and microphone are incorporated in the belt. By pulling a tag on this belt, communication can be achieved by groups of people.
Smart mp3 player
Aircraft maneuverability depends heavily on the movement of flaps found at the rear or trailing edge of the wings. The efficiency and reliability of operating these flaps is of critical importance. Most aircraft in the air today operate these flaps using extensive hydraulic systems. These hydraulic systems utilize large centralized pumps to maintain pressure, and hydraulic lines to distribute the pressure to the flap actuators. In order to maintain reliability of operation, multiple hydraulic lines must be run to each set of flaps. This complex system of pumps and lines is often relatively difficult and costly to maintain. Many alternatives to the hydraulic systems are being explored by the aerospace industry. Among the most promising alternatives are piezoelectric fibers, electrostrictive ceramics, and shape memory alloys.
The flaps on a wing generally have the same layout shown on the left, with a large hydraulic system attached to it at the point of the actuator connection. “Smart” wings system is much more compact and efficient, in that the shape memory wires only require an electric current for movement.
The shape memory wire is used to manipulate a flexible wing surface. The wire on the bottom of the wing is shortened through the shape memory effect, while the top wire is stretched bending the edge downwards, the opposite occurs when the wing must be bent upwards. The shape memory effect is induced in the wires simply by heating them with an electric current, which is easily supplied through electrical wiring, eliminating the need for large hydraulic lines. By removing the hydraulic system, aircraft weight, maintenance costs, and repair time are all reduced. The smart wing system is currently being developed cooperatively through the Defense Advanced Researched Project Agency (DARPA, a branch of the United States Department of Defense), and Boeing.
The earliest developed Apollo spacesuits contained an inner layer of nylon fabric with network of thin walled plastic tubing which circulated cooling water around the astronaut to prevent overheating. This inner layer was comfort layer of lightweight nylon with fabric ventilation ducts, and then a three layer system formed the pressure garment.
Then aluminized Mylar was used for heat protection, mixed with four spacing layers of Dacron. These were covered with a non flammable and abrasion protective layer of Teflon-coated beta cloth. The outer layer was Teflon communication cloth. The backpack unit contained a life support system providing oxygen, water and radio communications.
Thus we have considered the major interesting applications of smart textiles in various sectors. We have also considered the mechanism by which these smart systems operate and also reviewed the process of manufacturing.
Smart or Interactive Textiles is a new market segment resulting from the miniaturisation of electronics and the fall in price of components and manufacturing costs for both electronics and textiles. A simultaneous trend in the clothing industry toward manufacture of specific products for dedicated uses i.e. for running, skiing, golf and extreme sports has created a niche where smart and interactive textiles enable new functions and features that can enhance a garments performance and its wearers experience.
Low cost fibre and textile manufacturing in Asia and India has caused significant cut backs in production in Western Europe and has pressed traditional textile companies to look to new technologies to add value in the design phase of a production. Such new technologies are immature and often promoted by start-up companies that are spin-offs from professional research. With limited funding to commercialise their products, the result is that some of the most exciting technologies have not yet been exploited to the full.
Market Structure and stakeholders
While smart textile applications have made a limited commercial impact so far, with relatively small volumes of commercial products launched primarily in the high performance apparel sector predictions for growth of the smart textile market as a whole are huge. According to the Venture Development Corporation the market for electrically enabled smart fabrics and interactive textile technologies was worth US$340.0 million in 2005.
By 2008 it is expected to be worth US$642.1 million, representing a compound annual growth rate of 28.3%. While some predictions do not agree on the total value of the market, they are all agreed that the market for smart textiles is one of the most dynamic and fast growing sectors and offers huge potential for companies willing to take the plunge. Not surprisingly, most of the smart textile consumer products launched so far have been introduced onto the luxury end of the performance clothing market where development costs can be more readily absorbed by higher prices.
Companies dominating this segment are those who already have a significant market share such as Nike, Adidas and ONeill. Products launched in this sector show a clear trend toward strong design features coupled with simple to operate functions that are highly relevant to the garments wearer in the particular use situation.
A good example of this is the Nike plus running shoe. Cooperation with IT giant Apple has resulted in a simple user friendly web interface that enables runners to motivate themselves and each other by uploading data recorded by the sensor in the shoe and transferring it to a standard iPod nano. The system is stylish, simple to operate and enables runners to track their performance and set new targets to be reached.
Major actors in the performance clothing segment
- Adidas, Nike
- ONeill, Burton, North Face, Rosner
Monitoring health and vital signs, commercial products in 2007
- VivoMetrics (Lifeshirt)
- Adidas, Numetrex
- Eleksen, Peratech Ltd,
Electronics Components Manufacturers
- Interactive Wear, Ohmatex, Fibretronix
Areas of Possible Smart Textile Integrations
- Military (e.g. uniforms which can detect chemical threats in a battlefield)
- Airplanes (e.g. in manufacture of flaps found in aircraft wings)
- Biomedical field (e.g. manufacture of smart sutures, tissues)
- Space research (e.g. special spacesuits designed for astronauts)
- Comfort wears (e.g. fabrics which can maintain body temperature)
- Sports (e.g. fabrics which can make athletes feel comfortable even in stretched body conditions)
- Fashion clothing (e.g. fabrics which can change color according to ambient temperatures)
Smart textiles have a lot many applications besides the abovementioned ones, but before we discuss them let us concentrate on the fundamental mechanisms that make a fabric smart. In this new era the smart textiles are considered also as textronics.
The term textronics refers to interdisciplinary approaches in the processes of producing and designing textile materials, which began about the year 2000. It is a synergic connection of textile industry, electronics and computer science with elements of automatics and metrology knowledge.
A new quality is achieved as result of using component elements, which thanks to mutual feedback increase their affect. This can be obtained by the physical integration of microelectronics with textile and clothing constructions. The main task of textronics is to produce multifunctional, intelligent products with complex inner structures, but which have uniform functional proprieties. Textronic products are characterised by the following features:
Flexibility meaning facility in modifying the construction at the stage of design, production and exploitation; for example, modular construction;
Intelligence of the textiles referring to the possibility of an automatic change in properties influenced by external factors (parameters) and even taking decisions, which means learning or communication with the environment.
Multifunctionality, or the ease of realising different functions by one product.
It can be stated that textronics means the design and production of intelligent and interactive textile materials which are characterised by variable structures or electrical resistance, which include microchip elements and is characterised by self-adaptive features.
New markets for textiles
Chemical engineering developments in recent years have led to development of textile fibres with properties such as extreme strength, lightness in weight and where fibres can change their shape dependant upon temperature or other external stimuli. These features are just beginning to be exploited in entirely new sectors, where textiles have not traditionally been standard materials. Applications are widely predicted to be highly diverse, covering segments from EMI shielding in automotive, planes and the like to use as moulding forms for architectural components and to reinforce and strengthen concrete building elements.