W.S.T. Rowe

RMIT University, Melbourne, Victoria, Australia

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Publications (113)109.2 Total impact

  • S.N. Azemi, K. Ghorbani, W.S.T. Rowe
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    ABSTRACT: A new type of Frequency Selective Surface (FSS) with miniaturized resonator element is proposed. The FSS structure is shown to have a FSS unit cell dimension that is miniaturized to 0.067 $lambda_{{{0}}}$ . Miniaturization of the FSS unit cell is achieved by coupling two meandered wire resonators separated by single thin substrate layer. The capacitance due to the small separation between the meandered wire elements results in a lowering of the resonant frequency. To demonstrate the validity of the design, the meandered wire resonator FSS was fabricated and tested using a free space measurement facility. The FSS produces a stable angular response up to 80 degrees for TE and TM incident angles.
    IEEE Microwave and Wireless Components Letters 07/2015; 25(7):454-456. DOI:10.1109/LMWC.2015.2429126 · 2.24 Impact Factor
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    ABSTRACT: Due to the growing implications of energy costs and carbon footprints, the need to adopt inexpensive, green energy harvesting strategies are of paramount importance for the long-term conservation of the environment and the global economy. To address this, the feasibility of harvesting low power density ambient RF energy simultaneously from multiple sources is examined. A high efficiency multi-resonant rectifier is proposed, which operates at two frequency bands (478-496 and 852-869 MHz) and exhibits favorable impedance matching over a broad input power range (-40 to -10 dBm). Simulation and experimental results of input reflection coefficient and rectified output power are in excellent agreement, demonstrating the usefulness of this innovative low-power rectification technique. Measurement results indicate an effective efficiency of 54.3%, and an output DC voltage of 772.8 mV is achieved for a multi-tone input power of -10 dBm. Furthermore, the measured output DC power from harvesting RF energy from multiple services concurrently exhibits a 3.14 and 7.24 fold increase over single frequency rectification at 490 and 860 MHz respectively. Therefore, the proposed multi-service highly sensitive rectifier is a promising technique for providing a sustainable energy source for low power applications in urban environments.
    Scientific Reports 05/2015; 5:9655. DOI:10.1038/srep09655 · 5.58 Impact Factor
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    ABSTRACT: We demonstrate microwave metamaterial with enhanced nonlinearity enabled by a significant mass and loss reduction due to perforated SU-8 substrate supporting self-rotating split ring resonators utilizing gravity as a restoring force. Forces involved in resonator movement are analyzed, and mechanical features of the structure are optimized. Unconventional microfabrication technique allowing creation of metal coated SU-8 structures with non-coincident metal and substrate patterns is introduced, resulting in a robust micrometer sized mesh. The beneficial effects of perforated substrate are demonstrated on electromagnetic properties of single resonators as well as coupled nonlinear resonator pair. Improvement in quality factor of single resonator as a result of reduced substrate mesh density is shown in the microwave frequency range. Nonlinear resonant frequency shift by 0.067 GHz is achieved for a pair of coupled resonators upon increasing the microwave power from 1 mW to 1 W.
    Applied Physics Letters 11/2014; 105(18):181908. DOI:10.1063/1.4901267 · 3.52 Impact Factor
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    ABSTRACT: Increasing the thermal conductivity of PDMS (polydimethylsiloxane) based microfluidics is an important issue for the thermal management of hot spots produced by embedding electronic circuits in such systems. This paper presents a solution for enhancing the thermal conductivity of such PDMS based microfluidics by introducing thermally conductive alumina (Al2O3) nanoparticles, forming PDMS/Al2O3 nanocomposites. The materials are fully characterized for different concentrations of Al2O3 in PDMS for experiments which are conducted at different flow rates. Our results suggest that incorporation of Al2O3 nanoparticles at 10% w/w in the PDMS based nanocomposite significantly enhances the heat conduction from hot spots by enhancing the thermal conductivity, while maintaining the flexibility and decreasing the specific heat capacity of the developed materials. This proof-of-concept study offers potential for a practical solution for the cooling of future embedded electronic systems.
    Lab on a Chip 07/2014; 14(17). DOI:10.1039/c4lc00615a · 5.75 Impact Factor
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    ABSTRACT: The slotted waveguide antenna stiffened structure (SWASS) utilizes conventional hat-stiffeners or blade stiffeners in aircraft sandwich structures as microwave waveguides. Slotted waveguide antenna arrays may therefore be integrated into the structure by machining slots through the outer skin. However, the primary mechanical load applied to the structure governs the orientation of these slotted waveguides and so dictates the antenna scan plane. This work extends the SWASS concept by demonstrating a means to achieve electronic phase shifting along the waveguide axis for the purpose of beam steering. This is accomplished by incorporating a varactor loaded coaxial composite right/left-handed transmission line into the SWASS for approximate matched tuning of the dispersion diagram about the design frequency.
