Radio Frequency Identification Tag Antenna Research Articles

Material Selection and Design Methods for Flexible RFID Tag Antenna

In recent years, advancements in flexible printed electronics have significantly propelled the development of wearable devices, especially in areas of integration, comfort, and streamlined manufacturing. By incorporating electronic components and conductive coatings onto flexible substrates, circuits gain enhanced flexibility and some degree of stretchability. Among these circuits, radio frequency identification (RFID) tag antennas have emerged as a focal point in wearable device communication due to their adaptability in power selection and their compatibility with printed circuit technologies. When designing flexible and stretchable RFID tag antennas using printed electronics, two critical factors need to be addressed. The first is the antenna’s structural design, which must account for varying environments and usage contexts. The second is the development of the antenna prototype, involving the selection of conductive coatings and flexible substrates, as well as the printing processes and performance evaluation standards. This paper will explore common conductive coatings and substrate materials used in flexible printed electronics, along with the design methods of printed tag antennas for wearable applications. Lastly, a novel approach is proposed in which the flexible and stretchable RFID tag antenna itself functions as a strain sensor for posture or pressure detection. Unlike conventional strain sensors, this design eliminates the need for additional communication modules, offering a simplified structure that can be easily printed onto clothing, thereby streamlining the production process.

Review of Metal-Resistant Structures for Radio Frequency Identification Tag Antennas

Amidst the rapid expansion of e-commerce and the consequential surge in industries such as transportation, logistics, and supply chain management, there has been remarkable growth. Radio Frequency Identification (RFID) technology, along with its associated tags, plays a pivotal role in the transmission and tracking of crucial information within these sectors. However, the presence of metallic components within RFID systems poses a significant obstacle to efficient antenna transmission. Consequently, there is a pressing need for the development of RFID tag antennas endowed with metal-resistant properties. This paper undertakes a comparative analysis of existing designs and structures for metal-resistant RFID tag antennas, providing valuable insights into their prospective developmental trajectories and potential applications. Such analysis serves as a pertinent reference for research and engineering endeavors across related domains.

A Compact and Robust RFID Tag Based on an AMC Structure.

A platform-tolerant RFID (Radio-Frequency Identification) tag is presented, designed to operate across the entire RFID band. This tag utilizes a small Artificial Magnetic Conductor (AMC) structure as a shielding element for an ungrounded RFID tag antenna. It can be easily mounted on various surfaces, including low permittivity dielectric materials, metal objects, or even attached to the human body for wearable applications. The key features of this RFID tag include its ability to be tuned within the worldwide RFID band, achieving a maximum theoretical read range of over 11 m. Despite its advanced capabilities, the design emphasizes simplicity and cost-effective manufacturing. The design and simulations were conducted using CST Studio Suite.

Bio-Inspired Circular-Polarized UHF RFID Tag Design Using Characteristic Mode Analysis

This paper presents a bio-inspired circularly polarized ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna for metallic and low-permittivity substances. This tag design is based on a leaf-shaped radiator, two shorting stubs and slots etched on F4B substrate. Initially, the tag antenna is designed using characteristics mode analysis (CMA) by analyzing the first six CM modes and characteristic angles. The width of orthogonal slots is varied to get the resonance of CM modes in the required US RFID band. Moreover, the edges are blended to get orthogonal current distribution, which is necessary for circular polarization. Additionally, the proposed tag design is optimized further using CST Microwave studio and an RFID chip is exploited as a capacitive coupling element (CCE) to run CM modes with the orthogonal current pattern. This tag can also be tunable to European RFID (EU) band (866 – 868 MHz) by changing the length of shorter diagonal slot. The tag design offers a read range of 7 m and 4.5 m on 100 × 100 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> metals plate and low-permittivity substrates, respectively (for 902 – 928 MHz band). In EU band, the corresponding read ranges are 5.7 m and 3.5 m above metal and low-permittivity objects, respectively. This circularly polarized tag antenna is advantageous in terms of cost, circular polarization feature, and ease of fabrication due to the absence of vias, shorting pins, and matching circuits. Therefore, this tag design is suitable for labeling various low-permittivity objects, industrial conveyer belt applications, baggage handling systems, and IoT applications.

