Near-field Radio Frequency Identification Research Articles

Nature-inspired spider web shaped UHF RFID reader antenna for IoT and healthcare applications

This paper proposes a nature-inspired spider web-shaped ultra-high frequency (UHF) radio frequency identification (RFID) reader antenna and battery-free sensor-based system for healthcare applications. This antenna design consists of eight concentric decagons of various sizes and five straight microstrip lines.These lines are connected to the ground using 50 Omega resistors from both ends, except for one microstrip line that is reserved for connecting a feeding port. The reader antenna design features fairly strong and uniform electric and magnetic field characteristics. It also exhibits wideband characteristics, covering whole UHF RFID band (860–960 MHz) and providing a tag reading volume of 200 times 200 times 20 mm{^3}. Additionally, it has low gain characteristics, which are necessary for the majority of nearfield applications to prevent the misreading of other tags. Moreover, the current distribution in this design is symmetric throughout the structure, effectively resolving orientation sensitivity issues commonly encountered in low-cost linearly polarized tag antennas. The measurement results show that the reader antenna can read medicine pills tagged using low-cost passive/battery-free RFID tags, tagged expensive jewelry, intervenes solution, and blood bags positioned in various orientations. As a result, the proposed reader antenna-based system is a strong contender for near-field RFID, healthcare, and IoT applications.

Metamaterial-enhanced near-field readout platform for passive microsensor tags

Radiofrequency identification (RFID), particularly passive RFID, is extensively employed in industrial applications to track and trace products, assets, and material flows. The ongoing trend toward increasingly miniaturized RFID sensor tags is likely to continue as technology advances, although miniaturization presents a challenge with regard to the communication coverage area. Recently, efforts in applying metamaterials in RFID technology to increase power transfer efficiency through their unique capacity for electromagnetic wave manipulation have been reported. In particular, metamaterials are being increasingly applied in far-field RFID system applications. Here, we report the development of a magnetic metamaterial and local field enhancement package enabling a marked boost in near-field magnetic strength, ultimately yielding a dramatic increase in the power transfer efficiency between reader and tag antennas. The application of the proposed magnetic metamaterial and local field enhancement package to near-field RFID technology, by offering high power transfer efficiency and a larger communication coverage area, yields new opportunities in the rapidly emerging Internet of Things (IoT) era.

Near‐field radio frequency identification leaky‐wave antenna based on artificial transmission line

The artificial transmission line (ATL) has a good characteristic of wavelength shortening, which can effectively cut down the size of microwave devices. In this article, the near-field radio frequency identification antenna based on an ATL was proposed. It mainly includes the radiating unit structure on the upper layer and the feeding structure on the lower layer. The two layers are connected by copper pillars for feeding. The height of the copper pillars is 16 mm (h0), which can obtain the maximum bandwidth. The antenna unit based on ATL consists of three curved microstrip lines, two interdigital microstrip lines, and four open microstrip lines. The interdigital structure on the upper layer of the antenna unit mainly affects the resonant frequency of the antenna unit, and the asymmetric interdigital microstrip lines increase the impedance matching bandwidth of the antenna unit. Compared with previous antennas, the proposed antenna features a low profile, and a good miniaturization based on an ATL by bending inductance and interdigital capacitance. The leaky-wave characteristic makes the energy radiate at a certain angle on the surface of the antenna. The leaky-wave characteristic and circular polarization characteristic of the antenna achieve a uniform field distribution. The simulated and measured bandwidth cover from 0.78 to 1.1 GHz for |S11| less than −10 dB. More importantly, the antenna has a large recognition area. The measured results demonstrate that the proposed reader antenna has a 100% read rate in 400 × 350 × 400 mm3 area in the metal shelf.

Modeling and Design of a Large Segmented Loop Antenna With a Coplanar Parasitic Slot Loop for NF UHF RFID Readers

This work proposes an improved electrically large antenna based on segmented loops for near-field radio frequency identification readers. The paper applies dispersion analysis of an equivalent circuit model to optimize the segmented loop geometric dimensions and enlarge the tag detection perimeter of the antenna. The novel application of a coplanar parasitic slot loop is shown to improve the dispersion properties of the segmented loop and expand the read perimeter to more than 3.5 times the free-space wavelength at the operating frequency. Furthermore, using the proposed circuit model, a loop antenna with perimeter equivalent to 3.54 times the free-space wavelength is designed and tested for both bidirectional and unidirectional detection. The fabricated prototype demonstrated an improved read range reaching <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~mm$ </tex-math></inline-formula> for the bidirectional range and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$35\,\,mm {-}55\,\,mm$ </tex-math></inline-formula> for the unidirectional operation setup as well as impedance matching at the design frequency (0.915 GHz) located in the North American RFID band from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.902 {-}0.928\,\,GHz$ </tex-math></inline-formula> .