    IEEE Transactions on Microwave Theory and Techniques 03/2014; 62(4). DOI:10.1109/TMTT.2014.2308480 · 2.94 Impact Factor
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    ABSTRACT: Recently introduced passive wireless strain sensors based on microstrip patch antennas have shown great potential for reliable health and usage monitoring in aerospace and civil industries. However, the wireless interrogation range of these sensors is limited to few centimeters, which restricts their practical application. This paper presents an investigation on the effect of circular microstrip patch antenna (CMPA) design on the quality factor and the maximum practical wireless reading range of the sensor. The results reveal that by using appropriate substrate materials the interrogation distance of the CMPA sensor can be increased four-fold, from the previously reported 5 to 20 cm, thus improving considerably the viability of this type of wireless sensors for strain measurement and damage detection.
    Sensors 01/2014; 14(1):595-605. DOI:10.3390/s140100595 · 2.05 Impact Factor
  • Ali Daliri, W.S.T. Rowe, Kamran Ghorbani
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    ABSTRACT: Recently the Slotted Waveguide Antenna Stiffened Structure (SWASS) was introduced, where an antenna array is incorporated as an integrated part of a load bearing structure. The array element spacing and individual radiating element sizes play a critical role in the overall mechanical strength of the structure. These parameters are constrained by Slotted Waveguide Antenna (SWA) array design, and the coupling of the waveguide electromagnetic fields to the radiating apertures. In this letter, the radiation characteristics of a split-ring slot in the broad-wall of a rectangular waveguide are investigated for the first time. The simulated and measured results show that the split-ring slot radiates a linearly polarized wave with a total efficiency and realized gain close to those of conventional rectangular slots. The proposed split-ring slot has an outer diameter of $0.186 lambda _{0}$, a significant size reduction compared to a traditional $0.5 lambda _{0}$ rectangular slot and the previous limit of $0.25 lambda _{0}$ for metamaterial loaded rectangular slots. The reduced aperture size of the split-ring slot alleviates the impact of the radiating elements on the mechanical strength of the structure.
    IEEE Antennas and Wireless Propagation Letters 01/2014; 13:991-994. DOI:10.1109/LAWP.2014.2325934 · 1.95 Impact Factor
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    ABSTRACT: Reconfigurable and tunable frequency selective surfaces (FSSs) are of significant interest in applications such as tunable radomes and adaptive screening of unwanted wireless transmissions. Conventional FSSs require additional bias circuitry to tune the operating frequency or to change its characteristics. In this letter, a new tuning technique using a spring resonator element is proposed. This technique can be applied to FSS design to make it reconfigurable and/or to fine-tune the response. The FSS frequency response can be adjusted by changing the spring height $h$ with applied pressure. The functional characteristic of the FSS can also be altered between a bandstop and bandpass filter response. A parametric analysis of the novel spring FSS is undertaken in CST software, and the results are validated with experimental measurement .
    IEEE Antennas and Wireless Propagation Letters 12/2013; 12:781-784. DOI:10.1109/LAWP.2013.2270950 · 1.95 Impact Factor
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    ABSTRACT: The Slotted Waveguide Antenna Stiffened Structure (SWASS) utilizes conventional hat-stiffeners or blade stiffeners in aircraft sandwich structures as microwave waveguides. Slotted waveguide antenna arrays may therefore be integrated into the structure by machining slots through the outer skin. However, the primary mechanical load applied to the structure governs the orientation of these slotted waveguides and so limits electronic beam steering to just one plane. This work extends the SWASS concept by demonstrating a means to achieve electronic phase shifting along the waveguide axis. This is accomplished by incorporating a varactor loaded coaxial composite right / left handed transmission line (CRLH-TL) into the SWASS for approximate matched tuning of the dispersion diagram about the design frequency.
    2013 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS 2013); 09/2013
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    ABSTRACT: Slotted waveguide antenna stiffened structure (SWASS) integrates the slotted waveguide antennas (SWAs) into the carbon fiber reinforced polymer (CFRP) composites in airplane skins. SWASS utilizes conventional half-wavelength rectangular slots as elements of the SWA array. Size of the rectangular slots is an important factor affecting the mechanical performance of the SWASS and restricting its application. Subwavelength spiral slots are recently proposed to replace the rectangular slots and consequently improve the SWASS mechanical performance. In this paper, a four element array using subwavelength spiral slots is presented which demonstrates the feasibility of using such slots for SWASS application.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
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    ABSTRACT: In this work, we characterize the electromagnetic properties of polydimethylsiloxane (PDMS) and use this as a free-standing substrate for the realization of flexible fishnet metamaterials at terahertz frequencies. Across the 0.2-2.5 THz band, the refractive index and absorption coefficient of PDMS are estimated as 1.55 and 0-22 cm(-1), respectively. Electromagnetic modeling, multi-layer flexible electronics microfabrication, and terahertz time-domain spectroscopy are used in the design, fabrication, and characterization of the metamaterials, respectively. The properties of PDMS add a degree of freedom to terahertz metamaterials, with the potential for tuning by elastic deformation or integrated microfluidics. (C) 2012 American Institute of Physics. [doi:10.1063/1.3665180]
