Tag Antenna Impedance Research Articles

On the sensitivity of matching network to load variation for passive RFID sensor

ABSTRACTA novel study on sensitivity of matching network to load variation is presented in this work. In passive RFID sensor tag, it is desired that a small change in input impedance of tag antenna should yield a significant response, which can be achieved by a matching network with high sensitivity. In this work, network sensitivity is defined and maximum sensitivity matching network is acquired for certain source and load impedances. Several LC and microstrip matching circuits are designed and fabricated to verify the network sensitivity theory. By inserting a sensitive matching network to a temperature sensor tag in literature, three times higher sensitivity is achieved, which proves the merit of the theory. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:232–236, 2017

Alumina ceramic slot antenna for UHF RFID tag embedded in vehicles

ABSTRACTTo address the metallic interference problem in vehicular RFID (radio‐frequency identification) applications, this letter proposes a novel alumina ceramic slot tag antenna (ACSTA). The proposed antenna consists of a grounded thin alumina ceramic substrate and a slotted top layer rectangular patch, and the all four sides of the substrate are shorting walls. The slot can be equivalent to a horizontal magnetic current flow, so an excellent radiation performance is achieved according to the electromagnetic image theory. Meanwhile, due to the existence of the ground plane, the influences of metallic objects behind the ground to the tag antenna impedance can be maximally reduced. Combined with a commercial chip, this ACSTA is fabricated and measured, and the thickness of the novel tag is only 1mm. The tag antenna offers a half power coefficient bandwidth of 6.9% (0.87–0.93 GHz) with a stable gain about 3.6 dBi, and a similar half power coefficient bandwidth of 6.9% (0.89–0.95 GHz) with a gain about 4.8 dBi when it is attached to an 100 × 100 mm2 metallic plate, respectively. Moreover, the experimental results show that the maximum read range is about 27 or 30 m without or with a same attached 100 × 100 mm2 metallic plate, respectively. Simulation and measurement results show that the operating frequency band of the ACSTA covers US legal UHF RFID (902—928 MHz) band, and so it is a quite suitable candidate for vehicular RFID applications. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1150–1154, 2016

Straight‐forward impedance measurement for balanced RFID tag antenna

A method using 180° hybrid coupler and vector network analyser to measure the radio frequency identification tag antenna impedance is presented. The impedance of a prototype antenna is measured by different experimental methods and compared with simulation results. The comparison results show that the proposed method has a good accuracy and it is more convenient.

Signal strength readout and miniaturised antenna for metal‐mountable UHF RFID threshold temperature sensor tag

A new method for the wireless monitoring of a battery-free threshold temperature sensor based on a passive ultra-high-frequency radio-frequency identification (RFID) tag integrated with a bimetal thermostat switch is presented. The strategic placement of the switch brings about a strong modification in the tag antenna impedance as the temperature crosses over a threshold value. Optimisation of the narrow-band tag antenna to operate at the edges of the 902–928 MHz frequency-hopping spread spectrum RFID in the different switch states provides separate sub-bands for the readout above and below a threshold temperature. The results show that this enables an unambiguous sensor readout by monitoring the backscattered signal strength.

A Miniature Antenna for 2.45 GHz RFID Tag

On the basic of fractal theory and folded technique, a miniature antenna for 2.45 GHz radio frequency identification (RFID) tag applications is designed and analyzed in the present paper. In order to realize the miniaturization of tag antenna, a Hilbert fractal structure is used. Impedance matching between antenna and IC chip is of great importance for improving tag performances. A folded technique is employed to achieve impedance matching flexibly. The value of input impedance of tag antenna can be varied readily only by tuning the high of folded line. The dimensions for the designed tag antenna at 2.45GHz are 23.32mm×7.66mm, and its return loss, bandwidth, and gain are analyzed by HFSS. The detection distance is estimated by Friis transfer theory. Analysis results demonstrate that the tag antenna designed in this paper may satisfy the requirements of RFID tag applications.

