Integrated sensing and communication (ISAC) represent a critical technology for future wireless systems, enabling simultaneous environmental sensing and data transmission. In this paper, we experimentally demonstrate a novel integrated sensing and backscatter communication (ISABC) framework that uses a monostatic backscatter system for device-free indoor user localization. In contrast to most existing ISAC-related works in the literature, we consider energy harvesting backscattering tags as communication users, and our sensing application is non-intrusive, where we localise the target without tagging it. Specifically, we utilize Wireless Identification and Sensing Platform (WISP) tags and a machine learning model based on Support Vector Machines (SVM) to accurately estimate user positions within a defined sensing region. Through experiments conducted with off-the-shelf hardware, we systematically evaluate the influence of different numbers of tags, transmission power, and spatial resolution on localization accuracy and system through-put. Overall, our novel experimental demonstration indicates that the proposed ISABC framework achieves a localization accuracy that exceeds 90 % without a significant degradation in backscatter communication performance, highlighting its potential as a low-power and sustainable solution for next-generation Internet of Things (IoT) applications.
This paper evaluates the feasibility of powering low-power sensor nodes by conducting an RF power survey for ambient and dedicated emitters. The RF survey for ambient emitters was conducted at four locations of our campus -two indoors and two outdoors- from 150 MHz to 6 GHz, which covers six major frequency bands: DTT, LTE 800, GSM 900 and 1800, and Wi-Fi 2.4 GHz and 5.0 GHz. The results showed that in all cases, the RF power levels were below -30 dBm (the selected limit for powering sensor nodes), except in two cases: the GSM 900 band using a mobile phone as the emitter and the GSM 1800 band. To enhance the RF power level, a dedicated RFID reader was used and positioned at distances of 1 m and 10 m from the measurement setup, with a transmitting power range from 17.5 dBm to 39 dBm. At the standard maximum EIRP value of 35 dBm, received power levels of -14.1 dBm and -18.9 dBm were achieved at distances of 1 m and 10 m, respectively, which would allow powering sensor nodes. Finally, the results are compared with other works.
Self-healing (SH) functional polymers, composites, and blends offer innovative solutions for developing fully soft, elastic electronics, antennas, and sensors with the ability to heal themselves. In this paper, we demonstrate, for the first time, the stretching performance and SH functionality of passive UHF RFID tags fabricated of SH elastomer blends. We analyzed the functionality of the passive UHF RFID tag based on a dipole antenna with different conductor thicknesses after being bisected and stretched. After completely bisected, 82.6% of the tag's read range was regained within 24 hours, and it could be uniaxially stretched up to 75%. Our results provide important proof of concept for the development of stretchable and SH antennas, and wireless sensors. One of the most important aspects for future work is enhancing the performance of RFID tags under stretching by improving the bonding of the IC to the radiator with structural design that can also enable waterproofing, thereby making the tags suitable for wearable applications requiring washability.
Artificial Intelligence (AI) algorithms have emerged as a suitable solution for chipless RFID tag detection. However, key considerations for AI-based detection approaches include the generalization capability of the models and their deployability on computationally limited embedded digital signal processors, for their use in real-world applications. This paper presents a brief review of recently presented AI models in the literature. We evaluate the models' generalization capabilities by training and testing on measurements collected at different times, without guaranteeing the same exact set-up. Deployability is assessed based on two indicators: memory requirements and computational cost. The provided results manifest the necessity of evaluating AI models on entirely distinct datasets, with observed differences in accuracy of up to 0.2319 between testing on a subset of the training dataset and testing on a distinct dataset. The memory requirements of all the presented models indicate that they could be stored on simple embedded digital signal processors, with the largest model requiring less than 35 MB of memory. However, most of the models are computationally expensive, with the most demanding model requiring more than 825 million floating-point operations to perform an inference.
This paper investigates the robustness and performance of chipless RFID technology for identification and tracking, emphasizing its localization capabilities in dynamic and challenging warehouse environments. We examine how chipless tags placed on the ground can facilitate and enhance the real-time localization of autonomous guided vehicles. An evaluation of chipless RFID tags under harsh electromagnetic conditions, including moisture, dust, and physical obstructions, demonstrates their reliability in challenging environments. A co-polarized bistatic antenna pair, mounted on a tilted support, enhances the signal-to-noise ratio by reducing specular reflections, thereby improving detection performance. The impact of the tag's tilt orientation and translational movement on location accuracy is also analyzed. Dynamic measurements are conducted for two tag orientations: inclined placement (phi = 30 degrees) and flat placement (phi = 0 degrees). These measurements assess detection performance under motion tests, showing that the system can track tags at realistic warehouse speeds without any degradation in location performance.
