Reza Rezaiesarlak

Complex-Natural-Resonance-Based Design of Chipless RFID Tag for High-Density Data

Each scatterer responds to the incident wave in a unique manner. The backscattered signal from the scatterer is affected by two distinct phenomena: early-time response which emanates from the scattering centers of the scatterer and late-time response which is the summation of the complex natural resonances (CNRs) with some weighting residues. Based on the singularity expansion method (SEM), CNRs are aspect-independent parameters which include some structural information of the scattering target. Based on this fact, the data can be embedded on the RFID tag as CNRs associated to the structural parameters. In this paper, a low-profile chipless RFID tag as a suitable device for high-density data is introduced. By incorporating several slots on the chipless RFID tag, the data can be encoded as CNRs on the structure. The designed RFID tag operates in the frequency band of 3.1-10.6 GHz. The data are decoded in the reader by applying short-time matrix pencil method (STMPM) to the transient backscattered response of the tag. In addition, the turn-on times, damping factors, and resonant frequencies of the poles are distinguished. After studying the effects of various parameters of the tag, a 24-bit tag is designed on the area of 24 × 24 mm2, simulated and measured. The measurement is performed in the frequency domain and, after applying inverse fast Fourier transform (IFFT), STMPM is employed to extract the signature of the tag. The tag is successfully read remotely via its scattered fields.

Short-Time Matrix Pencil Method for Chipless RFID Detection Applications

In this paper, the concept of short-time matrix pencil method (STMPM) is introduced and experimentally demonstrated as an efficient approach to extract a set of embedded poles in a chipless RFID. Here, by incorporating a few notches on the elliptical dipole antenna as a chipless RFID, the data is encoded as complex natural resonant frequencies of the structure. In this new detection approach, a sliding time window is introduced and the matrix pencil method (MPM) is applied to extract embedded poles and residues from the sliding time-window at each snapshot of time. The resulting complex poles and residues have a time index which allows us to process them as a set of time-frequency data. This time-frequency analysis enables us to discriminate late-time from early-time. Furthermore, averaging complex poles over the time increases the accuracy of the technique in a noisy environment. The measured data agrees well with our simulations and support the STMPM effectiveness in comparison to the MPM.

A Space–Time–Frequency Anticollision Algorithm for Identifying Chipless RFID Tags

In this paper, the short-time matrix pencil method (STMPM) is efficiently employed as a time-frequency analysis methodology for the identification of multiple chipless radio-frequency identification (RFID) tags presented in the main beam of the reader antenna. Each tag represents a unique ID in the backscattered signal. Here, the data are embedded on the tag as the complex natural resonances (CNRs) of the structure. In the cases where more than one tag exist in the main beam of the reader antenna, the frequency-domain response is not sufficient to successfully distinguish the IDs of the tags. By applying the STMPM technique to the time-domain response, the poles and their residues are obtained at each snapshot of time. In order to obtain the exact values of the turn-on times of the poles, which are the roundtrip time of the tags to the antenna, high resolution in the time domain is needed which deteriorates the resolution in the frequency domain. Using mathematical descriptions, a simple formulation is derived which exhibits a duality between late-time response in the time domain and early-time response in the frequency domain. Therefore, a space-frequency representation can be simply obtained from the application of the short-frequency matrix pencil method (SFMPM) to the frequency-domain response of the tags. By possessing the exact values of the turn-on times and pole/residues of the tags, their backscattered responses can be reconstructed and associated IDs can be retrieved. With the proposed method in this paper, some scenarios are studied and discussed. As an experimental result, three 3-bit tags with different IDs (ID1:101, ID2:111, and ID3:011) are fabricated and placed away from each other. Exploiting the presented technique, the IDs of the tags and their locations are successfully distinguished. The simulation results are validated by the measured ones. The ranging error obtained by the proposed method is less than 1 cm.

Design of Chipless RFID Tags Based on Characteristic Mode Theory (CMT)

The induced currents and consequently the scattered fields from chipless RFID tags can be analyzed in different ways. In singularity expansion method (SEM), the currents on the tag are expanded by a series of the complex natural resonances (CNRs) and frequency-independent natural currents and an entire-domain function including the early-time response. On the other hand, in eigen-mode expansion method (EEM), the currents are expanded versus the frequency-dependent eigen-modes of the structure, which can be obtained by solving the homogeneous differential equation governing the structure under consideration. In this paper, the theory of characteristic modes as a generalized eigen-mode expansion approach is efficiently employed for the analysis and design of the chipless RFID tags. Three important parameters usually considered in the design of multibit tags are the quality factors, resonant frequencies of the resonators (as a signature of the tag) and the radar cross-section (RCS) of the tag. A slotted-wavelength resonator is considered as a tag prototype in this paper. After a short theoretical description of SEM and CMT, the resonant and radiation modes of the tag are accurately investigated versus some design parameters. By studying the effects of various structural parameters of the tag on the aforementioned factors, some design rules are extracted which can be useful in the design and implementation of the tag and additionally the identification process.

