Wearable Quarter-Wave Folded Microstrip Antenna for Passive UHF RFID Applications

Abstract

A wearable low-profile inset-fed quarter-wave folded microstrip patch antenna for noninvasive activity monitoring of elderly is presented. The proposed antenna is embedded with a sensor-enabled passive radio-frequency identification (RFID) tag operating in the ultra-high frequency (UHF) industrial-scientific-medical (ISM) band around 900 MHz. The device exhibits a low and narrow profile based on a planar folded quarter-wave length patch structure and is integrated on a flexible substrate to maximise comfort to the wearer. An extended ground plane made from silver fabric successfully minimises the impact of the human body on the antenna performance. Measurements on a prototype demonstrate a reflection coefficient (S11) of −30 dB at resonance and a −10 dB bandwidth from 920 MHz to 926 MHz. Simulation results predict a maximum gain of 2.8 dBi. This is confirmed by tag measurements where a 4-meter read range is achieved using a transmit power of 30 dBm, for the case where the passive wearable tag antenna is mounted on a body in a practical setting. This represents an almost 40% increase in read range over an existing dipole antenna placed over a 10 mm isolator layer on a human subject.

Wearable Antennas for Off-Body Radio Links at VHF and UHF Bands: Challenges, the state of the art, and future trends below 1 GHz

“…The antenna is 32mmx137mm wide, and it is realized with a 1.57mm-thick Rogers RT5880 substrate (ε r =2.2). Examples of quarterwavelength shorted patches can be found in [110], [116]. The shorted patch in [116] is made out of a copper foil attached onto a flexible and soft foam substrate (antenna thickness is equal to 3.2mm).…”

“…Examples of quarterwavelength shorted patches can be found in [110], [116]. The shorted patch in [116] is made out of a copper foil attached onto a flexible and soft foam substrate (antenna thickness is equal to 3.2mm). The 30mmx79mm shorted patch is attached on a 200mmx200mm silver fabric sheet to further decrease the antenna-body coupling.…”

Wearable Flexible Lightweight Modular RFID Tag With Integrated Energy Harvester

“…Powering enhanced RFID tags exclusively by RF energy transmitted by RFID readers restricts data logging, sensing, and computational operations to the coverage range of the RFID reader [23], [27]. Reliability, functionality, and operation range may be increased [9], [23] by combining an antenna with high radiation efficiency and tailored radiation pattern [9], [28] with energy harvesters relying on ambient sources, such as vibration [29], kinetic [17], solar [23], [30], or RF energy [26]. Second, enhanced RFID tags for body-worn applications must be low-profile, lightweight, and mechanically flexible, allowing unobtrusive integration [28].…”

“…Reliability, functionality, and operation range may be increased [9], [23] by combining an antenna with high radiation efficiency and tailored radiation pattern [9], [28] with energy harvesters relying on ambient sources, such as vibration [29], kinetic [17], solar [23], [30], or RF energy [26]. Second, enhanced RFID tags for body-worn applications must be low-profile, lightweight, and mechanically flexible, allowing unobtrusive integration [28]. Moreover, the tag should maintain its performance in the proximity of the human body and under harsh operating conditions [31].…”

“…In contrast, the tag described here possesses more functionality and a much larger communication range compared with these passive RFIDs. The wearable RFID tag that is the most closely related to our proposed RFID platform in terms of functionality is the one proposed in [28]. However, as the tag in [28] is exclusively powered by the RFID reader, a read range of only 4 m is achieved, provided that the RFID reader transmits at a 30 dBm power level.…”