Compact RFID Tag Antenna With Circular Polarization and Embedded Feed Network for Metallic Objects

A low-profile radio frequency identification (RFID) tag antenna is proposed with a compact size of 45 ×45 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and circular polarization (CP) for metallic surfaces. A star-shaped slot is etched onto the antenna for the CP and antenna size reduction. A terminal-grounded L-shaped feedline is embedded in the etched slot to efficiently excite the wideband CP mode, complexly match the tag-antenna impedance, and further reduce the antenna size. The embedded feed structure also helps achieve a relatively higher gain, resulting in a longer reading range. The proposed antenna can cover the impedance bandwidth of 60 MHz (from 880 to 940 MHz) as well as the 3-dB CP bandwidth of 12 MHz (from 905 to 917 MHz). Further results demonstrate that the proposed tag antenna provides a stable reading range when mounted on metal plates of various sizes.

A Folded RFID Tag Antennas Based on Hilbert Fractal Structure

Based on Hilbert theory and technique, a folded tag antenna for RFID application is presented in this paper. In order to reduce the size of tag, a Hilbert fractal structure is employed. Additionally, to match flexibly the impedance between antenna and chip, a folded technique is employed. The input impedance of tag antenna can be adjusted easily by changing the high of folded structure. A designed tag antenna dimension is 23.32mm×7.66mm, and its return loss, bandwidth, gain and theoretical detection distance are given at 2.45GHz by HFSS software. The simulation results show that the designed antenna can meet the requirements of the practical applications.

Testing the effects of temperature and humidity on printed passive UHF RFID tags on paper substrate

This article is an interesting substrate material for environmental-friendly printable electronics. In this study, screen-printed RFID tags on paper substrate are examined. Their reliability was tested with low temperature, high temperature, slow temperature cycling, high temperature and high humidity and water dipping test. Environmental stresses affect the tag antenna impedance, losses and radiation characteristics due to their impact on the ink film and paper substrate. Low temperature, temperature cycling and high humidity did not have a radical effect on the measured parameters: threshold power, backscattered signal power or read range of the tags. However, the frequency response and the losses of the tags were slightly affected. Exposure to high temperature was found to even improve the tag performance due to the positive effect of high temperature on the ink film. The combined high humidity and high temperature had the most severe effect on the tag performance. The threshold power increased, backscattered power decreased and the read range was shortened. On the whole, the results showed that field use of these tags in high, low and changing temperature conditions and high humidity conditions is possible. Use of these tags in combined high-humidity and high-temperature conditions should be carefully considered.

UHF RFID 태그와 GPS를 사용한 위치기반 수목관리용 RFID 시스템 구현

본 논문에서는 수목관리의 효율성과 정확성을 높이기 위해 UHF RFID 수목관리시스템 TMS(Tree Management System)를 GPS와 나무에 삽입용 태그를 사용하여 구현하였다. 나무의 정보를 인식하기 위하여 고유전율인 나무에 삽입 가능한 플라스틱 볼트 형태의 UHF RFID 태그 안테나를 설계하였다. RFID 태그 안테나는 부착된 물체의 전기적인 특성으로 인한 영향을 받으므로, 고유전율인 나무에 근접 시 태그 안테나의 임피던스 값이 변하게 되어 태그의 특성에 영향을 주게 된다. 따라서 이러한 영향을 고려하여 플라스틱 볼트 형태로 RFID 태그 안테나를 제작하였으며, 또한 본 태그를 사용하여 GPS를 이용한 TMS를 구현하여 수목관리의 위치 정보를 구글지도에(Google map) 표시함으로써 수목을 관리하는데 필요한 인건비 및 관리비 절감 등의 관리 효율성을 극대화 하였다. The paper introduces the RFID location based Tree Management System (TMS) using UHF RFID tag and GPS. The bolt shape tag has been developed since the wood material has high dielectric constant. Since the characteristics and impedance of tag antenna can be changed by the material next to the tag, the plastic bolt shape tag antenna has to be carefully designed with consideration of the high dielectric constant of the wood material. The RFID TMS system has been utilized with the bolt shape tag antenna and GPS. The TMS system uses and links Google map to locate the location of the trees. Therefore, this system allow us to manage the trees economically and efficiently.

