Passive UHF Radio Frequency Identification Research Articles

Performance evaluation of a UHF passive RFID tag embedded in a carbon fibre-reinforced polymer

Data collection during the production process plays a key role in the management and control of goods within the company. In this work, the main focus is on the possibility of embedding radio frequency identification (RFID) technology in carbon-fibre reinforced polymer (CFRP) components to evaluate the readability of commercial Ultra High Frequency system by varying their covers, which is also partly in CFRPS. The samples produced and the tags used derived on previous studies, in which configurations with the tag housed inside were established and studied. Two RFID tags were studied that could withstand the harsh environmental conditions, i.e., high temperatures and pressure. This work was not carried out in an ideal environment to assess the theoretical capabilities of RFID sensors, but to understand and evaluate the readability limits of commercial RFID tags embedded in CFRPs. Therefore, an experimental campaign was undertaken to assess the downstream readability of the curing process of tags in laminated mock-ups. It was observed that the curing process had minimal effect on the readability of the tags. Free-space tests were carried out in proximity of metallic elements to determine the change of the reading distance obtained during the test, keeping the fixed antenna used constant.

Monitoring Heart Rate Variability Based on Self-powered ECG Sensor Tag

This paper proposes a batteryless sensing and computational device to collect and process electrocardiography (ECG) signals for monitoring heart rate variability (HRV). The proposed system comprises of a passive UHF radio frequency identification (RFID) tag, an extreme low power microcontroller, a low-power ECG circuit, and a radio frequency (RF) energy harvester. The microcontroller and ECG circuits consume less power of only ~30 µA and ~3 mA, respectively. Therefore, the proposed RF harvester operating at frequency band of 902 - 928 MHz can sufficiently collect available energy from the RFID reader to supply power to the system within a maximum distance of ~2 m. To extract R-peak of the ECG signal, a robust algorithm that consumes less time processing is also developed. The information of R-peaks is stored into an Electronic Product Code (EPC) Class 1st Generation 1st compliant ID of the tag and read by the reader. This reader is functioned to collected the R-peak data with sampling rate of 100ms; therefore, the user application can monitor fully range of HRV. The performance of the proposed system shows that this study can provide a good solution in paving the way to new classes of healthcare applications.

An Adaptive Control Algorithm Based on Q-Learning for UHF Passive RFID Robots in Dynamic Scenarios

The Identification State (IS) of Radio Frequency Identification (RFID) robot systems changes continuously with the environment, so improving the identification efficiency of RFID robot systems requires adaptive control of system parameters through real-time evaluation of the IS. This paper first expounds on the important roles of the real-time evaluation of the IS and adaptive control of parameters in the RFID robot systems. Secondly, a method for real-time evaluation of the IS of UHF passive RFID robot systems in dynamic scenarios based on principal component analysis (PCA)-K-Nearest Neighbor (KNN) is proposed and establishes an experimental scene to complete algorithm verification. The results show that the accuracy of the real-time evaluation method of IS based on PCA-KNN is 92.4%, and the running time of a single data is 0.258 ms, compared with other algorithms. The proposed evaluation method has higher accuracy and shorter running time. Finally, this paper proposes a Q-learning-based adaptive control algorithm for RFID robot systems. This method dynamically controls the reader’s transmission power and the robot’s moving speed according to the IS fed back by the system; compared with the default parameters, the adaptive control algorithm effectively improves the identification rate of the system, the power consumption under the adaptive parameters is reduced by 36.4%, and the time spent decreases by 29.7%.

An AOA and Orientation Angle-Based Localization Algorithm for Passive RFID Tag Array

This paper proposes an indoor localization algorithm based on AOA (Arrive of Angle) and orientation angle (OA) for passive UHF RFID (Ultra-High Frequency Radio Frequency Identification) tag array. By utilizing a uniform linear tag array (ULA), the AOA, which is defined as the angle of the reader relative to the tag array, can be estimated by the Multiple Signal Classification (MUSIC) algorithm. The relationship between AOA, OA of the tag array, and the direction angle (DA) between each reader antenna to the geometric center of the tag array is analyzed, and an OA retrieval method based on rotating the coordinate system is proposed to calculate DA. The tag array localization is finally acquired by the DA of each antenna. Simulation and experiment results show that the proposed algorithm can achieve decimeter-level localization accuracy. The proposed algorithm achieves a mean accuracy of 0.216 m, which is a significant improvement compared with the traditional AOA localization algorithm.