MSCNN-LSTM Model for Predicting Return Loss of the UHF Antenna in HF-UHF RFID Tag Antenna

High-frequency (HF) and ultrahigh-frequency (UHF) dual-band radio frequency identification (RFID) tags with both near-field and far-field communication can meet different application scenarios. However, it is time-consuming to calculate the return loss of a UHF antenna in a dual-band tag antenna using electromagnetic (EM) simulators. To overcome this, the present work proposes a model of a multi-scale convolutional neural network stacked with long and short-term memory (MSCNN-LSTM) for predicting the return loss of UHF antennas instead of EM simulators. In the proposed MSCNN-LSTM, the MSCNN has three branches, which include three convolution layers with different kernel sizes and numbers. Therefore, MSCNN can extract fine-grain localized information of the antenna and overall features. The LSTM can effectively learn the EM characteristics of different structures of the antenna to improve the prediction accuracy of the model. Experimental results show that the mean absolute error (0.0073), mean square error (0.00032), and root mean square error (0.01814) of the MSCNN-LSTM are better than those of other prediction methods. In predicting the return loss of 100 UHF antennas, compared with the simulation time of 4800 s for High Frequency Structure Simulator (HFSS), MSCNN-LSTM takes only 0.927519 s under the premise of ensuring prediction accuracy, significantly reducing the calculation time, which provides a basis for the rapid design of HF-UHF RFID tag antenna. Then MSCNN-LSTM is used to determine the dimensions of the UHF antenna quickly. The return loss of the designed dual-band RFID tag antenna is and at 13.56 and 915 MHz, respectively, achieving the desired goal.

Miniature 3-D-Dipole Antenna for UHF RFID Tag Mounted on Conductive Materials

A novel compact 3-D-dipole antenna for a radio frequency identification (RFID) tag is presented in this article. The proposed antenna enables the tag to be read when mounted on surfaces composed of electrically conductive materials. A close match between the input resistance and reactance of the antenna to the desired conjugate impedance of an Alien Higgs-4 chip ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.2- j 148.5\,\,\Omega $ </tex-math></inline-formula> at 925 MHz) can be achieved by controlling the C-arm length and the width of the 3-D dipole. Experiments demonstrated that when an RFID tag antenna is attached to a conductive surface, a 0.2 mm gap between the antenna and the conductive plane enhances the antenna’s gain by increasing reflection from nearby surfaces (e.g., a metal object, a container of water, and a human wrist) within range of the antenna. Maximum read ranges are measured for the tag antenna fabricated with dimensions of 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 25\times3.2$ </tex-math></inline-formula> mm3 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.10\,\,\lambda _{0} \times 0.08\,\,\lambda _{0} \,\,\times0.01\,\,\lambda _{0}$ </tex-math></inline-formula> ) and mounted on various materials and objects. In an outdoor environment, an effective isotropic radiated power (EIRP) transmitted by the RFID reader of 4.0 W achieves the maximum reading distances of 5.1, 3.3, and 3.9 m when the proposed tag antenna is placed on a metallic plate, a container of water, and a human wrist, respectively. The experiment and simulation results have a good agreement with each other.

A compact radio frequency identification tag antenna with loaded coupling rings for two‐side anti‐metal design

A compact ultra-high frequency radio frequency identification tag antenna loaded with a pair of rectangular coupling rings for two-side anti-metal performance is proposed. It evolves from a planar inverted-F antenna and has the same upper and lower structures. A pair of coupling rings is symmetrically loaded on the inner sides of the upper and lower substrates, and the tag's maximum power transmission coefficient can be achieved when either side of the antenna is placed on a metallic plate. The proposed tag antenna maintains a compact size of 34 mm × 28 mm × 5 mm. The measured results show that it has the lowest sensitivity of −14.8 dBm when the lower side is on a metallic plate and the lowest sensitivity of −14.2 dBm when the upper side is on a metallic plate. The proposed tag antenna is featured in a compact size, low sensitivities, and anti-metal performance on two sides. It may be used in the areas such as the industrial internet of things.

Effect of fabric structure on the performance of screen-printed ultra-high frequency radio frequency identification tag antenna for wireless radio frequency energy harvesting

Textile materials are the ideal substrate of the antenna of eco-friendly wireless radio frequency (RF) energy harvesting technology for sustainable battery-free operation of wearable electronic devices, while few of the work published have been focused on the effect of textile properties on the energy harvesting performance. This work will clarify the effect of typical fabric surface structures on the energy harvesting performance of Radio Frequency Identification (RFID) antenna. The antennas were screen-printed onto three different weave structures, and performance for the different fabric-based antennas were studied. The results showed that the antenna printed on plain fabric, which has the smallest porosity and lower surface roughness, was able to achieve a maximum transmission distance of 110 cm and output voltage of 3.003 mV at 69 cm. Consequently, in order to improve the energy harvesting performance of antenna, the smooth and compact fabric surface is more beneficial to highly efficient energy harvesting.

