A new class of Radio Frequency IDentification (RFID) tags, namely the three-dimensional (3D)-printed chipless RFID one, is proposed, and their performance is assessed. These tags can be realized by low-cost materials, inexpensive manufacturing processes and can be mounted on metallic surfaces. The tag consists of a solid dielectric cylinder, which externally appears as homogeneous. However, the information is hidden in the inner structure of the object, where voids are created to encrypt information in the object. The proposed chipless tag represents a promising solution for anti-counterfeiting or security applications, since it avoids an unwanted eavesdropping during the reading process or information retrieval from a visual inspection that may affect other chipless systems. The adopted data-encoding algorithm does not rely on On–Off or amplitude schemes that are commonly adopted in the chipless RFID implementations but it is based on the maximization of available states or the maximization of non-overlapping regions of uncertainty. The performance of such class of chipless RFID tags are finally assessed by measurements on real prototypes.

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The scattering and diffraction of a 3D Complex-Source Beam (CSB) by a wedge made from a perfect electric

conductor (PEC) is analyzed in this paper. The analytic solution is based on the corresponding scalar (acoustic) fields

where both soft and hard boundary conditions have to be considered at the wedge faces. In particular, a new spherical-

multipole solution is presented for an incident uniform CSB which consists of both diverging and converging parts. First

numerical results include the scattering and diffraction of a scalar 3D uniform CSB by both acoustically soft and hard

wedges.

An extension of the Uniform Geometrical Theory of Diffraction (UTD) is proposed to analyze three-dimensional electromagnetic Complex-Source Beam (CSB) diffraction by a perfectly electrically conducting (PEC) wedge. The corresponding two-dimensional case has been already analyzed by the same authors in [1]. Again, the solution is derived in the framework of high-frequency ray methods and is written in terms of incident, reflected and diffracted contributions, so that it can be directly applied to calculate the scattering from more complex geometries with edges. It is worth noting that the three-dimensional electromagnetic scattering from a PEC wedge illuminated by evanescent waves has been already analyzed in [2], when the incident field is associated with an inhomogeneous plane wave. The proposed UTD solution is obtained by introducing higher-order terms in the asymptotic evaluation of the diffracted field. This also guarantees an improved accuracy when the observation point lies close to the diffracting edge. In particular, the accuracy of the solution is demonstrated through extensive comparisons with a rigorous solution obtained by a multipole expansion of the scattered field. In this regard, a new rigorous solution has been recently presented for 3D scattering by a wedge illuminated by a uniform CSB, which consists of both a diverging and converging part and which is analytic everywhere [3]. A simple UTD type solution can be obtained by a direct analytic continuation of the corresponding UTD formulation for sources in real space [4], by allowing angles and distances to assume complex values. It is observed that the proper discontinuities in the diffracted field are provided by the standard UTD transition functions, when they are extended to complex arguments. These discontinuities exactly compensate for those exhibited by the incident and reflected field, when crossing the incident and reflection shadow boundary, respectively. Relevant issues in the proposed solution consist in the interpretation of the involved physical phenomena in real space. These latter aspects constitute important objectives of the paper.

]]>Low cost wireless sensors are extremely appealing in pervasive sensors networks [1], [2]. The typical

configuration of commercial sensors consists of an electronic circuit in which a component induces a certain

variation of an observable quantity (frequency shift, phase delay) as a result of the interaction with an external

variable entity such as humidity, temperature, gas concentration. The sensing phenomenon is frequently observed

at low frequencies or in DC and sensors are usually wired and are interrogated by a direct access to the circuit.

Wireless sensors are usually designed by attaching a transceiver module to the sensor. These sensors are versatile

since, in their last releases, they can communicate up to 200 meters and can interface with smartphones [3]. The

main limitations are the finite lifetime of the battery and the cost that, although modest, is not lower than 20-30

USD.

Another class of sensors cheaper than abovementioned ones is emerging on the market: the RFID- based sensors.

The advantage of RFID-based sensors is the absence of any battery, which can be a huge benefit in terms of

maintenance and cost. RFID sensors are based on an RFID tag loaded with an additional circuit where the sensing

component is installed [2].

The most challenging approach to sense the environment wirelessly is to use an entirely passive device without

the aid of an electronic circuit. In this case the information is embedded in the electromagnetic footprint of a

resonator and the sensing is carried out by detecting the changes of the electromagnetic response of the device.

