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

Abstract EN

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.