Reader Antenna Research Articles

Passive UHF RFID Network Planning for Accurate 3-D Location via Restricted Genetic Algorithm

Indoor localization via radio-frequency identification (RFID) carries critical importance due to its high accuracy and low hardware requirement. The positions of reader antennas can affect the positioning accuracy and coverage in RFID network. In this letter, we present a novel RFID network planning (RNP) approach to optimize the deployment of reader antennas for accurate 3-D location. First, the 3-D antenna radiation mode of a passive UHF RFID system is set up. Then, the received signal strength (RSS) and path loss characteristics (PLC) are analyzed and a restricted genetic algorithm (RGA) is developed to obtain the optimal solution of the RNP via maximizing the total reward function with constraints. Finally, the convolutional neural network (CNN) and weighted <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -nearest neighbor (WKNN) algorithms are respectively used to verify the localization effect. For comparison, the Cramér-Rao lower bound (CRLB) is also derived. The experimental results show that the proposed approach can improve the positioning accuracy as well as the coverage, and enhance the anti-noise capability of the location system.

Monitoring Wound Health through Bandages with Passive LC Resonant Sensors.

This paper details a passive, inductor-capacitor (LC) resonant sensor embedded in a commercial dressing for low-cost, contact-free monitoring of a wound; this would enable tracking of the healing process while keeping the site closed and sterile. Spiral LC resonators were fabricated from flexible, copper-coated polyimide and interrogated using external reader antennas connected to a two-port vector network analyzer; the forward transmission scattering parameter (S21) magnitude was collected, and the resonant frequency (MHz) and the peak-to-peak amplitude of the resonant feature were identified. These increase during the healing process as the permittivity and conductivity of the tissue change. The sensor was first tested on gelatin-based tissue-mimicking phantoms that simulate layers of muscle, blood, fat, and skin at varying phases of wound healing. Finite element modeling was also used to verify the empirical results based on the expected variations in dielectric properties of the tissue. The performance of the resonant sensors for in vivo applications was investigated by conducting animal studies using canine patients that presented with a natural wound as well as a controlled cohort of rat models with surgically administered wounds. Finally, transfer functions are presented that relate the resonant frequency to wound size using an exponential model (R2 = 0.58-0.96). The next steps in sensor design and fabrication as well as the reading platform to achieve the goal of a universal calibration curve are then discussed.

Design of a Wide Planar Waveguide Antenna for UHF Near-Field RFID Reader With High Reading Rate

UHF near-field RFID reader antenna based on leaky waveguide is proposed and the performance is evaluated using numerical simulation and experiment. In order to suppress the standing wave along transverse direction, a pair of notches is placed on the transverse edge of the mesh layer of the planar waveguide. Diversity operation by switching impedance of the end terminal of the planar waveguide antenna is also introduced to suppress the standing wave effect along longitudinal direction. Numerical simulation and experiment show that the near-field null lines parallel to the longitudinal direction is almost removed by the presence of the notches and the distribution of the field strength becomes almost uniform because of the utilization of the switching diversity. It is demonstrated that the reading performance of the commercial RFID tags is greatly improved by using the proposed RFID reader antenna with the diversity operation of termination impedance.

Battery-Less Wireless Chipless Sensor Tag for Subsoil Moisture Monitoring

Inefficient soil management is a hindrance to food productivity and a contributing factor to the degradation of soil quality. Despite decades of research confirming the benefits of using sensors in effective soil management and crop yield, they are still not widely used in farms for several reasons including high cost, difficulty in large area deployment, and requirement of labor-intensive wiring. In this paper, we report a low-cost battery-less chipless wireless sensor tag that can be batch-manufactured for large-scale agricultural surveillance. The sensor tag works based on backscattering techniques for the wireless measurements of the volumetric water content (VWC) of the soil. The sensor tag consists of shorted dipole resonators whose resonance frequencies are dependent on the effective permittivity of the VWC of its surrounding soil. The resonant frequency of the sensor tag is measured by an orthogonally polarized reader antenna that observes the peak in the backscattered spectrum. As a proof-of-concept, a sensor tag with two resonators of length 10 cm and 9 cm, is buried at a depth of 10 cm in the soil and is wirelessly read from a free-space distance of 50 cm, to demonstrate its capability to measure the changes in VWC. The resonators of length 10 cm and 9 cm have demonstrated a linear change of −3.92 MHz/VWC and −4.85 MHz/VWC, respectively, within the VWC range 4-27%. By changing the functional passivation layers on the demonstrated sensor tag, this concept can be applied to a wide range of low-cost subsoil sensors for precision agriculture applications.

