Chipless Tag Research Articles

Efficiency Improvement for Chipless RFID Tag Design Using Frequency Placement and Taguchi-Based Initialized PSO.

Frequency encoding chipless Radio Frequency Identification (RFID) tags have been frequently using the radar cross section (RCS) parameter to determine the resonant frequencies corresponding to the encoded information. Recent advancements in chipless RFID design have focused on the generation of multiple frequencies without considering the frequency position and signal amplitude. This article proposes a novel method for chipless RFID tag design, in which the RCS response can be located at an exact position, corresponding to the desired encoding signal spectrum. To achieve this, the empirical Taguchi method (TM), in combination with particle swarm optimization (PSO), is used to automatically search for optimal design parameters for chipless RFID tags with a fast response time, to comply with the frequency encoding requirements in the presence of the mutual coupling effect. The proposed design method is validated using I-slotted chipless tag structures that are fabricated and measured with different sets of resonant frequencies.

Design of High Sensitivity Re-transmittable Chipless Tag Temperature Sensor based on Alumina Ceramic

Design of High Sensitivity Re-transmittable Chipless Tag Temperature Sensor based on Alumina Ceramic

Ultrathin and Bendable mm-Wave Chipless Tags Based on Grounded Periodic Surfaces

Depolarizing mm-wave chipless RFID tags based on grounded dipole resonators characterized by an extremely thin profile are proposed. The use of thin grounded substrate (below 0.15 mm) makes the tags bendable. The presence of the ground plane allows to isolate the response of the tag from surrounding objects making the proposed configuration suitable for non-planar lossy objects like filled water bottles or containers. The periodic surface configuration is employed to obtain a sufficiently large RCS to increase the read range of the tags. The proposed tags operate between 26 GHz and 40 GHz, which allows to achieve the miniaturization necessary for practical scenarios. Toward low cost, thermal printing fabrication is investigated taking lithographic one as a reference. The associated severely loss (introduced by both ultra thin substrate and thermal printing), and the rotation sensitivity of depolarizing label are discussed theoretically and well addressed experimentally. Rotation insensitivity up to 5 degrees and long read range up to 150 cm are experimentally verified. The readability of the proposed ultra-thin tags applied to filled bottles is successfully assessed comparing the performance of tags with and without ground plane.

Design of a Retransmitted Chipless Tag based on Multi-state Resonators

In order to increase the encoding capacity and reduce the size of the tag, this paper proposes the frequency sharing method to design a retransmitted chipless tag, which is composed of N resonators, a coupled microstrip transmission line, and the orthogonal transmitting antenna and receiving antenna. A pair of the same size resonators is placed symmetrically on both sides of the coupled microstrip transmission line. M open-ended stubs (OES) with different combinations are embedded in each resonator to obtain different resonance frequencies. The frequency sharing multi-state resonators’ chipless tags are designed where N=6, M=4, and the dimension of the tag is 46 mm × 30 mm, which can generate about 212 codes. Simulation and measurement results show good agreement and feasibility of the tag design. The chipless tag is small in size, has large encoding capacity and is easy to print. This kind of tag has no silicon chip so the cost is low. It can be widely used in logistics, supermarkets and other fields to replace the barcode.

Robustness Improvement for Chipless RFID Reading Using Polarization Separation

In this article, a novel method to improve the readability of chipless tags is presented. When the EM wave falls upon the tag’s surface at normal incidence or with a known incidence, the proposed approach permits to obtain a higher signal-to-noise ratio (SNR) of resonators whose orientation with respect to the normal to the plane in which the tag is positioned is unknown and, thus, to increase the reading distance of the tag. It introduces a technique based on the detection of this tag orientation in relation to the antennas; a projection of the signals will allow correcting this misalignment in order to always be able to decode the tag identifier on a signal that corresponds to an ideal alignment between the tag and the antennas. With this principle, it is also possible to separate the resonance mode of the resonator that is connected to the identifier from other parasitic resonance modes that may appear due to a possible misalignment between the tag and the antenna. This principle is applied to loop resonators commonly used in chipless radio frequency identification (RFID), which can present strong parasitic modes of resonance. Also, this method makes the reading orientation invariant, allowing to read the resonator whatever its orientation with respect to the normal to the plane in which the tag is positioned. Likewise, the proposed method can be also used to sense this resonator orientation. This method requires a dual-polarization antenna and a two-port vector network analyzer (VNA). Results are validated in simulation and with real-environment measurements for a single resonator and multiple resonators, as it is classically used in chipless RFID technology. Measurements in a harsh environment, as well as comparisons with classical techniques, such as time gating (TG), are presented. A study on the improvement of the read range is achieved to highlight the potential of the proposed technique. A reading distance of more than 80 cm was, thus, obtained, which represents 20 cm more than with the classic use of a postprocessor based on time gating. Finally, the principle of the measurement is generalized by applying it to a tag with a ground plane and considering that the antenna is not necessarily placed in normal incidence with respect to the plane of the tag.