Near-Field Fractal RFID Reader Antenna for Item Level Tagging

This paper proposes a novel methodology for designing near-field fractal antenna operating at European Ultra-High Frequency (UHF) for Radio Frequency Identification (RFID) systems. The principle of Oppositely Directed Current (ODC) technique is implemented to generate homogeneous magnetic field above the surface area meant for near-field RFID application. The conceptual theoretical framework of the design based on the fractal structure can be applied. The fabricated RFID reader antenna operates at 867 MHz with reflection coefficient S11 -30 dB, thus the reader antenna covering UHF RFID band range. The reading capabilities of the antenna are determined by the interrogation area of, 190mm x 243mm. It is adequate for object tracking and detection systems in pharmaceutical management and chemical industries.

Compact dual‐band near/far‐field dipole antenna/tag

This study presents a compact printed dipole antenna/tag loaded by metamaterial (MTM) inclusions for portable near/far-field communication/identification applications. It is shown that loading a printed dipole antenna by epsilon negative inclusions can lead to achieving the miniaturised, dual-band, low-profile antenna. To realise this concept, inductively loaded wire (ILW) has been proposed. To implement inductive loads a meander-line structure is designed and manufactured. Simulation results show that placing the MTM cell in the vicinity of a dipole antenna causes to having an additional resonant frequency which is lower than the natural resonant frequency of a simple unloaded dipole antenna. With the aid of ILW-MTM, a low-frequency band at 2400 MHz for the wireless local area network (WLAN) and near-field radio frequency identification applications is achieved. The higher frequency band is expanded for 5800 MHz services (4900–6500 MHz) WLAN and worldwide interoperability for microwave access band. The antenna prototype is fabricated and measured. Good agreement has been observed between the simulation and measurement results.

UHF pure near‐field RFID reader antenna based on CSRR

An ultra-high frequency (UHF) travelling wave antenna based on complementary split ring resonator (CSRR) element is investigated in this study for pure near-field radio frequency identification (RFID) system. The proposed antenna consists of a T-type power divider, 180 ° phase shifter, two microstrip transmission lines ended with two 50 Ω resistors and the metal ground loaded CSRR elements. The CSRR elements are loaded on the metal floor corresponding to the minimum current points and middle of the two transmission lines. The CSRR elements resonate at the centre frequency and introduce coupling to enhance the magnetic field. The measured − 10 dB impedance bandwidth of the proposed antenna is 46 MHz (889–935 MHz), which covers the standards of Chinese and American bands. The reading regions for near-field tag, far-field tag and anti-metal tag are 400 × 200 × 10 mm 3 , 400 × 200 × 70 mm 3 and 400 × 200 × 60 mm 3 , respectively. The far-field gain is less than − 22 dBi, which makes the antenna suitable for the pure near-field application.

A Novel Near-Field UHF RFID Reader Array Antenna for Configurable Electrically Large Reading Area

In this paper, a novel configurable loop array antenna based on resonator-loaded microstrip lines (RLML) is proposed to enlarge the interrogation zone of the reader antenna for near-field ultrahigh-frequency (UHF) radio frequency identification (RFID) system. The proposed loop array antenna is composed of a number of RLML loop units. By configuration of the RLML loop units sharing a common side with its adjacent RLML loop units which carry reverse-direction flowing current in the ${x}$ -axis and ${y}$ -axis directions, loop array antennas are created to generate a strong and uniform magnetic-field distribution over a large configurable interrogation area. As an example, loop array antennas with $1\,\times \,8$ and $2\,\times \,3$ RLML loop units implemented onto a piece of an FR4 printed circuit board (PCB) are designed, fabricated, and measured. The measured bandwidth ranges from 894 to 964 MHz for a $1\times 8$ array antenna with a reading area of $570 \,\,{\mathrm{ mm}}\times 150\,\,{\mathrm{ mm}}$ and 917–932 MHz for a $2\times 3$ array antenna with a reading area of $270 \,\,{\mathrm{ mm}}\times 240\,\,{\mathrm{ mm}}$ . The reading distances of an $1\times 8$ array antenna for loop-like tag, dipole-like tag, and antimetal tag are achieved up to 22, 42, and 45 mm, respectively. For a $2\times 3$ array antenna, the reading distances of three tags are achieved up to 23, 43, and 40 mm.