Effects of Stitch Density, Thread Tension and Using Conductive Yarn as Upper or Lower Thread on Reading Performance of Embroidered RFID Tag Antennas

Textile-based Radio Frequency Identification (RFID) tags are widely used in different applications such as sensing, localization, and identification applications. Embroidery is one of the methods in textile-based RFID tag production. The embroidered RFID tags are generally used in the follow-up of textile raw material production and inventory, and laundry of commercial textiles. They capture the transmitted electromagnetic wave and generate a new one with a special coding that includes the required information about the item. Therefore, the fabrication parameters of the embroidered antennas are important in terms of durability, cost, and working performance. The conductivity of an embroidered antenna depends on the conductivity of the thread, stitch density, thread tension, and sewing method of the embroidery. In this study, the effect of stitch density, thread tension, and using conductive yarn as needle (upper) or bobbin (lower) thread for embroidered RFID antennas were examined using a polyester yarn twisted with stainless steel that is plain stitched on cotton fabric. The read range performances of the samples were tested with an integrated circuit (IC) by using an indoor RFID reader. It was seen that the optimised stitch density has a significant impact while it was determining the amount of conductive element due to the length of the yarn. Additionally, using conductive yarn as lower thread gave nearly 50% better results in signal strengths.

A broadband antimetal UHF tag antenna based on symmetric resonator structures

AbstractA novel broadband ultra‐high frequency radio frequency identification (RFID) tag antenna attached to the metallic surface is proposed in this paper. A rectangular wide slot combined with a U‐shaped thin slot outside is adopted in the proposed antenna, and the size of the patch can be reduced by adjusting the length of the U‐shaped slot. Furthermore, a pair of symmetric resonator structures inside the rectangular slot are connected to both ends of the chip, which can excite a new resonant mode to broaden the frequency band. All the structures above are realized by etching rectangular slits on the same surface. The antenna has the advantages of wideband, simple processing, and good reading distance, and the 10 dB bandwidth of the antenna is 30 MHz (from 895 to 925 MHz), with a maximum directional gain of −3.5 dB. The reading distance can reach more than 5.4 m on a metallic surface.

Platform-Tolerant Nested-Slot RFID Tag Antenna Based on Jigsaw-Shaped Metasurface

A novel low-profile (<0.005 λ) jigsaw-shaped metasurface for platform-tolerant nested-slot radio frequency identification (RFID) tag antenna is proposed in this letter. It consists of a 4 × 4 array of rippled-edged patch units with a central through-via. Compared with the widely used patch-unit artificial magnetic conductor structure, the proposed jigsaw-shaped metasurface is proved to suppress the surface waves effectively and reflect the electromagnetic waves in phase in the industrial scientific medical band of 902–928 MHz, therefore, it could improve the frequency and radiation stability of the nested slot RFID tag antenna on different platforms, and enhance the radiation performance of the tag antenna. The prototype of the metasurface was fabricated and measured as an interlayer of the nested-slot RFID tag and different platforms. The measured operation frequency band remains stable, and the measured reading range has a range deviation of less than 8.7% on different platforms.

Design of a Flexible T-Matched Feed UHF RFID Tag Antenna

Abstract A flexible radio frequency identification (RFID) tag antenna with a T-match feeder is proposed in this paper. The T-match feed acts as the conjugate network matching of the tag antenna and 0.99 of power transfer coefficient was achieved. By incorporating a meander line and capacitive tip loading technique, the compact size is realized with a wide bandwidth of 44MHz that can cover the RFID spectrum allocated for the Malaysia region, from 919 to 923 MHz. The proposed antenna is printed on the flexible polyethene terephthalate (PET) substrate with a dimension of 90mm × 24mm × 0.143mm. By employing 4W EIRP power, the detection distance of 29.15m in free space. The proposed meandered line and capacitive tip loading tag antenna with T-match feed line is beneficial to be part of the RFID systems because of their compactness, wide bandwidth and high-power transfer coefficient.