Electromagnetic Modeling Strategy Supporting the Fabrication of Inkjet-Printed Chipless RFID Sensors

Inkjet printing fabrication techniques can be used for the manufacturing process of chipless radio-frequency identification RFID sensors. With respect to traditional silicon-based fabrication, flexible electronics induce the possibility to experiment new substrates and conductive materials. With the development of high-conductive nano-inks the low sintering temperature required to process them results compatible with a large variety of substrates. However, the requirements for the conductivity of the metallized printed patterns are particularly stringent for applications where the working frequency is high, like in the case of common chipless RFID tags working in the frequency range 3-10GHz. In chipless RFID systems, the higher the conductivity of the conductive parts and the better the signal response of the tag. However, in printed chipless RFIDs the conductivity can only give a partial indication of the goodness of the tag. The tag response is dependent on the sheet resistance, which is not only related to the conductivity of the ink but also to the thickness of the printed pattern. Therefore, if a sufficiently high-conductive nano-ink is selected, the signal efficiency of the printed tag can be further improved by making an evaluation based on the thickness of the patterns. The objective of this study is to propose a strategy for evaluating the signal response efficiency in inkjet-printed chipless tags by means of a first quantification of the average thickness of the printed layer, which is used to feed a finite element method simulation model to give the manufacturer an idea of the optimal number of layers to be printed in order to have a strong signal response.

Optimal Angle in Bistatic Measurement for Chipless Tag Detection Improvement

This article shows the use of a bistatic reading configuration by optimizing the angle between the two antennas, which allows isolating the contribution of the radio frequency identification (RFID) chipless tag from its nearby environment, thus enhancing the reading performance of the chipless tag for short-range applications. The idea is to extract as much useful signal (relating to the tag information or tag ID) from the total signal using a dedicated bistatic reading configuration. This extraction step is implemented from a hardware point of view, which is different from classical approaches based on signal processing. Indeed, based on this technique, it is possible to read tags even in highly reflective environments (metallic surfaces) without applying a calibration method, such as subtracting the environment without the tag or advanced postprocessing steps. For this purpose, a bistatic antenna configuration is employed, where the angle between the incident wave and the backscattered signal is chosen to maximize copolarization configuration. First, a model based on the general scatter theory is evaluated; it highlights the scattering mechanism involved in the problem. Then, a proof of concept (PoC) is evaluated, and afterward, a chipless tag composed of an array of dipoles is studied for identification purposes. The analytical evaluation and the channel modeling allow a general implementation of the proposed technique. Anechoic and real scenario measurements are evaluated considering the presence of surrounding objects. Finally, nonsystematic errors related to the positioning of the tag are considered each time without considering a reference (or background) measurement or the use of specific signal processing techniques.

Non-Invasive Lactate Monitoring System Using Wearable Chipless Microwave Sensors With Enhanced Sensitivity and Zero Power Consumption.