This paper addresses several key challenges in bistatic ambient backscatter communication (AmBC) regarding the direct path interference (DPI) problem, contributing to both theoretical insight and practical feasibility. To predict the power of the backscattered signal (BS) from the total power in the presence of an interfering direct signal without using complex signal processing algorithms, a power-centric theoretical model based on the phase difference of the interference between the AmBC signal and the direct signal (DS) is proposed for 5 G-NR free space. As a first approach, only a direct continuous wave (CW) signal at 3.5 GHz was considered. Knowing the BS power level is important for estimating the potential AmBC range. Knowing the ratio of AmBC power to the direct signal power (in dB) is also important for a robust reception of the AmBC signal without interfering with the active communication systems. Predicting this ratio allows to check if AmBC could co-exist with active communication by examining the interference at the legacy receiver (LR).
This paper presents an intermodulation sensor that can backscatter the third and fifth order intermodulation products and modulate each component by the rotational speed of the transponder. This sensor can be used to achieve accurate measurement and remote monitoring of the rotational speed of an object, even if other objects are rotating at different speeds in the vicinity of the sensor. This sensor can also be identified using the variation of the modulated power backscattered as a function of the frequency. This identification scheme is independent of the rotational speed of the sensor and provides a robust way to identify the sensor in a real environment compared to conventional motion-modulated sensors.
The automotive industry is undergoing a massive transformation, moving towards electrification, software-defined vehicles (SDVs) and vehicle connectivity. These new challenges indirectly impact transformation in cybersecurity, where the increase in remote access enables the risks of attacks, data leaks and system manipulation. These risks can significantly impact safety, particularly in critical systems such as the Battery Management System (BMS). The BMS plays a crucial role in vehicle functionality, performance, and safety, as well as its numerous connections to external systems. Therefore, the cybersecurity evaluation and protection of such safety-critical systems are crucial, especially when such systems rely on wireless technology. This paper presents a new BMS system prototype based on UHF RFID tags aimed at reducing complex wiring, increasing maintainability and improving battery cell monitoring. It assesses the cybersecurity risks by identifying the vulnerabilities and potential threats associated with the passive UHF RFID tags on a BMS System. Finally, it concludes with a proposal of relevant mitigation strategies for the identified risks.
Cu-sheet-based reader and tag antenna designs are proposed in this work, which are implemented for 2.45 GHz RFID applications. The proposed reader antenna design is based on circular and square slots to achieve circularly polarized waves, whereas the tag antenna consists of a meander line structure. The proposed reader antenna achieves a wide impedance matching at 2.45 GHz. The measured impedance bandwidth for S-11<-10 dB is from 2.42 to 2.55 GHz (0.13 GHz), and the axial-ratio (AR) bandwidth for AR < 3 dB is from 2.43 to 2.52 GHz. Also, the tag antenna provides an impedance bandwidth from 2.33 to 2.61 GHz. The peak gain at 2.45 GHz for reader and tag antenna is 9.12 dB and 2.35 dB, respectively. The proposed antennas are inexpensive and easily fabricated with almost no dielectric loss. The variations in S-11 and gain of the proposed tag antenna are studied for various textiles. At last, an Amplitude Shifting Keying signal is transmitted and received using these antennas employing the software-defined radios, so both antennas are suitable for compact RFID devices.
This paper presents a comprehensive electromagnetic characterization of an RFID tag antenna when placed in proximity to metallic environments. The study investigates how key geometrical parameters mainly the tag-tometal gap, metal thickness and the overall size of the metallic structure are able to affect critical antenna performance metrics such as resonant frequency ($f_{r}$), bandwidth ($B W$), gain and radiation efficiency ($R E$). A printed dipole RFID tag antenna, optimized for UHF operation at 915 MHz, is modeled and analyzed using ANSYS-HFSS. Through a systematic parametric study, the results reveal that the metal structure is highly affecting the RFID tag antenna characteristics and that taking into account this environment from the first design phase is crucial for optimal performance. These findings not only provide valuable insights into the reliable deployment of RFID systems in metallic environments but also pave the way for the integration of artificial intelligence (AI) models to forecast the impact of metallic surroundings and predict best spatial alignment of the antenna. This predictive capability would greatly enhance the design process and enable optimized tag placement strategies in real-life RFID applications.
This study explores the effects of electromagnetic coupling on the reverse link of an RFID system in terms of differential radar cross section. To model high-density tag environments, RFID tags are represented by loaded dipoles, providing a more robust model to analyse the backscattering behaviour of tags. The investigation considers mutual coupling, as well as the influence of tag position and orientation, by comparing isolated and coupled antennas.
This paper introduces a novel passive and wireless motion sensor that integrates a flexible piezoelectric substrate with a harmonic radar transponder to enable both motion and pressure sensing. A prototype circuit was developed to validate the concept, utilizing the voltage generated by the piezoelectric sensor to bias a diode. Transmission and reception experiments were carried out using a signal generator and a spectrum analyzer. The piezoelectric sensor was then integrated with the harmonic transponder, enabling the wireless transmission of motion frequency and pressure magnitude data. Experimental results demonstrated that when a 50 kg individual performed repetitive heel movements, the transmitted signal exhibited sidebands with an amplitude increase of approximately 20 dB and frequency shifts ranging from 1 Hz to 5 Hz. These findings confirm the feasibility of a fully passive, flexible, wireless sensor capable of detecting both motion and pressure, marking significant progress in the development of advanced sensing technologies.
