Farooq A. Tahir

3.56-bits/cm Compact Inkjet Printed and Application Specific Chipless RFID Tag

In this letter, a 28.5-bit chipless RFID tag, based on paper substrate and realized using inkjet printing technique is presented. Operating within ultrawideband, the tag occupies a compact size of 2 ×4 cm2. Focusing on applications requiring time and date identification, a novel encoding technique is presented that allows efficient frequency band allocation based on the number of required instances of time and date variables. A figure of merit (FOM) relating coding capacity and tag dimensions coined as code density is also introduced. A systematic design process followed by simulations and verified through measurements reveal a high code density of 3.56 bits/cm2 for the presented chipless tag.

A Compact Kapton-Based Inkjet-Printed Multiband Antenna for Flexible Wireless Devices

A low-cost inkjet-printed multiband antenna envisioned for integration into flexible and conformal mobile devices is presented. The antenna structure contains a novel triangular iterative design with coplanar waveguide (CPW) feed, printed on a Kapton polyimide-based flexible substrate with dimensions of 70×70×0.11 mm3. The antenna covers four wide frequency bands with measured impedance bandwidths of 54.4%, 14%, 23.5% and 17.2%, centered at 1.2, 2.0, 2.6 and 3.4 GHz, respectively, thus, enabling it to cover GSM 900, GPS, UMTS, WLAN, ISM, Bluetooth, LTE 2300/2500 and WiMAX standards. The antenna has omnidirectional radiation pattern with a maximum gain of 2.1 dBi. To characterize the flexibility of the antenna, the fabricated prototype is tested in convex and concave bent configurations for radii of 78 mm and 59 mm. The overall performance remains unaffected, except a minor shift of 20 MHz and 60 MHz in S11, for concave bending at both radii. The compact, lightweight and conformal design as well as multiband performance in bent configurations, proves the suitability of the antenna for future electronic devices.

Ultra-wideband cross polarization conversion metasurface insensitive to incidence angle

A broadband microwave cross-polarization-conversion (CPC) metasurface is designed, simulated, fabricated, and tested. The metasurface consists of coupled split-ring-resonators (SRRs) with two splits in each SRR and is designed on an FR4 dielectric substrate backed by a metallic ground plane. An efficient CPC, both for normal as well as for oblique incidence, is achieved with 3 dB fractional bandwidth of 73% from 5 to 10.8 GHz. This wideband polarization conversion results from multiple plasmonic resonances occurring at three neighboring frequencies. Owing to the sub-wavelength unit cell size and symmetric structure of the coupled SRRs, the response of the metasurface is independent of the polarization and incidence angle of the incoming wave, which makes it a potential candidate for many practical applications. The proposed design is validated both numerically and experimentally. Experimental results are found to be in good agreement with simulations.

Disposable, Paper-Based, Inkjet-Printed Humidity and H2S Gas Sensor for Passive Sensing Applications

An inkjet-printed, fully passive sensor capable of either humidity or gas sensing is presented herein. The sensor is composed of an interdigitated electrode, a customized printable gas sensitive ink and a specialized dipole antenna for wireless sensing. The interdigitated electrode printed on a paper substrate provides the base conductivity that varies during the sensing process. Aided by the porous nature of the substrate, a change in relative humidity from 18% to 88% decreases the electrode resistance from a few Mega-ohms to the kilo-ohm range. For gas sensing, an additional copper acetate-based customized ink is printed on top of the electrode, which, upon reaction with hydrogen sulphide gas (H2S) changes, both the optical and the electrical properties of the electrode. A fast response time of 3 min is achieved at room temperature for a H2S concentration of 10 ppm at a relative humidity (RH) of 45%. The passive wireless sensing is enabled through an antenna in which the inner loop takes care of conductivity changes in the 4–5 GHz band, whereas the outer-dipole arm is used for chipless identification in the 2–3 GHz band.

High capacity polarization sensitive chipless RFID tag

A radio frequency identification (RFID) chipless tag that achieves a high code capacity through multiple closed loop printed resonators is presented. By making the resonators polarization dependent, the same frequency band within UWB from 3.1 to 7.6 GHz is re-used, hence doubling the code capacity of the tag. The chipless tag is excited using linearly polarized vertical and horizontal plane waves and the radar cross section versus frequency is analyzed. Using frequency shift encoding enables each of the six resonators to represent more than one bit. Thus, in a small tag dimension of 6 × 3 cm2, encoding of 28.4 bits is demonstrated.