Triple-Resonance Chipless RFID Tag With Dual Circularly-Polarized Wideband Reader Antenna for Wirelessly Differentiating Liquid

To wirelessly differentiate specified liquid samples, this article presents a radio-frequency identification (RFID) front-end including wideband reader antenna with chipless tag. The proposed reader antenna employs left-handed circularly-polarized (LHCP) antenna for transmitter (Tx) and right-handed circularly-polarized (RHCP) antenna for receiver (Rx), to improve the Tx-Rx isolation and also liberate the orientation and polarization of chipless tags. This dual circularly-polarized (dual-CP) configuration also features wide bandwidths of impedance and axial ratio, by using sequentially-rotated structure. Moreover, the proposed chipless tag has three resonances, among them, one independent resonance provides a lookup table for fast and easy identification, and another two resonances can be used to reconfirm the identification results. For validation, dual-CP reader antenna array and chipless tag are numerically optimized, experimentally measured, and also in-vivo demonstrated to wirelessly differentiate liquid samples.

Multiple element of miniaturized printed log-periodic second series koch dipole array antenna for wideband chipless RFID tag reader

This paper aims to produce a low profile, wideband, and high gain antenna for chipless RFID tag readers. A miniaturized and wideband printed Log-Periodic Second Series Koch Dipole Array (LPSSKDA) with eleven elements operating over 0.8 GHz-3.2 GHz is designed using the FR4 board. The single LPSSKDA antenna, which acts as the chipless RFID reader antenna having gain between 5.2 and 6.1 dBi and frequency range from 1-3 GHz. A double element of the LPSSKDA antenna is proposed for improving the antenna gain to 6.9-7.9 dBi over the frequency range. The antenna is fabricated to validate the simulation and measurement results in terms of reflection coefficient, radiation pattern, and surface current distribution.

Characterization of Shorted Dipole Antennas for Low-Cost RFID Reader Applications

This article presents a comprehensive study on shorted dipole antennas aiming for low-cost radio frequency identification (RFID) reader applications. Starting from a low-profile shorted bowtie dipole antenna, it is found that by varying the shorting wall position, three different types of resonant antennas could be realized with different radiation features. A low-profile planar inverted F antenna (PIFA) -type dipole is obtained by moving the shorting wall toward the feeding, which exhibits a low resonance frequency without obvious back lobe radiation or sidelobes. When the shorting wall is placed in the middle of the radiating patch, a mushroom-type dipole antenna can be built. A zeroth-order mode is also observed. This structure differs from the magnetoelectric dipole due to a low-profile structure. Placing the wall toward the end of the dipole arm leads to a loop-type antenna with a broader beam and a reduced gain. It also shifts the resonance toward the higher frequency. Based on the PIFA- and mushroom-type structures, two circularly polarized antennas with crossed shorted dipoles are designed and investigated carefully. Finally, two optimized, compact, and low-cost RFID reader antennas based on simple metal stamping process and screws are designed, fabricated, and tested, showing an excellent RF reading range. This study demonstrates that for the shorted dipole antennas, miniaturization and bandwidth control can be achieved simultaneously. Particularly, for higher gain and smaller size, the shorting wall should be placed close to the feeding to suppress the loop mode. For omnidirectional radiation, the loop mode should be enhanced by moving the shorting wall close to the end of the dipole arm.

Corner Reflector Based Misalignment-Tolerant Chipless RFID Tag Design Methodology.

Chipless RFID is a relatively new and rapidly growing field that faces some practical implementation challenges. One of these challenges is extreme sensitivity to small misalignments between the tag and the reader antenna. These tilts and translations can lead to erroneous responses which can then be interpreted as incorrect IDs or sensing parameter values in identification and sensing applications, respectively. While there has been some work to mitigate this limitation through reading and post-processing methods, the problem has yet to be sufficiently addressed from the tag design perspective. This work proposes a misalignment-tolerant chipless RFID tag design methodology that utilizes trihedral corner reflector bases loaded with resonators to produce tags that are tolerant of pitch and yaw rotations up to ±40° and roll rotations up to ±180° (i.e., orientation independence as it is commonly defined in the chipless RFID field). This approach allows for linearly polarized monostatic reading schemes to be used and provides for a large radar cross-section and resonance depth, which increases the detectability of the tag response.