Monitoring lactate levels is an established method for determining hyperlactatemia in critically ill patients and assessing aerobic fitness. It is a widely used gold-standard technique in both professional and serious amateur sports. Non-invasive real-time lactate monitoring offers significant advantages over the current technology of finger-prick blood sampling. Possible candidate technology for developing non-invasive real-time lactate monitoring should be highly sensitive, flexible, and capable of real-time monitoring of lactate levels in interstitial fluid or within specific working muscle groups depending on the type of sport. Herein we describe a planar, flexible, passive, chipless tag resonator that is electromagnetically coupled to a reader placed in proximity to the lactate sensor tag. The tag resonator is a thin metallic tracing that can be taped on the skin. The resonance frequency of the tag fluctuates proportionately with changing lactate concentrations in a solution mimicking human interstitial fluid with very high sensitivity. The spectrum of the tag is reflected in the spectrum of the reader, which is a planar microwave resonator designed at a different frequency. The reader could be embedded in a cellphone or an application-specific wearable device for data communication and processing. The tag can accurately and reproducibly measure lactate concentrations in the range of 1 to 10 mM, which is in the physiological range of lactate observed at rest and during intense physical activity. Furthermore, the chrematistics of this technology will allow monitoring of lactate in specific working muscle groups.

An encoded reconfigurable RFID strain sensor and its information fusion method

Chip-based radio frequency identification (RFID) sensor systems have been investigated for structural health monitoring applications. However, the use of chips in sensor tags has drawbacks in terms of cost, durability, and detection capability. In this paper, we propose a reconfigurable RFID-based chipless tag sensor for strain detection, which detects structural strain by observing the offset of the resonant frequency of the antenna and incorporates an encoding unit for tag identification. To realize the reconfigurability of the antenna, a PIN diode is added to control the antenna, and the frequency reconfigurability of the antenna is realized by controlling the turn on/off of the PIN diodes. The Kalman filter algorithm is used to realize the information fusion of multiple sensors to improve the sensor detection accuracy, and the background noise data enhancement is used to expand the original data samples to fuse the information of the three sensors’ data, and the relative error after fusion is reduced by about 36% compared with the relative error before fusion compared with separate measurements. The antenna was fabricated by an etching process and measured using vector network analyzer to verify the accuracy of the antenna simulation results.

Mm-Wave Chipless RFID Decoding: Introducing Image-Based Deep Learning Techniques

Chipless RFID tag decoding has some inherent degrees of uncertainty because there is no handshake protocol between chipless tags and readers. This article initially compares the outcome of different pattern recognition methods to decode some frequency-based tags in the mm-wave spectrum. It will be shown that these pattern recognition methods suffer from almost 2%–5% false decoding rate. To overcome this misdecoding problem, two novel methods of making images of the chipless tags are presented. The first method is making 2-D images based on side-looking aperture radar concepts, and the second one is making virtual 2-D images from the 1-D backscattering signals. Then, a 2-D decoding algorithm is suggested based on a convolutional neural network to decode those tag images and compare the results. It is shown that this combined decoding method has very high accuracy, and it almost eliminates any ambiguity and false decoding problems. This is the first time a deep learning method is used with image construction methods to decode chipless RFID tags.

Design of a novel compact and flexible chipless RFID tag based on an improved U-shaped resonator

Miniaturization, flexibility and high coding capacity design are very important while considering the development of chipless tags. In this paper, a flexible high-encoding capacity chipless radio frequency identification (RFID) tag with a compact structure is designed using Polyimide, a flexible material with high-temperature resistance as the substrate. The tag works in the band of 1.5∼10.5 GHz, the coding density of 4.348 bits/cm2 is obtained with four alternating nested improved U-shaped resonance structures. Frequency shift coding is realized by changing the structural parameters of the resonator. The production process is simple because only one conductive layer is needed. Because of its flexible and low-cost characteristics, it provides more possibilities for the promotion of RFID technology. A good agreement between simulation and measurement validates the feasibility of the design concept.

Modified rectangular resonator based 15‐bit chipless radio frequency identification transponder for healthcare and retail applications

In this paper, a compact and fully passive chipless radio frequency identification planar tag is proposed based on a modified rectangular resonator. The tag is having a simple design and is fabricated using a low-cost FR4 substrate and acquires a physical footprint of 50 mm × 30 mm. The novelty of the proposed work describes a single passive tag having a reading distance of 84 cm with a 15-bit coding capacity in a compact profile. A spectral bit capacity of 2.727 bits/GHz is achieved in a wide range of frequencies from 0.5 to 6 GHz. A reference wideband horn antenna is used as the interrogator to study the tag detection procedure having gains of 6.6 and 18.77 dBi at 0.5 and 5.8 GHz respectively. The backscattered tag response is well suited to the measurement characteristic of the reader. The measurements are performed in a bistatic mode and the results confirm the 15-bit coding capacity of the chipless tag using frequency domain analysis with a maximum radar cross section of −15 dBsm. The multi-bit coded tag can be suitable for a wide range of wireless applications, viz. tracking, retailing, identification, and healthcare utilities.

