A novel low-cost chipless RFID tag sensor is presented. The tag sensor provides identification data as well as monitors relative humidity (RH) of tagged objects. The tag sensor is made of passive microwave circuit that uses humidity sensitive polymer material for RH sensing. The aim of this paper is to investigate RF sensing properties of moisture absorbing polymer polyvinyl alcohol (PVA) at microwave frequency. Moreover, frequency shifting technique is used to encode data bits for high data capacity. The overall size of the proposed tag sensor is 15mm x 6.8 mm and has 6 bit data capacity for ID generation and single bit for humidity sensing. Results presented here show about 607 MHz frequency deviation for 50% RH increase. The tag sensor has potential to be printed on flexible laminates like plastic and paper for ultra-low cost item level tagging and ubiquitous sensing.

Abstract-In this paper, an efficient spectral signature based chipless RFID tag is presented, where 4 N number of words can be coded using only N number of resonators. As data bit encoding element, the proposed tag utilizes a number of modified complementary split ring resonators (MCSRR). A novel resonance detuning mechanism proposed here allows the use of an MCSRR to independently encode two data bits instead of one bit. Compared with two separate rings based CSRR, the proposed MCSRR occupies 56% less area and also reduces the resonance bandwidth requirement by more than 60%. The multiresonator circuit and the UWB antennas are implemented on a thin (0.127 mm) substrate with only single sided metallization. The proposed tag has great prospect to yield an ultra-low cost chipless RFID tag that may replace barcode in the long run.

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Improved performances, compact size, and lower cost are the key driving factors for advancement of modern communication systems. To meet these stringent requirements, defected ground structures (DGS) can be an effective tool. In this article, a comprehensive review of various DGS configurations emphasizing the background and evolution, classification, equivalent circuit modeling techniques, and their applications in different areas of microwave engineering has been presented. A review of different DGS‐engineered band stop filters (BSFs), low‐pass filters (LPFs), and high‐performance band‐pass filters (BPFs) is included. An overview of the applications of DGS in performance improvements of microwave antennas in terms of impedance matching, size reduction, spurious response suppression, mutual coupling reduction, cross‐polarized radiation suppression, and application of DGS in accomplishing a beam‐steering operation for a phased array antenna has also been included. Radio frequency identification (RFID) and microwave sensors, which are finding increased application, are introduced, and applications of DGS in conventional and chipless RFID tag design as well as in low‐cost passive microwave sensor implementation are also discussed. Additionally, applications of DGS in high‐impedance microstrip line realization and in output power and operational efficiency enhancement of microwave active circuits like oscillators and power amplifiers are covered. Finally, some limitations and challenges of DGS implementation in microwave circuits and antennas are discussed. Overall, adaptation of DGS in conventional passive and active microwave applications and in new emerging fields, like RFID and sensors, are covered in this article.

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