Abstract-UHF passive Radio Frequency Identification technology is rapidly evolving from simple labeling to wireless pervasive sensing. A remarkable number of scientific papers demonstrate that objects could be in principle remotely tracked and monitored in their physical properties all along their daylife. The key background is a new paradigm of antenna design that merges together the conventional communication issues with more specific requirements about sensitivity to time-varying boundary conditions. This paper proposes a unified introdution to the tag-as-sensor problem with particular care to formalize the measurement indicators and the communication and sensing trade-off, with the purpose to understand and classify the state of the art and definitley provide a knowledge base to face a large variety of emerging applications.

All mechanical structures are subject 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. The present work hence shows a crack width wireless radio frequency identification (RFID) sensor, developed for applications on various materials (such as concrete and metal) and able to detect sub-millimeter deformations occurring on the object on which it is placed. A design method based on high sensitivity phase detection is shown.

Abstract-Low-cost wireless measurement of objects' temperature is one of the greatest expectation of radiofrequency identification technology for the so many applications in cold supplychain control and safety assessment in general. In this context, the paper proposes a dual-chip UHF tag embedding shape memory alloys (SMA) able to transform the variation of the tagged item's temperature into a permanent change of antenna radiation features. This event-driven antenna is hence able to selectively activate the embedded microchips according to the temperature above or below a given threshold. A general design methodology for the resulting two-ports tag antenna is here introduced and then applied to prototypes able to work at low (around 0 C) and high (80 C) temperatures.Index Terms-Radiofrequency Identification (RFID), shape memory alloy, temperature sensor.

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 crack's 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 sensor's 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.

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.

This paper discusses the design and manufacturing of a miniaturized 2x2 stacked patch antenna array, operating at E5a and E1 Galileo bands (i.e. respectively at central frequencies of 1176 and 1575 MHz), for robust navigation applications. The 2x2 array configuration has a total dimension of 100 mm x 100 mm, hence enabling its use in mobile applications. Due to the tight placement of nearby elements, mutual coupling problems arise. The reduction of the electromagnetic interaction among the elements is pursued by means of a metallic fence.

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Current standardization activities in the aeronautical community are paving the way to using multifrequency multiconstellation GNSS as a primary means of aircraft navigation. The increase in the number of satellites from different constellations as well as the increasing use of multiple frequency GNSS receivers promise improvements in the achievable accuracy in GNSS positioning. The effects of receiver antennas shall be investigated because of the stronger impact of possible imperfections on the overall error budget for multifrequency combinations. The scope of this paper is to show the possibility of properly modeling and indeed characterizing the antenna-induced GNSS pseudorange errors, through simulations and electromagnetic measurement. An insight into antenna characteristics giving rise to such errors will be given, by analyzing the impact of the feeding technique on the achievable pattern uniformity and hence on antenna-related pseudorange errors. The technique is then validated through GNSS field measurement.