An Ultralong-Range, Wideband Planar UHF RFID Tag With Two Split Arcs

A wideband planar passive UHF radio frequency identification (RFID) tag with an ultralong range is proposed in this letter. It is electrically small with a compact footprint of 59.6 mm × 33.3 mm (0.18 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> × 0.10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda$</tex-math></inline-formula> ). The tag is designed based on a T-matching network, and two split arcs are introduced to adjust the resistance and reactance of the tag for the first time. Due to the almost perfect conjugate matching, the power transmission coefficient of the proposed tag reaches 99.63 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . Finally, it has been fabricated and tested. The measured read range of the tag is greater than 6.2 m within the whole UHF-RFID band (860–960 MHz) with a maximum value of 21.3 m at 910 MHz (with 4 W effective isotropic radiated power).

Device-Free Multitarget Localization With Weighted Intersection Multidimensional Feature for Passive UHF RFID

The device-free localization (DFL) can locate the target without requiring the target to carry any radio equipment, which has a broad application prospect in the field of indoor positioning. Radio frequency identification (RFID), as a key technology for IoT implementation, has been widely used in objects identification and tracking. RFID-based radio tomographic imaging (RTI) method has received extensive attention due to its low cost, excellent real-time performance and easy to deployment. However, the indoor multipath effect, which leads to unpredictable variations of the received signal strength (RSS), especially in multi-target positioning. It is still a challenging problem to recognize the locations of multiple targets effectively in the complex indoor environment. In this paper, a novel method of intersection multidimensional feature analysis is proposed to solve this problem. The target impact region is introduced to extract the effective intersections, and then the multidimensional feature information is analyzed to determine the region where the real target may exist. The location estimation of the target is obtained by assigning appropriate weights to each intersection in the region. Extensive experiments are conducted with results are demonstrating that the method achieves high localization accuracy and localization stability in different indoor scenarios, while maintaining low computational complexity.

Efficient localization in warehouse logistics: a comparison of LMS approaches for 3D multilateration of passive UHF RFID tags

The Fourth Industrial Revolution, or Industry 4.0, aims at automating traditional manufacturing and industrial practices using modern smart technology. Autonomous mobile robots equipped with different sensors and employing different techniques have been proposed in the literature in the logistics and inventory warehouse management contexts. Efficient robot motion and planning depend on precise localization, mapping, and awareness of the environment. To properly localize items, recent attempts have been made employing radio frequency identification (RFID) in a 3D environment. This manuscript introduces four least mean squares methods to estimate the 3D positions of tags employing synthetic apertures and phase unwrapping. The proposed methods approach the localization problem solving a system of equations typical of multilateration methods to find the intersections of multiple hyperboloids. The novelty introduced here is the use of unwrapped phase distances to compute pseudo ranges for the multilateration problem. The use of such a technique is feasible thanks to precise mobile robot localization and custom navigation policies. All the analyzed methods are suitable for online localization due to reduced computation timings and have been tested on three different datasets. Two of them contain virtual data that has been generated by simulation, while the other one comes from an indoor experimental setup. Simulated tests show that combined antenna motions in 3D space (including Z-axis) improve the localization obtaining errors under the centimeter for 3D localization. Experimental tests obtained results as low as 13 cm of mean accuracy for 3D localization and 0.21 cm for 2D localization.

Localization and Tracking of an Indoor Autonomous Vehicle Based on the Phase Difference of Passive UHF RFID Signals.

State-of-the-art radio frequency identification (RFID)-based indoor autonomous vehicles localization methods are mostly based on received signal strength indicator (RSSI) measurements. However, the accuracy of these methods is not high enough for real-world scenarios. To overcome this problem, a novel dual-frequency phase difference of arrival (PDOA) ranging-based indoor autonomous vehicle localization and tracking scheme was developed. Firstly, the method gets the distance between the RFID reader and the tag by dual-frequency PDOA ranging. Then, a maximum likelihood estimation and semi-definite programming (SDP)-based localization algorithm is utilized to calculate the position of the autonomous vehicles, which can mitigate the multipath ranging error and obtain a more accurate positioning result. Finally, vehicle traveling information and the position achieved by RFID localization are fused with a Kalman filter (KF). The proposed method can work in a low-density tag deployment environment. Simulation experiment results showed that the proposed vehicle localization and tracking method achieves centimeter-level mean tracking accuracy.

