IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 10, 2011 123 Passive UHF RFID Tag for Airport Suitcase Tracking and Identification Carla R. Medeiros, Jorge R. Costa, Senior Member, IEEE, and Carlos A. Fernandes, Senior Member, IEEE Abstract—A passive UHF tag configuration is presented for suit- case identification and tracking in airport-handling applications. The proposed tag antenna solution is based on a conformal ge- ometry, consisting of a folded dipole with orthogonal arms, ap- propriate for integration into the wall of injection-molded suit- cases during its fabrication process. The tag antenna is designed for the ALIEN Higgs-2 integrated circuit. Simulated frequency de- pendence of the proposed UHF passive tag shows adequate perfor- mance across the world UHF RFID bands. Maximum tag detection range as well as detection isotropy were measured in several test environments both for a prototype tag attached to a suitcase and for a tag embedded in the suitcase wall. Full detection of the em- bedded tag was obtained for all suitcase orientations in the tested scenarios. Index Terms—Luggage tracking, quasi-omnidirectional detection, tag antennas, UHF RFID. I. INTRODUCTION T HE 2010 REPORT from the International Air Trans- port Association (IATA) states that lost baggage costs the air industry more than US $2.5 billion every year [1], corresponding to over 25 million mishandled bags globally. About 10% of the mishandlings result from poor barcode read rates. One initiative in the framework of IATA’s Baggage Improvement Program was to evaluate the potential of passive UHF RFID technology to replace barcodes and reduce mishan- dlings. Pilot RFID implementations in several airports around the world revealed that bag-tag read-success rate improved markedly from around 85%–90% with conventional barcode tagging to over 95% with RFID [2], [3], along with cost saving associated with baggage-handling time reduction. RFID is a fast growing technology that enables radio detec- tion and reading of tags associated with items [4], without re- quiring line of sight. RFID tags carry a univocal ID code and a memory that can store relevant baggage tracking information. In the referred pilot airport implementations, passive RFID tags Manuscript received January 03, 2011; accepted January 18, 2011. Date of publication February 04, 2011; date of current version March 14, 2011. This work was supported in part by Fundação para a Ciência e Tecnologia under Project RFID-Local PTDC/EEA-TEL/102390/2008 and INOV-Inesc Inovação, Portugal, under Contract QREN 1613 (Mala Segura). C. R. Medeiros and C. A. Fernandes are with the Instituto de Telecomuni- cações, Instituto Superior Técnico (IST), 1049-001 Lisboa, Portugal (e-mail: Carla.Medeiros@lx.it.pt). J. R. Costa is with the Instituto de Telecomunicações, Instituto Superior Téc- nico (IST), 1049-001 Lisboa, Portugal, and also with the Departamento de Ciên- cias e Tecnologias da Informação, ISCTE–Instituto Universitário de Lisboa, 1649-026 Lisboa, Portugal. Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LAWP.2011.2112326 were attached to the classical barcode labels around the baggage handler. In a few cases, these tags got wrapped during the bag- gage handling, precluding 100% reading score [2]. One interesting alternative is to embed the passive RFID tag within each suitcase wall during its manufacturing process. In this way, instead of the usual disposable tag solution, the embedded tag can be reused and reprogrammed at the airport checkin desk for each travel. This solution is fairly robust and less expensive for the airports. Additionally, the new generation of tags offers reasonable memory size, enabling a wealth of new applications that are already being considered like bag- gage self-service kiosks, real-time baggage tracking services, etc. [5]. Common UHF RFID tags for airport trials use typical dipole configurations [6] that, however, do not ensure the best reading score. The objective of this letter is to develop a new dedicated UHF passive tag solution, based on 3-D geometry [7], appro- priate for embedding into the suitcase wall during the injec- tion molding process, while presenting good omnidirectional detection, acceptable reading range, and full operation across the whole UHF RFID to ensure worldwide interoperability. A folded dipole tag configuration has been presented before for placement in sharp 90 corners of boxes [8]. However, sharp corners are not usual in travel bags, and [8] does not investigate tag performance for other conformal uses or for other place- ments to cope with shadowing and wall embedding constrains. Most importantly, the tag from [8] does not operate in full UHF RFID world band, which prevents worldwide interoperability The design challenge in this letter also includes finding the best tag positioning in the suitcase that minimizes misreading origi- nated by its content, by shadowing from other close or stacked bags or close presence of metal from the bag conveyors or other surfaces. In a preliminary study, the developed tag was simply at- tached to the suitcase surface [9]. This letter presents the results from the complete study, with the final test results of a fine-tuned RFID tag embedded in the wall of a standard in- jection-molded suitcase, after passing the industrial integration process. Systematic tests were conducted in a lab baggage scenario using empty and filled suitcases, with 100% reading score. Nonsystematic tests were also carried in a real airport environment with the same 100% reading score. These scores were reached with far less reader antennas than in usual RFID implementations [10]. II. TAG ANTENNA CONFIGURATION The geometry of the proposed UHF RFID tag is presented in Fig. 1. On its basic configuration, the antenna consists of an L-shaped dipole, where one arm is additionally folded to form a 1536-1225/$26.00 © 2011 IEEE