Passive UHF RFID Yarn for Relative Humidity Sensing Application

In this paper, a passive ultra-high frequency (UHF) radio frequency identification (RFID) humidity sensor tag inside a slenderly yarn is presented. The sensor tag antenna is designed within a very small diameter textile wire of less than 0.6 mm. The proposed solution is based on both theoretical analysis and detailed simulation results in coherence with theory. The tag system consists of capacitive based sensor where polyimide is used as a sensing material to adapt the change with relative humidity [5]. Any variation of capacitive values will change the response of the tag. More precisely, the resonance frequency of the tag is shifted from 864.5 MHz to 867.3 MHz covering European UHF RFID frequency band when the relative humidity (HR) is varying from 35% to 95%.

I. Introduction

Radio Frequency Identification (RFID) is a broadly used technology to identify any object wirelessly through the use of low resources and low energy consumption (even passive) devices called tags. Over the years, the demands of RFID tags have been tremendously increasing not only for identification and authentication, but also for real-time environmental data capturing. Amongst them, humidity sensor in RFID technology is proved to be a promising researched topic.