Near-field Radio Frequency Identification Reader Research Articles

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> .

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.

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.

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.

Review of Zero-Phase-Shift-Line Loop Antennas for UHF Near-Field RFID Readers

The design of electrically large loop-type antennas for ultra-high frequency (UHF) near-field radio frequency identification (RFID) readers is a challenge due to the inherent limitation of loop type antennas. This paper reviews the development of the zero-phase-shift-line (ZPSL) loop antennas for UHF near-field RFID systems. First, the state-of-the-art ZPSL loop antennas are briefed and then the modeling of the ZPSL structures is introduced. After that, some typical electrically large ZPSL loop antennas for UHF near-field RFID readers are demonstrated, including single-loop antenna, dual-loop antenna, grid loop array antenna, and artificial magnetic conductor backed directional loop antenna. All the patentable works have been applied for industry applications.

Novel UHF Near-Field RFID Reader Antenna Based on Double-Sided Parallel-Strip Line

A novel reader antenna based on double-side parallel-strip line (DSPSL) for ultra-high frequency (UHF) near-field radio frequency identification (RFID) systems is proposed. The antenna is composed of a phase inverter, DSPSL structures, and four dipoles. The fabricated antenna works from 887 to 938 MHz with reflection coefficient less than -10 dB. The maximum reading distances are 200 and 70 mm when the input power is 30 and 17 dBm, respectively. Measurement results show that the antenna has good performance in near-field UHF RFID systems.

One terminal improving method of open-circuit near-field antenna of UHF RFID system

A novel broadband dual-loop antenna is presented for the ultra high frequency (UHF) near-field radio frequency identification (RFID) applications. Owing to the novel structure, the current distribution along the loop is kept in phase, as well as the metal terminals exert less influence on the z-orientation magnetic field. The antenna with novel terminals is described and the principle of operation is explained. A comprehensive parametric study of the new model is carried out and the results are presented and discussed in detail. To prove the novel structure, a prototype is developed and fabricated. The measurement results demonstrate that the antenna could achieve a broad bandwidth and low gain, and produce a strong magnetic field with a relatively small z-orientation magnetic field empty hole in the near field. Hence, the work is very promising for UHF near-field RFID reader applications.

Electrically Large Dual-Loop Antenna for UHF Near-Field RFID Reader

An electrically large dual-loop antenna is proposed for ultra high frequency (UHF) near-field radio frequency identification (RFID) readers. The proposed antenna is composed of a main loop and a parasitic loop wherein the loops are constructed using segmented lines with distributed capacitors. The parasitic loop enhances and uniforms the magnetic field distribution in the central portion of the larger main loop so that the perimeter of interrogation zone of the dual-loop antenna can be extended up to three operating wavelengths. The measurement shows that a dual-loop antenna prototype printed onto a piece of FR4 printed circuit board (PCB) achieves good impedance matching over the frequency range of 845-928 MHz and produces strong and uniform magnetic field distribution with an interrogation zone of 250 mm 250 mm. A parametric study is carried out to provide the guidelines for the antenna design.

A Novel Fractal Antenna for UHF Near-Field RFID Readers

This letter accentuates a novel fractal protruded tapered slot (FPTS) antenna and its magnetic field analysis for ultra-high frequency (UHF) near-field (NF) radio frequency identification (RFID) readers. The principle of variable distance opposite direction current (VDODC) is employed here. The antenna operates over a bandwidth of 101 MHz (852-953 MHz) with a center frequency of 897 MHz. The interrogation area of 243 × 190 mm2 is achieved for this antenna at a distance of 50 mm from the plane of the antenna in z-direction. The antenna tested with the presence of different liquids and the performance is evaluated. The field analysis shows that antenna becomes handy over potential applications like tracking chemicals and pharmaceutical management.

Design of Antenna for UHF Near-Field RFID Reader

A segmented loop antenna is presented for ultra-high frequency (UHF) near-field radio frequency identification (RFID) reader. The segmented antennas have been constructed that can operate at resonant diameters while still providing good magnetic coupling. The antenna printed on a FR4 printed circuit board (PCB) with an overall size of 170× 170 × 1 mm3 achieves good impedance matching and uniform magnetic field distribution over an operating bandwidth of 840–1120 MHz, which is desirable for UHF near-field RFID reader applications.

Study of broadband near-field antenna for ultra-high-frequency radio frequency identification applications

A novel antenna for applications in an ultra-high-frequency (UHF) radio frequency identification (RFID) reader system is proposed and investigated. The antenna achieves a gain of lower than −10 dBi in all directions with strong magnetic field distribution over the entire UHF RFID band of 830–950 MHz as well as good performance in detecting tags when applied in UHF RFID systems. The antenna configuration is described and the principle of operation is explained. To investigate the effects of each parameter on the antenna performance, a comprehensive parametric study is carried out and the results are presented in detail and discussed. To prove the concept, a prototype is developed and fabricated. The measurement results demonstrate that the antenna can achieve a broad bandwidth and low gain, and produce a strong magnetic field with relatively concentrated field distribution in the near-field region of the antenna. Hence, this work is very promising for UHF near-field RFID reader applications.

UHF near-field RFID reader antenna with capacitive couplers

A segmented loop antenna with capacitive couplers is proposed for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications, which is capable of generating a strong and uniform magnetic field in a near-field zone even though the perimeter of the loop is comparable to the operating wavelength. As an example, an antenna printed onto an FR4 printed circuit board with an interrogation zone of 154 × 154 mm exhibits good impedance matching and uniform magnetic field distribution over an operating bandwidth of 790-1000 MHz, which is desirable for UHF near-field RFID reader applications.

Segmented loop antenna for UHF near-field RFID applications

A segmented loop antenna is presented for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications. The proposed segmented configuration makes the current along the loop remain in-phase even though the perimeter of the loop is comparable to the operating wavelength, so that a strong and uniform magnetic field is generated in the region surrounding the antenna. The antenna printed on a FR4 printed circuit board (PCB) with an overall size of 160×180×0.5 mm achieves good impedance matching and uniform magnetic field distribution over an operating bandwidth of 800–1040 MHz, which is desirable for UHF near-field RFID reader applications.