Indeed, as every electromagnetic device, the radio frequency response of these tags is dependent on the electric or

magnetic changes of nearby substrates or particles and on the variation of external environment. If these variations

are opportunely controlled and isolated, an indirect measurement of several environmental quantities, or

mechanical changes, can be extracted from the measured backscattering spectrum [4], [5]. This category of sensors

takes the name of chipless RFID sensors [6], [7] or metamaterial sensors [8], [9] This technology could be very

appealing for designing very low cost, green and embedded sensors. The absence of a chip and a battery gives the

opportunity to dramatically decrease the cost of the sensor and to achieve infinite lifetime. Given the absence of

any electronic circuit, chipless RFID sensors are potentially suitable for hazardous environments [4], [6], [10].

Clearly, one of the main limitations is that the reliable reading of the sensor can be achieved under specific

conditions. The interesting aspects of this sensors is that they can be directly printed on paper by using inkjet

printing technology and this fact makes them a promising solution for low-cost sensors. This paper aims to present

some novel low-cost inkjet-printed sensors.

This work summarizes the main outcomes of the EMERGENT project that was mainly focused on the design of chipless RFID sensors and their realization on green substrates. Three different sensors are presented for monitoring humidity, temperature and breathing.

Keywords: {Chipless RFID, chipless RFID sensor, frequency, selective surface, radar cross section}

]]>A method for detecting radio frequency chipless RFID tags is presented. The tags are interrogated through an open waveguide from a very short distance in order to realize a quasi-guided system which does not need any calibration procedure. The application scenario is to place the tag inside a plastic or cardboard box and read it by placing the waveguide on the external side of the box in the same position of the tag. The tag is designed to be commensurate with the waveguide in order to guarantee the correct operativity of the quasi-guided reading system. A prototype of the tag has been fabricated and some measurements to assess positioning error have been carried out.

**Keywords:** {chipless sensors, periodic surface}

URSI EM Theory Symposium, EMTS 2019, San Diego, CA, 27 – 31 May 2019

A comparison between two different uniform asymptotic high-frequency procedures for the evaluation of a typical diffraction integral is presented in this paper. In particular, attention is focused on the specific case of evanescent wave diffraction from a straight wedge [1]. The two procedures are the Pauli-Clemmow (PC) method [2], [3] and the Van der Waerden (VW) method [4], [5]. As well known, the usual leading term of the PC method is not able to provide the proper discontinuity compensation when the poles cross the Steepest Descent Path (SDP) away from the saddle point. However, by considering all higher order terms in the PC asymptotic expansion of the diffraction integral [6], it is shown that each higher order term provides a contribution of order K −1/2 . By suitably collecting all these terms of order K −1/2 , a modified leading term of the PC method is obtained, which results in a compact expression consisting of the standard UTD multiplicative form [1], plus a UTD slope-like correction term [7]. It can be easily demonstrated that the above modified leading term of the PC method exactly coincides with the usual leading term of the VW method. Consequently, in all those cases where the usual leading term of the PC method fails to be uniform, the UTD slope-like correction can be added to obtain a uniform solution.

The modified leading term of the PC method shows an apparent advantage from a numerical point of view, consisting in the fact that its first term coincides with the standard UTD multiplicative form. Moreover, this form has shown to work surprising well in the case of diffraction of a Complex Source Beam by a straight wedge [8], in most case without any need for the UTD slope-like correction.

[1] T.B.A Senior and J.L. Volakis, Approximate Boundary Conditions in Electromagnetics, IEE Electromagnetic Waves Series, The Institution of Electrical Engineers, London, United Kingdom, 1995, pp. 332-336.

[2] P. C. Clemmow, “Some Extensions of the Method of Integration by Steepest Descent,” Quart. J. Mech. Appl. Math., vol. 3, Jan. 1950, pp. 241-256.

[3] P. C. Clemmow, The Plane Wave Spectrum Representation of Electromagnetic Fields, Piscataway, NJ, USA: IEEE Press, pp. 56-58.

[4] B. L. Van der Waerden, “On the Method of Saddle Points,” Appl. Sci. Res. B, vol. 2, no. 1, 1952, pp. 33-45.

[5]. L.B. Felsen and N. Marcuvitz, Radiation and Scattering of Waves, Englewood Cliffs, NJ, USA: Prentice-Hall, 1973.

[6] C. Gennarelli and L. Palumbo, “A Uniform Asymptotic Expansion of a Typical Diffraction Integral with Many Coalescing Single Pole Singularities and a First Order Saddle Point,” IEEE Trans. Antennas Propag., vol. AP-32, no. 10, Oct. 1984, pp. 1122-1124.

