RFID in Textiles

There is hardly any business sector where RFID has not entered (or rather flourishing), and even RFID in Textiles is no exception. Today, the interaction of human individuals with electronic devices demands specific user skills. In future, improved user interfaces can largely alleviate this problem and push the exploitation of microelectronics considerably. In this context the concept of smart clothes promises greater user-friendliness, user empowerment, and more efficient services support. Wearable electronics in the form of RFID in Textiles responds to the acting individual in a more or less invisible way. It serves individual needs and thus makes life much easier.

We believe that today, the cost level of important microelectronic functions is sufficiently low and enabling key technologies are mature enough to exploit this vision to the benefit of society. In the following paragraphs, we present various technology components to enable the integration of electronics into textiles or RFID in Textiles. Key elements are a packaging and interconnect technology for deep textile integration of electronics, a silicon-based micro-machined thermoelectric generator chip for energy harvesting from body heat.

Interconnect and Packaging Technology is another form of RFID in Textiles: 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 form one lead. For the electrical connections the coating of the wires and the surrounding textile material is removed by laser treatment forming holes. A thin flexible printed circuit board (PCB) is then attached to the polyester fabric before the holes in the fabric are soldered and hence the basis for RFID in Textiles. Then the module is encapsulated for mechanical protection. The complete unit is molded forming a hermetically sealed casing that protects it against mechanical and chemical stress caused by wearing and cleaning the textile. As a demonstrator, a speech controlled MP3 player system is realized which is based on a DSP/µC-two processor system.

The RFID in Textiles system is composed of four units, all connected via the conductive textiles: the audio module which is a miniaturized PCB containing the audio chip with several auxiliary elements, a detachable module containing a rechargeable Li-ion battery and a Multi Media Card for data storage, an earphone and microphone module, and a capacitive keyboard module. The user can control the music player either by speaker-independent voice recognition or by means of the keypad. When integrating the proposed system into clothing, special care is necessary for the textile design. The materials are chosen according to maximum wear comfort and environmental compliance. E.g., the audio module has been fully covered by garment, so that the wearer still feels a textile touch.

Thermo generator for Harvesting is another form of RFID in Textiles: Electric Power from Body Heat Numerous wearable devices such as small remote wireless sensor units for medical applications dissipates only a small amount of power. The human body produces several 10 W of heat energy. Miniaturized thermoelectric generators can harness part of this energy and convert it into electrical power. These generators are built of a large number of thermocouples that are electrically connected in series and arranged in meanders to make best use of a given area. They consist of bars of different materials joined at one end. Due to the thermoelectric Seebeck effect, a temperature difference between both ends generates a voltage and an electrical current through a connected load.

Most available thermo generators are realized using compound semiconductors such as bismuth telluride. However, those are expensive, difficult to produce, not compatible with standard silicon chip fabrication processes and non disposable. They will thus not be the optimal choice for low cost applications such as wearable. In line with these arguments silicon appears to be a better choice.

Interwoven Antenna for a Transponder System in Textile Fabric: Today, radio frequency identification tags (RFID in Textiles) are among the smallest and least expensive electronic systems. They consist of a tiny (typically 1 mm2) silicon chip embedded into an inlay with a planar antenna structure. The two antenna contacts are connected to the respective contacts on the chip. Total cost is below 1 €. Neither external leads nor a battery are necessary. Both power supply and I/O are performed by the antenna.

Those functions are performed by a reader device that emits electromagnetic waves at a specific frequency received and modulated by the tag. RFID tags are self-contained systems allowing a hermetically sealed package. This fact facilitates their integration into fabrics subject to harsh cleaning procedures. For integration of RFID in Textiles fabrics the concept of a transponder system with a woven antenna coil structure is proposed. Applications include the item management in laundries or in logistics supply chains, the protection of branded goods and security applications such as access controls.

Due to the self-contained nature of RFID tags they have excellent properties in withstanding elevated temperatures, pressures, chemicals, and mechanic stress. Existing RFID antenna structures are not suited for the rough environment in textile applications. A conducting spiral can be realized by connecting orthogonally oriented conductive warp and weft threads in a fabric. By this means, the antenna structure is fully embedded into the fabric in an unobtrusive and robust way. The chip can be mounted by any one of the integration methods.