Chipless RFID Tag Research Articles

High Data Density Near-Field Chipless-RFID Tags With Synchronous Reading

Near-field chipless-RFID tags with high data density and synchronous reading capability are presented and experimentally validated in this paper. The tags consist of a chain of rectangular patches etched or printed at predefined positions on a dielectric substrate, including rigid or flexible (i.e., plastic or even paper) substrates. Patch dimensions determine the binary state, where the larger and smaller patches are associated with the logic `1' and `0' states, respectively, or vice versa. For sequentially and synchronously reading the bits, a sensitive element able to determine the presence of the patches and their size by proximity (through near field using microwaves) is considered. Such element is a microstrip line loaded with a pair of rectangular complementary split ring resonators (CSRRs), one etched inside the other in the ground plane. When the tag chain is displaced at short distance over the CSRRs, the larger patches modify the resonance frequency of both sensing CSRRs, whereas the lower patches do only alter the resonance frequency of the smaller CSRR. Consequently, the ID code is contained in the patch dimensions, and the presence of a patch (regardless of its size) determines the reading times (clock signal), necessary for synchronous reading. Tag reading in this system proceeds by feeding the CSRR-loaded line (reader) with a pair of harmonic signals tuned to the resonance frequencies of the bare CSRRs. Both signals are amplitude modulated (AM) at the output port as consequence of tag motion, and the respective envelope functions contain both the clock signal and the tag ID code. The ID codes of several 16-bit tags, implemented on different substrates (microwave substrate, plastic and paper) and exhibiting a per unit length density of 1.67 bit/cm, have been inferred with the dedicated reader for validation purposes.

Multi-Bit Chipless RFID Sensing Methodology for Rotation Determination.

Chipless RFID tags can be used for both identification and sensing applications. While binary codes are assigned to the responses of ID tags, they typically are not assigned to the responses of sensing tags. Instead, changes in tag response characteristics, like notches, are related to a sensing parameter. While this provides for a straightforward sensing mechanism, it can be limiting in terms of the dynamic range and sensing resolution that can be achieved. This paper proposes assigning multi-bit codes to the responses of sensing tags in order to better capture the effect of the sensing parameter on the tag response and provide greater sensing capabilities. This is done in the context of a rotation sensing with a tag that is capable of sensing 1° rotations from 0° to 180°. It is also shown that using tags with higher notch densities for sensing can result in better sensing resolution.

Wide-Angle RCS Enhanced Tag Based on Dielectric Resonator – Lens Combination

AbstractIn a novel mm-wave localization system, dielectric resonators (DR) have been proposed as passive chipless RFID tags to mark fixed reference nodes. To counter clutter and improve the limited read range due to the low RCS level of a DR at millimeter-wave frequencies we propose a combination of several DRs with a dielectric spherical lens which allows improvement of up to 30 dB. The paper presents the design principle and shows simulation results and experimental verification of a scaled tag operating in the 10–12 GHz range and covering a range of incidence angle of the reader signal of ± 50°. A frequency sweeping RF reader can identify the tag (information) by the peak of the RCS level at its DR resonant frequency. For a multiple-tag scenario we can realize up to 12 different tags which can be discriminated unambiguously by their resonant frequencies in a 1: 1.2 frequency bandwidth.

Low-cost thin-film passive RFID circuits and detector system

AbstractThis paper discusses the design of chip-less RFID tags of a standard pocket size of 69 mm by 156 mm. These tags are based on lumped elements of copper metal traces constructed on a thin polyamide flexible substrate. Moreover, a low-cost single-chip Bluetooth detector circuit system is demonstrated. Two different detection methods: variable coil load coupling and optical light intensity detection were combined to yield 256 unique ID codes. In the first method, by utilizing simple 4 MHz digital drivers and an integrated analog to digital converter (ADC) in the reader controller; various inductively coupled resonant loads corresponding to multiple distinct tags could be differentiated, yielding eight different (3-bit) ID codes. The additional via-based hole pattern reflectometer method creates additional 32 distinct levels (5-bit) utilizing 650 nm visible light-emitting diode and a simple trans-impedance operational along with the same analog ADC pins of a Bluetooth controller. The printed circuit board trace coil on the two-layer low-cost FR-4 waterproof sealed detector unit is simultaneously used as a Qi wireless power receiver to charge the120 mAh 2450 Lithium Polymer (LiR) battery. The device could remain operational for more than a month with a single charge; remaining connected with a mobile device and enabling 10 readouts daily.

