MR4RF: MEM-device with impedance and their usage with impedance matching networks for passive RFID tags in the UHF

The passive RFID tag in the UHF has been employed in several different applications including, tracking, logistics, and as a sensing platform for the Internet of things (IoT). The tag is ideal for this industry due to its unique design. It harvests all of its energy from the environment, and is small, cheap, and requires little to no maintenance. However, there are two major issues limiting the potential of the passive RFID systems: the limited power harvested by the tag, and the high susceptibility to interference and coupling. In particular, dynamic environments render the traditionally fixed, RF impedance matching network ineffective. A novel design for a flexible Impedance-Switching Network (ISN) for passive RFID tags in the UHF is presented in this thesis. This novel approach can maximize power harvested by the tag. We propose two approaches to implementing the ISN. First, a more traditional design with a series of varactors is developed and studied. Each varactor is placed in parallel impedance lanes that are controlled via a feedback loop to maximize harvested power. A four-lane ISN is designed, tested, and tuned. The simulations and experiments demonstrate that ISN is capable of compensating for negative effect of mutual coupling in a ferromagnetic-reach environment. The second design employs a new material called a memristive switch that can replace the varactors in the ISN. State of a memristive switch is non-volatile and requires little energy to operate, thus making it ideal for passive RFID tags. We are the first to characterize the Co3O4 based memristive switch in UHF range. The results show that it can be employed as a varying capacitor in the RF front-end design. We propose three general configurations for the ISNs --Abstract, page iii

Doctor of Philosophy

dissertationAntenna design and reduction of losses in antenna systems are critical for modern communications systems. Two categories of antennas suffer from limited power supply and difficult operating environments: implantable antennas and antennas for spacecraft applications. Minimizing and controlling losses in these two antenna types is critical for developing next-generation implantable devices, spacecraft, and satellites. Research suggests that future tattoo antennas will be made from low-conductivity ink utilizing the natural insulating property of the body's fat and lossy ground plane of muscle. This paper supports tattoo antenna work by: (1) demonstrating the insulating properties of fat and conductivity of muscle with various antenna systems, (2) showing the effect of biological materials on the current distribution of subdermal antennas, and (3) validating the use of lower-conductivity materials in subdermal antenna design including a novel gold nanoparticle material. Simulations and measurements are used to evaluate current distributions shared between solid, segmented, and meshed strip dipole antennas and surrounding body tissues. Fat insulates the antenna similar to a thin layer of plastic wrap. Muscle acts as a conductive ground plane. Dipole antennas with mesh or gap structures are more strongly coupled to body tissues than solid antennas. A minimum acceptable conductivity benchmark of 105 S/m is established for dipole antennas and Radio-Frequency Identification (RFID) antennas. This work also provides novel information on the design of low-cost, circularly polarized (CP), Ka-band (26 GHz), millimeter-wave, 50 Ω edge-fed, corners truncated patch antennas on RT/duroid 5880 (εr = 2.2, ½ oz. copper cladding). Microstrip feed width, axial ratio (AR) bandwidth, and best AR at 26 GHz are optimized by the use of 10 mil substrate. The effects of corner truncation are further investigated, showing that increasing corner truncation increases AR bandwidth, increases percent offset between best S11 and AR frequencies, and worsens the best AR. A truncation of 0.57 mm is a good compromise between these effects with AR bandwidth of 6.17 % (measured) and 1.37 % (simulated). Increasing ratio of substrate thickness to design frequency, t / λd, improves AR bandwidth. For t / λd below a certain threshold a corners truncated patch antenna will not produce CP. A new nearly-square, corners truncated patch antenna is measured and simulated as a method of increasing circular polarization bandwidth (CPBW)

Applications of Antenna Technology in Sensors

During the past few decades, information technologies have been evolving at a tremendous rate, causing profound changes to our world and to our ways of living. Emerging applications have opened u[ new routes and set new trends for antenna sensors. With the advent of the Internet of Things (IoT), the adaptation of antenna technologies for sensor and sensing applications has become more important. Now, the antennas must be reconfigurable, flexible, low profile, and low-cost, for applications from airborne and vehicles, to machine-to-machine, IoT, 5G, etc. This reprint aims to introduce and treat a series of advanced and emerging topics in the field of antenna sensors

EXPERIMENTAL INVESTIGATION OF READING PASSIVE UHF TAGS IN A MULTI-TAG ENVIRONMENT

Recently, the Internet of things (IoT) has emerged as a promising solution for several industrial applications. One of the key components in IoT is passive radio frequency identification (RFID) tags which do not require a power source for operations. Specifically, ultra-high frequency (UHF) tags are studied in this paper. However, due to factors such as tag-to-tag interference and inaccurate localization, RFID tags that are closely spaced together are difficult to detect and program accurately with unique identifiers. This thesis investigates several factors that affect the ability to encode a specific tag with unique information in the presence of other tags, such as reader power level, tag-to-antenna distance, tag-to-tag distance and tag orientation. ANOVA results report reader power level and tag spacing, along with effect interactions power level*tag spacing and tag spacing*tag orientation to be significant at the levels investigated. Results further suggest a preliminary minimum tag-to-tag spacing which enables the maximum number of tags to be uniquely encoded without interference. This finding can significantly speed up the process of field programming in item-level tagging