Frequency Reconfigurable Smart Antenna With Integrated Electroactive Polymer for Far-Field Communication

For the first time, the ionic polymer metal composite (IPMC) actuator is integrated with a radio frequency identification (RFID) tag antenna for achieving frequency reconfiguration in the ultrahigh-frequency (UHF) band. Here, the IPMC movable flap serves as an actuator that can effectively tune the tag resonant frequency. By applying a two-layer-crenelated structure and employing a surface patterned electrode for restraining back relaxation, the deflection of the IPMC actuator can be significantly improved. The IPMC actuator can move in two directions, enabling two-degree frequency tuning. Numerical and experimental data confirm that the tip displacement of the IPMC actuator can be enhanced up to 266% with the use of the two-layer-crenelated structure. The IPMC actuator allows the resonant frequency of the tag antenna to be tuned back by as much as 35 MHz, after deviating due to placing on an unintended object. UHF RFID application is also performed using a portable commercial RFID reader. Good frequency reconfiguration and broad tuning range, along with far read distances, have been achieved with our tunable UHF RFID tag antenna.

Graphene-Based RFID Tag Antenna for Vehicular Smart Border Passings

Globalization has opened practically every country in the globe to tourism and commerce today. In every region, the volume of vehicles traveling through border crossings has increased significantly. Smartcards and radio frequency identification (RFID) have been proposed as a new method of identifying and authenticating passengers, products, and vehicles. However, the usage of smartcards and RFID tag cards for vehicular border crossings continues to suffer security and flexibility challenges. Providing a vehicle's driver a smartcard or RFID tag card may result in theft, loss, counterfeit, imitation, or vehicle transmutation. RFID sticker tags would replace RFID tags as vehicle border passes to solve the mentioned problem. The RFID sticker tag adheres to the windscreen, side screen, dash, hood, or door of the vehicle, or any other acceptable location. Any damage or stripping from the installed location may cause data corruption and cannot be reused. Overall, these sticker tags will make the border crossings more secure and efficient. This article focuses on designing a rectangular-shaped RFID sticker tag antenna made of graphene sheets as a possible solution for smart border crossings. The proposed antenna is mathematically designed and analyzed with CST software to determine the optimum parameters. The design parameters are then used to create an antenna on a prepared graphene sheet. The performance results are carried out with CST software and a network analyzer. The designed RFID antenna stick on a car windscreen offers approximately 900 MHz bandwidth over the frequency range from 1.8 GHz to 2.7 GHz with an average gain of 1.23 dBi at the frequency to be used of 2.4 GHz microwave RFID band. The radiation is an omnidirectional pattern. The proposed graphene-sheet rectangular-shape monopole antenna is compact, low-cost, and bendable to fit into the windscreen of a car while retaining excellent wave propagation capabilities. These findings illustrate the suggested antenna's potential as an RFID tag antenna in a vehicular smart border pass system.

Low-Profile Interdigitated UHF RFID Tag Antenna for Metallic Objects

This article presents a novel miniature interdigitated ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna that can be placed on metallic objects. The tag structure comprises two horizontal strip lines, each loaded with seven identical open stubs, and an integrated circuit (IC) chip connected directly to the feed lines in the middle of the structure. The perfect match to the IC chip&#x2019;s impedance is realized by adjusting the length of the loaded open stubs and the spaces between the stubs. Molding the antenna&#x2019;s geometry can be applied to realize conjugated impedance with any sort of IC chip due to the flexibility of the tag structure. It is fabricated on a Polytetrafluoroethylene (PTFE) slab. Moreover, its structure does not involve any metallic vias or shorting walls, which makes its construction simple and suitable for mass production. The tag of the size of 55.2 <i>mm</i> &#x00D7; 44.2 <i>mm</i> &#x00D7; 1.5 <i>mm</i> yields a total realized gain of &#x2013;4.11 <i>dB</i> at the operating frequency while being placed on a 20 <i>cm</i> &#x00D7; 20 <i>cm</i> metallic plate. The measured detection distance is 8.14 m on metallic objects. A good match between the measured and simulated results is observed.

Strategies for a High Sensitivity Ferrite-Core RFID Tag Antenna Using in Oil Well Downhole Applications

As a very important part of the radio frequency identification (RFID) system, the tag antenna directly affects the performance of the whole RFID system. In this article, the design strategies for a high sensitivity ferrite-core RFID tag antenna using in oil well downhole applications is presented. Based on the derived formula of voltage sensitivity for the ferrite-core tag coil antenna, the parameters affecting the voltages sensitivity are studied. Then, through the theoretical analysis of the interactions between these parameters and sensitivity, the design of ferrite core and antenna coil winding are given in detail. Finally, the experiment results validate the proposed design strategies, and that a high sensitivity ferrite-core RFID tag antenna improves the performance of oil well downhole RFID system.