Microwave performance of flexo-printed chipless RFID tags

The chipless RFID tag is considered as a potential candidate to replace the expensive chip-based tags due to the possibility of high volume tag production by low-cost printing processes. In this paper, we report on the microwave performance of chipless tags printed by a benchtop flexographic printer using low-cost water-based silver ink obtained from NovaCentrix. The designed chipless RFID tags were based on the frequency-domain ‘Data Encoding’ due to its merit to encode a higher number of data bits compared to other domains of data encoding. The printed silver ink tracks were optimized for best printer settings in terms of the adjustments of the gap between the rollers, print speed and ink volume. The dependence of the RCS response on the actual tag area to be covered in metal ink, relative to the designed tag area, was investigated and a way to obtain an increased RCS response was studied. It was found that printing at least two copies of resonators can enhance the detected RCS response for any specific tag configuration. Tags printed on Mylar PET film gave the best RCS performance compared to tags printed on thermal paper and PVC film.

Design of phase coded spiral resonator based Chipless RFID tag for tracking applications

RFID (Radio identification) is a technology which deals with the wireless identification of people and products. This chipless RFID tag design is on research to replace chipped RFID tags, which employs high cost silicon wafer to store unique identification code. The main challenge in the design of chipless RFID tag is how to encode the data without a chip. This challenge is overcome by the use of electromagnetic properties of the resonators, filters etc to encode the data bits. In this work RFID tag is designed based on multiresonators with each resonator representing a data bit. The proposed tag consists of the multiresonating circuit to store information bits and transmitting and receiving UWB antenna for wireless communication with the RFID reader for identification. The multiresonating circuit designed consists of 4-spiral resonators electromagnetically coupled to the microstip coupled line. Each spiral resonates at unique resonating frequency representing the unique data bit. The data encoding is carried out with the help of phase ripples at the resonating frequency of the spirals. Three variations are observed and corresponding 3-logic states (0, 1, 2) are encoded. The designed tag is simulated in Advanced Design System (ADS) using RO-4003 substrate with the dielectric constant 3.38 and thickness of 20 mil. From the proposed methodology, a total of 34=81 unique tags can be designed that can be employed in cheap item tracking. The Monopole disc antenna is designed which operates for wide band covering all resonating frequency of the spiral resonator.

A 3-bit fully inkjet-printed flexible chipless RFID for wireless concentration measurements of liquid solutions

A fully inkjet-printed flexible chipless RFID tag is presented in this paper. It is based on a coplanar waveguide (CPW) coupled to a multiresonator circuit to encode the information in the frequency domain. Two cross-polarized ultra-wideband (UWB) antennas connected to the CPW receive and transmit the signals. As a proof-of-concept, three spiral resonators are used to encode a 3-bit signature, which can be easily expanded to more bits by adding more resonators. The RFID tag is applied for wireless concentration measurements of liquid solutions by characterizing the insertion loss response. Water/sodium chloride (NaCl) solution and water/isopropanol solution are measured wirelessly by the sensor. A capillary tube is placed on one of the resonators to allow the interaction between the sensor and the solutions. By the observations of measurements, different parameters are used to quantify the sensitivity. The change of the insertion loss at the resonant frequency |ΔS21| and the half-power 3-dB bandwidth, ΔBW are used to analyze the water/NaCl solution. |ΔS21| and the shift of resonant frequency, |Δfres| are used to analyze the water/isopropanol sample. The proposed RFID shows the potential for measuring liquid solutions wirelessly.

