Self-Tuning RFID Tag: A New Approach for Temperature Sensing

This paper aims to present a further exploration on a new concept regarding the operation of an ultrahigh frequency (UHF) radio frequency identification (RFID) sensor tag. Exploiting the antenna of a UHF RFID tag as a temperature transducer and a UHF RFID chip with self-tuning capabilities as the means of communication, a UHF RFID tag can operate as a very low-power sensor with high read range and small size. The antenna of the tag is taking advantage of the intrinsic characteristics of the used substrate to vary its overall complex impedance according to temperature. These changes of the impedance of the antenna are leading the self-tuning circuit of the used RFID chip to self-tune and based on the value it acquires an estimation of the sensed temperature can be made. This paper also reports a design and a set of measurements of a UHF RFID tag transformed to act as a temperature sensor. This concept is further explored for the assessment of the contribution of each of the constituents of the UHF RFID tag, i.e., antenna and UHF RFID chip, to the sensing procedure. This paper is accompanied by the simulation of a designed 3-D model of the UHF RFID sensor tag and by sets of measurement of the impedances of the UHF RFID chip and of the antenna.

I. Introduction

With Internet of Things (IoT) being one of the big goals of today’s industry, the development of sensors and actuators capable to form wireless sensor networks is a priority down the road of the implementation of the IoT concept. One quite popular vision for the IoT is the “Smart Dust” [1], where a massive number of sensors, primarily small, passive, or low powered and low cost are required. Currently, the most prevalent technology to fulfill this role is the radio frequency identification (RFID) technology and in particular the tags operating in the ultrahigh frequency (UHF) band.