Robot-Based Indoor Positioning of UHF-RFID Tags: The SAR Method With Multiple Trajectories

This article presents the application of the synthetic aperture radar (SAR) localization method for indoor positioning of ultrahigh-frequency (UHF)-radio frequency identification (RFID) tags when the robot-mounted reader antenna moves along multiple trajectories. By properly combining the phase data associated with a set of multiple paths, the whole length of the combined synthetic apertures enlarges, and then, the localization accuracy may improve. Besides, during consecutive inventory rounds, several tag position estimates are available, and they can be profitably combined to minimize the localization uncertainty. Different combination approaches are investigated to determine the best choice to improve the localization performance. The method capabilities are discussed through numerical analysis by considering different configurations of the multiple apertures and different measurement uncertainty sources. Finally, the proposed localization method is validated through an experimental analysis carried out with commercial RFID hardware and a robotic wheeled walker, in an indoor scenario, by employing different types of tags. The knowledge of the reader/robot trajectory required by the SAR method is here achieved with an optical system.

Optically Transparent Flexible Robust Circularly Polarized Antenna for UHF RFID Tags

Optically transparent flexible tag antennas are highly desired for some applications, where unobtrusiveness and capability of mounting on curved surfaces are required. On the other hand, circular polarization minimizes signal degradation due to polarization mismatch between the reader and tag antennas, thus ensuring good communication quality and accuracy. In this letter, we present an optically transparent and flexible radio frequency identification passive tag antenna operating in the ultrahigh frequency band and exhibits circular polarization. It is thin, lightweight, and completely encapsulated inside transparent polymer, which protects it against dust, water, heat, and mechanical stress. The tag antenna is made by utilizing highly flexible and transparent conductive-mesh-polymer composite through a simple and low-cost manufacturing process. The antenna design is based on a planar square ring. It achieves a measured maximum read range of about 8.3 m and approximately 47 MHz (885-932 MHz) 3 dB axial-ratio bandwidth (ARBW).

Mathematical Model of Chipless RFID Tags for Detection Improvement

A mathematical model to characterize a frequency-coded chipless radio frequency identification (RFID) is presented. A chipless tag is comprised of multiple high-quality factor resonators. The model exploits the bandpass and band-stop characteristics of a frequency-coded tag and the channel model of the reader and tag system. The proposed model accurately reconstructs the time and frequency responses of the tag read by a reader antenna. The model is universal to any type of chipless tag. To validate the model, first, a tag is designed with CST Microwave Studio, a full-wave electromagnetic solver, and its resonant characteristic is extracted. The model is used to validate the simulation and measurement results of the same tag. Also, the tag is measured in a cluttered environment. The results show that the tag is successfully decoded in the presence of a relatively large metallic reflector to verify the robustness of the model, without any calibration. The investigation provides a comprehensive understanding of the tag and the reader system, and it is a step toward reading a chipless tag in a realistic environment.

Passive wireless UV SAW sensor

This paper presents studies of a passive wireless ultraviolet (UV) surface acoustic wave (SAW) sensor operating in the frequency range 436–440 MHz. The sensor contains two SAW delay lines (DLs). The first DL is measuring, and the second is the reference. In the measuring DL, receiving–transmitting inter-digital transducer (IDT) is connected to the antenna and the sensing element zinc oxide film. In the reference DL, the receiving–transmitting IDT is connected to another antenna and does not contain a UV-sensitive element. Two methods of information reading from the sensor are proposed: based on the Fourier transform of the frequency dependence of the parameter S11 of the reader antenna and using reading pulses of 1.5-μs duration, which have carrier frequencies corresponding to the central frequencies of the measuring and reference channels. The sensor can measure UV intensities from 10 to 40,000 μW/cm2 with a maximum sensitivity of 6000 ppm/(μW/cm2) at low intensities, and which rapidly decreases as the UV intensity increases (less than 100 ppm at the UV intensity of 40,0000 µw/cm2).

