Modeling, Design and Experimentation of Wearable RFID Sensor Tag

Abstract

Design of effective wearable tags for UHF RFID applications involving persons is still an open challenge due to the strong interaction of the antenna with the human body which is responsible of impedance detuning and efficiency degradation. A new tag geometry combining folded conductors and tuning slots is here discussed through numerical analysis and extensive experimentation also including the integration of a passive motion detector. The achieved designs, having size comparable with a credit card, may be applied to any part of the body. The measured performance indicates a possible application of these body-worn tags for the continuous tracking of human movements in a conventional room.

Miniaturised wearable UHF-RFID tag with tuning capability

“…Miniaturisation of wearable passive tags generally produces a remarkable degradation of the antenna bandwidth as well as of the radiation efficiency due to the presence of the lossy human body. As a consequence, this can negatively affect the interoperability in different countries and the stability of the performances with respect to the specific body placement.Starting from previous experiments of the same authors with wearable tags in [2], this Letter proposes a new layout over a flexible and low-cost substrate with reduced external dimensions. The geometry provides a two-step tuning mechanism that permits in principle to easily adapt the same tag to any frequency inside the world-wide UHF RFID band (866-956 MHz) and even to make finer corrections for the specific placement.…”

“…Passive devices are particularly attractive for bodycentric platforms owing to their light weight, low cost and the absence of battery recharging. In particular, tags integrated into clothes, eventually hosting specific sensors, make it possible to remotely monitor human body activity [1,2]. In recent years, several on-body passive dipole and patch tags have been presented [3 -5] for the UHF (866-956 MHz) RFID frequency, but smaller layouts are however needed in some applications in order to simplify the integration with clothes or plasters.…”

“…Starting from previous experiments of the same authors with wearable tags in [2], this Letter proposes a new layout over a flexible and low-cost substrate with reduced external dimensions. The geometry provides a two-step tuning mechanism that permits in principle to easily adapt the same tag to any frequency inside the world-wide UHF RFID band (866-956 MHz) and even to make finer corrections for the specific placement.…”

“…1a shows the shape of the proposed tag antenna. The layout is similar to a 'square smile' comprising a folded patch (the 'head') to achieve a partial decoupling from the human body, connected to the RFID microchip by an H-shaped slot (the 'glasses') as in [2]. The form factor of the H-slot provides the required inductive reactance to balance the microchip impedance.…”

“…In practical applications, the length of mouth and whisker can be easily modified by adding or removing narrow strips of adhesive copper, as shown later on. The resulting external size is about half that the H-slot antenna previously presented by the authors in [2]. Prototype and performance: A 4.5 × 3.5cm prototype of the miniaturised wearable tag (Fig.…”