    Journal of Applied Physics 06/2013; 100. DOI:10.1063/1.3665180 · 2.19 Impact Factor
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    ABSTRACT: A low-profile pneumatically switchable graded index metamaterial lens operating at 9 GHz is proposed and practically demonstrated. An effective graded refractive index is engineered using an array of electric resonators of differing resonant frequency. Normal orientation of the resonators allows ultrathin single metamaterial layer lens design. Switching between focusing and non-focusing states is practically demonstrated by shorting the gaps in split ring resonators and eliminating the resonant response and the phase difference between the elements across the lens with pneumatically actuated metal patches that are pressed against the gaps of the resonators as the pressure in the chamber is reduced.
    Applied Physics Letters 01/2013; 102(3). DOI:10.1063/1.4788918 · 3.52 Impact Factor
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    S.N. Azemi, K. Ghorbani, W.S.T. Rowe
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    ABSTRACT: A mechanical tuning technique for architectures employing stacked ring resonators is proposed. The stacked rings are separated by a plastic spring structure allowing the ring spacing to be mechanically adjusted. This technique can be applied to Frequency Selective Surface (FSS) to not only tune the transmission or reflection frequency response, but also reconfigure the functional characteristic of the FSS operation between stop and pass band topologies with applied pressure. A parametric analysis of the novel spring loaded FSS is undertaken in CST simulation software.
    Microwave Conference (EuMC), 2013 European; 01/2013
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    S.N. Azemi, K. Ghorbani, W.S.T. Rowe
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    ABSTRACT: A novel 3D tapered Frequency Selective Surface (FSS) which is independent of incident angle is proposed. This new type of FSS is a modification from a 3D FSS consisting of square cross section cylinder unit elements. By enlarging the aperture of the square cross section cylinder resonators, the transmittance of the FSS becomes independent of the incident angle of radiation. Moreover, transmission response is stable under oblique incidence angles from 0 to 45 degrees. The influence of key design parameters on 3D Tapered FSS characteristics has been investigated using CST simulation software.
    Microwave Conference (EuMC), 2013 European; 01/2013
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    ABSTRACT: A new form of a conformal load-bearing antenna structure that consists of a cavity-backed slot in a carbon-fiber reinforced polymer (CFRP) panel is presented. The antenna is fed via a coaxial cable and patches that capacitively couple energy into the highly conductive carbon fibers without the requirement to abrade off the nonconductive epoxy resin layer on the surface. Computational simulations, which are validated by experiments, show that this feed configuration is as effective as soldering in a brass slot antenna. Backing the slot with a CFRP cavity enhances gain and front-to-back ratio by 2 and 13 dB, respectively. Gain is increased further by orienting the inner surface ply of the CFRP cavity to the same direction as the local E-field. Finally, the dimensions of the slot and cavity are optimized to minimize the antenna size. The resultant low-profile cavity is 14% of the volume of the original antenna design, but maintains similar gain and resonant frequency.
    IEEE Antennas and Wireless Propagation Letters 12/2012; 11:1028-1031. DOI:10.1109/LAWP.2012.2214197 · 1.95 Impact Factor
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    ABSTRACT: This paper reports the realization and characterization of a pneumatic microswitch integrated with a high-frequency radio frequency (RF) transmission line on an elastomer substrate. A process for the fabrication of low-loss RF coplanar transmission lines on flexible elastomeric polydimethylsiloxane (PDMS) substrates was developed, and devices realized using this process were used to determine the characteristics of PDMS as an RF substrate with uniform low loss and low dielectric constant being measured. To demonstrate the capabilities of this elastomer-based RF platform, a micromechanical switch exploiting a pneumatic membrane valve was integrated with the PDMS RF transmission line. Repeatable switching was observed with greater than 20-dB suppression in the “off” state and minimal degradation of the transmission line characteristics in the “on” state being achieved over a multioctave 2-20-GHz bandwidth. These valve-integrated transmission lines had an insertion loss of 0.16 dB·mm-1 at 20 GHz. This proof-of-concept device represents a novel combination of the areas of micropneumatics, flexible electronics, and broadband microwave devices with excellent RF properties, low interference, bias-free pneumatic switching, and relatively simple fabrication.
    Journal of Microelectromechanical Systems 12/2012; 21(6):1410-1417. DOI:10.1109/JMEMS.2012.2208220 · 1.92 Impact Factor