Chipless-RFID: A Review and Recent Developments

In this paper, a review of the state-of-the-art chipless radiofrequency identification (RFID) technology is carried out. This recent technology may provide low cost tags as long as these tags are not equipped with application specific integrated circuits (ASICs). Nevertheless, chipless-RFID presents a series of technological challenges that have been addressed by different research groups in the last decade. One of these challenges is to increase the data storage capacity of tags, in order to be competitive with optical barcodes, or even with chip-based RFID tags. Thus, the main aim of this paper is to properly clarify the advantages and disadvantages of chipless-RFID technology. Moreover, since the coding information is an important aspect in such technology, the different coding techniques, as well as the main figures of merit used to compare different chipless-RFID tags, will be analyzed.

Slot Resonator Based Novel Orientation Independent Chipless RFID Tag Configurations

The design of two novel orientation-independent slot resonator-based chipless RFID tags is proposed in this paper. These tags make use of multiple L-shaped slots of different lengths on a lossy substrate and are appropriate for item tracking and identifications. The data are encoded in the backscattered signal from the tag after its illumination. The first tag configuration includes multiple L-shaped slot resonators cascaded with each other. It exhibits wideband features and enables the addition of extra resonators for encoding of additional data without an increase in the tag size. The second configuration has alternate resonators on one side of the substrate while the remaining resonators are inverted and are on the other half of the substrate. It leads to reduced mutual coupling between the resonators and hence an improved performance and improved printing flexibility. The proof of concept is demonstrated through the design of tags in CST Microwave Studio and prototype development on the Rogers 5880 substrate. Both the tags are compact, printed on 20 mm $\times$ 20 mm substrate, encode 8-bits in a bandwidth of 3 GHz and thus advance the state of the art significantly. An interesting feature of the proposed tags is the orientation independence and this is a very useful feature for applications, such as tracking of items in a smart retail scenario where the products need to be read by the readers from any orientation.

A secure multi-frequency resonator for printable chipless RFID tag based on multifractal planar geometry

ABSTRACTIn this paper, we are presenting a secure, compact and directly printable resonator for chipless RFID tag based on multifractal planar shape. The multifractal Cantor set shows an interesting performance of the monostatic radar cross section for chipless RFID tag. Unlike the classical RFID tag, where for each frequency a resonator is needed, so the number of resonators increases when the identification range increases, by using the Iterated Function System (IFS) the obtained resonator has many resonant frequencies leading to decreasing the number of resonators in chipless RFID tag. In addition, due to their auto similarities and multiscale resolutions resonant frequencies generated by the multifractal Cantor set are not independents: all resonant frequencies are correlated, so we cannot map a frequency peak to only one resonator, because the resonator itself represents a multi frequencies signature. These lead to a more secure tag, which is a challenge for many growing applications.

High-Density Microwave Encoders for Motion Control and Near-Field Chipless-RFID

A novel microwave system for measuring linear displacements and velocities with sub-millimeter resolution and for the implementation of near-field chipless radiofrequency identification (chipless-RFID) systems with very high data capacity is presented. The system is based on a reader, consisting of a half-wavelength straight resonator coupled (through capacitor gaps) to a pair of access lines, and a microwave encoder, in relative motion to the reader and consisting of a linear chain of strips orthogonally oriented to the chain axis. By displacing the encoder over the half-wavelength resonator of the reader, with the encoder strips parallel oriented to the reader axis, the relative velocity and position between the encoder and the reader can be inferred. For that purpose, the reader is fed by a harmonic signal tuned to the resonance frequency that results when an encoder strip is perfectly aligned with the reader. The encoder motion amplitude modulates the feeding signal at the output port, and both the position and the velocity are measured from the peaks, or dips, of the resulting envelope function. Moreover, by making certain strips inoperative, the system can be used for coding purposes. Due to the small period of the encoder (0.6 mm), a high per-unit-length data density in these near-field chipless-RFID tags (i.e., 16.66 bits/cm) is achieved. To illustrate the functionality and potential of the approach, 100-bit chipless-RFID tags with various ID codes are implemented and read.

