Experimental Characterization of Bodycentric Passive RFID Systems. S.Manzari (1) ,C. Occhiuzzi (2) ,G. Marrocco (3) DISP, University of Roma Tor Vergata Via del Politecnico,1, 00133, Roma (ITALY) (1) sabinamanzari@hotmail.it (2) occhiuzzi@disp.uniroma2.it (3) marrocco@disp.uniroma2.it Abstract—Recent progresses in the design of wearable RFID tag antennas stimulate the idea of passive bodycentric systems wherein the required power to drive the wearable tags is directly scavenged from the interrogation signal emitted by the reader unit. While active bodycentric links have been extensively investigated, the feasibility of passive systems is still questionable due to the poor sensitivity of the tags and to the modest read distances. This paper describes an articulated measurement campaign with textile wearable low-profile tags in the UHF RFID band. It is demonstrated that both on-body and off-body links are feasible with a power budget fully compliant with the available technology. The experiments permits to identify the most efficient tag placements and to propose some quantitative and general guidelines useful to characterize and design this kind of new systems. I. I NTRODUCTION The RadioFrequency Identification (RFID) technology is increasingly adopted in Logisting, Manufaturing and Security, while pioneristic applications are currently experimented in Sensor Networks, Personal Healthcare and even Entertainment and Social Arts ([1]-[7]). Thanks to the advances in low- power electronics, battery-less (passive) devices are particu- larly attractive: in these systems the RF power required to the transponder element (the tag) to respond to the query device (the reader) is scavenged from the interrogation signal by the tag itself. Since passive RFID tags do not require regular re- charging, they are particularly suited to disposal usage and to the pervasive and long-term distribution within environments. In some applications the tag device, comprising an antenna integrated with a microchip transponder and eventually with additional sensors or actuators, needs to be worn onto the human body ([8]-[13]). Tags integrated into clothes could work as a body-centric passive RFID system able to track people’s position and/or to monitor life parameters every time and everywhere. Compared with active bodycentric systems, RFID solution could furthermore offer a higher degrees of pervasivity than the active systems due to lower cost and to the absence of local power supply. These kind of systems deserve additional challenges since RFID antennas do not transmit but backscatter the power received by the reader and hence they need to achieve efficient energy scavenging in presence of the very lossy human body while keeping the antenna size small at the involved frequency (UHF: 866-970 MHz including European, US and Asia sub-bands). Up to now, however, the true feasibility and reliability of these class of devices is still questionable, especially concerning the achievable read ranges in real environments in case of real body motion and postures. As in the more mature active bodycentric systems, interest- ing RFID communication modalities are on-body and off-body links. The off-body communication could be useful for exam- ple to locate and monitor people inside buildings by means of fixed readers placed in different rooms or by a wearable reader and ambient-disseminated tags [21]. A possible application could be the access control in dangerous or restricted areas. The on-body communication is instead typical of unusual sce- narios where a fixed communication infrastructure is missing. It could be the case of a sportman or a fireman equipped with different RFID sensors (inside his garment) interrogated by his hand-held standard communicator in harsh environments [22],[23]. Starting from our recent experience with wearable RFID tags ([8],[9],[24]), this paper discusses the feasibility of a bodycentric system including passive RFID textile tags, derived from a previous teflon prototype. Now, an articulated experimental campaign is aimed to understand the achievable read ranges, the minimum number of required tags and their most suitable positions over the body for reliable on-body and off-body links. Activity and shadowing effects will be also taken into account in order to understand the possibility to establish robust and safe communications. II. ANTENNA DESIGN AND CHARACTERIZATION A 3mm thick synthetic felt sample has been chosen as sub- strate for the wearable antenna. The electromagnetic features of the felt have been experimentally evaluated by means of parameter identification techniques using numerical models of planar test antennas. The achieved permittivity and conduc- tivity at 870MHz, which is the European frequency for RFID systems, are ǫ =1.17 and σ =2 · 10 -4 S/m. The resulting fabricated prototype, of overall size 7 × 9 cm, is shown in Fig.1. The electromagnetic tag’s performances have been experimentally characterized with respect to the 1000 978-1-4244-9561-0/11/$26.00 ©2011 IEEE AP-S/URSI 2011