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    ABSTRACT: Carbon fibers are finite conductors with a weak diamagnetic response in a static magnetic field. When illuminated with a high-frequency alternating electromagnetic wave such that the skin depth is greater than the fiber diameter, carbon-fiber composites are shown to exhibit a strong dynamic diamagnetic response. The magnetic susceptibility (χm) is controlled by the polarization angle (θ), which is the angle between the incident electric field and conductor direction. A closed form solution for this behaviour was derived using Maxwell's equations and an understanding of the induced conductor currents. The equation was verified using simulation and free space “wall” and waveguide measurements on unidirectional IM7/977-3 carbon fiber reinforced polymer laminates. The measured responses ranged from non-magnetic at θ = 90°, χm = 0, up to strongly diamagnetic at θ = 30°, χm = −0.75, over the 8-18 GHz bandwidth. The experimental results are in good agreement with theoretical predictions and computational simulations.
    Journal of Applied Physics 12/2012; 112(11-11):11392-1. DOI:10.1063/1.4764041 · 2.19 Impact Factor
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    ABSTRACT: The concept of wireless passive strain sensors has been introduced in the last few years for applications such as structural health monitoring. This study investigates the use of circular microstrip patch antenna (CMPA) sensors for wireless passive measurement of strain. The strain induced in an aluminium plate was measured wirelessly up to 5 cm away from the sensor using a CMPA made from commercial FR4 substrate, and at a distance up to 20 cm using a CMPA made from Rogers® RT/duroid 6010™. These results show the substrate of antennas is one of the factors affecting the interrogation distance. The interrogation distance between the sensor and the patch antenna was improved significantly using the Rogers® substrate.
    ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 09/2012
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    ABSTRACT: The next-generation design of structural components involves combining multiple functions. The goal of such Multi-functional structures (MFS) is to incorporate various tasks and functions such as structural, electrical and thermal features within a structural housing. The performance and behaviour characteristics of the multi-functional structures can be affected by degradation of any of the sub-components. This can have consequences on the safety, cost, and operational capability. Therefore, the timely and accurate detection, characterization and monitoring of the degradation in these sub-components are major concerns in the operational environment. This calls for Structural Health Monitoring (SHM) as a possible method to improve the safety and reliability of structures and thereby reduce their operational cost. As the application of SHM systems to monitor the status of the MFS increase, it will be increasingly important to determine the durability, reliability, and reparability of the components of SHM system such as sensors. The sensors themselves must be reliable enough so that they do not require replacement at intervals less than the economic lifetime of the structures and components they are monitoring. This is especially important when the deleterious structural changes in the sensor occurs without any discernible change in the structure being monitored In the present work, an assessment is carried out to quantify the degradation in the electric and electromechanical characteristics of polymer composite PZT sensors, under fatigue loading. Changes in the electrical properties of these sensors such as capacitance and inductance have been measured. The strain measurements of the sensor have also been compared to the theoretically calculated strain. The results show that the delineation of structural damage from sensor degradation is possible by monitoring the changes in the key electrical properties of the sensor components such as electrodes and PZT fibers as well as the comparison of experimentally measured and theoretically calculated strain values.
    ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 09/2012
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    ABSTRACT: The slots in spiral antennas induce stress concentrations and hence may adversely affect the load-carrying capacity of the structural antenna. To minimise the detrimental effect of the slots, appropriate fillers are required to provide structural reinforcement without compromising the radar performance of the antenna. This paper presents an investigation of the effects of electrical and mechanical properties of potential filler materials on the performance of slot spiral antennas. Finite element analysis is carried out for a slot spiral that is designed to work in the C-Band range of frequencies (4–8 GHz). Computational simulations performed using commercial software packages ANSYS® and HFSS® show that by using commercially available filler materials the stress concentration factor of the spiral slot can be reduced by 20%. The results from this research enhance the previously introduced advantages of this type of conformal load-bearing antenna structure (CLAS). This CLAS concept provides a promising solution of replacing conventional externally mounted antennas, thus reducing aircraft weight and aerodynamic drag.
    ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 09/2012

Publication Stats

355 Citations
109.20 Total Impact Points

Institutions

  • 2003–2015
    • RMIT University
      • School of Electrical and Computer Engineering
      Melbourne, Victoria, Australia
  • 2003–2014
    • University of Vic
      Vic, Catalonia, Spain
  • 2013
    • Victoria University Melbourne
      Melbourne, Victoria, Australia
  • 2000–2006
    • Melbourne Institute of Technology
      Melbourne, Victoria, Australia