A Read Range Maximization Approach for UWB Surface Acoustic Wave (SAW) RFID Tags based on Interdigital Transducer (IDT) as a Reflector Kasyap Suresh Department of Electrical and Electronics Engineering Universiti Teknologi PETRONAS (UTP) Perak, Malaysia kasyap_16005685@utp.edu.my Varun Jeoti Department of Electrical and Electronics Engineering Universiti Teknologi PETRONAS (UTP) Perak, Malaysia varun_jeoti@utp.edu.my Micheal Drieberg Department of Electrical and Electronics Engineering Universiti Teknologi PETRONAS (UTP) Perak, Malaysia mdrieberg@utp.edu.my Abstract—Radio Frequency Identification (RFID) technology using readers and ID tags has been deemed to be a promising candidate compared to bar codes, QR codes and others due to Non Line of Sight (NLOS) operability, bulk readability, and longer read range. Silicon based Integrated Circuit (IC) active and passive RFID tags are quite popular. However, such tags are constrained by several factors such as inability to operate under hazardous conditions, less cost efficient, susceptibility towards electromagnetic interference and poor accuracy in metallic environments. To combat such effects, a special type of passive tag called Surface Acoustic Wave (SAW) RFID tag, which possess a very high potential due to its robustness against the above mentioned effects, has received a lot of attention among the researchers. A very popular approach called Open Circuit/Short Circuit (OC/SC) using a strip reflector design to design unique codes has been in existence and can provide a range of 2.4 m on average. Nevertheless, this range is not sufficient to be considered for a remote interrogation RFID system for many long range RFID applications. This paper uses a different reflector design for Ultra Wide Band (UWB) SAW RFID tags based on Inductive Resonant Loading (IRL) where an inductor is loaded across the reflecting IDT. Simulation results show that there is a 15 dB improvement in reflected power using this design which corresponds to an extended range of up to 9.6 m. Such tags can prove to be very useful in various identification applications leading to a better detection of the tags that are located roughly 10 meters away from the RFID reader. Keywords—Surface Acoustic Wave (SAW), resonant loading, open circuit, short circuit, Interdigital Transducer (IDT) I. INTRODUCTION Successful target identification or tracking is the key element and primary objective in many applications where the suppliers have to identify and keep track of all the inventory that is present at that time. This is an important task in many tracking applications as the profit depends on the quantity of items or pallets that are present or distributed. Hence, being able to identify all the items with a greater accuracy and remotely is an important problem, without leaving any item undetected. A recent major study by the Walmart had shown that the probability of detecting an item can be as low as 66% [1]. To alleviate the detection probability, several automatic identification technologies have been adopted which are namely bar codes, magnetic stripes, Optical Character Recognition (OCR), Electronic Article Surveillance (EAS) security tags and Radio Frequency Identification (RFID). While technologies such as bar codes and others for labeling items are constrained by factors such as unobstructed line of sight to read the data, poor read range and inability to simultaneously identify multiple coded items, RFID technology has been proved to be useful and is devoid of such stringent conditions. It provides an efficient means of labeling and identifying several such items at a time [2]. Initial development of RFID created its first silicon based passive IC tag that was interrogated by an RFID reader [3]. Active IC tags came into existence much later and contains an internally localized battery source. But active tags are generally expensive and cannot provide better range during harsh climatic conditions such as high temperature and pressure [4]- [6]. Passive IC tags also face a similar issue such as poor read range in the order of a few feet and inability to withstand during extreme environmental conditions, except that it is much cheaper than active tags. Hence to improve the versatility and performance of RFID tags, another special case of passive tag based on Surface Acoustic Wave (SAW) technology have been in development since early 1980’s and has attracted a lot of attention from both academia and industry due to its robustness. SAW tags typically contain an input Interdigital Transducer (IDT), a delay line followed by a series of reflectors separated by another finite delay line between them where the SAW wave propagates over the surface of a piezoelectric substrate which could be Lithium Niobate (LiNbO 3), Quartz etc. The reflectors contain the electronically stored information of the item such as the code, serial number, date of manufacture, date of shipment, expiration date and so on. Several design techniques to code them have been developed such as Orthogonal Frequency Coding and Open Circuit (OC) and Short Circuit (SC) using strip reflectors among which the OC/SC configuration based design is very popular, mainly due to its simple design [7]-[10]. Several work pertaining to OC/SC design has been carried out and is still in research. The authors provide an analysis into the reflectivity of open and short circuited strip reflectors for a 128 o Y-Z cut LiNbO3 [11]-[13]. An average read range was estimated to be around 1 m. Papers [14] and [15] explain the programmability of reflectors based on OC and SC configuration using strip reflectors with which an estimate of a meter range was achieved. In paper [16], the authors have developed a coded strip reflector based on open circuit design where 3 and 10 strip reflectors were deposited on top of a 128 o Y-Z LiNbO3 substrate. A reader interrogation was performed to evaluate the interrogable range with the design. A maximum of 2.4 m was achieved for a tag loss of 40 dB (approximately). Despite the research, such designs cannot be used for applications such as identifying a pallet or an item which is several meters away in a warehouse or monitoring a patient from a remote location or even identifying an individual in a 978-1-7281-5503-6/20/$31.00 ©2020 IEEE 978-1-7281-5503-6/20/$31.00 ©2020 IEEE 978-1-7281-5503-6/20/$31.00 ©2020 IEEE 1 Authorized licensed use limited to: UNIVERSITY TEKNOLOGY PETRONAS. 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