Compact wideband circularly‐polarized antenna for universal UHF RFID handheld reader

AbstractA compact wideband circularly‐polarized (CP) RF identification (RFID) handheld reader antenna based on inverted‐F antennas (IFAs) is proposed. The antenna consists of an upper layer of rotationally symmetric radiation structure and lower layer of feed network. Firstly, the feed network is verified by microwave circuit simulation software. Then the antenna is modeled and simulated with the aid of the full‐wave electromagnetic simulation software. Finally, a prototype is fabricated using FR4 plate and its performance of the proposed antenna is validated. The measured impedance bandwidth of 10 dB and the axial ratio (AR) bandwidth of 3 dB are wider than 13%. The peak gain is greater than 2.2 dBic, and the minimum AR is less than 1.1 dB, with the symmetrical and stable radiation patterns. The antenna has the compact size of 60 × 60 × 15 mm3. The proposed antenna can not only meet the requirements of RFID handheld reader applications in universal ultra‐high frequency (UHF) band (840‐960 MHz), but also has the advantages of wideband, small size, lightweight, low cost, and simple structure. Therefore, the design has a good application prospect in the field of Internet of Things.

Radio Frequency IDentification for Meat Supply-Chain Digitalisation.

Digitalised supply-chain traceability systems can offer wide prospects both for improving safety as well as enhancing perceived quality. However, the coupling between physical goods and information is often difficult for agri-food items. A solution could be the use of RFID (Radio Frequency IDentification) systems. Due to its wide reading range, Ultra-High Frequency (UHF) technology is already widely used in logistics and warehousing, mostly for the identification of batches of items. A growing interest is also emerging in Near Field Communication (NFC), as several smartphones embed an integrated NFC antenna. This paper deals with the automatic identification of meat products at item level, proposing and evaluating the adoption of different RFID technologies. Different UHF and NFC solutions are proposed, which benchmark tag performances in different configurations, including four meat types (fatty beef, lean beef, chicken and pork), by using a specifically designed test bench. As avoiding the application of two different tags could be advantageous, dual frequency devices (UHF and NFC) are also considered. Significant differences in tag performances, which also depend on meat type and packaging, are highlighted. The paper highlights that tag positioning should consider the geometry of the packaging and the relative positioning of tag, meat and reader antenna.

Novel UHF RFID Near-Field Reader Antenna with Uniform Vertical Electric Field Distribution

This paper presents two novel UHF RFID near-field reader antennas with uniform vertical electric field distribution. The two antennas have the following common characteristics. First, the radiating parts of the two antennas are simulated and fabricated by the microstrip lines and work using the leakage wave principle of microstrip lines. Second, the end of microstrip lines match the load to form a traveling wave mode of operation, so the two antennas have broadband characteristics. Third, both antennas are fed in a coaxial manner at the center of the antenna. The simulation and measurement results can show that the proposed three-branch antenna and four-branch antenna achieve good impedance matching in the range of 883–960 MHz and 870–960 MHz, respectively, and achieve uniform distribution of the vertical electric field component in a certain area. The reading areas of the three-branch antenna and the four-branch antenna are 70 mm × 70 mm × 90 mm and 100 mm × 100 mm × 120 mm (length × width × height), respectively. Due to the introduction of the ground plate, the antenna gain is low, which meets the design requirements of near-field antennas.

The Influence of the Nonideal Phase Offset on SAR-Based Localization in Passive UHF RFID

The existing radio frequency identification (RFID) localization methods typically regard the initial phase of the signal as constant. This is feasible when the antenna and the tag are stationary. However, in synthetic aperture radar (SAR) RFID localization, the relative motion of the reader antenna and tag changes the antenna phase center and tag orientation, thus resulting in a continuous change of the initial phase. This change, which will cause the nonideal phase offset (NPO) and, thus, have an adverse effect on positioning, has been neglected in most previous SAR RFID studies. In this article, we investigate the antenna phase uncertainty and the tag orientation-dependent phase offset and analyze their influence on localization accuracy. To the best of our knowledge, this is the first time that the initial phase is regarded as a variable in SAR RFID localization. In addition, a novel motion model-based localization (MoLoc) method is proposed, which exploits the relative motion model and visualizes the influence of NPO more intuitively. Compared with the conventional grid-matching methods, MoLoc shows higher accuracy and much lower computation time. Both the influence of NPO and the performance of MoLoc are verified by experiments implemented in real scenario. The experiments also evaluate the influence of NPO on the grid-matching method. The experimental results show that NPO has a significant impact on the accuracy of SAR-based localization methods.

