W.S.T. Rowe

University of Vic, Vic, Catalonia, Spain

Are you W.S.T. Rowe?

Claim your profile

Publications (119)93.55 Total impact

  • S.N. Azemi · K. Ghorbani · W.S.T. Rowe
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jul 2015 · IEEE Microwave and Wireless Components Letters
  • Source
    Negin Shariati · Wayne S T Rowe · James R Scott · Kamran Ghorbani
    [Show abstract] [Hide abstract]
    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.
    Preview · Article · May 2015 · Scientific Reports
  • Source
    Wai Siang Yeoh · Wayne S. T. Rowe
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel formation of a conical monopole antenna is presented for ultra-wideband (UWB) and multiple other wireless services. The proposed antenna design is compatible with many wireless standards, including Wi-Fi (2.4 GHz), Bluetooth (v1.0 - v4.0), WiMAX (~2.5-5.5 GHz) and Bluetooth 4.0 or Wireless USB (3.1-10.6 GHz). It is also has a suitable frequency response for close range radar and satellite communication in the X band (~8-12 GHz) and Ku band (~12-18 GHz) applications. The proposed design is approximately 0.24λ in length with respect to the lowest frequency boundary at the 2.4 GHz Wi-Fi band. The structure consists of two mechanical parts, which are the cone and a cylindrical block (disc). The proposed conical monopole antenna displays a fractional bandwidth of 8.3:1 and a simulated maximum efficiency of over 95% across the whole frequency range. The radiation patterns are largely omnidirectional. Furthermore, it displays a useful level of gain across the impedance bandwidth and the time domain response indicates promising performance for radar and impulse radio. In short, the proposed conical monopole offers ultra-broad bandwidth with omnidirectional radiation patterns, in a reasonably small and easy to construct structure.
    Full-text · Article · Jan 2015 · IEEE Antennas and Wireless Propagation Letters
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Nov 2014 · Applied Physics Letters
  • Negin Shariati · Wayne S. T. Rowe · Kamran Ghorbani
    [Show abstract] [Hide abstract]
    ABSTRACT: RF (Radio Frequency) energy harvesting is a promising technique to provide a sustainable energy source for the long-term conservation of the environment and the global economy. To address this, we proposed an efficient rectifier over a wide low input RF power range (-40 to -10 dBm) for broadcasting band (520- 590 MHz) to determine the usefulness of exploiting freely available RF energy sources in this band. The input reflection coefficient and rectified output power demonstrate the practical feasibility of this low-power rectification technique. Power conversion efficiency (PCE) of 53% and 1.5% are achieved for a single-tone input power of -10 dBm and -40 dBm respectively. Therefore, this innovative technique has the potential to generate a viable perpetual energy source for low power applications in urban environments.
    No preview · Conference Paper · Oct 2014
  • Source
    [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.
    Full-text · Article · Jul 2014 · Lab on a Chip
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Mar 2014 · IEEE Transactions on Microwave Theory and Techniques
  • S. N. Azemi · K. Ghorbani · W. S. T. Rowe
    [Show abstract] [Hide abstract]
    ABSTRACT: A novel 3D Frequency Selective Surface (FSS) with horn shaped resonators is proposed which exhibits a very wide stop band. This new horn shaped resonator is a modification from a 3D FSS consisting of square cylinder unit elements. This feature introduces frequency-selective surfaces with the added advantage of lowering the sensitivity of the FSS frequency response with respect to the incidence angle. Simulation results prove that the FSS can realize broad selectivity of waves with the bandwidth more than 57%. The wideband transmission behavior is stable under oblique TM incidence angles from 0 to 80 degrees. The influence of various key parameters on 3D Horn Shape FSS characteristics has been investigated using the CST simulation software tool. By understanding the effect of each parameter, a comprehensive study for a better design of 3D Horn Shape FSS with wideband response is presented.
    No preview · Conference Paper · Mar 2014
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Jan 2014 · Sensors
  • Ali Daliri · W.S.T. Rowe · Kamran Ghorbani
    [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jan 2014 · IEEE Antennas and Wireless Propagation Letters
  • Source
    S.N. Azemi · Kamran. Ghorbani · Wayne S. T. Rowe
    [Show abstract] [Hide abstract]
    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 .
    Full-text · Article · Dec 2013 · IEEE Antennas and Wireless Propagation Letters
  • K. J. Nicholson · W. S. T. Rowe · P. J. Callus · K. Ghorbani
    [Show abstract] [Hide abstract]
    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.
    No preview · Conference Paper · Sep 2013
  • Ali Daliri · Wayne S. T. Rowe · Kamran Ghorbani · Chun H. Wang · Sabu John
    [Show abstract] [Hide abstract]
    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.
    No preview · Conference Paper · Jul 2013
  • Source
    [Show abstract] [Hide abstract]
    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]
    Full-text · Article · Jun 2013 · Journal of Applied Physics
  • [Show abstract] [Hide abstract]
    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.
    No preview · Article · Jan 2013 · Applied Physics Letters
  • Source
    S.N. Azemi · K. Ghorbani · W.S.T. Rowe
    [Show abstract] [Hide abstract]
    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.
    Full-text · Conference Paper · Jan 2013
  • Source
    S.N. Azemi · K. Ghorbani · W.S.T. Rowe
    [Show abstract] [Hide abstract]
    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.
    Full-text · Conference Paper · Jan 2013
  • Wayne S.T. Rowe · Xutao Tang
    [Show abstract] [Hide abstract]
    ABSTRACT: The concept of switching microwave structures that interact with propagating electromagnetic waves using pneumatic techniques is studied in this paper. The pneumatic actuation is achieved using a toggling of air pressure and vacuum to separate or unite the metallic poles of the switching elements. Pneumatic actuation can be applied across a broad area such as a metamaterial surface, or at a localized point as a switching or shorting element. In this paper, pneumatically actuated metallic patches are applied to microstrip patch antennas for the first time. It is shown that the pneumatic actuation can tune the resonant behavior of the patch antenna and even switch the mode of feeding without the need for applied DC bias. The pneumatic cell itself is non-metallic, hence it does not greatly interfere with the electromagnetic operation of the microwave structure.
    No preview · Conference Paper · Jan 2013
  • Source
    Saidatul Norlyana Azemi · Kamran Ghorbani · Wayne S. T. Rowe
    [Show abstract] [Hide abstract]
    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.
    Full-text · Conference Paper · Dec 2012
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Dec 2012 · Journal of Applied Physics