Multipolarized Reader Antenna With Periodic Units Based on Electric Field Coupling for UHF RFID Near-Field Applications

This paper presents a multipolarized reader antenna with periodic units based on electric field coupling for near-field applications of ultra-high frequency (UHF) radio frequency identification (RFID). The antenna units are composed of two branches that are mirror-symmetric with respect to the ${x}$ -axis and produce ±45° linear polarization. A 90° phase difference is produced between the upper and lower branches by introducing a phase shifter into the upper branch, so that the near-field electric fields excited in the horizontal plane exhibit a quasi-circular polarization distribution. The proposed design is validated by simulations and experiments using prototype 4-unit and 6-unit antennas. The proposed antennas can generate strong and uniform electric fields and provide reading volumes of 400 mm $\times \,\,320$ mm $\times \,\,300$ mm and 560 mm $\times \,\,320$ mm $\times \,\,300$ mm for the 4-unit and 6-unit antennas, respectively, regardless of the orientation of the tags in the horizontal plane. In addition, the far-field gain is low with a maximum of −6 dBi, thus the misreading of tags outside the reading region is avoided. The proposed antenna achieves impedance matching over the Chinese UHF RFID band (920–925 MHz) and therefore meets the application requirements of near-field RFID reader antennas.

Electrically Large Segmented Dipole Array Antenna With Reflectors for UHF Near-Field RFID Applications

A novel electrically large segmented dipole array antenna with reflectors for ultrahigh-frequency near-field (NF) radio frequency identification applications is proposed in this communication. It consists of eight electrically large segmented dipoles and two reflecting plates of convex parabolic shape. Each dipole has 12 identical parts connected by appropriate capacitive loads, which almost achieves an in-phase surface current distribution. The two plates act as reflectors to limit the strength of the NF magnetic fields outside of the reading area and to improve the impedance matching. The proposed antenna generates a strong and uniform magnetic field distribution in a finite area, which could effectively reduce the misreading rates outside of the interrogation zone. A prototype was fabricated and tested for verification. The measured results showed that a strong and uniform magnetic field distribution was generated within an interrogation zone of $480\,\,\text {mm} \times 300$ mm. A broadband of approximately 117 MHz ( $\vert \text{S}_{11}\vert dB), from 843 to 960 MHz, was achieved, covering the ETSI and FCC standards.

4D full-vector radio frequency complex magnetic susceptibility mapping. Near-field imaging of RFID tags

Radio frequency identification (RFID) is a technology permeating both everyday life and scientific applications alike. The most prolific passive tag-based system uses inductively-powered tags with no internal power source [V. Chawla and D. S. Ha, “An overview of passive RFID,” IEEE Commun. Mag. 45(9), 11–17 (2007)]. Here we demonstrate an inductive magnetic field mapping platform on the example of passive near-field RFID tags (ID-1), operating at 13.56 MHz (HF) [Identification cards - Contactless integrated circuit(s) cards - Proximity cards - Part 1: Physical characteristics, ISO/IEC 14443-1, 2000; Part 2: Radio frequency power and signal interface, ISO/IEC 14443-2, 2010; Part 3: Initialization and anticollision, ISO/IEC 14443-3, 2011; Part 4: Transmission protocol, ISO/IEC 14443-4, 2008]. With smaller modules currently being integrated in wrist-bands, watches and items of jewelry, a possible counter-measure to the reduced size is the use of flux-concentrating magnetic material - low-permeability insulating ferrites or high-permeability metallic μ-particle systems such as sendust. Sendust is a magnetically soft iron-rich alloy of Fe, Al and Si - a higher permeability cheaper alternative to permalloy. The integration of sendust components in RFID tags creates a non-trivial multiple-parameter optimization problem, which requires a quantitative RF field imaging system to be used. The RF susceptibility mapping system is comprised of a stepper-motor-driven 4-axial table, which holds the device under test (DUT) or the RFID tag assembly, a source coil (2 turns of 0.5 mm diameter wire, of overall diameter of 21 cm), a 4-micro-coil assembly, allowing for the measurement of Hx, Hy, Hz and dHz/dz, and a 4-channel Vector Network Analyzer (VNA). Four complex transmission spectra are obtained for each spatial point of a rectangular (x, y) grid, and then repeated for a different z-cut. 4D Complex Vector field maps are thus obtained. Simultaneous fitting of the real and imaginary parts of the frequency spectra is possible, at essentially any point of space, to a model comprised of two damped harmonic oscillators. This type of 3D-spatial, full-vector, complex magnetic susceptibility imaging opens ways to the integration of magnetic materials in near-field systems, and is not limited to RFID.

