W.S.T. Rowe

RMIT University, Melbourne, Victoria, Australia

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Publications (97)80.75 Total impact

  • [Show abstract] [Hide abstract]
    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; · 5.70 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). · 2.23 Impact Factor
  • A. Daliri, W.S.T. Rowe, K. 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. · 1.67 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. · 2.05 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 01/2014; · 5.70 Impact Factor
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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. · 2.21 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). · 3.79 Impact Factor
  • 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
  • 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
  • S.N. Azemi, K. Ghorbani, W.S.T. Rowe
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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 01/2013; 12:781-784. · 1.67 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 01/2012; 112(11):11392-1. · 2.21 Impact Factor
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    ABSTRACT: A chain of complementary split ring resonators (CSRRs) operating at terahertz frequencies have the potential to sustain surface plasmon polaritons (SPPs). As a first step, the transmission spectra of a 2D periodic array of scaled CSRRs operating at terahertz frequencies were obtained. A second investigation, explored the effect of a polydimethylsiloxane (PDMS) substrate on the resonance of CSRRs. These simulations confirm the strong resonance of the CSRRs and their potential for supporting SPPs.
    Optoelectronic and Microelectronic Materials & Devices (COMMAD), 2012 Conference on; 01/2012
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    ABSTRACT: We propose the design of graded index metamaterial lens using pneumatic actuation for switching between focusing and non focusing states and operating at 9 GHz. Graded refractive index is engineered by using split ring resonators of different widths. Choice of electrical resonators allows planar design and significantly reduced thickness of the lens. Switching between focusing and non focusing states is based on shortening the gaps in split ring resonators with pneumatically actuated metal patches. This leads to the disappearance of the resonant response of split rings and flattening of phase difference between the elements across the lens. The concept is demonstrated by fabrication and measurement of two versions of the lens representing focusing and non focusing states.
    Microwave Conference Proceedings (APMC), 2012 Asia-Pacific; 01/2012
  • S.N. Azemi, K. Ghorbani, W.S.T. Rowe
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    ABSTRACT: The transmission and reflection characteristics of a dual cylinder 3D Frequency Selective Surface (FSS) is discussed in this paper. A simulation based investigation shows that the length of the cylinder has significant effect on the stop band frequency selective characteristics of the FSS. This can result in a closely spaced band pass and band stop response. A comparison is drawn to the introduction of dielectric materials into a single 3D cylindrical FSS.
    Microwave Conference Proceedings (APMC), 2012 Asia-Pacific; 01/2012
  • ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems; 01/2012
  • W.S. Yeoh, W.S.T. Rowe, K.L. Wong
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    ABSTRACT: A linearly polarised decoupled dual-dipole rectenna (DDDR) with a novel microstrip-decoupling structure is presented for wireless battery charging applications at the 2.4-GHz industrial, scientific and medical (ISM) band. It consists of decoupled dual dipole (DDD) antenna and a Villard's voltage doubler (VVD) rectifier, and is able to operate close to a conducting surface. The DDD provides 5.6% bandwidth centralised at ~2.42 GHz and about 4 dBi gain from each element. The half power beam width (HPBW) of this design in the XZ-plane is about 120° from each antenna. High isolation is achieved with only 3-mm edge-to-edge separation. The DDD is 37° smaller than two standard patch antennas located on the same substrate without a decoupling structure. The DDDR is able to fully charge a standard 4.8-V NiMH battery to 5.1°V in 5°h over a distance of 23°cm.
    IET Microwaves Antennas & Propagation 01/2012; 6(2):238-244. · 0.84 Impact Factor
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    ABSTRACT: Uninsulated overhead distribution cables are evaluated in terms of their propagation and radiation behavior when excited by a partial-discharge (PD) pulse. Low attenuation levels at high frequency and a traveling-wave radiation pattern are observed for a single aluminum cable. The dominant radiated frequency components of surface discharge and dryband arcing are experimentally evaluated, and a high level of activity is observed in the 400-600-MHz and 900-1000-MHz bands. High directivity values at specific angles are also recorded at 400 and 900 MHz for single- and three-cable distribution systems. These findings show that a PD signal will travel for a significant distance along a cable and leak radiation predominantly in a specific direction, thus assisting the design of the RF-based discharge detection and localization system.
    IEEE Transactions on Power Delivery 01/2012; 27(3):1116-1123. · 1.52 Impact Factor
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    ABSTRACT: The slotted waveguide antenna stiffened structure (SWASS) is a conformal load bearing antenna concept that aims to replace existing aircraft antennas with a structurally integrated equivalent. In SWASS, slots are cut through the skin of hat-stiffened or blade-stiffened aircraft panels to create slotted waveguide antennas. The structural integrity of these panels is at maximum when the slot dimensions are minimised. An architecture that retains the slotted waveguide antenna performance while minimising the slot dimension by means of a single well placed wire element is demonstrated.
    Electronics Letters 01/2012; 48(12):676-677. · 1.04 Impact Factor
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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 01/2012; · 1.67 Impact Factor
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    ABSTRACT: In this paper we present a microfabricated mesh substrate for use in gravitational magnetoelastic metamaterials. The high resolution technique allows the manipulation of the electromagnetic properties of the substrate towards free space-like performance. This is achieved via removal of predetermined substrate areas while simultaneously shaping the required mechanical features.
    Optoelectronic and Microelectronic Materials & Devices (COMMAD), 2012 Conference on; 01/2012