Using the zeroth order resonance of an inter‐digital capacitive unit‐cell to design antennas for passive UHF RFID tags

Meander-line and multi-layer antennas have been used extensively to design compact UHF radio-frequency identification (RFID) tags; however the overall size reduction of meander-line antennas is limited by the amount of parasitic inductance that can be introduced by each meander-line segment and multi-layer antennas can be too costly. In this paper, a new compact antenna topology for passive UHF RFID tags based on zeroth order resonant (ZOR) design techniques is presented. The antenna consists of lossy coplanar conductors and inter-connected inter-digital capacitor (IDC) unit-cells with a ZOR frequency near the operating frequency, which is a key component in the design process because the unit-cells chosen for the design are inductive at the operating frequency. This makes the unit-cells very useful for antenna miniaturization. The new design in this work has several benefits; namely the coplanar layout can be printed on a single layer, matching inductive loops that reduce antenna efficiency are not required and ZOR analysis can be used for the design. Finally, for validation, a prototype antenna was designed with a unit-cell ZOR resonant frequency of 900 MHz, fabricated and characterized. A maximum read-range of 7.6 m was determined.

Non-Line-of-Sight Localization of Passive UHF RFID Tags in Smart Storage Systems

The UHF radio-frequency identification (RFID) has gained growing attention for tagged object localization in smart storage systems. Due to Non-Line-Of-Sight (NLOS) condition, it is challenging to accurately locate the position of tags inside closed spaces. In this paper, we propose a precise and cost-effective solution for tagged object localization in closed spaces, using only received signal strength (RSS) information. We establish a RSS profile for each tag and discover some important features of RSS profiles including uniqueness, time-variation, column-dependence and waveform-similarity. Based on these features, we propose a reference-free RSS-profile (RFRP) localization scheme. The advantage of our propose scheme is to accurately localize multiple tags in closed spaces by overcoming the challenges including the lack of pre-deployed reference tags, NLOS propagation, multi-path propagation and coupling effect. The RFRP scheme first roughly estimates tags’ coordinates based on Peak Asymmetry Factor, then acquires reference-tag substitutes through the similarity of RSS sequences. Subsequently, our scheme refines the relative positions of all tags by these substitutes. Finally all tags’ absolute positions are estimated through a RSS-ranging model. Extensive experiment results demonstrate that our approach can achieve high ordering accuracy and localization accuracy for the tags inside closed spaces.

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.

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.

Dynamic Frame Update Policy for UHF RFID Sensor Tag Collisions.

The current growing demand for low-cost edge devices to bridge the physical–digital divide has triggered the growing scope of Radio Frequency Identification (RFID) technology research. Besides object identification, researchers have also examined the possibility of using RFID tags for low-power wireless sensing, localisation and activity inference. This paper focuses on passive UHF RFID sensing. An RFID system consists of a reader and various numbers of tags, which can incorporate different kinds of sensors. These sensor tags require fast anti-collision protocols to minimise the number of collisions with the other tags sharing the reader’s interrogation zone. Therefore, RFID application developers must be mindful of anti-collision protocols. Dynamic Frame Slotted Aloha (DFSA) anti-collision protocols have been used extensively in the literature because EPCglobal Class 1 Generation 2 (EPC C1G2), which is the current communication protocol standard in RFID, employs this strategy. Protocols under this category are distinguished by their policy for updating the transmission frame size. This paper analyses the frame size update policy of DFSA strategies to survey and classify the main state-of-the-art of DFSA protocols according to their policy. Consequently, this paper proposes a novel policy to lower the time to read one sensor data packet compared to existing strategies. Next, the novel anti-collision protocol Fuzzy Frame Slotted Aloha (FFSA) is presented, which applies this novel DFSA policy. The results of our simulation confirm that FFSA significantly decreases the sensor tag read time for a wide range of tag populations when compared to earlier DFSA protocols thanks to the proposed frame size update policy.

Finger-Worn UHF Far-Field RFID Tag Antenna

This letter presents the design and measurement of an experimental passive UHF radio frequency identification (RFID) tag worn as a ring with applications particularly in healthcare or secure environments. Three sizes of rings were designed for the European UHF RFID band over two different substrates at varying heights off the skin. Designing effective body-mounted antennas for passive RFID is very challenging, particularly when mounted directly upon the skin. The rings were simulated with a commercial electromagnetic simulation software and then constructed and tested on an adult male ring finger over several angles of RF illumination so that read ranges and directivity could be determined. Main beam read distances between 2 and 5 m were achieved dependent on the ring substrate height.