Design of a Near-Field RFID Antenna Array in Metal Cabinet Environment

A four-element near-field radio frequency identification (RFID) antenna array for smart telecommunication cabinet is proposed to achieve a uniform electric field distribution in the target interrogation zone in a metal cabinet environment. In order to determine the distribution of excitations that generate the desired uniform near-field distribution, the method of maximum power transmission efficiency has been used. By introducing more than one test receiving antennas in the interrogation zone and maximizing the power transmission efficiency between the array to be designed and the test receiving antennas, an optimized distribution of excitations can be obtained and then realized by a feeding network. The designed reader antenna is demonstrated to be able to track all the tags inside the metal cabinet and can be easily adjusted to various cabinet configurations.

A Reader Antenna for UHF Near-Field RFID Applications Based on the Segment-Line Oppositely Directed Currents

A reader antenna based on the segment-line oppositely directed currents is proposed in this letter for the ultrahigh frequency near-field (NF) radio frequency identification applications. The proposed antenna consists of two identical electrically large dipole elements without additional impedance matching network. To keep the surface currents along the dipole elements in-phase, the segmental and loaded method is adopted. Through the dispersion analysis, the maximum length of the dipole elements is one and a half guide wavelength with 12 segments and 0.7 pF lumped capacitors at 920 MHz. Subsequently, adjusting an appropriate distance between the dipole elements can form the oppositely directed currents, resulting in a strong, uniform, and large NF magnetic field distribution. The measured results show that the bandwidth is 53 MHz from 884.5 to 937.5 MHz covering the FCC standards. The interrogation zone is approximately equal to 480 mm × 250 mm under the observing height of 50 mm above the antenna surface. Thus, the proposed antenna is suitable to be used for the smart showcases and shelves.

Segmented Solenoid Coil Antenna for UHF RFID Near-Field Reader Applications

A segmented solenoid coil antenna for UHF near-field radio frequency identification (RFID) applications is reported herewith for the first time. A large read zone, in comparison to the antenna size, is achieved using an antenna made of 4-turns of wire, wrapped around a cylinder of diameter 5 cm and height 2.6 cm. Similar to HF RFID reader antennas, it has been proved that by increasing the number of turns, it is possible to concentrate and make magnetic field in the antenna surrounding zone uniform, and thus increase the read range. This improvement first modeled in simulations is then realized and validated experimentally. In the optimum configuration, the maximum read range is increased by 6 cm in comparison to a single turn planar loop. In addition to the enhancement in read performance, this antenna is fabricated on a flexible substrate using a low cost printing process.

A Novel Printed Dual-Log-Periodic Array Antenna for UHF Near-Field RFID Applications

A novel printed center-fed dual-log-periodic array antenna is proposed for ultrahigh frequency (UHF) radio frequency identification (RFID) applications. The proposed antenna is composed of two reversed wideband printed log-periodic dipole array antennas. Two closely spaced oppositely directed currents are thus introduced to achieve intensive and uniform magnetic fields in the near-field zone. A prototype antenna is fabricated and measured in practical application environment. The measurement results agree well with the simulations, and demonstrate that the proposed antenna is suitable to be implemented in RFID systems. The operated frequency band of the antenna is 824–953 MHz (14.5%), covering the UHF band in China, the Federal Communications Commission band, and the European Telecommunications Standards Institute band. With the proposed printed dual-log-periodic array antenna, measurement results also show that the RFID system delivers a 100% guaranteed reading rate within 2.0 cm and a maximum reading range of 19.0 cm.

