There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A dual-band passive radio frequency identification (RFID) tag antenna applicable for a recessed cavity in metallic objects such as heavy equipment, vehicles, aircraft, and containers with long read range is proposed by using an artificial magnetic conductor (AMC) ground plane. The proposed tag antenna consists of a bowtie antenna and a recessed cavity with the AMC ground plane installed on the bottom side of the cavity. The AMC ground plane is utilized to provide dual-band operation at European (869.5 869.7 MHz) and Korean (910 914 MHz) passive UHF RFID bands by replacing the bottom side of the metallic cavity of a PEC-like behavior and, therefore, changing the reflection phase of the ground plane. It is worthwhile to mention that the European and the Korean UHF RFID bands are allocated very closely, and the frequency separation ratio between the two bands is just about 0.045, which is very small. It is demonstrated by experiment that the maximum reading distance of the proposed tag antenna with optimized dimensions can be improved more than 3.1 times at the two RFID bands compared to a commercial RFID tag.

Dual-Band Long-Range Passive RFID Tag Antenna Using an AMC Ground Plane

The design of antennas for metal-mountable radio-frequency identification tags is driven by a unique set of challenges: cheap, small, low-profile, and conformal structures need to provide reliable operation when tags are mounted on conductive platforms of various shapes and sizes. During the past decade, a tremendous amount of research has been dedicated to meeting these stringent requirements. Currently, the tag-reading ranges of several meters are achieved with flexible-label types of tags. Moreover, a whole spectrum of tag-size performance ratios has been demonstrated through a variety of innovative antenna-design approaches. This article reviews and summarizes the progress made in antennas for metal-mountable tags, and presents future prospects.

Advances in antenna designs for UHF RFID tags mountable on conductive items

A low-cost, wideband patch antenna for radio frequency identification tags mountable on metallic surfaces is presented. A novel proximity-coupled feed structure, in which the direction of the microstrip feed line is parallel to that of the resonant length of the radiating patch and one end of the feed line is shorted to the ground, is proposed to perform simple and wideband impedance matching between the antenna and tag chip without any additional matching networks. The proposed design is verified by simulation and measurement. The measured 3-dB return-loss bandwidth is about 49 MHz, which totally covers the 26-MHz bandwidth requirement in North America. The measured read range is about 8.9 m when the tag antenna is mounted on a metal plate with a size of 200 × 200 mm2.

Wideband RFID Tag Antenna for Metallic Surfaces Using Proximity-Coupled Feed

A wearable low-profile inset-fed quarter-wave folded microstrip patch antenna for noninvasive activity monitoring of elderly is presented. The proposed antenna is embedded with a sensor-enabled passive radio-frequency identification (RFID) tag operating in the ultra-high frequency (UHF) industrial-scientific-medical (ISM) band around 900 MHz. The device exhibits a low and narrow profile based on a planar folded quarter-wave length patch structure and is integrated on a flexible substrate to maximise comfort to the wearer. An extended ground plane made from silver fabric successfully minimises the impact of the human body on the antenna performance. Measurements on a prototype demonstrate a reflection coefficient () of −30 dB at resonance and a −10 dB bandwidth from 920 MHz to 926 MHz. Simulation results predict a maximum gain of 2.8 dBi. This is confirmed by tag measurements where a 4-meter read range is achieved using a transmit power of 30 dBm, for the case where the passive wearable tag antenna is mounted on a body in a practical setting. This represents an almost 40% increase in read range over an existing dipole antenna placed over a 10 mm isolator layer on a human subject.

/pdf/wearable-quarter-wave-folded-microstrip-antenna-for-passive-4y7qb45drt.pdf

Wearable Quarter-Wave Folded Microstrip Antenna for Passive UHF RFID Applications

An open stub feed planar patch antenna is proposed for UHF RFID tag mountable on metallic objects. Compared to conventional short stub feed patch antenna used for UHF RFID tag, the open stub feed patch antenna has planar structure which can decrease the manufacturing cost of the tags. Moreover, the open stub feed makes the impedance of the patch antenna be tuned in a large scale for conjugate impedance matching. Modeling and simulation results are presented which are in good agreement with the measurement data. Finally, differences between the open stub feed patch antenna and the short stub feed patch antenna for UHF RFID tag are discussed.

