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This effort presents an analysis of a system intended for wireless crack sensing and based on zero-power harmonic transponders. The sensors, which are fabricated by using a paper substrate, are suitable for both structural health and supply-chain monitoring. In the text, different techniques to recover information from the proposed tags are firstly explored, with a particular focus on the potentialities and trade-offs of each approach. Then, the impact of the presence of multiple-nodes on the performance of the system is considered and, finally, some proposals for crack localization in presence of multiple tags are explored and experimentally evaluated.

In this paper the experimental results of a compact low-power rectenna in paper substrate, designed to operate in the Wi-Fi band, are presented. The complete prototype, based on an annular slot antenna and a single-diode rectifier, features a weight of 1.5 grams and shows an RF-to-dc conversion efficiency in the design band of about 40 % for a -10 dBm available input power, of about 28 % at -15 dBm, and in the range [10, 22] % at -20 dBm, corresponding to an output DC voltage in the order of 320, 240 and 60 mV respectively. Additionally, the rectenna features an efficiency higher then 7 % in the whole band 1.8-2.7 dBm for a power density estimated around 3 μW/cm2.

This paper presents the design of a novel rectenna based on a tapered annular slot and a single-diode rectifier, optimized to operate in the Wi-Fi band and in presence of low input power (Pavs=-15 dBm). In order to obtain a compact layout a double-layer architecture has been considered, according to which the interior metal surface of the annular slot is employed as ground plane for the rectifying circuit placed on the other side of the substrate. As a result, a rectenna with an active area of only 40 × 33 mm2 and an efficiency included between 26.5 and 28% has been obtained. The antenna has been fabricated in paper substrate and tested in the anechoic chamber. Then, the rectifier has been designed and optimized within the Advanced Design System suite. Finally, the rectenna performance has been discussed and compared to the State of the Art (SoA).

This paper presents the design and implementation in paper substrate of a harmonic RFID chipless sensing tag. The proposed sensor is based on a Wheatstone bridge, where two of the four impedances change dynamically according to a physical parameter that has to be monitored. The passive tag is interrogated by a signal at f 0 = 1.04 GHz and the signal transmitted back to the reader at 2f 0 = 2.08 GHz is proportional to the magnitude of the parameter variation. A harmonic RFID experiment proves that this kind of architecture is capable of providing a dynamic range of more than 40 dB.

This work proposes a chipless radio frequency identification approach based on the working principle of the harmonic radar. A frequency multiplication stage is performed by a non-linearity (i.e. a Shottky diode) on the tag in order for the tag answer to be insulated from the interrogation signal, thus avoiding the need for clutter cancellation techniques. Firstly, the performance of a simple one-bit harmonic tag relying on a low-power frequency doubler is analyzed and then a novel crack sensor, implemented by adding a disposable band-stop filter, is presented. Both solutions demonstrate tag-to-reader operational distances beyond 1 m. The characterizing blocks (namely the frequency doubler and the filter) are fabricated on cellulose substrates (i.e. regular photographic paper), thus being conformal to their implementation for applications in the new paradigm of Internet of Things.