Stefano Caizzone

RFID Grids: Part II—Experimentations

The RFID Grid is a model for generally coupled multitudes of tags including single-chip tags in close mutual proximity or a single tag with a plurality of embedded microchips. Some properties of this new entity, useful for passive Sensing and for Security, are the possibility to increase the read-range and to provide responses rather insensitive to the interrogation modalities. These recently introduced issues are here experimented for the first time with many real-world examples comprising multi-chip configurations designed for improved power scavenging and for passive sensing of things.

Wireless Crack Monitoring by Stationary Phase Measurements from Coupled RFID Tags

The possibility to wirelessly monitor the state and the evolution of cracks is of increasing interest in emerging structural health monitoring systems. A simple and effective measurement method considers the placement of two passive radio frequency identification (RFID) antennas on top of the crack, so that the cracks evolution will produce a change of the inter-antenna coupling and in turn of the phase of the backscattered field. An ad-hoc design technique, based onto the coupled-modes physics, permits to maximize the sensors sensitivity avoiding, or at least mitigating, the read range reduction during the evolution of the displacement that is instead typical of amplitude-oriented RFID displacement sensors. The proposed idea is demonstrated by numerical and experimental examples showing the possibility of sub-millimeter resolution with low-cost devices.

Wireless Passive RFID Crack Width Sensor for Structural Health Monitoring

All mechanical structures are subjected to deformation and cracks, due to fatigue, stress, and/or environmental factors. It is, therefore, of uttermost importance to monitor the mechanical condition of critical structures, in order to prevent catastrophic failures, but also to minimize maintenance costs, i.e., avoid unnecessary inspections. A number of technologies and systems can be used for this purpose: among them, the ones proposing the use of wireless passive crackmeters have a strong impact potential, in terms of simplicity of installation and measurement and low cost. This paper, hence, shows a crack width wireless radio-frequency identification sensor, developed for applications on various materials (such as concrete and metal) and able to detect submillimeter deformations occurring on the object, on which it is placed. A design method based on high-sensitivity phase detection is shown.

Compact planar L-band antenna arrays with optimal diversity performance

At L-band (1-2GHz) due to significantly large free-space wavelengths, compact antenna arrays with small inter-element separation i.e., d < λ/2, are a suitable choice for overall size reduction. However, mutual coupling becoming prominent in compact arrays results in a degradation of the diversity degrees-of-freedom, which are required for beamforming capabilities in modern receivers. In this paper we discuss a potential approach to mitigate this limitation. We present empirical results for an eigenmode analysis applied to the radiation matrices of compact planar arrays, derived from the far-field integration of complex realised-gain matrices. Furthermore, optimal arrangements for compact planar arrays with respect to the highest possible value of minimum eigenmode efficiency are discussed. It could be shown that planar arrays have higher efficiencies and lower radiation correlation, hence better diversity degrees-of-freedom than linear arrays, particularly in a compact configuration.

Constrained Pole-Zero Synthesis of Phase-Oriented RFID Sensor Antennas

Passive sensing by means of radiofrequency identification has been extensively explored for various applications, such as gas detection, temperature change, and deformation. The sensing indicator is generally based on the amplitude and phase of the backscattered field. However, a degradation of the communication performance must be usually accepted for achieving the sensing capability. This work introduces a design method suitable for phase-based RFID sensors that permits to shape the phase response while preserving the impedance matching between the antenna and the microchip. The RFID sensor is modeled as a two-ports scatterer comprising a lumped sensor at one of the ports and an RFID chip at the other port. A pole-zero representation of the electromagnetic interaction between the reader and the RFID sensor allows to introduce a constrained design of the antenna with a full control on the sensor dynamic range and on the communication performance. The proposed method is numerically and experimentally validated by means of a pair of strongly coupled dipoles connected to a voltage-controlled varactor emulating a dynamic sensor response.

Feasibility of wireless temperature sensing by passive UHF-RFID tags in ground satellite test beds

Satellite ground testing is nowadays suffering from long and complicated measurement procedures, where cabled sensors are involved: as such, it could strongly benefit from wireless sensing capabilities, enabling simplified measurement setup procedures and substantial cost reduction. Passive RFID wireless sensors are improving in maturity and robustness for Earth use and could be optimal candidates also for Space-related applications. The present work shows a first attempt to evaluate the performance of newly developed temperature-monitoring RFID sensor tags for satellite ground testing, both from a sensor point of view and from a EMC/EMI perspective.

Miniaturized Dielectric Resonator Antenna Array for GNSS Applications

The increase in global navigation satellite systems (GNSS) availability and services is fostering a new wave of applications related to satellite navigation. Such increase is also followed by more and more threats, aiming at signal disruption. In order to fully exploit the potentialities of precise and reliable navigation, being able at the same time to counteract threats such as interference, jamming, and spoofing, smart antenna systems are being investigated worldwide, with the requirements of multiband operation and compactness. In order to answer such need, the present work proposes a miniaturized dielectric resonator antenna (DRA) 2 × 2 array able to operate at E5/L5, L2, and E6 bands, with an overall footprint of only 3.5′′ (89 mm).

A multi-band conformai antenna array for GNSS applications

The position accuracy in satellite navigation is enhanced when low elevation satellites are included in the triangulation due to the contribution of satellite geometry. Moreover, improved reception of low elevation signals leads to a higher overall system availability. However, the receiving antenna characteristics usually suffer from low-gain and high axial ratios at low elevations. In this contribution, an antenna array conformal to a spherical cap is presented. The array consists of a single antenna on top of the cap and six, radially directed, equally spaced elements on a ring. The manufactured antenna achieves a gain between 0 dB and 4 dB with low axial ratio in the forward hemisphere at the E5a/b and E1 center frequencies of 1.176 GHz, 1.207 GHz and 1.575 GHz, respectively.

Investigation of suitable parameters for setup-independent RFID sensing

RFID systems are growing in use also for sensing purposes. In the last years, there has been quite a lot of effort in identifying RFID parameters most suited to sensing and at the same time wirelessly recordable: there are however still some open issues to solve. The use of wirelessly recordable parameters being independent from the measurement setup is surely one of the most interesting open questions and promises, if solved, significant improvements to the state of the art of RFID sensing. This work shows hence two such parameters and analyzes their performance in terms of setup independence.

Compact GNSS antenna with circular polarization and low axial ratio

The investigation and development of a compact antenna for GNSS high-performance applications over a high-DK substrate are presented. In order to reduce multipath and achieve best performances, a very good polarization purity over a possibly wide bandwidth is needed. Therefore, a substrate which has both high DK and high thickness is used. However, because of the use of such substrate, the performance of the antenna may severely degrade when the total footprint (i.e. substrate and ground plane dimensions) change or when the antenna is used in array configurations. The reason for that are mainly waves excited into the substrate itself, producing spurious radiation and a high coupling between adjacent antennas. To overcome this drawback, a soft/hard surface (SHS) is employed, resulting in an antenna which has lower coupling with adjacent elements, as well as a relatively broad axial-ratio bandwidth.