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RFID Sheet Antennas Enable Unique Shelf-Management Systems

Measuring only six millimeters in thickness, the short-range antennas—marketed by Teijin Fibers and Convergence Systems Ltd.—are being installed on shelving, along with EPC UHF readers, to track the locations of tagged items.
By Claire Swedberg
Dec 16, 2011Japanese company Teijin Fibers, employing technology from Hong Kong RFID firm Convergence Systems Ltd. (CSL) and Cellcross Co. Ltd., is marketing a new shelf-management system consisting of an RFID sheet antenna that can be placed on a shelf in order to track RFID tags on items placed on that shelf. The solution, which Teijin Fibers plans to officially launch this month in Japan, includes an EPC Gen 2 ultrahigh-frequency (UHF) CS468 RFID reader and a CS790 antenna designed and built by CSL, with a Cellcross-designed sheet antenna embedded in Teijin's polyester fibers.

The sheet antenna limits the range of RF waves to better control the RF field, thereby reducing the amount of "bleed over" of RF transmission beyond the shelf's edges, as well as the range at which it reads tags. The antenna is very thin—approximately 6 millimeters (0.2 inch) in thickness. Teijin's solution also comes with the company's software for storing and interpreting read data, in addition to CSL's EPC Gen 2 UHF passive RFID tags. Teijin expects to launch the system commercially in Japan on Dec. 19.

(Illustration courtesy of Cellcross Co.)

Teijin's Cell Form sheet antenna employs @CELL technology, developed a decade ago by Cellcross—an incubator company founded in 2002 by researchers at the University of Tokyo that includes Teijin Fibers as an equity partner. The @CELL RFID system is based on research carried out by Hiroyuki Shinoda, an associate professor at the University of Tokyo and a Cellcross cofounder, and is designed to enable the use a RFID technology at a very short range, with a flat, ultra-thin reader antenna placed on a shelf on which tagged goods will be stacked.

The antenna is designed to limit the RF signals within the "two-dimensional" sheet, comprising a bottom layer of conductive material and a top sheet of conductive mesh material, with a dielectric layer sandwiched between them. When a reader's signal enters the bottom sheet, that signal passes upward through the dielectric and mesh layers, creating what Cellcross terms an "evanescent wave" that does not propagate, as a typical UHF signal would do. Instead, the RF signal seeps through gaps in the mesh, which is designed to allow that energy leakage and thereby create a highly localized RF field. The intention, the company explains, is to reduce the risk of security breaches that might result from transmissions that are less controlled (for example, extended far beyond the shelf), and to control the read range so that a tag's removal from the shelf would be detected even if that tag were not moved far from the shelf.

Teijin Fibers' current focus market for the technology is libraries, the company reports, with several pilots currently underway at an unnamed university library and an educational resource center, at which books are tagged and CSL's CS790 sheet antennas (powered by CSL's CS468 interrogators) are installed on shelves to identify where books are located, based on each tag's unique ID number. When a tagged book is removed from a shelf, Teijin software updates that book's status, indicating that the tag is no longer detected, and that the book has thus been removed from the shelf. Teijin's shelf-management system includes up to eight Cell Form sheet antennas, a CSL read/write software module and 400 EPC Gen 2 RFID tags.

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