Design of a single layer reflectarray unit cells based on hexagonal ring for wideband operation

In this paper, a microstrip reflectarray unit cell with different configurations of hexagonal element is presented. The aim is to have a large reflection phase range with comparatively linear phase slope as a function of element size to achieve a wider operational bandwidth of a reflectarray antenna. Full-wave EM simulations are used to investigate the phase characteristics and performance of reflectarray unit cells. The simulated results show that a single-resonance hexagonal ring provides an insufficient reflection phase range (<; 360°). It is also shown that multi-resonance hexagonal elements (double hexagonal ring, triple hexagonal ring and hexagonal patch/ring) can provide a reflection phase range exceeding 360°. A centre fed 81-element microstrip reflectarray antenna using one of the proposed structure (double hexagonal ring) is also designed. The simulated results show a constant 3-dB gain bandwidth around the frequency band of 9-12 GHz.

Multi-Scale Approach for the Electromagnetic Simulation of Finite Size and Thick Frequency Selective Surfaces

The scattering analysis from metallic Grid FSS consisting of rectangular perforations on a thick metallic screen illuminated by an oblique incident plane wave is presented. The grid structure is analyzed using Scale Changing Technique (SCT) which is based on the partition of the grid-plane into planar sub-domains deflned at various scale-levels. Electromagnetic interaction between subsequent scales is modeled by mutually independent Scale-Changing Networks and flnally the complete structure is simply represented by a cascade of these networks. Very good agreement is obtained between simulation results from SCT and the Finite Element Method (FEM) when computing the re∞ection/transmission coe-cients and electromagnetic fleld backscattered by thick and flnite size frequency selective surfaces. The computation time is signiflcantly reduced when using SCT-based software compared with the FEM simulation tool. The accurate prediction of the electromagnetic scattering by flnite size arrays is of great practical interest in the design and optimization of modern frequency selective surfaces (FSSs), re∞ect-arrays and transmit-arrays. A complete full-wave analysis of these structures requires generally enormous computational resources due to their large electrical dimensions which would require prohibitively large number of unknowns to be solved. The unavailability of e-cient and accurate design tools for these applications limits the engineers with the choice of low performance simplistic designs that do

A Super Wideband printed antenna with enhanced gain using FSS structure

Super Wideband (SWB) printed antenna with enhanced gain covering the impedance bandwidth ranging from 3-20GHz is presented. Gain enhancement of the antenna is achieved using appropriately designed frequency selective structure (FSS) acting as a band stop filter i.e. reflector, while keeping the bandwidth of antenna unchanged. The FSS used effectively reflects the in-phase radiations with a very low transmission coefficient over the entire bandwidth which is key requirement for providing antenna gain enhancement for wide frequency range. Hence significant improvement in antenna gain has been achieved using low profile and without compromising the impedance bandwidth. Results show a significant improvement in gain (i.e. 4-5dB) over the whole frequency range.

An angularly stable dual-broadband anisotropic cross polarization conversion metasurface

A dual broadband anisotropic cross-polarization-conversion (CPC) metasurface is designed and tested. The unit cell of the proposed metasurface consists of a two-slit rectangular split-ring-resonator inside of which a metallic cross element is placed. The unit cell is printed on a dielectric substrate backed by a metallic plane. Excellent CPC is achieved in two wide frequency bands from 5 to 9.7 GHz (4.7 GHz bandwidth) and from 11.2 to 15 GHz (3.8 GHz bandwidth) for both normal and oblique incidences. The wide CPC bandwidth is due to the plasmonic resonances occurring at three distinct frequencies. The unique physical structure, sub-wavelength size, and electrically small substrate thickness make the response of the metasurface identical for both x and y polarizations and insensitive to incidence angles (up to 60°). The physical mechanism behind polarization conversion is also elucidated through surface current distribution and through the concept of a high impedance surface. The proposed design is validat...

Design and analysis of a novel tri-band flower-shaped planar antenna for GPS and WiMAX applications

Abstract This paper presents the design of a tri-band flower-shaped planar monopole antenna operating at three frequencies i.e. 1.576 (GPS), 2.668, and 3.636 GHz (Mobile WiMAX). The radiating element of the antenna is backed by a 1.6 mm thicker FR-4 substrate having a dielectric constant of 4.3. The substrate is backed by a truncated ground plane. The antenna is fed through a 50 Ω microstrip line. The flower shape of the radiating element is derived from the basic circular shape by introducing in it rounded slots of various radii. The upper part of the antenna is flower shaped while the lower part comprises a microstrip feed line and two branches, each having two “leaves” at the end. The leaves and branches contribute in the impedance matching of the lower (1.576 GHz) and middle (2.668 GHz) frequency bands. The antenna gives an acceptable simulated efficiency >70% in the three frequency bands. Suitable gains of 1.63, 2.59, and 3.23 dB are obtained at 1.576, 2.668, and 3.636 GHz, respectively. The antenna matched with a VSWR < 1.2 in the three frequency bands. The prototype of the antenna is fabricated and tested in the laboratory, and good agreement in simulated and measured results is achieved. The proposed design is a visually appealing and may find uses as an external antenna in GPS and WiMAX applications.