[7] R. G: Kouyoumjian, G. Manara, P. Nepa, and B. J. E. Taute, “The Diffraction of an Inhomogeneous Plane Wave by a Wedge,” Radio Science, vol. 31, no. 6, Nov./Dec. 1996, pp. 1387-1397.

[8] H.-T. Chou, P. H. Pathak, Y. Kim, and G. Manara, “On Two Alternative Uniformly Asymptotic Procedures for Analyzing the High-Frequency Diffraction of a Complex Source Beam by a Straight Wedge,” IEEE Trans. Antennas Propag., vol. AP-66, no. 7, July 2018, pp. 3631-3641.

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URSI AP-RASC 2019, New Delhi, India, 09 - 15 March 2019

A Uniform Geometrical Theory of Diffraction (UTD) solution for inhomogeneous plane wave diffraction by a Perfect Electrically Conducting (PEC) wedge has been presented in [1]. More recently, this solution has been extended to analyze the case of an incident field radiated by a source located in the complex space (Complex Source Beam, CSB) [2], [3]. This solution has shown to be very accurate when compared with reference data obtained by a rigorous multipole expansion of the field. The purpose of this communication is to further investigate some interesting properties of the extended UTD solution, opening the way to a better understanding of the physical phenomena connected to an evanescent behavior of the waves impinging on the edge. In the context of high-frequency techniques, the UTD solution for CSB diffraction in [2] has been written in a simple and compact form which includes the incident, the reflected and the diffracted ray contributions, so that it can be directly applied to calculate the scattering from more complex geometries with edges [4], [5]. Here, the analysis is oriented to gain a better understanding of the mechanism which controls discontinuity compensations at shadow and reflection boundaries. Also, attention is focused on the identification of shadow and reflection boundaries, as well as in determining both the shape and the extension of the pertinent transition regions. All these investigations are verified through comparisons with a rigorous multipole expansion solution.

1. R.G. Kouyoumjian, G. Manara, P. Nepa, and B.J.E. Taute, “The diffraction of an inhomogeneous plane wave by a wedge,” Radio Science, vol. 31, Nov./Dec. 1996, pp. 1387-1397.

2. S. Terranova, G. Manara, L. Klinkenbusch, A Physical Insight into Complex-Source Beam Diffraction by a Wedge,” 2nd URSI Atlantic Meeting, May 28 – June 1st, 2018, Gran Canaria, Spain.

3. L. B. Felsen, “Complex source-point solutions of the field equations and their relation to the propagation and scattering of Gaussian beams,” in Symposia Matematica, Istituto Nazionale di Alta Matematica, London, U. K., Academic, 1976, Vol. XVIII, pp. 40 – 56.

4. M. Katsav, E. Heyman, and L. Klinkenbusch, “Beam diffraction by a wedge: exact and complex ray solutions,” IEEE Transactions on Antennas and Propagation, Vol. 62, No. 7, pp. 3731 – 3740, July 2014.

5. H.-T. Chou, P. H. Pathak, Y. Kim, and G. Manara, “On Two Alternative Uniformly Asymptotic Procedures for Analyzing the High-Frequency Diffraction of a Complex Source Beam by a Stright Edge,” IEEE Transactions on Antennas and Propagation, Vol. 66, No. 7, pp. 3631-3642, July 2018.

]]>https://www.mdpi.com/2079-9292/8/1/35

Published in MDPI Electronics as part of the Special Issue RFID, WPT and Energy Harvesting

In this paper, a low-cost chipless reader for detecting depolarizing tags is described. The reader operates in the frequency band (2–2.5) GHz, and it is compact and integrated in a single board. The reader architecture and its transmitting and receiving antennas are presented. Reader antennas comprise of two orthogonally placed, E-shaped patches with a decoupling below −35 dB. The reader performance is evaluated on a four-bit tag formed by four obliquely placed dipoles on top of a metallic ground plane.

]]>Chipless sensors are entirely passive devices whose electromagnetic signature is intelligible in time or frequency domain. The variations of the electromagnetic response of these devices can be used to sense environmental parameters at a very limited cost and with a minimum environmental impact. The most relevant configurations for designing environmental sensors are described and the main benefits and drawbacks of this technology are discussed.

**Keywords:** {Chipless RFID; Humidity sensors; RFID; Sensors}

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