Planar UHF RFID Tag Antenna With Open Stub Feed for Metallic Objects

For the ultrahigh frequency radio frequency identification (UHF RFID) metal tag, it always has the difficulties of compact designing, especially for the conjugate impedance matching, low antenna gain, and fabrication or environmental detuning. In this paper, a tunable compact UHF RFID metal tag is designed based on CPW open stub feed PIFA antenna. By changing the length of the open stub, the impedance of the PIFA antenna could be tuned in a large scale for conjugate impedance matching. The open stub makes it easy to tune the resonant frequency to alleviate the fabrication detuning or the environmental detuning, even after the manufacture. Moreover, the CPW structure of the open stub feed can resist the effects of the metallic surface and increase the antenna gain for the compact PIFA antenna. Modeling analysis and simulation are in good agreement with the measurement results. It showed that the UHF RFID metal tag could be designed compact with good performance based on the CPW open stub feed PIFA antenna.

/pdf/tunable-compact-uhf-rfid-metal-tag-based-on-cpw-open-stub-15f01o4n2b.pdf

Tunable Compact UHF RFID Metal Tag Based on CPW Open Stub Feed PIFA Antenna

Ultra-high-frequency radio frequency identification (RFID UHF) vehicle license plate is a promising technology for traffic management because of its special advantages. In practical applications, the reading effect is closely related to the vehicle velocity. This paper analyzed the effective vehicle velocity for the steadily reading of the UHF RFID vehicle license plate. The smallest time for one single tag to be effectively read, the relationship between the tags reads and the vehicle velocity, the maximum vehicle velocity to be effective read, are analyzed and measured. Measurement results were in good agreement with the theoretical analysis. Studies have shown that the reading stability of the UHF RFID vehicle license plate is closely related to the effective read range of RFID tags, readers reading cycle and the vehicle velocity. In general vehicle velocity, UHF RFID vehicle license can be effectively read.

Velocity Analysis for UHF RFID Vehicle License Plate

In many RFID practical applications, it is required that reader can effectively read tags which are placed in radiation covering area randomly. In this paper, a passive UHF dual-dipole tag antenna with quasi-isotropic patterns is designed, which can reduce the sensibility of tag read-orientation in a long distance. Two dipoles with four-axis reflection symmetric structure are used, and the two arms of the dipole are bent to fill the space of the antenna. In this way, a quasi-isotropic tag is easier to be obtained. The test results show that the gain deviation of the proposed antenna was less than 3.25 dB, and the maximum reading range in different directions was from 6.9 m to 10.0 m, with better quasi-isotropic performance and reading range than other commercial tags.

/pdf/dual-dipole-uhf-rfid-tag-antenna-with-quasi-isotropic-29jp0vgch4.pdf

Dual-Dipole UHF RFID Tag Antenna with Quasi-Isotropic Patterns Based on Four-Axis Reflection Symmetry

The invention discloses an ultrahigh frequency radio frequency identification anti-metal tag antenna with a plane structure, which comprises a metal ground, a metal radiating surface, a substrate, an embedded groove, a first feeder line, a second feeder line and a radio frequency identification chip. The substrate is rectangular; the metal radiating surface, the embedded groove, the first feeder line, the second feeder line and the radio frequency identification chip are positioned on the upper surface of the substrate; the metal ground is positioned on the lower surface of the substrate; the embedded groove is embedded on one side of the metal radiating surface; one end of the embedded groove of the metal radiating surface is connected with one end of the first feeder line; the radio frequency identification chip is arranged between the other end of the first feeder line and one end of the second feeder line; and the other end of the second feeder line is provided with an open circuit. The ultrahigh frequency radio frequency identification anti-metal tag antenna manufactured by the invention has the plane structure; and the manufacturing cost of the tag antenna can be effectively reduced so as to contribute to mass production.

Chunfang Qin

Papers

Planar UHF RFID Tag Antenna With Open Stub Feed for Metallic Objects

Tunable Compact UHF RFID Metal Tag Based on CPW Open Stub Feed PIFA Antenna

Velocity Analysis for UHF RFID Vehicle License Plate

Dual-Dipole UHF RFID Tag Antenna with Quasi-Isotropic Patterns Based on Four-Axis Reflection Symmetry

Ultrahigh frequency radio frequency identification anti-metal tag antenna with plane structure