A Space-Frequency Technique for Chipless RFID Tag Localization

In this paper, a new technique is proposed for the accurate localization of chipless RFID tags presented in the reader area. The reader area is subdivided into some triangular unit cells. Each unit cell is covered by three antennas located at the vertices of the triangle in order to extract the positions of the tags. Assuming the reader area as the scatterer medium, the tags act as the scattering centers of the medium. Employing some mathematical description, it is shown that by applying the narrow-frequency matrix pencil method (NFMPM) to the frequency response of the tag, the distance of the tag from the antennas can be found from a space-frequency diagram. Having three distances and coordinates of the antennas, the position of the tag can be obtained easily by triangulation technique. Different scenarios are simulated and validated with the measured results. The measured range and angle errors achieved based on the proposed approach are less than 1.5 cm and 2.6 ° for a tag with area of 15 × 25 mm2.

Miniaturized Low-Cost Phased-Array Antenna Using SIW Slot Elements

In this letter, a miniaturized C-band phased-array antenna based on a novel series-fed network is introduced. The series-fed network, radiating elements, and phase shifters are the main parts of the proposed phased-array antenna. In order to use the identical phase shifters, quarter-wavelength transformers are used in the design of the series-fed network. Furthermore, by choosing the proper place of the quarter-wavelength transformers, the distance between adjacent radiating elements is significantly reduced to 0.33λ0. To reduce mutual couplings between radiating elements, miniaturized negative-order substrate integrated waveguide (SIW) slot antennas are chosen as radiating elements. A low-cost and compact 4-bit composite right/left-handed (CRLH) phase shifter is used due to the capability of being placed in a series-fed network. The proposed low-cost phased-array antenna is fabricated on a single-layer printed circuit board (PCB), and good agreement between the simulation and measurement results is obtained. The beam scanning range is 38°, and the impedance bandwidth of the phased-array antenna is 25 MHz at the center frequency of 5 GHz.

On the Application of Short-Time Matrix Pencil Method for Wideband Scattering From Resonant Structures

A time-frequency technique called short-time matrix pencil method (STMPM) is efficiently employed to analyze wideband scattering from resonant structures. After investigating various parameters of the technique such as time-window length and filtering parameter, some scenarios are studied. First, the proposed technique is applied to the backscattered response from two dipoles spaced 20 cm from each other. The dominantly excited resonances and scattering centers are successfully derived from the time-frequency diagram. Finally, the proposed technique is applied to the time-domain backscattered response from an open-ended circular cavity. Different scattering mechanisms such as resonant, scattering center, and dispersion are studied in the time-frequency diagram of the response. The results are compared with those of the short-time Fourier transform (STFT) and reassigned joint time-frequency (RJTF) techniques. Good resolution in time and frequency domains and its capability of finding low-energy excited poles of the scatterer are the major features of the proposed technique. By utilizing the proposed technique, the damping factor or equivalently the quality factor of the resonances are straightforwardly obtained, which can be useful in the study of resonant-based scatterers.

A new anti-collision algorithm for identifying chipless RFID tags

A new methodology, based on short-time-matrix-pencil-method (STMPM) is proposed for separating IDs of multiple chipless RFID tags presented in the main beam of the reader antenna. In this approach, turn-on times of the complex natural resonances (CNRs) of the tags are employed as the roundtrip times of the tags from the antenna and by marking the tags with some specific resonances in addition to ID poles, the interfering poles from background objects and antennas in the reader zone are distinguished from the tag poles.

Accurate Extraction of Early-/Late-Time Responses Using Short-Time Matrix Pencil Method for Transient Analysis of Scatterers

We present a new efficient technique for accurately distinguishing the early-time and late-time modes of the transient response from multiscatterer targets. In multiple resonant-based scatterers where the complex natural resonances (CNRs) are used as the ID of the target, the early-time response of the second scatterer might overlap with the late-time of the first, introducing some difficulties in the detection of the second scatterer and additionally, identification of the first one. In such circumstances, the separation of the late-time CNRs (ID of the scatterer) from the early-time poles (scattering centers) is challenging. The smaller the distance between two scatterers, the more difficult the detection process is. Here, by sliding a window along the time axis and applying short-time matrix pencil method (STMPM), the poles corresponding to the early-time and late-time responses are distinguished. It will be shown that when the early-time response is located at the center of the sliding window, its CNRs are located on the imaginary axis of the pole diagram. By monitoring the zero-crossing points in time damping-factor diagram, the locations of the early-time responses (or equivalently scattering centers) can be detected. Some scenarios are discussed, simulated, and confirmed by measurement results to show the effectiveness of the proposed technique in practical applications.

On the application of characteristic modes for the design of chipless RFID tags

In chipless RFID tags, the structure functions both as a scatterer and an encoder in response to the incident wave. The embedded resonances on the tag incorporate the ID of the tag and its RCS determine the read-range of the tag. In this paper, the theory of characteristic modes is employed to study the resonant and radiation modes of chipless RFID tags. By studying the effects of various parameters on the characteristic modes, some hints are proposed to improve the characteristics of chipless RFID tags for high density applications.