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This article presents a tag antenna for radio frequency identification (RFID)-based wireless structural health monitoring systems. An ultra-high frequency (UHF) microstrip patch tag antenna is designed with a new generation RFID tag chip for the Australian UHF RFID frequency band. Simulation studies with optimized slits demonstrate the ability of the antenna to tolerate the influence of construction materials such as concrete and metal on its resonant frequency, maximum gain, and read range. Noncontact measurement of the resonant frequency and experimental verification of the maximum gain of the fabricated tag antenna show good agreement with simulated performance. Read range measurements are conducted to verify the performance of the tag antenna on metal structures. It is also shown that the proposed tag antenna can be easily modified to operate in other UHF RFID frequency bands. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2231–2237, 2016

Ultrawide band (UWB) nondestructive testing and evaluation techniques can provide the detection of defects and damages in construction materials and members. The development of UWB antennas with proper dimensions and high performance for these systems is one of the major challenges. In this letter, an antipodal Vivaldi antenna (AVA) has been developed to be used in UWB techniques for nondestructive detection of cracks in concrete members. To obtain a desirable antenna performance including the wider impedance bandwidth, the higher directivity, and higher front-to-back ratio rectangular-shaped slits (RSS) and a half-circular-shaped lens (HCSL) have been added in the design of a conventional tapered slot AVA. A parametric study on the dimensions of the slits is provided to optimize performance and size of the proposed antenna. The optimum size of the proposed antenna is 40 × 80 × 0.508 mm3, and it operates over the frequency range from 3.4–40 GHz. It is shown that the RSS increase impedance bandwidth especially at the lower frequencies. Directivity of the proposed antenna at higher frequencies has been increased by the HCSL. The feasibility of the proposed antenna for nondestructive evaluation of concrete members is demonstrated by investigation into its performance with concrete specimens possessing an air-gap inside a concrete specimen. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1573–1578, 2015

Non-destructive detection and evaluation of stress-induced fatigue cracks in metals is an important practical issue in several critical environments including surface transportation (steel bridges, railroad tracks, railroad car wheels, etc.), aerospace transportation (aircraft fuselage, landing gears, etc.) and power plants (steam generator tubings, etc.). Although there are several standard non-destructive evaluation techniques, near-field microwave and millimetre wave techniques have shown tremendous potential for significantly adding to the available non-destructive 'toolbox' for this purpose. This paper serves as a review of recent advances made in this area and the capabilities of these techniques for detecting cracks and evaluating their various dimensional properties including determining a crack tip location accurately. These techniques include using open-ended rectangular probes (in two distinct modes) and open-ended coaxial probes.

In this paper, the results of analytical and numerical investigation of whispering gallery modes (WGMs) in parallel-plates-type cylindrical anisotropic and isotropic dielectric resonators are presented. The dependence of the WGMs' resonant frequency, Q-factor, and energy-filling factor upon resonator parameters for the wide range of the azimuthal index has been studied numerically. The optimization of resonator parameters for sensing applications is discussed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 96–101, 2004; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/mop.11296

New results of theoretical and experimental investigation of an open hemispherical image dielectric resonator (HIDR) with whispering gallery modes (WGM) are presented. The dependences of the WGM complex resonator frequencies on resonator parameters have been studied by the integral equation method. The dependences of the delay factor and Q-factor of HIDR WGM on resonator parameters and wavelength have been calculated numerically. It is shown that the WGM spectrum density of HIDR is smaller than that of a dielectric sphere. It is discovered that the dependence of the Q-factor of an open dielectric resonator WGM on the polar index has a maximum. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 252–257, 1999.

New results of theoretical and experimental investigations of nonuniform dielectric resonators (DRs) with higher-order azimuthal waves (whispering-gallery modes) are presented. The frequency splitting and modal coupling phenomena are studied. The effect of the space-frequency field separation of the modes is found. Application of nonuniform dielectric resonators for the study of various materials (semiconductive and dielectric plates and films, high-Tc superconductors), and for the design of millimeter-wave filters and oscillators is proposed. © 1995 John Wiley & Sons, Inc.