Measurement of Inkjet-Printing Parameters for Accurate Chipless RFID Tag EM Simulation.

The use of Chipless RFID tags has been increasing for many applications, especially for structural health monitoring (SHM) applications where they are either affixed or embedded in materials and structures. The practical utility of chipless RFID is dependent upon the ability to manufacture tags in a cost-effective manner. One approach for achieving this is through the use of an inkjet printer and conductive ink. However, in order to harness the benefits of printed tags, it is necessary to know the dielectric properties of the substrates on which the tags are printed, as well as the conductivity of the printed conductors (i.e., ink) so that the tags can be properly simulated using electromagnetic (EM) models. It is also necessary to understand the performance differences that occur when tags are manufactured via inkjet-printing vs. when they are manufactured as printed circuit boards (PCBs). This work presents the dielectric property measurement results for three different paper substrates commonly used in tag printing from X-band (8.2 - 26.5 GHz) to K-band (18 - 26.5 GHz). Additionally, conductivity measurement results for silver nano-particle inkjet-printed conductors are also reported. These dielectric property and conductivity parameters are then used in tag EM simulations, and in the future when they are applied for SHM applications. PCB and printed tags are manufactured and measured to compare their performance both to each other and to simulation results.

Elliptical slot based polarization insensitive compact and flexible chipless RFID tag

A miniaturized, polarization insensitive, and fully passive chipless radio frequency identification tag is proposed in this research article. The realized tag is based on slotted elliptical structures in a nested loop fashion with identical lengths and widths of slot resonators. Alteration of data sequence is accomplished by addition and elimination of nested resonators in the geometric structure. The tag is capable to encode 10 bits of data and covers spectral range from 3.6 to 15.6 GHz. The formulated structure demonstrates polarization insensitive characteristic. The data encoding structure is analyzed and optimized for different substrates that are, Rogers RT/duroid/5880, Rogers RT/duroid/5870, and Taconic TLX‐0 over the miniaturized footprint of 22.8 × 16 mm2. The presented tag is robust, novel, compact, and flexible exhibiting a stable response to impinging electromagnetic waves at various angles of incidence.

Accurate Positioning System Based on Chipless Technology.

In this paper, we present an accurate method to localize an object on a 2D plan using the chipless technology. This method requires a single antenna and a chipless tag. Phase difference between a reference position and an unknown position is used to estimate the distances between each resonator and the antenna. Then, multi-lateration is used to determine the position of the chipless tag in the plan. This method provides a better accuracy compared to classical ones based on received signal strength indicator (RSSI) or round-trip time-of-flight. In a square of 10 cm side above the antenna, error over distance determination between each resonators and the antenna is less than 2 mm and localization error on the tag coordinates in the 2D plan is lower than 1 cm. To increase the robustness of this method, we propose also a selection of a subset of the resonators used by the multi-lateration process. This method permits to increase the localization area by more than 20%. All the results have been obtained in real environment, and at different heights to show the robustness of the proposed approach. Finally, localization sensors based on this method can also be used as classical chipless RFID tag for identification with the same coding capacity.

Practical implementation of Chipless RFID System

The Radio frequency identification technology (RFID) can detect and identify the tagged items in supermarkets and also used in fake objects authentication. However, the costly chip of current RFID tags is making it hard to compete with low-cost barcode identification system. The chipless version of RFID tags is designed, fabricated and printed in this research work to develop low-cost RFID system. The thesis work is mainly focused on the development of chipless RFID tag via low-cost printing technology and design of printed tags with improved performance in terms of data capacity and readability.