차량 범퍼에 부착된 번호판용 태그 안테나의 설계

본 논문은 차량 범퍼에 부착된 번호판을 이용한 900 MHz 대역 RFID 태그 안테나의 설계를 기술하고 있다. 차량 번호판의 위쪽 중앙 지점에 위치한 제안된 태그 안테나의 크기는 162.5<TEX>${\times}$</TEX>40<TEX>${\times}$</TEX>1 <TEX>$mm^3$</TEX>이다. 설계 안테나의 공진 주파수와 - 10 dB 이하의 반사 손실을 가지는 대역폭은 각각 900 MHz와 약 720 MHz(640<TEX>${\sim}$</TEX>1,360 MHz)이다. 설계에 고려된 상용 칩의 임피던스는 16-j131<TEX>${\Omega}$</TEX>이었고, 칩의 복소 공액 임피던스가 태그 안테나의 입력 임피던스로써 사용되었다. 측정된 반사 손실과 방사 패턴은 계산된 결과들과 잘 일치하였다. 단지 차량 번호판 위에 설계된 태그 안테나의 측정된 인식 거리는 11.5 m였다. 또한, 번호판과 차량 범퍼가 볼트와 너트에 의해 고정되어진 제작된 태그 안테나의 인식 거리는 10.4 m로 관측되었다. 이 측정된 인식 거리는 상용 태그 안테나의 평균 인식 거리보다 약 5 m 이상 먼 거리였다. This paper describes a design for RFID(Radio Frequency Identification) tag antenna using license plate attached the vehicle bumper in 900 MHz band. The proposed tag antenna size which is located on upper center position of a vehicle license plate is 162.5<TEX>${\times}$</TEX>40<TEX>${\times}$</TEX>1 mm<TEX>$^3$</TEX>. A resonant frequency of design antenna and the bandwidth which has return loss of -10 dB below are 900 MHz and about 720 MHz(640<TEX>${\sim}$</TEX>1,360 MHz), respectively. The commercial chip impedance considered on design was 16- j131 <TEX>${\Omega}$</TEX> and the complex conjugate impedance of chip was used as input impedance of tag antenna. The measured return loss and radiation pattern were agreed well with the calculated results. The measured readable range of the proposed tag antenna designed on only the vehicle license plate was 11.5 m. Moreover, its range of the fabricated tag antenna that the license plate and the vehicle bumper were fixed by volt and nut was observed 10.4 m. These measured readable range showed about 5 m above far distance more than the average readable range of commercial tag antenna.

Effect of Lossy Dielectric Overlays on the Read-Range of UHF RFID Tags

The effect of a lossy overlay on the read-range of UHF RFID tags is studied. The design of the tag antenna is optimized for long read-ranges and then the effects of a lossy overlay (cover) on its properties are studied. The tags are simulated with and without the lossy overlay material. The input impedance of tag antenna, power transmission coefficient and read-range are calculated and compared for the two cases of with and without overlay. Further, optimization of tag with lossy dielectric overlay is carried out. It is observed that even with the overlay of a lossy dielectric, read-range up to 9 m can be obtained by properly matching the antenna with the RFID IC.

910 MHz 대역 RFID용 태그 안테나의 소형화 설계

본 논문은 910 MHz 대역에서 동작하는 RFID (radio Frequency identification) 태그 안테나의 소형화 설계 기법을 제안한다. folded-dipole 구조와 미앤더 선로 구조를 적용하여 태그 안테나의 소형화 설계를 행하였다. 최대 전력 전달을 위해서 테그 안테나와 칩의 임피던스의 허수부는 공액 정합되었다. 최적화된 안테나의 크기는 <TEX>$50\;nm\;{\times}\;40\;nm\;{\times}\;1.6\;nm$</TEX>로, 참고문헌 [4]와 비교하여 크기가 62 % 줄었다. 제작된 태그 안테나의 측정결과들은 예상과 잘 일치하는 것으로 확인되었다. 칩이 내장된 태그 안테나의 인식거리는 약 5 m로 관측되었다. This paper presents a miniaturization design technique of radio frequency identification (RFID) tag antenna operated in 910 MHz band. Miniaturization structure design for a tag antenna is performed by structure application of the folded dipole and meander line. In order to realize the maximum power transmission, imaginary part of a chip impedance and a tag antenna impedance is matched by complex conjugate number. The optimized tag antenna size is <TEX>$50\;nm\;{\times}\;40\;nm\;{\times}\;1.6\;nm$</TEX> and its size is reduced about 62 % comparison with antenna size of reference [4]. The measured results of fabricated tag antenna are confirmed the reasonable agreement with prediction. The read range of the tag antenna with chip observed about 5 m.