Internal Damage Detection of Composite Structures Using Passive RFID Tag Antenna Deformation Method: Basic Research

This manuscript deals with the detection of internal cracks and defects in aeronautical fibreglass structures. In technical practice, it is problematic to accurately determine the service life or MTBF (Mean Time Between Failure) of composite materials by the methods used in metallic materials. The problem is mainly the inhomogeneous and anisotropic structure of composites, possibly due to the differences in the macrostructure during production, production processes, etc. Diagnostic methods for detecting internal cracks and damage are slightly different, and in practice, it is more difficult to detect defects using non-destructive testing (NDT). The article deals with the use of Radio frequency identification (RFID) technology integrated in the fibreglass laminates of aircraft structures to detect internal defects based on deformation behaviour of passive RFID tag antenna. The experiments proved the potential of using RFID technology in fibreglass composite laminates when using tensile tests applied on specimens with different structural properties. Therefore, the implementation of passive RFID tags into fibreglass composite structures presents the possibilities of detecting internal cracks and structural health monitoring. The result and conclusion of the basic research is determination of the application conditions for our proposed technology in practice. Moreover, the basic research provides recommendations for the applied research in terms of the use in real composite airframe structures.

Machine Learning Enabled Food Contamination Detection Using RFID and Internet of Things System

This paper presents an approach based on radio frequency identification (RFID) and machine learning for contamination sensing of food items and drinks such as soft drinks, alcohol, baby formula milk, etc. We employ sticker-type inkjet printed ultra-high-frequency (UHF) RFID tags for contamination sensing experimentation. The RFID tag antenna was mounted on pure as well as contaminated food products with known contaminant quantity. The received signal strength indicator (RSSI), as well as the phase of the backscattered signal from the RFID tag mounted on the food item, are measured using the Tagformance Pro setup. We used a machine-learning algorithm XGBoost for further training of the model and improving the accuracy of sensing, which is about 90%. Therefore, this research study paves a way for ubiquitous contamination/content sensing using RFID and machine learning technologies that can enlighten their users about the health concerns and safety of their food.

A facile process combined with roll-to-roll flexographic printing and electroless deposition to fabricate RFID tag antenna on paper substrates

A reliable and low-cost solution-processing procedure to synthesize low-resistivity metal antenna for radio frequency identification (RFID) tags on paper substrates via roll-to-roll printing combined with electroless deposition (ELD) is demonstrated in this paper. The silver precursor ink has good printability and can maintain stable performance for more than 60 days via adding hydroxyethyl cellulose (HEC) and adjusting the ratio of ink components. Through a series of characterizations proved that a copper layer with good crystallinity, uniformity and high purity had been formed on the substrate when the electroless copper plating time was 25 min. In addition, the narrow copper wire of 89 μm can be obtained, while the electrical resistivity was as low as 2.22 μΩ cm. It is proved that the RFID copper layer antenna prepared by flexographic roll-to-roll printing has qualified mechanical properties and excellent impedance matching with the IC chip, and even after 800 bends, the reading distance of the RFID tag can still maintain 96%. It can be concluded that the improved technology can be used to fabricate metal antenna for RFID tags on a paper substrate. Furthermore, these results suggest the great potential of this particle-free precursor ink in the field of large-scale flexible printed electronics.

Radiation Beam Pattern Control of UHF RFID Tag Antenna Design for Automotive License Plates

This paper presents a design of a radio frequency identification (RFID) tag antenna in the ultra-high-frequency (UHF) range, which is applicable to a vehicular license plate attached to a vehicle bumper. The main goals are to first improve the identification ratio by controlling the radiation beam pattern and, second, to control the beam direction. Since every vehicle has a license plate, the available plate structure is used to design the antenna. The shape of the tag is rectangular and has a dimension of 525 mm × 116 mm, which is smaller than the typical size of standard plates, 540 mm × 120 mm, used in Europe and Korea. The fabricated tag antenna, the license plate, and the vehicular bumper are fixed by volt and nut. For vehicle tracking and identification, RFID readers are deployed on the road side. For efficient identification, a long distance passive UHF RFID license plate with a patch antenna is proposed to provide not only line-of-sight identification but also left and right beams. Unlike the general UHF tag antennas, in this paper, the patch antenna is designed to attach to the metal part of the car, the license plate holder. The beam patterns of the RFID tag antenna can be controlled by the patch antenna parameter values. The simulation result demonstrates that the proposed UHF RFID tag antenna has a beam radiation pattern as required at 920 MHz. In addition, the estimated read range of the proposed plate meets the requirement of RFID systems.