In this article, a millimeter-wave (mmWave) chipless radio-frequency identification (RFID) tag is developed to operate in the V-band for authentication applications. A novel approach based on tag backscattered E-field measurements at different orientation angles for unitary classification is proposed. The concept is based on the hardness to identically reproduce materials due to the inherent randomness in the fabrication process. These uncertainties are transcribed in very small variations that can be observed in the tag electromagnetic response. A set of 16 identical tags were fabricated, and each tag shares the same fabrication mask and manufacturing process method. Spatial diversity using the tag backscattering pattern (at two different angles) adds independent characteristics for estimating authenticity of each tag. To better exploit the large amount of data collected with this approach, a machine learning (ML) sighting classification is used, which enhances the system performance. The probability of error (PE) achieved with the method is around 1%. This PE is four times lower than the one obtained with a similar approach implemented in the X-band.

In this study, we present the implementation of a neural network model capable of classifying radio frequency identification (RFID) tags based on their electromagnetic (EM) signature for authentication applications. One important application of the chipless RFID addresses the counterfeiting threat for manufacturers. The goal is to design and implement chipless RFID tags that possess a unique and unclonable fingerprint to authenticate objects. As EM characteristics are employed, these fingerprints cannot be easily spoofed. A set of 18 tags operating in V band (65–72 GHz) was designed and measured. V band is more sensitive to dimensional variations compared to other applications at lower frequencies, thus it is suitable to highlight the differences between the EM signatures. Machine learning (ML) approaches are used to characterize and classify the 18 EM responses in order to validate the authentication method. The proposed supervised method reached a maximum recognition rate of 100%, surpassing in terms of accuracy most of RFID fingerprinting related work. To determine the best network configuration, we used a random search algorithm. Further tuning was conducted by comparing the results of different learning algorithms in terms of accuracy and loss.

This paper discusses a bistatic reading configuration that employs a frequency-spatial encoding strategy to enhance the data encoding capacity in chipless radio frequency identification (RFID) systems. The proposed method allows for the estimation of resonant frequencies associated with each scatterer and the determination of relative resonator positions. The approach relies on an imaging algorithm that evaluates the positions of the resonators by considering a single-frequency point corresponding to the resonant frequency of each scatterer. Consequently, the proposed method does not seek to image the shape of the metal scatterers but rather to locate their positions geometrically for different frequencies. Indeed, once the resonance frequencies have been detected, a geometric representation of the backscattered field is created by limiting the observable frequency band to the resonance frequencies. The use of individual processing with single-frequency steps enables the distinction of the side-by-side gap between resonators, even at resolutions below the conventional image resolution. Furthermore, this method has the capability to differentiate the gap spacing, which can be as small as λ/8, between resonators operating at different resonance frequencies. This technique significantly increases the coding capacity associated with the chipless tag. A proof of concept (PoC) is evaluated based on loop resonators for identification purposes. Then, anechoic and real scenario measurements (3D displacement table and conveyor belt) are considered in different acquisition configurations. An office environment reading range of up to 20cm has been reported.

This paper shows the use of a bi-static reading configuration by optimizing the angle between the two antennas that allows isolating the contribution of the 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 bi-static 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 post-processing steps. For this purpose, a bi-static antenna configuration is employed, where the angle between the incident wave and the backscattered signal is chosen to maximize co-polarization configuration. Firstly, 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, non-systematic 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.

This letter presents the development of a generation technique of antennas to enhance security identification on physical layer applications. Differently from the logical bit-level, frequency-diverse metasurface antennas are explored as a solution for enhancing security and ensuring end-to-end communication integrity from a physical layer point of view. The antennas are generated using the morphogenesis theory, which favors the radiation of uncorrelated fields in space and polarization. The proposed antennas are evaluated within the K-band to assess aspect-independent information through the difference between measured near-field aperture signals at two orthogonal polarizations. Statistical classification is employed to quantify the security level, demonstrating the feasibility of uniquely identifying the morphogenetic metasurface antennas based on the diversity of information contained in their aperture and polarization information.

Tag RFID sans puce en bande millimétrique pour applications sécurisées: Les systèmes d'authentification pratiques visent optimiser le rapport entre la fiabilité et l’implémentation face à la complexité du système. Dans ce contexte, de nouvelles technologies d'authentification considérant les solutions basées sur l’identification de radiofréquence sans puce sont proposées et évaluées. L'authentification par technologie RFID sans puce fournit une méthode non-invasive basée sur la distinction de signature électromagnétique et, en plus, il ne nécessite pas d’un alignement pour extraire l’information de l’objet et ces solutions seront très bas coûts, car issues des techniques de l’industrie papetière, biosourcées et recyclables, ces deux derniers critères limitant l’empreinte environnementale. Les tags RFID sans puce ont le potentiel de produire une signature électromagnétique unique et quasi-infalsifiable assurant et améliorant le niveau d’authenticité. Par conséquent, la demande pour des nouvelles applications comportant le faible coût, imprimes directement sur des matériaux flexibles et fiables nécessitent des nouvelles solutions basées sur l'apprentissage automatique, l'amélioration de la robustesse de lecture et des systèmes d'imagerie. Dans ce travail, différents systèmes d'authentification sont proposés en considérant des tags RFID sans puce. Le concept repose sur l’idée qu’il est extrêmement difficile de reproduire à l’identique des matériaux qui comportent un côté aléatoire, il s’agira donc de transcrire ce côté aléatoire du tag sur sa signature réponse électromagnétique. Plus précisément, nous proposons de concevoir, fabriquer, caractériser et analyser la richesse en information de plusieurs structures utilisant une analyse sur les paramètres électromagnétiques que portent une caractéristique unique et incopiables. D’ailleurs, la possibilité d'authentifier des objets avec des tags sans puce, en utilisant une méthode non intrusive basée sur l'exploitation de la signature électromagnétique à ondes millimétriques est évalué. Parmi les objectifs, évaluer la «richesse» de l’information de cette empreinte est donc un point essentiel pour les applications entrevues. La richesse des informations contenues dans les signatures des tags sera évaluée analytiquement en termes de sa probabilité d’erreur. Plus précisément, chaque signature contient des informations relatives au tag et l’environnement dont le tag est présent, ces informations représentent un facteur unique que seront utilisées pour la méthode d’authentification, ainsi en augmentant à la confidentialité et robustesse de la technique. Des résonateurs canoniques en band X sont évalués puis convertis pour l’opération en bande V. En plus, les limitations pour l’opération en bande V sont analysées.D’abord, le niveau d'authentification est évalué par le maximum de vraisemblance classique. Ensuite, une nouvelle méthode considérant l'ajout de différentes informations relatifs au signal rétrodiffuse du tag est proposée et, par conséquent, évaluée par une méthode d'apprentissage automatique que vise minimiser le numéro de faux positifs et fausses négatives. Une amélioration significative est notée malgré la fabrication des tags dans le même tour d’impression. Tags sans puce d'ordre superior sont proposés pour assouplir les contraintes dans la fabrication des tags en bande V. Enfin, un système basé sur l'imagerie est proposé visant la localisation géométrique des résonateurs en fonction de leur fréquence de résonance. L'analyse comparative des différentes applications permettra à la définition de la précision de chaque approche. De plus, la détermination des principales caractéristiques en termes de variation du signal conduira ultérieurement à la définition d'un cadre adapté aux données mesurées permettant de fournir un haut niveau d'authentification en combinant les avantages de chaque solution.