A Standalone RFID-Based Mobile Robot Navigation Method Using Single Passive Tag

This article proposes a standalone radio frequency identification (RFID)-based mobile robot navigation method, in which a mobile robot equipped with reader antennas can be continuously guided to a static object marked with a single passive UHF RFID tag. An observation model based on the RFID phase difference is built and integrated into a particle filter, by which the instantaneous relative position between the mobile robot and the tagged object can be detected in real time. Based on the position information extracted from the RFID system, the mobile robot adjusts its pose to move toward the RFID-tagged object. Compared with the existing RFID-based mobile robot navigation methods, the proposed method requires no external sensors other than the RFID and requires only a single passive tag. Experiments using commercial off-the-shelf (COTS) RFID devices are performed, and the results indicate that the mobile robot can satisfactorily realize navigation task with a distance accuracy of 4.04 cm and a bearing accuracy of 2.23°. The proposed method is well applicable for the navigation scenes in which the absolute position of the tagged target object is not known beforehand. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —UHF radio frequency identification (RFID) has been widely applied as an asset management ID sensor in many fields. RFID-based mobile robot navigation technology can further increase its application value as a location sensor. This article proposes a standalone RFID-based mobile robot navigation method, in which the reference tag and the external sensors other than RFID are both not required. In the proposed method, only a single passive tag is attached to the static target object. Experimental results indicate that the proposed method can enable navigation task with good performance in situations in which the absolute navigation goal position is not known in advance.

Solving a chipless RFID inverse problem based on tag range estimation

Moving toward commercialisation of chipless radio-frequency identification (RFID) systems, there is a significant challenge for the detection of chipless tag in a practical application, in which the conventional calibration techniques such as background subtraction are insufficient or even impractical. In this study, first, a processing algorithm for an inverse problem based on the range estimation is introduced. In an inverse problem, the tag ID and its distance to the reader are unknown. Employing the proposed algorithm, provided the specification of the reader antenna is known, the desired component of the received signal corresponding to the tag ID can be extracted without the requirement of background calibration. Then, a post-processing algorithm is proposed for the extraction of the tag ID, which provides a sustained detection outcome at an arbitrary distance. The proposed algorithms are verified with the help of a few datasets acquired from the simulation environment as well as measurement setups. A typical backscattering chipless RFID tag with six resonances is examined. The distance between the tag and the reader antenna is estimated, and the binary tag ID extracted successfully.

Analysis, Design and Implementation of a Fully Integrated Analog Front-End for Microwave RFIDs at 5.8 GHz to Be Used With Compact MIMO Readers

In this paper we present the system and circuit level analysis and feasibility study of applying microwave Radio Frequency Identification (RFID) systems with multipleinput multiple-output (MIMO) reader technology for tracking machining tools in multipath fading conditions of production environments. In the proposed system the MIMO reader interrogates single-antenna tags, and a high RFID frequency of 5.8 GHz is chosen to reduce the size of the reader's antenna array. According to the requirements dictated by the performed system analysis at 5.8 GHz, a low power fully integrated analog frontend (AFE) is designed and fabricated in a standard 65-nm CMOS technology for low power passive transponders. Performance of the Differential Drive Rectifier (DDR) topology as the core of the energy harvesting unit is investigated in detail. A multi-stage DDR power scavenging unit is dimensioned to provide a 1.2 V rectified voltage for 20-30 kQ load range, with a high power conversion efficiency (PCE) for high frequency and low input power level signals. The rectified voltage is then converted to a 1 V regulated voltage for the AFE and the baseband processor with 30 to 50 μW of estimated power consumption. Transistors with standard threshold voltage (VT) have been used for implementation. Measurements of the fabricated multi-stage configuration of the circuit show a maximum PCE of 68.8% at -12.46 dBm, and an input quality factor (Q-factor) of approximately 10. Amplitude-shift keying (ASK) demodulator and backscattering modulator with 80% modulation index, operating according to EPC-C1G2 protocol are applied for data transfer. The AFE consumes less than 1 μW in the reading mode. The AFE tag chip is 0.55 × 0.58 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

An UHF RFID Reader Antenna with Multitag Identification for Extremely Low-Temperature Medical Systems

A radio frequency identification reader antenna having multitag identification for medical systems is presented, which consists of four PIFAs, two hybrid couplers, and four power dividers. The high isolation is achieved by the symmetric design of the antenna geometry and four power dividers, which are fed by two hybrid couplers. The experimental results show an isolation of more than 40 dB in the North American (902–928 MHz), Korean (917–923.5 MHz), and Japanese (916.7–923.5 MHz) RFID frequency bands.