Chipless RFID Sensors for Wearable Applications: A Review

Radio frequency identification (RFID) is a quickly growing innovative wireless data capturing technology for automatic identification, product tracing, security investigation, automatic toll fee, vehicle tracking, and e-Health. Wearable sensing technology and on-body structures have achieved pervasive responses due to their fabulous potential in the Internet of Things (IoT), healthcare, and smart homes. Inexpensive chipless RFID tags for on-body sensing are the upcoming research for such wearable devices. Its sensing skill offers the unified real-time monitoring of vital signs. This paper reviews various chipless passive RFID tag sensors for wearable applications. The main goal of this research work is to study the basics of chipless RFID sensors and their working principles. Further, chipped RFID sensors are very costly for mass implementation. Hence, chipless tag sensors have grown into a cost-effective and maintenance-free substitute, fulfilling the requirements of the society for the emergent technologies, where lots of these sensors can be used. Understanding the importance in emerging applications, essential materials needed for different sensors, basic circuit models for chipped and chipless sensors, and challenges with limitation of recent chipless RFID sensors are also discussed in this article.

Chipless RFID Based on Micro-Doppler Effect

This article demonstrates how motion effect can be exploited to read moving chipless radio frequency identification (RFID) tags at larger distances compared to what has been reached without taking into account the movement. According to the Doppler effect, due to the time-variant behavior of moving chipless tags, the tag backscattered field contains frequency components different from those that are transmitted. These motion-induced frequency components can be utilized to efficiently detect the tag at large distances, in a real environment composed of stationary objects. A circuit-based analytical model verified by full-wave simulations is presented to effectively predict the quasi-stationary backscattered field from moving scatterers, with fast computation process. The developed analytic model is applied to rotating dipole scatterers and is used to design chipless tags, including an identifier. In terms of identification, good agreement is observed between the measurement results and those are predicted by the model. Finally, read range enhancement is proven experimentally by a real environment measurement where the chipless tags are readable at distances up to several meters.

Chipless RFID Tags Placement Optimization as Infrastructure for Maximal Localization Coverage

Indoor localization based on asynchronous and chipless radio frequency identification (RFID) infrastructure has a wide potential for real-world emerging applications like simultaneous localization and mapping (SLAM) systems and mobile material characterization transceivers. Effective deployment of chipless tags within the indoor environment as infrastructure plays an important role to attain connectivity between the infrastructure and the objects of interest at any time and position in the room. As an example, assuming an indoor localization system, a moving or flying robot should be connected to k reference chipless tags in order to enable self-localization. From system design point of view, the reference tags should be deployed in the room to guarantee that each point in the room is covered by at least k tags, which is denoted as 3D k-coverage. In this paper, we propose to formulate the reference chipless tags placement as a binary integer programming to ensure achieving 3D k-coverage with the minimum number of tags considering system and propagation constraints. Since mm-localization accuracy could be prevailed at Terahertz (THz) band, the optimization problem considers the chipless tags limited distance and angle coverage at this band as optimization constraints. Since discretization of the optimization domain might cause blank areas that are not covered, we propose an iterative method aiming at filling those blank areas and assuring their k-coverage. Performance evaluation is performed to examine the performance of the proposed algorithms. Results show that the proposed algorithms achieve desirable performance by promoting 3D k-coverage with minimum number of tags.

Realization of Chipless RFID Tags via Systematic Loading of Square Split Ring With Circular Slots

This paper presents a unique design approach of frequency domain based chipless radio frequency identification (CRFID) tags. A miniaturized square-split-ring is systematically loaded with circular-slots through an iterative procedure. Hence, a number of miniaturized resonators are produced which can be arranged in different configurations to realize multiple chipless tags operating at different frequency bands. This design approach provides a great control and flexibility in designing chipless RFID tags with different bit capacities. The proposed chipless tags are fabricated by printing the resonating elements on both front and back sides of the dielectric substrate hence doubling the capacity of the tags. All the tags are tested and measured.