Effective Design of Microstrip-Line Chipless RFID Tags Based on Filter Theory

This paper presents an effective design method of chipless RFID tags. With $n$ -bit first- and second-order chipless tags’ equivalent circuits proposed based on filter theory, the relationship between bits and frequency bands of tags is characterized by formulas. Combining with microstrip-line theory, the first-order chipless tag with single quarter-wave open-circuited (O.C.) shunt stub units, and second-order chipless tag with parallel pairs of quarter-wave O.C. shunt stubs are designed, respectively. The pros and cons for each type of the chipless tag are discussed. Two types of 5-bit chipless tag examples are given with good consistent simulated and measured results. In addition, for the second-order chipless tag, we propose a miniaturization scheme, enhancing the antidamage ability simultaneously. Damage test shows that the second-order chipless tag has the good antidamage ability, especially for the miniaturized tag. Finally, the bit extension by the formulaic method is discussed, emphasizing a promising practicability.

Design and Analysis of Chipless RFID Tags Based on Retro-Radiators

Chipless RFID tag is a promising technique for future RFID systems due to its low cost and high reliability. In this paper, three chipless RFID tags are designed based on retro-reflective structures, in order to increase the reading range and enhance the tag's robustness to the direction of the interrogating signals. The three tags include two linearly polarized tags with non-symmetric and symmetric filters and a circularly polarized tag. Before introducing the tag antennas, the design guidelines on how to arrange the filters for higher detection accuracy are provided based on standing wave analysis. Following the rules, retro-radiating tags with filters are designed. Since the E fields from the retro-radiating antennas add constructively in the direction of the incoming signal automatically, the reading distance is greatly increased compared with the conventional tags with orthogonally placed antennas. The tag with symmetric filters and arrangements can further enhance the detection robustness regardless of the reader's positions. Moreover, the circularly polarized tag is insensitive to the polarization of the incoming signals. The experimental results measured in the anechoic chamber show that the retro-radiator based tag can reach a reading distance of 60 cm, which is longer than most of the existing chipless tags. In the measurement, the proposed tag was well detected even when the reader antennas were not at the boresight.

K-State Resonators for High-Coding-Capacity Chipless RFID Applications

This paper presents a new, compact, high-coding-capacity resonator suitable for applications in chipless RFID tags. These tags consist of multiple resonators and two cross-polarized ultra-wide band antennas. Each resonator contains a U-shaped coupled microstrip frame with isolated (K-1) legs inside. One of the legs is designed to be connected to the U-frame via a metallic strip in order to adjust its resonance frequency. Using this feature, the frequency of each resonator can be reconfigured to be equal to one of the K-resonance frequencies. Therefore, each resonance presents one of the K-states of the resonator. This allows each resonator to represent more than one bit of information; this arrangement also permits N resonators tags to provide KN codes. The structure can store large volumes of data in a small area and can simplify the detection process by only reading N resonance frequencies for each code. When N resonator tags are used in the proposed structure, the amount of data that can be encoded increases to $2^{(\log K / \log 2)N}$ compared to $2^{N}$ in the case of conventional one-bit resonator (2-states) tags. An additional arrangement is also proposed and investigated in order to improve the spectral efficiency by allowing the bandwidth of each single resonator to be shared between two resonators. Several tags for codes with K = 8 are designed and implemented on the RT Duroid 5880 substrate as a proof-of-concept. An 8-state of the proposed resonator can be implemented in an area that is almost the same size as the area of a conventional 2-state resonator operating at 5 GHz. A satisfactory agreement between the empirical and simulated results is then confirmed.

FREQUENCY SHIFT ENCODING TECHNIQUE FOR MULTIRESONATOR BASED CHIPLESS RFID TAG

This paper presents an encoding technique for multiresonator based chipless RFID tags for enhancing the packing density of bits both in space and frequency band. The data are encoded by uniquely identifying the patterns of relative distances of the notch frequencies for different combinations of resonator dimensions from a static reference frequency in the reader. The proposed tag consisting of 5 resonators operates over 6-9 GHz by which 16 bits are encoded in a space of 8.6 × 5 cm2. The proposed design and encoding technique makes the tag highly scalable, less costly and more data-dense. It also requires smaller reading band or enquiring spectrum and less reading cost.

Novel Butterfly Slot Based Chipless RFID Tag

A compact chipless RFID tag with robust readable features is presented in this paper. The tag is made up of novel concentric butterfly slot resonators. Bit data is encoded in the frequency signatur ...