Development of Sensor Integrated and Inkjet-Printed Tag Antennas for Passive UHF RFID Systems

Abstract

Radio frequency identification (RFID) is a form of automated identification technology that is nowadays widely used to replace bar codes in asset tracking and management. Looking ahead to the future, our lives will be surrounded by small, embedded and wireless electronic devices that provide information about everything for everybody through pervasive computing. At the core of this vision lie two key concepts of ubiquitous sensing and the Internet of Things. RFID technology is seen as one of the most prominent technologies of today for the implementation of these future concepts.

Ubiquitous sensing describes a situation, where small embedded sensors monitoring various environmental parameters are found everywhere. The second concept, the Internet of Things, requires that all objects, even the most insignificant everyday items, surrounding us should encompass computing and communication capabilities of some sort. In its simplest form, such computing could be a transponder that allows the unique identification and tracking of the item. Together these future concepts could truly revolutionize our lives by delivering significantly more information from our living environment. The objectives of this thesis are twofold. Firstly, passive ultra-high frequency (UHF) RFID technology is utilized to develop low cost, completely passive, wireless sensor devices for ubiquitous sensing applications. Secondly, inkjet-printed passive UHF RFID tag antennas are developed and optimization techniques are presented to lower the cost of such tag antenna implementations. The latter objective aims to facilitate the advancement of the Internet of Things by enabling tag antennas to be directly printed on or in to various objects. As a result of the research work presented in this thesis, three different passive UHF RFID based sensor tags were developed. Two of these designs monitor temperature and one is developed for relative humidity measurements. For the first time, the applicability and accuracy of such passive sensor tags was demonstrated. The results show that UHF RFID sensor tags have potential to be utilized as low cost sensor devices in ubiquitous applications. In addition, this thesis presents methods to lower the costs of inkjet-printed tag antennas. A technique was developed to reduce the ink consumption significantly to produce high performance tag antennas. Moreover, a special type of tag antenna design consisting of very narrow lines was developed. Finally, novel electronic materials were used as tag antenna substrate materials for inkjet-printed tag antennas. The use of a high permittivity ceramic-polymer composite, wood veneer, paper and cardboard were demonstrated. In each case, it was shown that inkjet-printing is a feasible form of fabrication on such materials, producing passive UHF RFID tags with long read ranges. This shows that tag antennas can be inkjet-printed directly on to various items to advance the realization of the Internet of Things.