Different Substrate Materials for Designing a Passive UHF RFID Tag Antenna

The Radio Frequency Identification (RFID) technology has been increasingly used for various application such as tracking of products, smart cards, identification, item management, security etc. In this paper, the performance parameter of the passive UHF RFID tag antenna has been studied for four different substrate materials viz., FR4 epoxy, PET, Rogers 4350, Taconic TLY materials. A simple meandered dipole antenna has been designed using a T-match stub for impedance matching of the tag antenna with the attached RFID chip. These different substrates are then designed separately, for the same antenna geometry. The effect of using these substrates on RFID tag antenna parameters such as reflection coefficient, antenna gain, VWSR, radiation pattern, impedance, ease of optimization level, read range, and radiation efficiency are then observed.

Electromagnetic Performance Evaluation of UHF RFID Tags With Power Discretization Error Cancellation

The rigorous electromagnetic characterization of passive UHF radio frequency identification (RFID) tags is a challenging task. Among various solutions, in a previous work, an automatic tool for the over-the-air evaluation of significant RFID tag metrics has been presented. Once the distance is fixed, the system, based on the estimation of the minimum power emitted by the off-the-shelf interrogating reader capable to energize the tag under test, exhibits an accuracy that, although adequate, is affected by the minimum power step at the reader side. In this communication, an evolution of a new platform whose working principle has already been introduced by the same authors is presented. It is based on an analytical model opportunely derived to overcome this limit while preserving flexibility and cost-effectiveness. The platform can automatically vary with continuity the interrogation distance—which becomes a new degree of freedom—and it is able to estimate the couple power distance for each frequency, which practically annuls the estimation error due to the power discretization. Moreover, the enhanced system now allows for a pretest phase that is useful to verify whether or not the implemented analytical model is valid in the specific environment, even if not electromagnetically anechoic.

Multipath Mitigation Algorithm for Multifrequency-Based Ranging via Convex Relaxation in Passive UHF RFID

Radio frequency identification (RFID) is a promising technology in indoor localization. However, multipath cannot be avoided in indoor passive ultrahigh frequency RFID localization environment, which results in poor localization accuracy. In this paper, a range-based localization scheme has been developed to mitigate the effect of multipath errors and improve the localization accuracy. The proposed localization methods are based on semi-definite programming and second-order cone programming and do not require any statistics of multipath error. First, all the phase information of multifrequency is utilized. Dual-frequency phase difference of all dual-frequency combinations can be obtained to range. The ranging error is assumed to follow the Gaussian distribution. Then, convex relaxation methods with limiting the mean ranging error to one standard deviation of the Gaussian distribution are proposed. Finally, in order to solve the feasibility problem, the constraint of the mean ranging error is relaxed. Simulation results demonstrate that the proposed methods outperform some existing localization algorithms in multipath environment.

The Optimization for Hyperbolic Positioning of UHF Passive RFID Tags

This paper presents a fine-grained positioning method for radio frequency identification (RFID). The proposed method applies hyperbolic positioning to locate ultrahigh frequency passive RFID tags. In our design, finding the tagged object's location is formulated as an optimization problem. Phase values, collected by the moving antenna, are exploited to achieve the optimal solution. The intuition of hyperbolic positioning lies in that the difference of distances from a target tag to two antennas can be inferred from phases. When integrating hyperbola curves together, optimization method can be performed to achieve the object's location. Particle swarm optimization is then applied to enhance computational ability. For random phases, polynomial regression is employed to model the relationship between phase values and distances. We implement a prototype of hyperbolic positioning optimization to pinpoint the RFID tag's location and evaluate its performance in our laboratory environment. Compared with other RFID localization methods, i.e., received signal strength indicator based and phase-based approaches, our design shows greater tolerance to tag diversity and tag orientation.

IoT Localization for Bistatic Passive UHF RFID Systems With 3-D Radiation Pattern

Passive radio-frequency identification (RFID) systems carry critical importance for Internet of Things (IoT) applications due to their energy harvesting capabilities. RFIDbased position estimation, in particular, is expected to facilitate a wide array of location-based services for IoT applications with low-power requirements. In this paper, considering monostatic and bistatic configurations and 3-D antenna radiation pattern, we investigate the accuracy of received signal strength-based wireless localization using passive ultra high frequency RFID systems. The Cramer-Rao lower bound (CRLB) for the localization accuracy is derived, and is compared with the accuracy of maximum likelihood estimators for various RFID antenna configurations. Numerical results show that due to RFID tag/antenna sensitivity, and the directional antenna pattern, the localization accuracy can degrade at blind locations that remain outside of the RFID reader antennas' main beam patterns. In such cases optimizing elevation angle of antennas are shown to improve localization coverage, while using bistatic configuration improves localization accuracy significantly.