Miniaturized antenna and transponder based wireless sensors for internet of things in healthcare

Future medical and healthcare systems will be largely improved by the wide-spreading of internet of things (IoTs). One of the crucial challenges of IoTs for healthcare is at the wireless sensors. Miniaturization of sensor node profile, minimizing power consumption as well as lowering down design/production cost of antenna, RF circuits and sensor modules have become the key issues for realizing more exciting applications in medical and healthcare fields that never seemed to be possible before. In this dissertation work, we first focus on electrically small antenna (ESA) design and fabrication for medical telemetry. A comprehensive analysis of the radiation properties of a novel electrically small folded ellipsoidal ESA is presented, showing its ability to self-resonate and impedance match without external components. It will benefit various size-restricted applications especially with wireless medical implants. The second focus is on healthcare sensors using ESA as the sensing agent, which saves the power and cost by eliminating the need of extra sensing modules. Specifically, miniaturized helix ESAs are integrated with drug reservoirs to function as wireless transponder sensors for real-time drug dosage monitoring. We also introduce a system level innovation of a passive wireless harmonic transponder/harmonic sniffer/frequency hopped interrogator based sensing system. The μL- liquid level resolution and absolute-accuracy passive sensing is demonstrated in the presence of strong direct coupling, background scatters, distance variance as well as near-filed human body movement interference. Furthermore, we investigate how modern ubiquitous wireless sensor networks could take advantage of sensitive nanostructure materials for enhanced performance. Here we propose a new paradigm of chemically-gated mixed modulation on a single homogeneous graphene device in which the chemical exposure directly modulates an electrical carrier signal. To make the device ubiquitously reusable, a method of precisely tuning the charge neutrality point (Vcnp) is introduced by electrochemical calibration with gate voltage pulse sequence. Such chemically gated graphene modulator can be potentially used in a harmonic transponder as a passive ubiquitous sensor node for chemical and bio sensing applications. Overall the research work presented in the dissertation will help enable cost and power-efficient wireless sensor networks in future healthcare IoTs.Electrical and Computer Engineerin

Digitally Fabricated Epidermal Transfer Tattoo UHF Radio Frequency Identification Tags

This thesis focuses on the inkjet printing of UHF RFID tags in the form of transfer tattoos for use on the skin. Inkjet printing of these tags is proposed as a cheaper and more appropriate alternative to conventional etching. The work seeks to assesses the performance of inkjet printed epidermal RFID tags using parameters such as read range, transmitted power and backscattered power. The effect of different printing parameters such as the number of conductive ink layers, sintering time and temperature on the performance of the tags are assessed by simulation and measurement. Additionally, techniques to reduce the volume of conductive ink used for the fabrication of the tag are also examined and compared with an aim to determine which has the best achieved read range and ink utilization balance. This would help to reduce the cost of fabrication of the tags. Also, due to some defects being introduced to the tags during the printing process because of printing conditions and characteristics inherent to the printing technology, the effects of these defects on the performance of the printed tag is also examined by simulation and measurement. The robustness of the epidermal transfer tattoo tag was further experimentally determined by exposure to everyday use conditions and situations involving sweat and mechanical friction. Finally, a diversity study on an inkjet printed tag integrated with a medical sticking plaster was performed. This involved the use of two to four tags placed horizontally and vertically in order to determine which orientation offers better read coverage in each of the diversity setups while a volunteer carried out a set of motions

When learning meets RFIDs: The case of activity identification

Over the past decades have seen booming interests in human activity identification that is widely used in a range of Internet-of-Things applications, such as healthcare and smart homes. It has attracted significant attention from both academia and industry, with a wide range of solutions based on cameras, radars, and/or various inertial sensors. They generally require the object of identification to carry sensors/wireless transceivers, which are not negligible in both size and weight, not to mention the constraints from the battery. Radio frequency identification (RFID) is a promising technology that can overcome those difficulties due to its low cost, small form size, and batterylessness, making it widely used in a range of mobile applications. The information offered by today\u27s RFID tags however are quite limited, and the typical raw data (RSSI and phase angles) are not necessarily good indicators of human activities (being either insensitive or unreliable as revealed by our realworld experiments). As such, existing RFID-based activity identification solutions are far from being satisfactory. It is also well known that the accuracy of the readings can be noticeably affected by multipath, which unfortunately is inevitable in an indoor environment and is complicated with multiple reference tags. In this thesis, we first reviewed the literature and research challenges of multipath effects in activity identification with RFIDs. Then we introduced three advanced RFID learning-based activity identification frameworks, i.e., i2tag, TagFree and M2AI, for tag mobility profiling, RFID-based device-free activity identification and tag-attached multi-object activity identification, respectively. Our extensive experiments further demonstrate their superiority on activity identification in the multipath-rich environments