This paper presents the evaluation of the conversion loss (CL) of a novel self-resonant dual-band differentially fed dual quarter-wave harmonic transponder antenna of dimensions 81x10.7x0.76 mm(3) loaded by a Schottky diode HSMS 2820 operating at frequencies f(0) = 1 GHz and 2f(0) = 2 GHz. We explain the setting up of the antenna operating modes to achieve self-resonant behavior, which provides an input impedance complex conjugate to the diode impedance without the need for external matching elements. The CL of the diode is calculated from the measured power balance, which includes the radiation efficiency of the antenna and the transmission coefficient between the antenna and the diode impedance. The result is compared with the analytical value of the diode CL.
This work presents a numerical analysis concerning a mobile robot trajectory reconstruction method based on Synthetic Aperture Localization with passive UHF-RFID technology and sensor fusion. A mobile robot is equipped with RFID tags and rotary encoders on wheels. A moving antenna, installed at the room ceiling, generates a synthetic aperture that can be exploited to estimate the most probable robot trajectory through phasors conjugate matching between the measured phase data and trajectory models built through odometry data. A simulated analysis details the potential of the proposed method.
In this work, a label-assignment and tracking system combining LiDAR and UHF-RFID systems to monitor workers and other obstacles positions in construction sites is presented with the aim of achieving a smart, reliable and efficient safety system. The proposed algorithm identifies clusters from 2D LiDAR cloud point maps and associates them with RFID tags identifier attached to targets by cross-correlating phase data with the cluster motion. The herein presented system is validated in an indoor environment.
The tunnel diode is a mature device that has recently received new attention for low-powered electronics due to its extraordinarily low zero-bias responsivity. One of the practical challenges with using these discrete devices is measuring the current-voltage (I-V) behavior due to selfoscillation. Although this oscillation may be damped through manual tuning at various biases, the tunnel diode I-V data is typically incomplete or poorly sampled. In this work, we discuss the nuances of picoammeters and testing tunnel diodes. Furthermore, measured data from a commercially available tunnel diode is presented with two methods to automatically create a SPICE model for the device when I-V data is incomplete.
This communication presents the design and comprehensive evaluation of an RFID reader antenna tailored for UHF applications (868-915 MHz). The proposed design incorporates a metallic rectangular cavity, two arc-shaped planar feeding elements, and an annular slot extruded on the upper surface of the cavity. By combining these elements, the antenna achieves an operational bandwidth of 11.4% and a directivity of 8.13 dBi at 868 MHz and 8.49 dBi at 915 MHz. Moreover, the antenna consistently maintains an axial ratio below 1.6 dB at both frequencies, ensuring excellent circular polarization performance. The radiation pattern's -3 dB beamwidth exceeds 71 degrees, which provides a wide coverage area suitable for complex communication environments. These performance characteristics demonstrate that the proposed antenna design is highly effective for enhancing the reliability and efficiency of RFID systems in various industrial and logistics applications.
EDA tools are required by analog and RF designers to assist the circuit sizing stage, thereby reducing work effort and time to market. Several optimisation-based tools have been proposed in the literature since the 1980s, and their use has presented important improvements due to efficient design space exploration. However, these tools often require extended knowledge about the tool's algorithm implementation, making them hard to use for IC designers. Precisely controlling their configuration is mandatory for good design flow tuning. As a result, these tools are not well-received by designers. In this way, this work proposes a Python-based optimization tool that presents an Easy-to-Use user interface, integrated with a widely available commercial EDA. With a simplified three-step setup, the proposed tool can be configured in less than 2 minutes. The proposed tool is presented and applied to the design of a 915 MHz RF to DC converter implemented in a CMOS 65 nm process. Different design optimisation scenarios illustrate the flexibility of the tool to requirements.
This paper presents a novel smart contact lens (sCL) for wireless ocular monitoring, fabricated using Laser-Induced Graphene (LIG) directly patterned on a polyether ether ketone (PEEK) substrate. The antenna, designed as a planar loop structure, is integrated with an EM4152 RFID microchip and a tuning inductor, forming a fully passive ultra-high frequency (UHF) system. The device was tested on a porcine eye phantom, which mimics the anatomy and dielectric properties of the human eye. Electromagnetic simulations guided the antenna design to balance miniaturization constraints with radiation performance. Experimental results demonstrate that the 6 mm diameter loop performs stable communication at a distance of nearly 2 cm, achieving a measured realized gain of -37 dB at 915 MHz. These findings validate the feasibility of LIG-based RFID sCLs for non-invasive, real-time eye health monitoring using a compact handheld reader.
This article investigates the details of Long-Term Evolution ambient backscattering communication from the backscattering device (BD) antenna perspective. In our scenario, the tag exhibits two different modes of operation for the uplink frequency band (idle) and downlink frequency band (backscattering). We show that in backscattering mode the BD does not need to be matched to the antenna impedance alleviating the efforts in antenna design compared to other frequency-agile antenna systems. A miniature antenna is designed seeking to optimize its radiation efficiency.
