Design of a UHF RFID Fiber Tag Antenna with Electric-thread using a Sewing Machine

Design of a UHF RFID Fiber Tag Antenna with Electric-thread using a Sewing Machine

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RFID (Radio Frequency Identification) technology is an automatic identification method, transferring object data wirelessly, and is a core technology for fast and effective business process in various industrial applications such as logistics and factory automation. In SCM (Supply Chain Management) system, RFID technology makes continuous product flow management feasible including manufacturing, transportation, and distribution of products, and it becomes widespread as Wal-Mart has began its effort to requiring its suppliers to use RFID in its end product packaging [1-2]. Textile and clothing industries are very import to human being and the application of the RFID system to these industries is necessary. In these industries, various items are treated and the inventory of them is done monthly, and the real-time inventory is almost impossible. However, the real-time inventory considering all the sorting elements such as color and size is possible and the processing time can be significantly reduced. In addition, Just-In-Time system for real-time inventory supplement can be realized by knowing the moving route and the history information of the products. For this purpose, an RFID tag should be attached on each clothes. General label type RFID tags can not be directly used and an additional process needs to be included, which increases the total cost of the clothes. To resolve this problem, a new design method of a RFID fiber tag antenna with electric-thread using sewing machine is proposed in this paper. In addition, brand or company mark can be used as an RFID tag by using the proposed method.


As is well-known, copper is the most widely used electrical conductor. Like most metals, it has several disadvantages: flexibility, manufacturability, and price. Fibers that conduct electricity could be the solutions to these problems. An embedded UHF RFID tag using electro-thread can be applied to wearable and flexible tag antenna attached to any flexible surface or wire [3]. When a RFID tag antenna is designed using electro-thread, the conductivity of the electro-thread has to be considered. The conductivity is related to the radiation efficiency of tag antenna which influences the reading range of tag. Friis’s Transmission formula is used to calculate the maximum reading range ( max r ) of a RFID system [4].

Design, Fabrication and Measurements Figures 2 and 3 are the geometry of a proposed antenna and the picture of a fabricated antenna. The size of the antenna is about 130 x 37mm and it is designed by the shape of alphabet characters (RFID). From the results of the simulation of this antenna with 2e3 conductivity of electric-thread, the radiation efficiency is about 33% at 912MHz which is the center frequency of Korea UHF RFID frequency band. From eq. (3), this means that the read range of this antenna decreases about 0.57 times compared to 100% radiation efficiency. The RFID tag chip manufactured by Impinj inc. is used. As shown these figure, the results of the simulation and the measurement are a little different. The reasons are that the surface of the antenna is not uniform and finishing of sewing is not clear. The reading range is presented in Fig. 7. In an anechoic chamber, the maximum measured reading range is about 2.5m using ALR-9800 reader.

An RFID tag antenna with electric-thread using a sewing machine is proposed. The characteristics of the electric-thread used as tag antenna are studied and the changes of conductivity for different sewing methods are analyzed. The electro-thread tag antenna is designed by the shape of alphabet characters. The radiation efficiency is about 33% and the measured maximum reading range is about 2.5m in an anechoic chamber. It is demonstrated that the electro-thread is possible to be directly applied to clothes as a brand or company marks. However, it is necessary to develop some additional technology for packaging to protect a tag chip from laundry and wrinkle.

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