System Development of Calibration-Free 20.7-Bit Chipless RFID Without Iterative Optimization of Tag Configurations

Earlier studies have improved the data capacity of frequency-coded chipless radiofrequency identification (RFID) to 100 bits, but these high-density tags may suffer from two limitations, including the design complexity for billions of tags and an additional procedure for measuring clutter. In this paper, a calibration-free chipless RFID system with 20.7-bit capacity is proposed; moreover, the design of the 1.68 million tags is highly efficient, preventing individual and iterative optimization for such large numbers of configurations. These distinct features are obtained by integrating the signal processing of reader and the resonance synthesis of tags. The signal processing employs short-time Fourier transform (STFT) and enhanced filtering to achieve calibration-free detection. The resonance synthesis features minimized numbers of geometric parameters, reduced mutual coupling between resonators, and response surface models for the resonant frequency to realize noniterative optimization. The proposed system is validated by three approaches. First, residual plots indicate that the range of residuals is confined to the average bandwidth of frequency slots. Second, 36 IDs are sampled and automatically transformed into chipless tags. The measured reliability of four bands is as high as 100%, 95.0%, 98.3%, and 93.9%, respectively. Finally, the parameterization of signal processing is validated by time-frequency analysis and reliability.

Linear Time-Variant Chipless RFID Sensor

In this paper, we present the first chipless sensor which does not satisfy the definition of a linear time-invariant system. This rotational sensor is able to break the time-invariance classically associated with chipless technology by modulating the reflected power in the time domain. As a result, this sensor is able to backscatter power at a frequency different to the one used by the reader and function of the rotational speed. A new identification scheme based on the power of the modulated backscattered tag signal is also introduced and allows to identify different tags. Coding capacity has been evaluated at 11 bits with a probability of correct detection of 98%. Linear time-variant systems allow also to simplify the reader architecture, read multiple tags and increase the read range for both sensing and identification. We show that the proposed chipless sensor could be read at a distance higher than 10 m. This result outperforms classical read range of chipless tag by a factor of 30.

Chipless RFID: A Unique Technology for Mankind

The present era of digitization is looking forward to updating the manual system with automation. The chipless Radio Frequency Identification (RFID), a well-known wireless technology, eliminates the hurdle of human intervention and comes into the Automatic Identification (Auto-ID) technology market. Although the low cost of optical barcodes dominates them for many years, their restricted read distance, reduced information storing capacity, and significant manual involvement in their operation call out the need for an alternative. The conventional RFID overcomes all the above-mentioned shortcomings of an optical barcode. But the cost of the RFID is an important problem. This article reviews chipless RFID which benefits over existing Auto-ID technologies. An overview of the basic RFID system, categories of RFID tags, and a comparison of chipless and chipped RFID tags are outlined. Understanding the relevance of chipless RFID in the future, the classes of chipless RFID tags, the challenges that come across in designing a chipless RFID, the principle of operation of a backscattering chipless tag, and design parameters like Radar Cross Section (RCS) are discussed. This article throws light on RFID tag printing, data capturing techniques of chipless RFID, certain materials used for tag manufacturing, chipless RFID-based sensors, potential applications, followed by current challenges and future directions of chipless RFID tags.

Modified rectangular resonators based multi‐frequency narrow‐band RFID reader antenna

AbstractIn this article, a chipless RFID reader antenna based on a modified rectangular‐resonator is presented. The reader antenna is fabricated and measured to validate multiple narrowband resonance behavior. The measurement results show that the reader antenna can detect 11‐bit multi‐frequency coded chipless tag and depict gains of 4.7 and 5.2 dBi at 0.58 and 2.4 GHz, respectively. The cubic interpolation approach as a signal processing technique is applied at the reader end to eliminate the unnecessary drops at the measurement. Further study of Chu and Mclean's fundamental limit demonstrates that the physical dimensions of the proposed antenna and the radiation characteristics fulfilling the limitations. The multiple narrow‐band responses of the reader antenna can be suitable to detect multi‐bit tags which are of high demand because a multibit tag can be used for multiple frequency applications for hassle‐free wireless environment, viz. tracking, retailing, identification, and healthcare utilities.