A Directional, Closely Spaced Zero-Phase-Shift-Line Loop Array for UHF Near-Field RFID Reader Antennas

A zero-phase-shift-line (ZPSL) loop array with two closely spaced elements is proposed to achieve a directional distribution for ultrahigh frequency (UHF) near-field radio frequency identification (RFID) applications. The proposed array consists of two coaxially positioned ZPSL loop antenna elements of the same size, with an aperiodic ZPSL loop acting as a driven element and a periodic ZPSL loop functioning as a parasitic element. A directional magnetic field distribution can be achieved when an out-of-phase current along the parasitic loop is induced. A ZPSL loop array prototype with an interelement spacing of 15 mm, or 0.046 of the operating wavelength at 915 MHz, achieves a desired directional magnetic field distribution over a circular interrogation zone with a diameter of 160 mm. As a UHF near-field RFID reader antenna, the proposed array is able to achieve a 100% detection rate of SAG tags up to 120 mm by using an Impinj Speedway reader with an output power of 30 dBm.

A Grid-Shaped Microstrip Traveling Wave Antenna With Selective Differential Feeding Networks for CM-Level Position Detection Systems

In this paper, a near-field ultrahigh-frequency radio frequency identification (RFID) system, which has cm-level 2-D positioning precision, is proposed. The system consists of a grid-shaped microstrip traveling wave antenna (TWA) and four-port switched differential feeding networks. To selectively form tag-read sections, opposite directional currents (ODCs) are used. To introduce a microstrip TWA for cm-level 2-D positioning, the influence of $H_{z}$ fields in microstrip TWAs is theoretically analyzed. In addition, to utilize field reinforcement and achieve precise 2-D localization, a grid-shaped microstrip TWA with four-port selective switched differential feeding networks is proposed and investigated. The proposed antenna and feeding network were fabricated on FR-4 substrates. The simulated and measured results demonstrate that precise 2-D tag positioning is achieved using the proposed system utilizing ODC along two selected adjacent microstrip lines in the TWA.

Isolator-Less Near-Field RFID Reader for Sub-Cranial Powering/Data Link of Millimeter-Sized Implants

Implants for brain–machine interface (BMI) systems require both wireless powering and data communication to be practical for reliable long-term use. Sub-cranial radio-frequency identification (RFID) readers can receive backscattered data, while providing wireless power to operate the implant. This paper presents a novel reader architecture for an efficient near-field fully integrated RFID reader meant to deliver power to and receive data from BMI implants, where a modified Class-E/Fodd power amplifier (PA) with a current-sense resistor differentially drives a single segmented antenna and acts simultaneously as TX and RX. It operates at 309 MHz and has 54% efficiency. The non-linearity of the switching PA is able to demodulate the backscattered signal to baseband. And the data can be recovered from a current-sense resistor without the need for bulky RF isolators, separate RX/TX antennas, or different frequencies for data/power delivery. The reader, as tested with a proprietary RFID tag through pig-skin and cow-bone, can deliver a maximum of 790 $\mu \text{W}$ to an implant through the skull while consuming 39.4 mW of power. It has a 2-Mb/s data rate with a bit error rate of less than 1e–6.

Transformation of Barcode Into RFID Tag, Design, and Validation

This letter demonstrates the possibility of combining advantages of barcode and radio-frequency identification (RFID) technologies on the same smart label. In this letter, several UHF RFID tag designs based on barcodes of different standards and sizes are realized and measured using a professional RFID measurement system. Measurements of all realized prototypes are in good agreement with simulations. Interesting results are obtained with a maximum RFID read range reaching around 12 m while keeping the prototypes readability as a standard barcode. Another tag configuration which avoids soldering the IC to the structure and based on the coupling of a near-field RFID tag to the barcode is also presented, showing a read range of more than 7 m.

Effect of added resonators in RFID system at 13.56 MHz

In this study, a reader antenna including resonators is proposed to improve detection of a small moving tag in the case of tracking a radiofrequency identification (RFID) system. The near-field RFID technology is based on load modulation, the input impedance on the reader coil and the mutual inductance between the reader and tag coils are the main parameters for performing detection. They are calculated from the impedance matrix parameters. The added resonators change all the parameters of the impedance matrix consequently the input impedance and mutual inductance are also changed. In this study, analytical formulation defining the equivalent impedance matrix parameters is developed. These formulae are used to evaluate the performance of the proposed design according to the tag misalignment (lateral and angular). From the calculation and simulation results, a frequency shift in the equivalent input impedance is found. To avoid this problem, optimising the positioning of the resonators on the reader coil is performed. This study is confirmed by measures of RFID detection for a reader prototype (with and without resonators) and a small commercial tag. Both the surface and volume of detection of the small moving tag (lateral and angular misalignment) are improved by the principle of added resonators.